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HUMAN CHEMOSENSATION AND WINE EXPERTISE: THE BIOLOGY OF WINE TASTING LAURA JOHANNA WEINKLE A Thesis Submitted to the Division of Social Sciences New College of Florida in partial fulfillment of the requirements for the degree Bachelor of Arts in Biological Psychology Under the sponsorship of Dr. Gordon Bauer Sarasota, Florida March, 2010
ii Acknowledgements First, I would like to express my thanks to my thes is sponsor Dr. Gordon Bauer. Your guidance, support, and positive words of advice helped me mai ntain the energy and spirit I needed throughout my thesis project. Additional (and endless) thanks to my mom and dad: Astrid and Bill Weinkle for taking the time to have me and subsequently raise me to be the tena cious woman I am today. Both of you ooze intelligence that inspires me to pursue my academic dreams. My sisters Brette and Daena thank you for driving me crazy as a young girl and helpin g me want to leave the nest. I love you both. Lynne and Marc thank for being the eccentric but do wn-to-earth people who give me perspective. Also, the Weinkle family you have taug ht me the true meaning of family, love and support. You are all some of my most important role models. A special thanks to the people I spend the most tim e with. First, the twins, Alana and Camila. You have both been the most wonderful spirits to ha ve in my life, thank you for being so comfortable in your own skin and for broadening my horizons. Julian, you are my love and my grape! Thank you for your support and kind words wh ile I wrote this piece of thesis, you help keep me calm. Amanda, thanks for graduating before the rest of us because you inspire dedication. I am glad we understand each other in w ays I never thought we would. Karin, my monkey, you are my soul sister. Your smile is enoug h to illuminate my day, thank you for being there in some of the toughest times. And to all of my stellar and loving friends at New College, this has been a truly invaluable experience growing up around you. To each of the above I extend my deepest appreciati on. This thesis is dedicated to my family and friends.
iii HUMAN CHEMOSENSATION AND WINE EXPERTISE: THE BIOLOGY OF WINE TASTING Laura Johanna Weinkle New College of Florida, 2010 Abstract Wine experts are regarded to have a finer capacity to discriminate and describe the fragrance and flavor of wine. To address the basis of this exper tise, I examine human olfaction and gustation as the modalities crucial to experts sensory evalu ations of wine. This thesis explores the peripheral olfactory and gustatory systems, the ana tomy of the central olfactory and gustatory system, functional processing of chemosensory stimu lus information, and the representation of flavor perceptions in the brain. My thesis examine s the development of perceptual skill, conceptual knowledge, and descriptive language thro ugh formal training and extensive experience within the domain of wine. I hypothesiz e that wine expertise develops as a product of perceptual learning by facilitating the developm ent of finer discrimination and enhanced chemosensory recognition. In turn, an improved dis crimination and recognition skill provides the foundations for constructing a sophisticated kn owledge of wines that is tied to a precise lexicon of wine descriptive terms. Dr. Gordon Bauer Division of Social Sciences
iv List of Figures Figure. 1: Peripheral olfactory system............. ................................................... ...........................21 Figure. 2: Inside the olfactory bulb............... ................................................... ..............................26 Figure. 3: Mammalian tongue and gustatory papillae. ................................................... ...............33 Figure. 4: The taste bud........................... ................................................... ...................................33 Figure. 5: Neuroanatomical directions.............. ................................................... ..........................47 Figure. 6: Central olfactory structures............ ................................................... ............................50 Figure. 7: Model of central olfactory pathway...... ................................................... .....................51 Figure. 8: Central gustatory structures............ ................................................... ............................68 Figure. 9. Model of central gustatory pathway...... ................................................... .....................69
v Table of Contents Acknowledgements................................... ................................................... ...................................ii Abstract........................................... ................................................... ............................................iii Acknowledgements................................... ................................................... ..................................iv Chapter.1 Introduction............................. ................................................... .....................................1 Wine tasting....................................... ................................................... ................................................... .1 Smell and Taste in Humans......................... ................................................... .........................................1 Thesis Goals...................................... ................................................... ................................................... 4 Research Through The Years........................ ................................................... .......................................5 Events of The Peripheral Chemosensory Systems..... ................................................... ..........................7 Central Chemosensory Projections.................. ................................................... .....................................9 Psychological Foundations of Wine Expertise....... ................................................... ............................12 Summary........................................... ................................................... ..................................................1 5 Chapter. 2 Peripheral Olfactory and Gustatory Syste ms................................................. ..............16 Introduction....................................... ................................................... ..................................................1 6 Olfaction.......................................... ................................................... ................................................... .18 Olfactory Epithelium............................... ................................................... ........................................18 Olfactory Neurons.................................. ................................................... .........................................19 Receptors.......................................... ................................................... ...............................................20 Odorant Signal Transduction........................ ................................................... ..................................22 The Olfactory Bulb................................. ................................................... .........................................25 Olfactory Coding in the Periphery.................. ................................................... ................................28 Gustation.......................................... ................................................... ................................................... .30 Gustatory Epithelium............................... ................................................... .......................................30 Taste Buds......................................... ................................................... ..............................................30 Taste Cells........................................ ................................................... ...............................................31 Receptors.......................................... ................................................... ...............................................35 Tastant Transduction............................... ................................................... ........................................39 Gustatory Coding in the Periphery.................. ................................................... ................................41 Conclusion......................................... ................................................... ..................................................4 3 Chapter. 3 The Neural Substrates of Olfaction, Gust ation and Flavor................................... .......44 Introduction....................................... ................................................... ..................................................4 4 Central Olfactory System........................... ................................................... .........................................48 Anatomy............................................ ................................................... ................................................48 Primary Olfactory Structures....................... ................................................... ...................................48 Rostromedial Olfactory Structures.................. ................................................... ................................49 Secondary Olfactory Structures..................... ................................................... .................................52 Connections........................................ ................................................... .............................................52 Function: Neural Processing of Olfactory Informatio n.................................................. ......................54 Odor Intensity..................................... ................................................... .............................................56 Odor Quality....................................... ................................................... .............................................57 Odor Memory and Olfactory Learning................. ................................................... ..........................59 Odor Discrimination................................ ................................................... ........................................62 Odor Recognition and Identification....... ................................................... ........................................64 Central Gustatory System........................... ................................................... .........................................65 Anatomy.......................................... ................................................... ..................................................6 5 Primary Gustatory Relay............................ ................................................... .....................................65
vi Primary and Secondary Gustatory Cortex............. ................................................... ..........................66 Connections........................................ ................................................... .............................................67 Function: Neural Processing of Gustatory Info rmation............................................ ............................70 Taste Quality ..................................... ................................................... .............................................72 Taste Intensity.................................... ................................................... .............................................74 Flavor Perception.................................. ................................................... ...............................................75 Central Representation of Retronasal Olfaction..... ................................................... .........................76 Functional Neuroimaging Data of Flavor Perception.. ................................................... ...................78 Conclusion......................................... ................................................... ..................................................8 0 Chapter. 4 The Psychology of Wine Expertise........ ................................................... ...................82 Introduction....................................... ................................................... ..................................................8 2 Understanding Wine Expertise....................... ................................................... .....................................87 Perceptual Learning........................... ................................................... .............................................87 Perceptual Skill.............................. ................................................... .................................................90 Conceptual Change............................. ................................................... ............................................96 Descriptive Skill............................. ................................................... ..............................................103 Conclusion......................................... ................................................... ................................................110 Chapter. 5 Conclusion.............................. ................................................... .................................114 Bibliography....................................... ................................................... ......................................121 Image Bibliography................................. ................................................... .................................132 Appendix I. List of Abbreviations.................. ................................................... ..........................134 Appendix II. Glossary of terms..................... ................................................... ............................136
1 Chapter 1 Introduction Wine is a complex beverage made up of hundreds of diverse odor and taste compounds, which humans have been consuming for tho usands of years. Wine tasting, or the critical assessment of wine, is a means by w hich humans have enhanced their appreciation for the olfactory and gustatory attrib utes of wines. Wine experts, also known as sommeliers, are individuals who through ex tensive training and experience, have developed skills to objectively evaluate the a roma and flavor of wines. This expertise weighs heavily upon the olfactory and gus tatory sensations that occur during the tasting process, and how they are ultimately perceived. Humans experience a variety of odors and tastes ei ther through the consumption of food and drinks, or by breathing in the air of o ur environment (Kandel et al. 2000; Spector 2000). Independently and together, the che mical senses allow humans to interact with countless chemical stimuli within our world. For most animals, including humans, olfaction provides information about potential dang er, food selection, and social interactions (Kandel et al. 2000; Rawson 2000). Wh ile, taste imparts information about the ingestion and/or rejection of foods, extracted from the five taste qualities: salty, bitter, sour, sweet, and umami. The fifth taste umami is a lso known as savory. It is a unique taste quality that is associated with glutamate. T hese five sapid sensations enable humans to evaluate food pertinent to the maintenance of th eir energy supply and electrolyte balance, as well as to avoid foods that are toxic o r spoiled (Simon et al. 2006; Breslin 2001; Smith and Davis 2000; Spector 2000).
2 Humans are generally deemed microsmic, possessing a poor sense of smells, with inferior olfactory abilities compared to other mamm als (Shepherd 2004). By and large, humans rely on other sensory channels, like sight, audition, and touch, to evaluate the world. Accordingly, humans are not mammals that gr eatly depend on their sense of smell to get around, principally due to the fact that our noses are a good distance from the ground. In spite of this, like other mammals, huma ns are capable of detecting and discriminating a large library of odors (Gottfried 2006; Shepherd 2004; Kandel et al. 2000). Humans are unique in that we employ higher cognitive processes to evaluate our experiences with different olfactory and gustatory stimuli. Our extraordinary capacity to appraise food and beverages is especially seen in o ur reflections of the percept of flavor. It is therefore argued that because humans are skil led at discriminating odors and tastes, and using language to describe flavor perceptions, we are not as poor at olfaction as we are historically assumed (Gottfried 2006; Shepherd 2005; Kandel et al. 2000). Since everything we eat and drink must enter throu gh the oral cavity, a portal for both odors and tastes is provided for the generatio n of chemical sensations in response to food items and beverages. Olfaction and gustation are the largest contributing senses in the perception of flavor (Shepherd 2006; Breslin 20 01). Oral somatosensation also contributes to our sense of flavor, telling us abou t the temperature, fat content, spiciness, etc. of a food or beverage. Odors access the olfac tory epithelium by one of two paths: orthonasally, or retronasally (Welge-Lssen et al. 2009; Hummel 2008; Shepherd 2006; Small et al. 2004). When odors are transmitted ort honasally, by sniffing, they appear to exist in our external world. Conversely, odors tra nsmitted retronasally are perceived as a
3 fused part of the gustatory sensation in the mouth. Interestingly, the path through which odors reach the olfactory epithelium significantly alters how the odors are perceived. During eating and drinking, volatile odors are rel eased from food or beverage and travel retronasally to the olfactory epithelium suc h that both gustatory and olfactory sensations are thought to be experienced in the sam e location as a single sensation (Small 2008; Small and Prescott 2005). This powerful fusi ng of the two chemosenses causes the common confusion that retronasal olfaction is actua lly part of taste (Small 2008; Small and Prescott 2005). This phenomenon can be observe d if you plug your nose while eating. You will notice that very little informati on about the identity of food can be obtained from just taste, a common phenomenon also experienced during a cold when food appears tasteless. Taste does not function as an independent sense since it is typically perceived as part of flavor, which is the perceptual culmination of oral chemosensory, and somatosensory stimulus informatio n (Small 2008; Shepherd 2006; Simon et al. 2006; Small 2006; de Araujo et al. 200 3; Laing and Jinks 1996). Therefore, gustatory qualities, or tastes, solely refer to per ceived qualities of sweet, salty, sour, bitter, or umami in a food item or drink. Humans appear to have a cultural trend towards ide ntifying and describing chemosensory experiences, noticeably when we are ex posed to perfume, food, and beverages such as wine. Over the years, increasing ly more consideration has been paid to the development of superior chemosensory skills in humans to aid in the creation of perfume, as well as the assessment of food or drink As the domain of wine expertise has grown, the aptitude of a human to identify complex odors, tastes, and flavors among a host of others, and subsequently communicate their sensory experience, inspires
4 researchers to try to determine those facets of the olfactory and gustatory systems that facilitate the superior sensory abilities of a wi ne expert (Jackson 2009; Hughson 2008; Parr 2008; Castriota-Scanderbeg et al. 2004). It h as been reported that wine experts are able to distinguish over 100 different components o f a taste based on the combinations of flavor and aroma (Small 2008; Shepherd 2006; Kandel et al. 2000). What accounts for a wine experts talent to discri minate among the aroma and flavor components and characteristics of a wine upo n smelling and subsequently tasting it? Moreover, what allows experts to accurately des cribe the features of the wine they sample? Are wine experts genetically pre-determined with more acute chemosensory receptors, and an innate ability to discriminate th eir chemosensory perceptions? Or, is wine expertise a skill that is learned and honed th rough training and experience with wines? When asking these questions, it is pertinent to remember that a wine itself does not have a taste, or smell, these are percepts of t he human brain, and are inherent to the perceiver. Furthermore, the representation of a wi ne is the interpretation by an individual at a specific physiological and psychological condi tion, at a given time (Herdenstam et al. 2009; Jackson 2009; Parr 2008; Shepherd 2006; Hughs on and Boakes 2001). In this thesis, I address wine expertise in terms of the significance of the peripheral chemosensory systems, and their contribu tions to the initial odor and taste code. I proceed by reviewing the anatomy and ensui ng neural substrates of olfactory, gustatory, and flavor processing, paying attention to areas of connectivity and integration throughout these neural systems. Lastly, I address the cognitive components such as perceptual learning, memory, and knowledge that con tribute to the skilled discriminative and descriptive performance of wine experts. I wil l review the literature that attends to
5 these questions with specific attention paid to the roles of the olfactory and gustatory systems. Throughout the years, researchers have been faced with challenges in developing precise methods, which accurately elucidate and por tray the events taking place at the various levels of integration in the chemosensory s ystems during evaluation and description of a wine. It is of interest how the c hemical sensation begins with the interaction of odor or taste stimuli at the sensory epithelium to initiate a distinctive sensory percept. There is also inquiry into how th e signals from the chemosensory receptors are then processed and coded in the corti ces as a specific neural representation to be synthesized into an odor, taste, or flavor pe rception. Additionally, researchers are still working to classify how and what sorts of cog nitive processes are orchestrated together to allow humans to gain expertise in the e valuation, discrimination, recognition and description of wine. In 1955, researchers Gibson and Gibson inquired, what defines a wine expert? Hughson and Boakes (2002) defined wine expertise as the superior ability to discriminate between, recognize and describe differ ent wines. Consequently, where in the chemosensory systems does recognition and discr imination of odors and flavors start? To begin to disentangle the intricacies of the olfa ctory and gustatory systems and their roles in wine sensory analysis, researchers have tr ied to illustrate the structural characteristics of odor or taste stimuli. It is th ought that by modeling the chemical structure of an odorant or tastant, researchers wil l likely be more able to comprehend the representation of odor and taste compounds, respect ively, in the human olfactory and gustatory systems.
6 An odorant is a volatile chemical, which interacts with the receptors of the olfactory epithelium to elicit a smell sensation (J ackson 2009; Shepherd 2005; Rawson 2000). An odor is typically composed of a mixture of volatile compounds, classified according to common features like chain length, as well as number and polarity of side groups (Gottfried 2006; Rawson 2000). Chemical and molecular features of the odor stimulus like side groups, polarity, molecular weig ht, conformation, and bond types, are shown to be vital in determining the odorous qualit ies of the compound. These are the fundamental sensory elements (primitives) of a smel l, and represent the within-molecule features that are detected by and processed in the peripheral sensory pathway (Shepherd 2005). These odor determinants control which receptor pro teins will interact with the odor compound, and consequently, the pattern of olf actory neuron activity elicited by those receptor interactions (Jackson 2009; Floriano et al. 2004; Rawson 2000). However, correlating odor ligands (compounds) with their res pective receptors is the greatest challenge in chemosensory research. In regards to olfaction, the major question is how over 300 receptor proteins account for humans abil ity to detect over one thousand different odors (Parr 2008; Buck 2004; Thorngate 19 97). In the end, this is linked to our poor understanding of how odorant structure determi nes receptor recognition, in other words, which receptor proteins recognize features o f the odorant. This is compounded by the fact that molecules that are structurally very similar can either have dissimilar perceptual qualities, or similar perceptual qualiti es (Wilson and Sullivan 2003). A tastant is characterized as the one of the five qualities: salty, sweet, sour, bitter and umami (Small 2006; Simon et al. 2006; Breslin 2 001; Kandel et al. 2000; Rawson
7 2000; Smith and Davis 2000). Taste receptors of the taste bud are tuned to recog nize all ligands (tastants) representative of the quality th e receptor is tuned to, such that sweet receptors only recognize sweet compounds, and bitte r receptors recognize bitter compounds, likewise for umami compounds (Bachmanov and Beauchamp 2007; Roper 2007; Tomchik et al. 2007; Simon et al. 2006). On the other hand, salt and sour qualities are conducted across ion channels, which are docume nted as conducting both types of taste compounds (Roper 2007; Chandrashekar et al. 2 006; DeFazio et al. 2006; Sugita 2006; Glendinning et al. 2000). Only specific rece ptors respond to a given quality, but that receptor is tuned to respond to various compou nds representative of that quality. Other common taste descriptors such as minty, spicy or hot, are representative of the oral somatosensory modalities critical to gustatory perc eptions (Breslin 2001; Glendinning et al. 2000). Although oral somatosensation is an int egral sense in the percept of flavor, this thesis will focus on the involvement of olfaction a nd gustation in flavor perception and wine expertise. Nevertheless, gustation is a multi dimensional sense that relies on the unification of smell, taste, and tactile informatio n from the oral space to create a flavor perception (Jones et al. 2006; Shepherd 2006; Simon et al. 2006; Liang and Jinks 1996). Therefore, a taste substance is wholly defined alon g olfactory, gustatory and oral somatosensory dimensions to address how it is able to stimulate a variety of senses (Breslin 2001). Minor organization and encoding of information abo ut the odor or taste compounds occurs in the peripheral system so that v arious characteristics of the odorant or tastant are embedded in a signal (Ishimaru 2009; Jackson 2009; Chandrashekar et al. 2006; Rawson and Yee 2006; Simon et al. 2006; Buck 2004; Meierhenrich et al. 2004;
8 Floriano et al. 2004). The fundamental role of the peripheral systems is to detect, transduce and encode olfactory and gustatory stimul i. Information processing in the peripheral olfactory systems is thought to function through combinatorial coding, such that odor information is transmitted as patterns of cellular activity across the olfactory epithelium and olfactory bulb (Jackson 2009; Rawson and Yee 2006; Christensen and White 2000). Gustatory information coding has been the topic of much debate since it is unclear whether taste information is transmitted al ong labeled-lines, or in an across-fiber pattern (Ishimaru 2009; Chandrashekar et al. 2006; Jones et al. 2006; Simon et al. 2006; Smith and St. John 1999). The labeled-line model s uggests that taste information is processed through segregated circuits, so that indi vidual taste receptor cells detect only one quality. The across-fiber pattern model contra stingly proposes that individual taste cells recognize more than one quality, and that tas te information is represented in a pattern of activity across cells. Overall, the cod ing of odor and taste information in the periphery is important to ones ability to learn ab out odors and tastes in the environment. Regardless, these peripheral systems neither predic t nor define an individuals ability to develop advanced discriminatory and descriptive ski lls of wine expertise (Gottfried 2008; Parr 2008; Wilson and Stevenson 2003b). Odorant receptors fixed in the olfactory epitheliu m directly transmit a signal about an odors structure along the olfactory crani al nerve (C.N. I) to the olfactory bulb (Gottfried 2006; Kratskin and Belluzzi 2003). The axons of the neural output cells of the olfactory bulb coalesce to form the olfactory tract and allow information about the identity of an odor to reach central olfactory area s (Cleland and Linster 2003). In contrast to odorant receptors, taste receptor cells sense taste qualities and then
9 communicate this information to other cells that po ssess synaptic connections in the taste bud (Roper 2007; DeFazio et al. 2006). Once stimul ated, synaptic cells excite the peripheral gustatory afferent fibers of the gustato ry cranial nerves and transmit a message about the quality of a taste. Taste buds in the an terior tongue and soft palate are innervated by the afferent fibers of the chorda tym pani (CT) and greater superficial petrosal (GSP) branch of C.N. VII (Jackson 2009; Sm all 2006; Witt et al. 2003; Katz et al. 2002; Zatorre and Jones-Gotman 2000). The ling ual branch of C.N. IX innervates the posterior tongue and the superior laryngeal branch of C.N. X innervates the laryngeal and pharyngeal areas of the oral cavity. The central processing of smell, taste and flavor in humans, highlights the highly integrative nature of chemosensory perceptions. Od orant information from the olfactory bulb is projected through the olfactory tract to th e primary olfactory cortex within the frontal and temporal lobes of the brain (Gottfried 2006; Cleland and Linster 2003; Zald and Pardo 2000; Zatorre and Jones-Gotman 2000). Th e principal receivers of the olfactory tract include the regions of the piriform cortex (facilitates the development and encoding of odor memories), amygdala (associated wi th emotion-related memories and social interaction), and rostral entorhinal cortex (involved in consolidating memories) (Jackson 2009; Howard et al. 2009; Zelano et al. 20 09; Li et al. 2006; Kratskin 2003; Cleland and Linster 2003). The primary olfactory c ortex is extensively interconnected through corticocortical fibers to the orbitofrontal cortex, insula, additional amygdala subnuclei, thalamus, hypothalamus, basal ganglia, a nd hippocampus (Cleland and Linster 2003; Wilson and Sullivan 2003). The primary olfac tory cortex also sends feedback connections to the olfactory bulb, thereby creating pathways for the top-down regulation
10 of olfactory information processing. Coupled toget her these neural olfactory areas generate the basis for odor-guided directives of be havior, feeding, emotion, and memory (Gottfried 2008; Gottfried 2006; Wilson and Stevens on 2003a; Wilson and Stevenson 2003b; Savic et al. 2000; Zald and Pardo 2000; Jone s-Gotman and Zatorre 1993). Experience with odors has a substantial impact on odor perception. A scent, whether orthoor retronasal, is able to pull up a memory from the past in which that odor was first experienced, making odors tools for some intuitive and emotional knowledge of the world (Wilson and Stevenson 2003a; Wilson and S tevenson 2003b; Wilson and Sullivan 2003; Le Gurer 2002; Rawson 2000). When odors are repeatedly experienced, neurons build expanded synaptic connections. In th e future, when an odor pattern is recognized, it concurrently recalls other memories with which it was developed. When humans decide to ingest food, factors like its appe arance, familiarity, odor, texture, temperature, post-ingestive effects impacts our cho ice. This decision is influenced by the social, emotional, and cognitive context it which i t is presented (Gottfried 2006; Simon et al. 2006; Rawson 2000). Through the olfactory syst ems close ties with the areas of the brain involved in emotion, learning, and memory, th e evocativeness of odor-associated memories is facilitated (Jackson 2009; Wilson and R ennaker 2009; Wilson and Stevenson 2003a; Wilson and Stevenson 2003b; Christ ensen and White 2000; Rawson 2000). Taste information from cranial nerves VII, IX and X projects to the rostral solitary nucleus and tract, synapsing with first-order neuro ns in the medulla (Small 2006; Rolls and Scott 2003; Witt et al. 2003). From there fibe rs ascend the brainstem and project to thalamus where they synapse with second-order neuro ns of the ventroposterior medial
11 nucleus of the thalamus (Small 2006; Breslin 2001). Dorsal thalamic projections terminate on areas of the anterior insula and front al operculum. The caudolateral orbitofrontal cortex receives direct projections fr om the anterior insula and overlying operculum, and also projects back to the insula and operculum (Small 2006: Katz et al. 2002). The amygdala receives gustatory information from both the orbitofrontal cortex and anterior insula (Jones et al. 2006; Small 2006) Although, there are feedforward and feedback connections between the central and periph eral gustatory systems, unlike olfaction, little is known about top-down controls of gustation (Rolls and Scott 2003). Each of these cortical areas deals with varying asp ects of gustatory perceptions, with each region respectively processing different components of the neural code for taste (Small 2006; Kringelbach et al. 2004; Schoenfeld et al. 20 04). The multimodal experience of flavor is seen as an overlapping representation of the varying contributing sensory modalities within the paralimbic cortex (Shepherd 2006; Small 2008; Small 2006; Small and Prescott 2005). In the course of investigations of the olfactory and gustatory areas, researchers have iso lated a network of areas responsible for odor/taste integration and ultimately flavor percep tion (Small 2008; Small et al. 2007; Small and Prescott 2005; de Araujo et al. 2003; Lia ng and Jinks 1996). Taste and smell are both unimodally represented in the insula, oper culum, and orbitofrontal cortex, however, independent presentation of either stimula tes overlapping activation in these regions (Small et al. 2007; Small 2006; Kringelbach et al. 2004; de Araujo et al. 2003; Rolls and Scott 2003; Gottfried et al. 2002; Savic et al. 2000; Small et al.1997a). This evidence has led to the suggestion that these areas play a vital role in the integration of the distinct sensory input that make way for the pe rception of flavor.
12 The fusing of the chemosensory modalities into the holistic percept of flavor creates stable associations between the two modalit ies (Small et al. 2007; Small and Prescott 2005; Small et al. 2004). Odors that have strong connections with sweetness, such as strawberry, have the greatest influence on enhancing the sweet taste of sugars. These odors are likewise capable of reducing the pe rceived sourness of citric acid (Jackson 2009; Small et al. 2004). Reciprocally, t aste qualities have strong influence on the perception of associated odor qualities, such a s sweetness evoking the perception of fruitiness in odors. The stability of these crossmodal associations helps to explain why aromatic compounds appear to have gustatory attribu tes, and tastes influence the perceived odor intensity. It is my hypothesis that the skill of wine experts to discriminate, recognize, and describe odor and taste components and overall qual ity of a wine, is due to higher cognitive processes of the central nervous system, in particular perceptual learning. J. J. Gibson (1963) described perceptual learning as any relatively enduring and consistent change in the perception of a stimulus array, a phe nomenon following practice or experience with the array. Through perceptual lear ning, wine experts are believed to be able to gain a specific knowledge of wines and wine related information that is further supported with a lexicon of wine relevant descripto rs (Hughson 2008; Wilson and Stevenson 2003a; Wilson and Stevenson 2003b; Hughso n and Boakes 2001; Gawel 1997). Research that reveals learning is a major c ontributor to wine expertise, and an innate, or genetically determined superior sensory ability does not underlie wine expertise, is used to support this hypothesis (Gott fried 2008; Parr et al. 2004; Wilson and Stevenson 2003b; Parr et al. 2002; Bende and Nordin 1997; Livermore and Laing 1996).
13 It should be noted that learning and experience do not influence a humans basic sensitivity to chemosensory stimuli. Instead, lear ning and experience through training modify the cognitive components of perception withi n domain-specific experiences (Gottfried 2006; Wilson and Stevenson 2003a; Wilson and Stevenson 2003b; Hughson and Boakes 2001). These modifications are subsequ ently reflected as changes in cognitive functions like perception, memory and con ceptualization that allow for the development of expertise in a domain (Ballester et al. 2008; Parr et al. 2005; Hughson and Boakes 2002; Parr et al. 2002; Gawel 1997; Solo mon 1997). Wine experts are statistically superior at recognizing, discriminati ng, and describing different wines as a result of the changes that occur to their cognitive processes (Ballester et al. 2008; Hughson 2008; Parr 2008; Parr et al. 2004; Hughson and Boakes 2002; Parr et al. 2002; Hughson and Boakes 2001; Bende and Nordin 1997; Gaw el 1997; Solomon 1997; Livermore and Laing 1996; Solomon 1990; Lawless 198 4). In Young (1986), three things are necessary for th e proper training of the sensory perceptions in reference to wine. First, one must have knowledge for how a wine appe als to the various senses, and how those senses respond. Second, a disciplined c oncentration, which allows one to identify minute traces of chemical substances, as well as a multitude of other wine components, must be developed, thereby creati ng a memory that will recall characteristics of an odor or taste. Third, a pre cise language and vocabulary must be used to describe the objective qualities of a w ine and communicate ones experience with that wine.
14 Little is known about the precise cognitive process es involved in wine sensory analysis, but the sophistication of the senses in regards to expert wine analysis is investigated by studying the perceptual, learning, semantic and epi sodic memory, and thinking processes of humans (Parr 2008). When wine experts go through the process of tastin g a wine they first let the aroma of the wine, orthonasally reach the receptors of the olfactory epithelium. They continue the process by sipping from the glass and holding the wine in their mouth. In the mouth, volatile odors are released and travel r etronasally. Taste qualities present in the wine, usually sweet, sour, or bitter, are sense d by taste cells in the taste buds dispersed across the tongue. Additionally, textura l and temperature qualities of the wine are transduced by somatosensory fibers innervating the tongue. Combined, these four sensory qualitiessmell, taste, and temperature an d touchcreate information about the wines flavor. The sensory analysis/evaluation of wine, displayed through discriminative and descriptive performance, has two goals: quality eva luation and description of wine properties (Parr 2008; Young 1987). Qualitative se nsory descriptions usually refer to the perceived characteristics of the stimuli and their intensities (Gawel 1997; Amerine and Roessler 1983). Information about the relative int ensities of the appearance, aroma, taste and textural attributes of a wine, and how these el ements relate to each other in terms of balance and structure, are also conveyed in sensory descriptions. Wine descriptions are also personal comments that describe whether a wine met the tasters expectations (Gawel 1997).
15 Although the messages from the periphery contain p ertinent chemosensory information, it is the cortical chemosensory struct ures that are largely responsible for the creation of odor, taste, and flavor perceptions. T he extensive feedforward and feedbackward connectivity between the central and p eripheral chemosensory areas allow the two systems to work cohesively to design percep tions of smells, tastes, and flavors. Nonetheless, wine expertise would not fully develop without the peripheral olfactory and gustatory systems, which have the initial responsib ility of sensing and transducing (encoding) primitive features of the odor and taste objects. By reviewing the several levels of processing and i ntegration that are vital to wine sensory analysis, I explore the roles both the peri pheral and central chemosensory systems play during critical assessment of wine. W ine expertise is specifically due to the refinement of cognitive functions when developing d omain-specific expertise. Smelling and tasting a wine creates a pattern of sensory rec eptor activation in the periphery. The information about the aromas (odor) and flavors (od or-taste) composing a wine is subsequently represented in the central olfactory a nd gustatory structures. These structures have the responsibility of encoding vari ous dimensions of the stimulus including its quality, intensity, cross-modal assoc iations, and memories. Through practice and experience with evaluating the qualiti es of wine, a series of essential cognitive functions such as integration of sensory modalities (taste, smell, oral somatosensation, vision), memory, perceptual learni ng, and conceptual knowledge are modified. Individuals become more adroit at organi zing their perception to subsequently retrieve, more specific and meaningful information from memory (Hughson 2008; Parr 2008; Hughson and Boakes 2002; Gawel 1997; Solomon 1997).
16 Chapter 2 Peripheral Olfactory and Gustatory systems Introduction When a molecule stimulates the olfactory epitheliu m or taste buds, an intricate series of reactions are initiated. The binding of a chemical stimulus activates receptors or channels to convert the energy created from interac ting with a molecule, into a signal that passes on to the central nervous system to create t he perception of a particular smell or taste. The peripheral olfactory and gustatory syst ems enable humans to interact with and analyze odorants and tastants within their environm ent. But how is this possible if there are countless odors and tastes that individually co mposed of a myriad of molecular components? This chapter addresses the sensory cell s of the olfactory and gustatory epitheliums, considering our current understanding of the transduction and coding events that occur in peripheral chemosensory systems, and highlighting what importance the initial chemosensory events have in coding of odor or taste information that will be passed onto the central olfactory and gustatory str uctures. The chemosensory pathway requires integration at e ach point within the system to sense and qualitatively encode odors and tastes. H ow is this accomplished at the level of the receptor? In olfaction, the specialized odorant receptors of the olfactory epithelium are designed to have broad selectivity and acute se nsitivity for the detection and discrimination of a large library of odor compounds (odorants). Additionally, the receptors are capable of responding to the intensit y and quality of the odorant, a vital component of the odor code (Nef et al.1992). As fo r gustation, humans are known to respond to five categories of tastants, which are s alt, sour, bitter, umami and sweet.
17 These taste qualities are mediated through differen t transduction pathways, specified by the expression of receptors or ion channels that se nse ligands or conduct ions representative of a particular taste quality, respe ctively (Smith and Margolskee 2001; Adler et al. 2000; Kinnamon and Cummings 1992). Re ceptors and ion channels for taste compounds are specifically tuned to respond to only one particular taste quality, i.e. sweet, bitter, umami, sour or salt. However, the r eceptors and ion channels are also broadly tuned to recognize various stimuli, which a re representative of the taste quality to be detected. Sensory coding of information about the physical c haracteristics of a chemical stimulus is fundamentally about how the stimulus is recorded and filtered during transduction, and about how information continues t o be filtered and integrated at various levels along the complete pathway (Breslin and Huan g 2006). Investigations about the nature of the olfactory code reveal a peripheral sy stem that interacts with structural features of an odor complex, and combines the infor mation from the responses of various odorant receptors activated by an odorant. Axons o f the olfactory receptor neurons project and converge on specific second order neuro ns in the olfactory bulb, where a second level of organization and integration of the olfactory message occurs. Likewise, the gustatory code is established through the respo nses of multiple receptors to a particular taste quality. Receptor cells transmit the message to adjacent synaptic cells, which in turn, have projections that converge on pa rticular afferent fibers. Generally, the spatial and temporal aspects of the odor or taste s timulus are incorporated into the sensory code, and these components account for vari ous characteristics of the quality and intensity perceived by an individual.
18 It is important to note that the peripheral chemos ensory systems of humans are largely similar to that of other mammals, in terms of function, epithelium, cellular morphology, sensory transduction, information encod ing, and behavior. However, the majority of the research on chemosensation in the p eriphery has not been drawn from human studies. Our current understanding of the ce llular morphology and molecular physiology of the mammalian olfactory and gustatory systems is largely compiled from studies in mice and rats. These rodents have serve d as model systems for olfaction and gustation research given that the have extremely si milar peripheral systems to sense and encode the characteristics of odor and taste compou nds. Olfaction The Olfactory Epithelium The olfactory epithelium (OE) is located in the su perior region of the nasal cavity and it is the site where odorant molecules first in teract with olfactory receptor neurons (ORNs) [Note: a list of abbreviations can be found in Appendix I] (Doty 2001; Morrison and Costanzo 1990). Initial histological examinati ons of the OE indicated that it is assembled in several layers of cell nuclei with epi thelial cells concentrated in different regions through out the epithelium (Farbman 1992). It has been revealed that the OE is a pseudo-stratified epithelium made up of three main cellular components that are morphologically and biochemically distinct. These are bipolar sensory neurons and nonneuronal supporting (sustentacular) cells. There i s also a thin basal lamina of globose and horizontal basal cells that serve as progenitor cells of the OE (Menco and Morrison 2003; Doty 2001; Farbman 2000; Morrison and Costanz o 1992).
19 Olfactory neurons Olfactory sensory neurons comprise a bipolar soma t hat extends a dendrite into the apical OE, and an unmyelinated axon that projec ts basally toward second order neurons in the olfactory bulb (Menco and Morrison 2 003; Moon and Ronnett 2003; Doty 2001; Firestein 2001; Farbman 2000; Schild and Rest repo 1998; Farbman 1992; Morrison and Costanzo 1990). Individual axons join together to form small bundle of nerves, known as fascicles that project through the cribiform plate to terminate in glomeruli structures of the olfactory bulb. Numero us axons are ensheathed by Schwann cells into a single mesaxon to form the olfactory n erve, cranial nerve I (C.N. I) (Doty 2001; Farbman 2000). A single, un-branched dendrite grows from the apica l region of the soma of the neurons, and extends into the OE. When mature, the dendrite terminates as a knob-like swelling with numerous non-motile cilia extending o ut into neuroepithelium (Moon and Ronnett 2003; Kandel et al. 2000; Farbman 1992; Mor rison and Costanzo 1990). These cilia vary in their lengths, and ultimately grow in to a densely packed blanket, lying in the mucus of the OE (Doty 2001; Firestein 2001; Farbman 1992; Morrison and Costanzo 1992; Morrison and Costanzo 1990). There is signif icant evidence that supports the ciliary extensions as the sites for odorant detecti on, provided by the data collected in physiological, morphological, and biochemical studi es, which depict the necessity of cilia in the transduction pathway (Doty 2001; Firestein 2 001; Farbman, 1992). Thus, they are recognized as the site where odorant compounds firs t elicit sensory transduction of olfactory stimuli (Floriano et al. 2004; Moon and R onnett 2003; Firestein 2001). Furthermore, electrophysiological data indicate tha t odorant sensitivity and odorant-
20 induced currents are homogeneously dispersed across the cilia (Moon and Ronnett 2003). This evidence implies that the cilia house all the machinery required for the first signal response to odorants. Receptors When the proteins assumed to be odorant receptors ( ORs) were first discovered, and identified, they belong to the family of G-prot ein coupled receptors (GPCRs) (Munger 2009; Buck and Axel 1991). GPCRs are a fam ily of transmembrane receptors, coupled to guanosine triphosphate (GTP)-binding reg ulatory proteins (G-proteins) that are activated by extracellular molecules to initiat e intracellular signal transduction (Kandel et al. 2000). Most mammals have olfactory GPCRs to signal the presence of odor stimuli by initiating a biochemical cascade wi thin the receptor cell (Munger 2009). Electrical activity measurements in ORNs have ascer tained that these proteins are functional odor receptors (Munger 2009; Menini et a l. 2004; Moon and Ronnett 2003; Doty 2001; Firestein 2001). Genomic libraries furt hered this line of evidence by illustrating vertebrates have as many as 1000 olfac tory receptor genes, with humans having around 300-400 functional genes encoding for ORs (Buck 2004; Menini et al. 2004; Moon and Ronnett 2003; Firestein 2001). ORs possess the same general structure as other GP CRs, including seven helical transmembrane motifs, which contain the sites belie ved to interact with the incoming odorants (Floriano et al. 2004; Doty 2001). Consid erable differences exist in the sequences of the third, fourth and fifth transmembr ane regions, most likely accounting for a ligand binding pocket (Menini et al. 2004). The extreme variability observed in these regions has provided a molecular foundation for con ceptualizing the range and diversity
21 Figure. 1: Peripheral olfactory system. An enlargem ent section illustrating the olfactory receptor neurons and their connections to the olfactory bulb. Olfactory receptor neurons are embedded in the olfactory epit helium and they projects their axons to the olfactory bulb. Image based on Rinaldi (2007).
22 of odorants detected and discriminated by ORNs (Fir estein 2001). Studies suggest that each OR is narrowly tuned to sense a few odorants w ith particular structural features, known as odotopes (Farbman 2000). Calcium imaging studies, as well as single-cell reverse transcriptase RT-PCR, has shown that within a single ORN, only one type of OR protein is expressed (Rawson and Yee 2006; Wilson a nd Mainen 2006; Buck 2004; Meierhenrich et al. 2004; Rawson et al. 1997). Add itionally, electrophysiological evidence demonstrates that each ORN is responsive t o a wide, but limited range of odorants (Doty 2001). In other words, the protein expressed enables the ORN to interact with numerous discrete odorants. In turn, a partic ular odorant is capable of eliciting a response from various different ORs (Buck 2004; Flo riano et al. 2004; Menini et al. 2004; Moon and Ronnett 2003; Firestein 2001; Nef et al. 1992). These studies ultimately demonstrate that olfactory receptors can have a hig h or low affinity for a particular odorant and when that odorant interacts with multip le receptors the signal generated is a combination of these various ORN responses. Odorant signal transduction Once an odorant becomes bound to an OR, a cascade o f events is triggered to translate the chemical energy generated from bindin g, into a neural signal representing an odor (Kandel 2005; Floriano et al. 2004; Matthews a nd Reisert 2003; Moon and Ronnett 2003; Doty 2001). Before the OR has bound an odor ant molecule, the GPCR it is in an inactive state, and thus bound to guanosine diphosp hate (GDP) (Kandel et al. 2000). When an odorant binds to an OR, the GPCR undergoes a conformational change and becomes dissociated from its G-protein. The G-prot ein then replaces GDP with a GTP, thereby activating second messengers that are requi red to open ion channels embedded in
23 the cellular membrane (Rawson and Yee 2006; Ache an d Restrepo 2000; Farbman 1992). Activation of these second messengers stimulates th e cell to depolarize. Upon reaching a depolarizing threshold, a current is induced and sp read passively throughout the cell, generating action potentials that are propagated al ong the olfactory axon (Pifferi et al. 2006; Rawson and Yee 2006; Menini et al. 2004; Matt hews and Reisert 2003; Moon and Ronnett 2003). Data from functional, genetic and c alcium (Ca2+) imaging studies demonstrates the existence of two distinct second m essengers systems in ORNs, both having a proposed role in sensory transduction of o dorants. In one signal cascade, the cyclic nucleotide cAMP i s implicated as the principal secondary effector (Moon and Ronnett 2003). In thi s pathway, the G-protein Golf dissociates from the GPCR complex, to associate wit h the enzyme adenylyl cyclase III (AC III), thereby stimulating increased AC III prod uction (Rawson and Yee 2006; Matthews and Reisert 2003; Firestein 2001; Ache and Restrepo 2000). As the concentration of ACIII increases, intracellular ade nosine triphosphate (ATP) is transformed into cyclic-3,5-adenosylmonophosphate ( cAMP), resulting in an increase in cAMP levels as well (Rawson and Yee 2006; Firestein 2001; Ache and Restrepo 2000). cAMP binds to cyclic nucleotide-gated channels (cNG cs), opening them to allow an influx of extracellular calcium (Ca2+) and sodium (Na+) to be conducted into the ORN (Matthews and Reisert 2003; Firestein 2001; Kandel et al. 2000). Increased intracellular Ca2+ and sodium (Na+) concentration causes the receptor cell to become depolarized (Rawson and Yee 2006; Menini et al. 2004; Firestein 2001). Additionally, prior to odorant activation, ORNs have a high concentration of intracellular chloride (Cl-). Ca2+ ions entering the cell also activate a chloride Clion channel (Pifferi et al. 2006; Rawson
24 and Yee 2006; Firestein 2001). When these negative ion channels open, an efflux of chloride occurs, and further adds to the positive d epolarizing charge the receptor cell builds up, during odorant stimulation. There is also evidence for production of a differen t second messenger, inositol triphosphate (IP3), in response to odorant stimulat ion (Rawson and Yee 2006; Moon and Ronnett 2003; Kandel et al. 2000; Farbman 1992). I n humans, the IP3 pathway mediates a component of the Ca2+ response (Pifferi et al. 2006; Rawson and Yee 2006 ). The intracellular enzyme phospholipase C (PLC) is activ ated when GTP becomes associated with it. The lipid phosphatidylinositol-4,5-bispho sphate (PIP2) is then hydrolyzed by PLC-GTP complex to produce IP3 and diacylglycerol ( DAG) (Rawson and Yee 2006). Like cAMP, IP3 and DAG are capable of acting direct ly on the cNGcs to elicit an influx of positive ions, like Ca2+, through the channel. IP3 production also stimula tes the release of Ca2+ from intracellular stores resulting in depolarizat ion of the cell (Rawson and Yee 2006; Moon and Ronnett 2003). When an odorant activates one of these two cascades the ORN builds a depolarizing charge that excites the cell to genera te self-propagating action potentials transmitted along the olfactory axon (C.N. I). Thi s triggers the release of glutamate where the olfactory axon synapses with second order neuronal glomeruli in the olfactory bulb. The rate of action potential generation and firing is determined by unique properties of an odorant, which elicit either excit atory or inhibitory neuronal activity within the receptor cells. This duality is believe d to exist to improve the signal to noise ratio generated by an odorant binding to high and l ow affinity ORs. And thought,
25 thereby, to enhance the signal from the ORs that ex hibit the largest responses to a particular odorant (Rawson and Yee 2006). The olfactory bulb The olfactory bulb (OB) has a triad of neuronal ele ments, an input fiber, an output neuron and an interneuron, essential in the transpo rt of odor information from the OE to the olfactory cortex (Kratskin and Belluzzi 2003). Two OBs emerge as rostral extensions from the cerebral hemisphere of the brain creating the bridge for olfactory information from the periphery to be processed before being sen t to cortical olfactory areas (Rawson and Yee 2006; Kratskin and Belluzzi 2003; Christens en and White 2000; Mori et al. 1999; Farbman 1992). The bulb is made of four cel l types, mitral cells (MCs), tufted cells (TCs), periglomerular cells (PGCs), and granu le cells (GCs), which stretch throughout five layers in the OB, to create an exci tatory and inhibitory neural network for odorant molecule processing (Kratskin and Belluzzi 2003; Farbman 1992). In the superficial glomerular layer, the axons of the ORNs project basally to the OB where they establish excitatory synaptic network s in glomeruli with the dendrites of MCs and TCs (Rawson and Yee 2006; Kratskin and Bell uzzi 2003; Mori et al. 1999; Farbman 1992). Glomeruli are distinct round masses of neuropil that work in conjunction with their output neurons as a fundamen tal coding unit within the OB, organizing the neural space in early olfactory proc essing. The glomeruli and their local neuronal circuits process and transmit odor specifi c information to the cortical areas by mediating lateral inhibition and firing discharges from the output neurons. MCs and TCs are the output neurons of the OB, and each possesse s primary and secondary dendrites
26 Figure. 2: Inside the olfactory bulb. Drawing of th e cells and their connections within the olfactory bulb. Periglomerular, mitral and tuft ed cells synapse with olfactory receptor axons inside a single glomerulus. Mitral a nd tufted cells also make reciprocal synapse with granule cells and are the output neuro ns of the bulb, carrying information to the central nervous system. Image based on Kandel et al. (2000).
27 that form excitatory and inhibitory connections wit h axons of the ORNs and interneurons (Farbman 1992; Price and Powell, 1970). The intern eurons, which regulate the activity of the output neurons, are PGCs and GCs (Schoppa an d Urbana 2003). The primary dendrites of MCs and TCs penetrate the glomeruli an d form excitatory synapses with the axons of the ORNs. A direct excitatory input that is glutamatergic is created by these connections, and functions to establish the firing signal of the output neurons (Schoppa and Urbana 2003; Christensen and White 2000). Acti vation of the primary dendrites of MCs also results in intra-glomerular excitation and can excite other MCs within a glomerular unit to further affect the output signal of these neurons (Schoppa and Urbana 2003). Only about 20 output neurons contribute den drites to a single glomerulus, so there is a strong convergence of the olfactory receptor a xons onto the dendrites of MC and TC in glomeruli. The primary dendrites of MCs also form dendro-dend ritic synapses inside a glomerular module, with the dendrites of PGCs (Scho ppa and Urbana 2003; Christensen and White 2000). These dendro-dendritic connectio ns establish an inhibitory GABAergic connection to mediate intra-glomerular in teractions. That is to say, PGCs inhibit communication between MCs within a given gl omerular unit. Additionally, PGCs form dendro-axonic synapses with ORNs to inhibit tr ansmission of their signal into the glomeruli, further regulating the firing pattern of the output neurons (Schoppa and Urbana 2003; Mori et al. 1999; Shipely and Ennis 19 98; Farbman 1992). Inhibitory connections made by PGCs decrease activity in the v icinity of activated glomeruli to enhance the contrast between highly activated glome ruli, and their neighbors. Additionally, signal discrimination is thought to b e increased or preserved, further
28 shaping the representation of the odor stimulus. T he secondary dendrites of MCs and TCs are associated with GCs through reciprocal dend ro-dendritic synapses that are inhibitory and GABAergic in nature (Rawson and Yee 2006; Kratskin and Belluzzi 2003; Schoppa and Urbana 2003; Christensen and White 2000 ; Mori et al. 1999; Price and Powell, 1970). Inter-glomerular interactions betw een the secondary dendrites of MCs and TCs projecting to different glomeruli are media ted by the GABAergic inhibitory activity of GCs (Schoppa and Urbana 2003; Mori et a l. 1999). These reciprocal connections establish a means of lateral inhibition to stop the activity of MCs in one glomerulus from influencing MC activity in another glomerulus. Ultimately, these varying connections exist to arb itrate interactions between functionally distinct MC and TC groups, with PGC re gulating mostly intra-glomerular interactions and GCs mediating inter-glomerular act ivity. These mechanisms are believed to exist for the refinement of odor-evoked activity, assisting in the creation of an odor code, which will eventually be deciphered into a particular olfactory perception in the higher cortical areas. Olfactory coding in the periphery ORNs expressing a particular OR protein are capable of binding to multiple odorants, and a given odorant is able to bind to a multitude of ORs (Rawson and Yee 2006; Buck 2004; Meierhenrich et al. 2004; Christen sen and White 2000; Mori et al. 1999). The broadly tuned nature of the ORNs begins the process of encoding an odorant since different structural features of a particular odorant are detected by ORs. These discrete structural features are thought to activat e a particular combination of ORs in such a way that different combinations of OR activation represent different odorants (Buck
29 2004; Meierhenrich et al. 2004; Uchida et al. 2000) This particular activation pattern serves to initially encode the identity of an odora nt by coding for its diverse structural features (Buck 2004; Meierhenrich et al. 2004). ORNs expressing the same OR converge their axons in to a particular glomerular unit, leading to the implication that each glomerul us is devoted to a particular OR (Johnson and Leon 2007; Rawson and Yee 2006; Uchida et al. 2000; Mori et al. 1999). These distinct observations of specific convergence have provided data in support of a combinatorial code for odorant information processi ng, a model that explains how humans are capable of distinguishing such a variety of odorants (Floriano et al. 2004; Menini et al. 2004; Meierhenrich et al. 2004; Moon and Ronnett 2003; Nef et al. 1992). This combinatorial strategy begins with the ORNs ex pressing a particular receptor whose axons converge onto a single glomerulus; subsequently, od orants will activate a certain set of overlapping but non-identical patterns of gl omeruli (Johnson and Leon 2007; Buck 2004; Firestein 2001; Uchida et al. 2000). The odorant code is established in the OB as a map of glomerular activation, so that each glomerulus is likely to reflect one class of activated odorant receptor (Schoppa and Urbana 2003; Uchida et al. 2000). In the OE, t he identity of an odorant is encoded across a set of ORNs, however, once the odorant inf ormation is carried to the OB it is represented by a stereotyped map of glomeruli stimu lation (Johnson and Leon 2007; Buck 2004; Uchida et al. 2000). This action is sen sed by the MCs, spurring a distinctive MC activity pattern that is further sharpened through the intraand inter-glomerular activity of the PGC and GC connections (Rawson and Yee 2006; Schoppa and Urbana 2003; Christensen and White 2000; Mori et al. 1999) These neuronal relationships
30 suggest that all components of the pattern contribu te to the code (Rawson and Yee 2006; Buck 2004) This activity is carried to the olfactory cortex by the axons of MCs and TCs to be decoded as a specific odor perception. Gustation Gustatory Epithelium The gustatory region of mammals consists of the to ngue, soft palate, pharynx and larynx areas (Finger and Simon 2000). The gustator y region is innervated by afferent fibers of cranial nerves (C. N) VII (Facial), IX (G lossopharyngeal) and X (Vagus). These three nerves are responsible for carrying informati on from the anterior and posterior tongue as well as the pharynx and larynx to the cen tral nervous system (Breslin and Haung 2006). Dispersed across these particular gus tatory areas are raised epithelial protrusions called papillae. Arrangements of papil lae housing taste receptor cells of taste buds are distributed in these areas, lingual papill ae are locate on the tongue and nonlingual papillae are located in the palate, pharynx and larynx (Bachmanov and Beauchamp 2006). Sensory transduction of taste sti muli is initiated in the oral cavity where tastants interact with the taste buds of the tongue, soft palate, pharynx and larynx to create a message that will ultimately be perceiv ed as taste. Taste Buds Taste buds (TB) are the focal units of gustatory r eceptors distributed throughout the oral space, and overall, TBs occupy a very low percentage of the total surface area of the circumvallate, foliate and fungiform papillae i n both lingual and extralingual locations (Herness and Gilbertson 1999; Roper 1989) Electron microscropy has revealed that TBs are highly organized bulb-shaped spherical structures of around 50-100 neuroepithelial cells. These comprise taste recept or cells, supporting (sustentacular)
31 cells, and basal cells (Simon et al. 2006; Gilberst on et al. 2000; Herness and Gilbertson 1999). Taste cells are elongate and span from the basal lamina to a small opening in the apex of the TB called the taste pore (Roper 1989). Taste Cells Ultrastructural and immunocytochemical profiling o f the mammalian TBs has characterized four varieties of intragemmal bipolar taste cells (TCs), type I, II, III and IV, embedded in the stratified epithelia of the gustato ry papillae (Ishimaru 2009; Lindemann 2001). These morphologically distinct TCs are also implicated with distinct roles in tastant detection, transduction events, and cellula r development (Ishimaru 2009). Furthermore, functional imaging and immuno-staining techniques have allowed researchers to identify the individual, and distinc t roles each of these cells play in the interaction with tastants (Roper 2007). Type II ce lls microvilli accommodates the receptor proteins and ion channels responsible for signal detection of sweet, umami, bitter and salty taste stimuli, while type III cells detec t sour stimuli and posses the synaptic connections responsible for producing the final out put signal of the TB (Roper 2006, Simon et al. 2006). Type I cells ensheath type II cells and are thought to modulate TC activity. Lastly, basal cells serve as the progeni tor cells within the bud. Type I, II, and III are thin columnar TCs that are structurally differentiated on the basis of their microvilli, nucleus shape, and cytop lasmic electron density (Finger and Simon 2000). Histological examination of TCs has s hown that the apical microvilli of type I, type II and type III cells converge and ter minate within the taste pore, where they interact with the fluid entering from the oral cavi ty (Scott 2005; Lindemann 2001).
32 Receptor (type II) cells comprise around 20-30% of the cells in the TB (Vandenbeuch et al. 2008; Roper 2006; Gilbertson et al. 2000; Herness and Gilberston 1999; Kinnamon and Cummings 1992; Roper 1989) Recep tor cells express G-protein coupled receptors (GPCRs) for sweet, umami and bitt er stimuli (Tomchik et al. 2007; DeFazio et al. 2006). These cells also express the signaling proteins essential for transduction cascade, including phospholipase C b 2 (PLC b 2), a subfamily of transient receptor potential channel melastatin (TRPM-5), and inositol 1,4,5-triphosphate receptor 3 (IP3R3) (Miura et al. 2006, DeFazio et al. 2006; Tomchik et al. 2007). Type II cells also possess voltage gated Na+ and K+ channels but no voltage gated Ca2+ channels (Vandenbeuch et al. 2008). When stimulated, type I I cells are also observed to release ATP in a non-vesicular manner through pannexin or c onnexin hemichannels for cell-cell communication between the neighboring cells (Ishima ru 2009; Huang et al. 2007). However, these receptor cells lack any distinguisha ble synaptic connections to gustatory afferent fibers (Roper 2007; Miura et al. 2006; Tom chik et al. 2007). Presynaptic (type III) cells comprise only 5-15% o f the cells in the bud (Finger and Simon 2000; Kinnamon and Cummings 1992; Roper 1 989). Numerous investigations have illustrated that although type III cells lack GPCRs, they do form unique synaptic connection to the afferent fibers o f the gustatory cranial nerves innervating the area (Roper 2007; Tomchik et al. 20 07; DeFazio et al. 2006; Miura et al. 2006; Roper 2006). Moreover, type III cells are ex cited when depolarized with potassium chloride (KCl-) but not by taste stimulation (Roper 2007).
33 Figure. 3: The mammalian tongue and its three types of gustatory papillae. Taste buds are housed within the papillae and interact with sapid stimuli. Image based on Kandel et al. (2000). Figure. 4: The taste bud is made up of receptor and synaptic cells with microvilli that interact with tastants in the mouth. Taste rec eptor cells contain the receptor proteins and ion channels necessary for signal tran sduction. Synaptic cells transmit information from receptor cells to the gustatory ne rve fibers. Image based on Chandrashekar et al. (2006).
34 Recent immuno-staining evidence suggests that these cells express proteins and channels involved in synapses and synaptic transmitter relea se, such as synaptosome-associated protein (SNAP-25) and neural adhesion molecule (NCA M) as well as the machinery responsible for sour taste transduction (Roper 2007 ; Tomchik et al. 2007; DeFazio et al. 2006). Additionally, voltage gated Na+, K+ and Ca2+ channels are observed in these cells (Vandenbeuch et al. 2008; Roper 2007). Supporting cells (type I) are glia-like cells as they are seen to wrap around the other cells in the TB with lamellar processes (Rope r 2006; Stone et al. 2002; Finger and Simon 2000; Kinnamon and Cummings 1992; Roper 1989) Type I cells have a demonstrated role in uptake of neuropeptides to pre vent them from diffusing too widely throughout the TB during stimulation (Roper 2007). Type I cells express an ecto-ATPase responsible for breaking down the ATP secreted by t ype II cells, thereby limiting the spread of ATP during TC stimulation (Roper 2007). The precise function of type I cells in signal transduction still eludes researchers but current evidence suggests that by ensheathing other TCs, a protected environment for cell-cell communication is facilitated (Vandenbeuch et al. 2008; Roper 2007). How are receptor type II cells, which lack the ult rastructural features of synaptic vesicle clusters and presynaptic membrane thickenin g, able to stimulate afferent fibers and adjacent presynaptic cells? The fact that type II and type III cells are both involved in the transduction pathway, one directly detects the stimulus signal while the other produces a synaptic output, suggests that these cel ls participate in some form of cell-cell communication. It has been established that in the TB receptor type II cells release ATP upon stimulation and that presynaptic type III rele ase serotonin (5-HT) (Ishimaru 2009;
35 Tomchik et al. 2007). This secretion of ATP during taste stimulation was revealed to excite sensory afferent fibers and adjacent presyna ptic cells in parallel (Roper 2007; Huang et al. 2006). Whether serotonin acts to regu late sensory receptor cell threshold or modify the membrane properties of TCs is uncertain and the exact functional role of serotonin in the TB remains indeterminate. Frequent ly, serotonin is regarded to act as a neurotransmitter or neuromodulator within TBs (Rope r 2007). Receptors Taste receptor cells transduce taste stimuli to ac commodate the prototypical salt, sour, bitter, sweet and umami tastants. Although e xtensive research has been completed in attempts to elucidated the receptors involved in each of these transduction pathways, the molecular mechanisms behind salt and sour conti nue to be somewhat of a mystery, while the receptors and downstream events involved in sweet, umami and bitter taste transduction are fairly well characterized (Ishimar u 2009). Sweet, umami and bitter tastants interact with a f amily of G-protein coupled receptors (GPCRs) known as the Tas1R and Tas2R. Th ese GPCRs are selectively expressed in receptor (type II) TCs (Bachmanov and Beauchamp 2007). Although the taste GPCRs signal through a common transduction pa thway, the cells expressing a particular receptor are tuned for only one tastant (Tomchik et al. 2007; Simon et al. 2006). In 1999, Hoon et al. demonstrated that Tas1 R family is the putative taste receptor cells, mediating sweet and umami tastants. Structu ral investigations established that the Tas1R are class c GPCRs with seven-transmembrane he lices. A distinct feature of this class of GPCRs is the formation of heptahelical dom ains, large extracellular aminoterminal, and an intracellular carboxyl-terminal (B achmanov and Beuchamp 2007).
36 Tas1Rs assemble into heterodimeric complexes and th eir amino-terminal extracellular domain is thought to mediate ligand recognition and binding (Bachmanov and Beauchamp 2007; Roper 2007; Gilberston et al. 2000) The Tas1R family of GPCRs is subdivided into three different proteins, Tas1R1, Tas1R2 and Tas1R3 (Bachmanov and Beuchamp 2007; Bre slin and Huang 2006; Miura et al. 2006). Expression of Tas1R3 is documented i n all types of TBs and is frequently observed to form heterodimeric receptor units with Tas1R1 or Tas1R2 (Ishimaru 2009; Roper 2007; Breslin and Huang 2006; Chandrashekar e t al. 2006; Simon et al. 2006; Adler et al. 2000). Although Tas1R3 is co-localize d with Tas1R1 and Tas1R2, the Tas1R1 and Tas1R2 proteins are rarely co-expressed within the same taste receptor cell (Chandrashekar et al. 2006; Simon et al. 2006). Ty pical patterns of expression between the Tas1R family have been observed and genetically verified (Bachmanov and Beauchamp 2007). Receptor cells co-expressing Tas1 R3/Tas1R2 mediate responses to all sweet tasting compounds (Roper 2007; Chandrashe kar et al. 2006; Simon et al. 2006). Receptor cells expressing a Tas1R3/Tas1R1 pattern i nteract with L-amino acids and glutamate to mediate umami taste (Roper 2007; Bresl in and Huang 2006; Chandrashekar et al. 2006; Simon et al. 2006). The second family of GPCRs is Tas2Rs. These GPCRs have seven transmembrane motifs and a short extracellular amin oand carboxyl-terminals (Roper 2007; Bachmanov and Beauchamp 2007; Miura et al. 20 06; Adler et al. 2000). The extracellular loops and transmembrane domains of th e Tas2R gene vary to a large extent from one receptor cell to the next, suggesting liga nd specificity and their role in binding structurally diverse tastants (Roper 2007; Adler et al. 2000). Searches of the human
37 genome database revealed that humans express around 25 Tas2R genes and 11 pseudogenes to encode for bitter receptor proteins (Roper 2007). Variations in this gene are likely to account for our ability to respond to various bitter compounds, supported by data that shows Tas2Rs have high specificity and se nsitivity for the recognition of bitter tastants (Bachmanov and Beauchamp 2007; Breslin and Huang 2006; Chandrashekar et al. 2006; Miura et al. 2006; Adler et al. 2000). T as2Rs are selectively expressed in type II receptor cells. A particular receptor cell may express many Tas2Rs allowing it to responds to a few bitter compounds. Salt and sour taste receptors have proven to be si gnificantly more challenging to elucidate. The current body of evidence for the se nsory machinery and transduction events has been gathered mostly from indirect studi es, where chemical antagonists are applied to block certain ion channels. The prototy pical salt and sour tastants enter TCs directly through specialized membrane channels on t he apical surface of the TC (Roper 2007; Chandrashekar et al. 2006; Simon et al. 2006; Sugita 2006; Lindemann 2001; Glendinning et al. 2000; Gilbertson et al. 2000; Ki nnamon and Margolskee 1996; Kinnamon and Cummings 1996). Blocking Na+ channels with amiloride has demonstrated that at l east two distinct mechanisms for salt taste transduction exist (Ishim aru 2009; Roper 2007; Simon et al. 2006; Glendinning et al. 2000; Kinnamon and Margols kee 1996; Kinnamon and Cummings 1992). Salt (Na+) and other cations are partially transduced by the passive influx of sodium through amiloride-sensitive epithe lia sodium channels (ENaCs), which are located apically on the TC (Sugita 2006; Glendi nning et al. 2000; Kinnamon and Margolskee 1996). Although application of amilorid e significantly reduces sodium
38 responses, it does not completely ablate responses in TCs, suggesting the presence of an amiloride insensitive salt tastant pathway (Ishimar u 2009; Roper 2007; Simon et al. 2006; Kinnamon and Margolskee 1996). There is strong evi dence for the existence of amiloride-insensitive channels that also transduce salt tastants (Ishimaru 2009; Roper 2007; Sugita 2006; Simon et al. 2006). Salt ions a re also believed to cross the epithelial surface through tight junctions to enter amilorideinsensitive channels located basolaterally in the taste receptor cell (Roper 2007; S ugita 2006; Glendinning et al. 2000). The particular amiloride-insensitive receptor respo nsible for salt taste has not been fully characterized however. Assortments of cell types, receptors and mechanism s have been suggested for the transduction of sour tastants (Ishimaru 2009; Roper 2007; Chandrashekar et al. 2006; Simon et al. 2006; Sugita 2006; Gilbertson et al. 2 000). Only a few of the candidate receptors proposed have been accepted as potential sour receptor in mammals; most have been challenged and bear inconsistent and inclusive results (Ishimaru 2009; Roper 2007). Most recently, studies have revealed that presynapt ic (type III) TCs express the transduction machinery for sour tastants (Tomchik e t al. 2007). One of the more widely accepted candidates is a two-pore domain potassium (K+) channel (K2P) (Ishimaru 2009; Roper 2007; Chandrashekar 2006). Data suggests tha t sour transduction is the result of intracellular acidification of potassium matrix mem brane proteins such as TASK-1 (Roper 2007). Investigations have also revealed th at amiloride-sensitive ENaC may also contribute to transduction of sour stimuli by allow ing protons (H+) to permeate the channel (Ishimaru 2009; Roper 2007; Simon et al. 20 06; Glendinning et al. 2000; Gilbertson et al. 2000). Lastly, functional studie s have identified a member of the
39 transient receptor potential (TRP) family to be nec essary for sour transduction, known as the PKD2L1 and PKD1L3 channels, which are selective ly expressed in type III presynaptic cells (Isimura 2009; Simon et al. 2006; Chandrashekar et al. 2006). Tastant Transduction A variety of transduction mechanisms are employed by TCs to transduce sweet, bitter, umami, salt and sour stimuli, however, only a fraction of these mechanisms are found to occur within a particular TC (Roper 2007; Glendinning et al. 2000; Herness and Gilbertson 1999; Kinnamon and Margolskee 1996; Kinn amon and Cummings 1992). Typically, sapid stimuli initially interact with th e apical membrane of TCs. This stimulus-membrane interaction leads to a change in membrane conductance, which results in depolarization of the cell, influx of Ca2+, generation of an action potential and subsequent release of neurotransmitters onto gustat ory afferent fibers (Sugita 2006; Glendinning et al. 2000). The perception of sweet, umami and bitter tastes a re all initiated by the interaction of sapid molecules with a taste G-protein coupled r eceptor and their associated second messenger systems (Sugita 2006; Glendinning et al. 2000). When the taste compound binds to the taste GPCR the linked heterotrimeric G -protein dissociates from the complex in a GTP dependent mechanism (Glendinning et al. 20 00; Spector 2000). Stimulation of taste GPCRs appears to elicit two major courses of intracellular molecular interactions in which cyclic adenosine monophosphate (cAMP) and Ca2+ are both recognized as downstream effectors in the transduction cascade (R oper 2007) Data demonstrate that both Tas1Rs and Tas2Rs are p artially expressed in cells that also express the a -subunit of gustducin, a G-protein signaling molecu le specific for
40 taste (Sugita 2006; Adler et al. 2000). Furthermor e, a -gustducin has an unequivoval role in the mediation of bitter, sweet and umami respons es (Sugita 2006; Gilbertson et al. 2000; Herness and Gilbertson 1999; Kinnamon and Mar golskee 1996). The a -subunit of gustducin modulates the activity of phosphodiestera se (PDE) through increasing or decreasing cAMP levels (Gilbertson et al. 2000; Her ness and Gilbertson 1999). There is also evidence for the expression of the a -subunit of transducin, another G-protein, in TCs responsive to umami stimuli (Sugita 2006). One intracellular messenger stream involves cAMP a s the signal stimulating depolarization (Roper 2007). In general, binding o f sweet, umami or bitter taste stimuli to GPCRs causes the G-protein to associate with and activate the enzyme adenylyl cyclase (AD). AD stimulation causes an increased c AMP production, which in turn phosphorylates protein kinase A (PKA) and closes a K+ channel in the basolateral membrane region of the cell (Sugita 2006). Closure of the K+ ion channel results in TC depolarization, and subsequent activation of voltag e-gated ion channels to bring forth an action potential. This action potential ultimately drives an influx of intracellular Ca2+, thereby triggering secretion of neurotransmitter on to sensory neurons to further transmit the message. The second intracellular messenger stream involves inositol-1,4,5-trisphosphate (IP3) (Roper 2007). In bitter, sweet and umami tas te transduction the dissociated bg subunit of the G-protein is seen to activate the do wnstream messenger phospholipase C b 2 (PLC b 2). This downstream effector then hydrolyzes phosp hatidylinositol 4,5bisphosphate (PIP2) into diacylgylcerol (DAG) and I P3 (Roper 2007; Sugita 2006; Glendinning et al. 2000; Gilbertson et al. 2000). IP3 then activates type III IP3 receptors
41 (IP3R3) to release intracellular stores of Ca2+ (Glendinning et al. 2000; Herness and Gilbertson 1999). This rapid increase of Ca2+ opens basolateral TRPM5 ion channels to allow an influx of Na+, and cell membrane depolarization (Roper 2007; Sug ita 2006). Ion channels appear to mediate transduction of sal t and sour stimuli in TCs (Sugita 2006). Mechanisms of salt transduction inv olve Na+ ions and other cations permeating amiloride-sensitive ENaCs on the apical membrane of the TC (Ishimaru 2009; Roper 2007; Sugita 2006; Glendinning et al. 2 000). Na+ entry into the cell is also facilitated through the paracellular pathway as sod ium ions diffuse across tight junctions and permeate the TC through basolateral ion channel s (Glendinning et al. 2000). The influx of sodium into the cell initiates membrane d epolarization and consequent generation of an action potential. Research strongly suggests that since protons (H+) are capable of permeating tight junctions, the paracellular pathway is important fo r sour tastants (Sugita 2006; Glendinning et al. 2000). Protons permeating the c ell are capable of modifying the environment; therefore, intracellular proton concen tration is regarded as the proximate stimulus for sour taste (Roper 2007; Sugita 2006; G lendinning et al. 2000; Kinnamon and Margolskee 1996). Similiarly, sour stimuli also ut ilize ENaCs to permeate the TC. The flow of protons through such ion channels directly influences membrane depolarization within the receptor cell and generation of an actio n potential (Roper 2007; Glendinning et al. 2000; Kinnamon and Margolskee 1996). Gustatory coding in the periphery Two models have been proposed for the coding of gu statory information from taste receptor cells to the central gustatory syste m, they are the labeled-line and across-
42 fiber pattern models (Ishimaru 2009; Chandrashekar et al. 2006; Simon et al. 2006; Sugita 2006; Smith and St. John 1999). There is ev idence to support both labeled-line and across fiber pattern models (Chandrashekar et a l. 2006; Simon et al. 2006). The across-fiber pattern model suggests that indiv idual taste receptor cells recognize either one or multiple taste qualities an d that individual gustatory fibers transmit the signal from multiple tastes (Ishimaru 2009). This model claims that TCs are broadly tuned so that stimulus identity and intensi ty are specified by a distinctive combinatorial pattern of activity distributed acros s populations of TCs (Simon et al. 2006). Data supports this model by demonstrating t hat a single taste receptor cell and gustatory nerve respond to multiple taste stimuli ( Ishimaru 2009). Electrophysiological and functional imaging studies supports taste infor mation following an across-fiber pattern by indicating that both taste receptor cell s and gustatory afferents are broadly tuned to taste qualities (Chandrashekar et al. 2006 ). The labeled-lines model purports that that sensory information is processed through segregated and feed-forward circuitry conne cting peripheral receptors to gustatory structures in the central nervous system. This model theorizes that individual taste receptor cell detect only one taste quality, and individual gustatory fibers transmit the signal for only one tastant (Ishimaru 2009; Sim on et al. 2006). The model suggests taste receptors for the sweet, bitter, umami, sour and salt taste qualities exist in segregated, non-overlapping populations of cells ex pressing distinct receptors (Ishimaru 2009; Roper 2009; Chandrashekar et al. 2006; Sugita 2006). Studies in support of this model, illustrate that sweet, umami and bitter tast ants each activate distinct cell types and most likely transmit information along distinct fib ers (labeled-lines) (Roper 2009; Sugita
43 2006). Additionally, both sour and amiloride-sensi tive and -insensitive salt tastes appear to excite distinct populations of cells along a uni quely tuned labeled-line pattern. These processes of encoding tastant information are event ually interpreted as a particular taste perception when processed by the gustatory cortical areas. Conclusion Reviewing the initial events involved in the percep tion of odors and tastes reveals that although the peripheral chemosensory is vital to building the message which depicts an stimulus, it is not the peripheral systems that account for highly developed perceptual discrimination abilities of wine experts.
44 Chapter 3 The Neural Substrates of Olfaction, Gustation and F lavor Introduction Humans are unique in their innovative approach to consuming foods and beverages. We have crafted food preparation into an art that utilizes different styles of cooking and seasoning, so that humans alone are abl e to experience the flavors in a food or drink in ways no other mammal does. Not surpris ingly, humans have evolved a distinct cortical system that deals with the blendi ng of odors, tastes, and oral tactile stimuli, derived from the food and drink we consume into a unified perception of flavor. This chapter reviews the central olfactory and gus tatory systems individually, as well as their involvement in flavor perception. In addition to odors and tastes, flavor perceptions are shaped by oral somatosensory stimul i, which provide information about the texture, temperature, and irritant features (sp icy, minty, alcoholic, etc.) of food and drink. This chapter will attend to the involvement of olfactory and gustatory information in flavor perceptions. Through functional neuroima ging studies that employ techniques like positron emission tomography (PET) and functio nal magnetic resonance imaging (fMRI), information about neural activity in olfact ory, gustatory and flavor areas during the neural processing of stimulus information can b e gathered. Studies using PET, record activity in the brain by measuring regional cerebra l blood flow (rCBF) increases during the scan (Cleland and Linster 2003; Zald and Pardo 2000). During fMRI scans, the signal seen reflects neural activity as blood-oxyge nation level-dependent (BOLD) contrast, in other words the local activity-depende nt changes in blood flow (Zatorre and Jones-Gotman 2000).
45 A wealth of the information gathered on the neural areas involved in odor, taste and flavor processing also come from human brain le sion studies. Lesion studies involve patients who have had areas of their brain removed, or suffered damage to chemosensory neural structures (Gottfried 2006; Small 2006; Zato rre and Jones-Gotman 2000). Evidence from these studies has been compiled in or der to classify primary and secondary, olfactory and gustatory structures invol ved in the chemosensory functions that shape our perception of smells, tastes, and flavors Lesion and functional imaging studies in humans are bolstered by more abundant data from the primate brain. Primate studies indicate that the cortical structures involved in p rimates sense of olfaction, gustation, and flavor are highly similar to those in humans (Gottf ried 2006; Small 2006; Cleland and Linster 2003; Rolls and Scott 2003). This chapter is divided into olfactory, gustatory and flavor sections. I start by discussing the anatomy of the central olfactory sys tem, and connections between those areas and the periphery. Then I address neural are as involved in particular facets of orthonasal odor information processing, including b asic and complex olfactory processes. Similarly, I present the central gustatory anatomy, and disperse connections between central and peripheral areas. I then discuss the n eural structures active during the basic processing of taste quality and intensity informati on, and briefly discuss areas involved in taste quality recognition. I finish this chapter w ith a discussion of flavor perception in humans. I briefly address retronasal perception of odors, and then review evidence from current functional imaging studies of human flavor perception, including a study, which explored neural processing of flavor in sommeliers.
46 Unfortunately, there has been significantly less r esearch to investigate the anatomical and functional nuances of the central gu statory system in humans (Landis et al. 2009; Small 2006; Kringelbach et al. 2004; Spec tor 2000). Consequently, my review of the anatomy of cortical taste areas and the repr esentation of taste information (neural coding) are limited. Studying gustation with funct ional neuroimaging techniques has proved to be difficult, partially due to the positi on of the primary gustatory cortex (it is located deep within the brain underneath more exter nal structure) as well as its mixed modality (neurons responsive to other modalities ex ist there) (Frank et al. 2003; Zatorre and Jones-Gotman 2000). These factors make it tric ky to locate and distinguish gustatory neural activity from the activity of other modaliti es. Studies that have investigated the neural processing of taste information have mostly focused on processing and encoding of quality, intensity, and valence (pleasant vs. un pleasant) of a taste stimulus. Beyond that, many functional gustatory studies have looked at the relationship between tastants and how they alter feeding behavior, a topic outsid e the realm of this paper. Wine experts and non-experts (humans with little o r no wine training) share the same gross anatomy of the central olfactory and gus tatory systems, and the structures involved in chemosensory integration for flavor per ception. General human chemosensory and flavor studies have contributed gr eatly to our current understanding of chemosensory and flavor perceptions. These studies have explored basic information processing in cortical olfactory and gustatory stru ctures to address the encoding of the quality, intensity and valence of the chemical stim ulus. Furthermore, investigations have sought to elucidate humans use of higher-cognitive processes for odor, taste and flavor percepts.
47 Figure. 5: Neuroanatomical directions Image based on Diamond et al. (1987)
48 On the whole, there is little specific research on the neural activity in the brain of sommeliers during the wine tasting process. Howe ver, general (non-wine expert) human studies have provided great insight into whic h structures become active in the brain of wine experts during chemosensory evaluatio ns of wine. Castriota-Scanderbeg et al. (2004) are one of the few research teams that h ave gathered evidence from a brain imaging study with sommeliers to identify the brain areas active when experiencing and evaluating the sensory qualities of wine, particula rly the flavor. For the most part, psychophysical, neuroimaging, and neurophysiologica l studies of sommeliers have focused on olfactory function, and odor processing, during the evaluation process. For that reason, this chapter mostly concentrates on hu man olfaction in the central nervous system. Nevertheless, human gustation also has an important role in sensory evaluations of wine, as an independent chemosense and in its co ntribution to flavor. Central olfactory system Anatomy: Primary olfactory structures The output neurons of the olfactory bulb (OB) are mitral and tufted cell axons, which synapse within various olfactory nuclei as th ey travel ipsilaterally (along the same side) towards the posterior. As the output bulbar afferents leave the OB they coalesce to form olfactory tracts (OT) on both the right and le ft sides that lie in the olfactory sulcus of the basal forebrain [Note: A list of abbreviatio ns for neural structures can be found in Appendix I] (Gottfried 2006; Cleland and Linster 20 03; Diamond et al. 1985). The olfactory peduncle is created immediately as bulbar afferents exit the bulb, within the olfactory peduncle those axons synapse in the anter ior olfactory nucleus (AON), and olfactory information is communicated across the bu lbs through the anterior commissure
49 (Gottfried 2006; Zatorre and Jones-Gotman 2000; Buc k 1996). Additionally, pyramidal cells of the AON send projections via the anterior commissure to contralateral (on the opposite side) areas of the primary olfactory corte x (POC). As the bulbar afferents continue posterior, they p redominantly form the thickly myelinated lateral olfactory tract (LOT), which ser ves as the main relay to the primary olfactory cortex (POC). Collateral axons of the LO T branch off to terminate in various olfactory neural areas; along with the AON, these s tructures constitute the POC (Cleland and Linster 2003; Buck 1996; Kratskin 1995). These areas include: the anterior and posterior piriform cortices (PC), the periamygdaloi d cortex (PAC), anterior and posterior nuclei of the corticomedial amygdaloid complex (CAC ), and the entorhinal cortex (EC) (Cleland and Linster 2003; Zatorre and Jones-Gotman 2000). The PC lies in the junction of the frontal and temporal lobes, the caudolateral aspect of the orbitofrontal lobe, and continues into the dorsomedial aspect of the tempor al lobe (Zattore and Jones-Gotman 2000; Zald and Pardo 2000). The PAC is situated in the medial region of the anterior temporal lobe, and along the dorsomedial aspect of the amygdala. The most caudal projection of the bulbar afferents is the lateral E C, which lies at the rostral end of the temporal lobe (Gottfried 2006; Cleland and Linster 2003). Rostromedial olfactory structures Medial to the LOT are structures that constitute ro stromedial olfactory cortices: the supracallosal gyrus (part of the hippocampal fo rmation), the dorsal tenia tecta (part of the anterior hippocampal continuation), and the ven tral tenia tecta (Cleland and Linster 2003).
50 Figure. 6: Central olfactory stru ctures. A ventral view of the brain with the cerebe llum and brainstem removed. The structures with color ar e those that olfactory information from the periphery is projected to. Image based on Haines (2008) and Purves (2001).
51 Figure. 7: Central olfactory pathway. A schematic i llustration of the olfactory structures that odor information is carried to in central nerv ous system. Image based on Purves (2001) and Kandel et al. (200 0).
52 Animal models demonstrate that the ventral tenia te cta (VTT), dorsal tenia tecta (DTT) and supracallosal gyrus (SG) are recipients of bulb ar afferents extending from the AON (Gottfried 2006; Cleland and Linster 2003). The DT T and SG of the hippocampal formation receive direct input from the EC. Bulbar afferents also travel in the olfactory tubercle, a part of the ventral striatum, which lie s caudal to the olfactory peduncle, medial to the OT, and dorsomedial to the AON; the olfactor y tubercle caudally joins the rostromedial cortices (Cleland and Linster 2003). The POC sends projections that converge in the mediodorsal and submedial thalamic nuclei, while the SG and DTT send projections to the anterior thalamic nuclei. Secondary olfactory structures From the POC, secondary projections arise to conve rge on the rostral orbitofrontal cortex (OFC), agranular insular cortex (AI), other amygdala subnuclei, thalamic nuclei, medial and lateral hypothalamus, basal ganglia, and hippocampus (Gottfried 2006; Cleland and Linster 2003; Zatorre and Jones-Gotman 2000). The main neocortical recipients of POC projections are the OFC and AI. Olfactory information from the POC is relayed to the OFC and AI indirectly via the med iodorsal nucleus of the thalamus. Direct projections from the PC to the OFC also exis t (Gottfried 2006; Wilson and Sullivan 2003; Kandel et al. 2000; Zald and Pardo 2 000; Kratskin 1995). The OFC lies along the ventral surface of the caudal frontal lob es, medially it includes the gyrus rectus, and laterally, the insular cortex wraps around the caudal orbital surface (Gottfried 2006). Connections As the bulbar afferents exit the bulb they diverge to innervate a range of olfactory structures, the majority of which are interconnecte d (Cleland and Linster 2003).
53 Additionally, all primary olfactory areas but the o lfactory tubercle and SG send direct feedback projections to the OB. The bulk of this f eedback is believed to synapse on granule cells of the OB, and some even extend into the glomerular layer to synapse with mitral and tufted cells there (Cleland and Linster 2003). These centrifugal input to the OB, include the feedbacks from cortical olfactory a reas as well as, cholinergic endings from the horizontal limb of the diagonal band, nore pinepherine containing fibers from the locus coeruleus, and serotoninergic synapses from t he raphe nucleus (Wilson and Sullivan 2003). The massive centrifugal input influences neural dy namics in the OB, which are vital for olfactory learning and processing. In addition to receiving olfactory centrifugal input, the OB receives centrifugal input that is no n-olfactory (Wilson and Sullivan 2003). This non-olfactory input modulates cellular unit ac tivity in the bulb, thereby affecting OB output and responsiveness to odorants. Some of the non-olfactory centrifugal input is derived from gustatory cortical areas. The OB is t herefore under constant dynamic regulation by olfactory and non-olfactory centrifug al input responsive to behavior state and non-olfactory events. The AON is the main source of feedback connections to the OB. Additionally, the AON receives input from the PC, the EC, a regio n from the hippocampal formation, and the VTT. Projections from the AON reach the PC olfactory tubercle, VTT, OFC and hypothalamus (Cleland and Linster 2003). The PC re ceives corticocortical input from all primary olfactory areas (except the olfactory tuber cle), as well as the OFC, insular cortex, hippocampal formation, basal forebrain, brainstem, thalamus, and hypothalamus. The lateral olfactory cortices send highly convergent p rojections to the mediodorsal and
54 submedial nuclei of the thalamus, while the rostral olfactory cortices send projections to the anterior thalamic nuclei (Cleland and Linster 2 003) The POC has relationships with limbic structures s uch as the amygdala, the hypothalamus, and the perirhinal cortex, which like ly accounts for the emotional evocativeness of odor (Wilson and Rennaker 2009). The PAC and CAC are the recipients of many direct bulbar afferents (Gottfri ed 2006). Output targets of the amygdaloid complex are the PC, EC, and agranular in sular area, and there are reciprocal connections between the amygdala and OFC. The stro ngest projection from the EC is to the hippocampal formation; however, it is also has projections to the OB, and cortical olfactory areas such as the AON, VTT, SG, PC, olfac tory tubercle, and amygdala (Cleland and Linster 2003). The hypothalamus recei ves projections from the AON, PC, amygdaloid nuclei, and the olfactory tubercle (Clel and and Linster 2003; Kandel et al 2000). There are also associational fibers that fo rm connections between the primary olfactory areas, excluding the olfactory tubercle. These associational fibers have been grouped into local, intrinsic short connections tha t exist between neurons in a given neural structure; and associative connections that exist between neurons in various cortical areas (Cleland and Linster 2003). Function: Neural processing of olfactory information It is obvious from the anatomical descriptions abo ve that processing of olfactory information incorporates a range of neural structur es that are complexly interrelated. This system works through both feedforward and feed back connections, to create our olfactory perceptions. Brain-imaging studies in pr imates and humans have contributed greatly to our understanding of the neural substrat es active during olfactory processing
55 (Gottfried 2006; Shepherd 2005; Cleland and Linster 2003). Researchers have designed methods to induce specific olfactory functions in h umans to visualize which brain areas become active. These imaging studies show odor rel ated activity in numerous neural structures during olfactory stimulation. It has fu rther been concluded from these studies that the structures that become active are strongly influenced by the nature of the olfactory task, i.e. detection, discrimination, mem ory, etc. In 2000, Savic and coworkers used PET to investiga te the activation induced by olfactory tasks hierarchically organized in terms o f demands. The authors reported taskspecific recruitment of cortical regions subserving the olfactory task: starting with olfactory detection, activity was observed in the a mygdala, piriform cortex (PC), orbitofrontal cortex (OFC), cingulate cortex, and t halamus; the discrimination of odor intensity revealed additional recruitment of insula and cerebellum; discrimination of odor quality additionally involved the prefrontal cortex frontal operculum, caudate and subiculum; and finally, odor recognition memory sho wed additional recruitment of temporal and parietal regions. A caveat to this st udy is that it looked at the global processing of olfactory information and did not iso late odor detection from other olfactory tasks. Brain lesion studies have also im plicated neural loci in parts of olfactory processing, as determined through observations of a deficit in olfactory tasks. By inference, those neural areas removed or damaged in patients are coupled with a loss of olfactory function. Generally, in humans, central olfactory functions include processing and encoding information that corresponds to odor intensity, odo r valence, odor quality, and odor memory (Zatorre and Jones-Gotman 2000). Wine exper ts, who need to discriminate and
56 identify wine odors, rely heavily on odor memory to assist them through the evaluation process. In the evaluation of a wines aroma, a wi ne expert assesses several characteristics. These include the quality (how it smells), intensity (relative magnitude of the smell), and temporal attributes (how the qualit y and intensity of the smell changes over time) of the wines aroma (Jackson 2009). In this section, I discuss the neural structures a ctive during basic odor intensity and quality processing in humans. I then focus on the neural areas active during the complex cognitive functions of odor memory and olfa ctory learning that include odor discrimination, recognition and identification (ver bal labeling). Inherently, this cortical system incorporates olfactory learning and odor mem ory to shape an individuals perceptions of odors. Wine experts maximize on the neural foundations of olfactory learning. Through long-term experience and trainin g, wine experts develop a stable memory store (knowledge) of wine relevant odors tha t guides their superior odor discrimination and recognition skills. Odor intensity Odor intensity is the relative magnitude of the od or stimulus and is frequently associated with the odors valence (Gottfried 2006; Anderson et al. 2003). For many sensory modalities, intensity is closely coupled to valence. Intensity and valence are difficult to disentangle from one another since in many instances a highly aversive stimulus is also rated as more intense (Rouby et al 2009; Gottfried 2006; Winston et al. 2005; Anderson et al. 2003). Researchers have thus sought to dissociate these two dimensions to help identify the areas involved sole ly in odor intensity processing (Anderson et al. 2003; Zald and Pardo 2000; Zatorre and Jones-Gotman 2000).
57 In one study that dissociated the two olfactory in formation processes, odor stimuli were presented to subjects at either high or low co ncentration (intensity) with a pleasant or unpleasant valence (Anderson et al. 2003). The results reveal that the amygdala becomes activated by the intensity of an odor stimu lus, not the valence, implying that the amygdala processes odor intensity (Anderson et al. 2003). In another study that incorporated neutrally valenced odors alongside pos itive and negative ones with high and low intensity odors, the amygdala responded to odor intensity at extreme valances. Thus the neural activity in the amygdala is also believe d to reflect the overall behavioral salience of an odor (Rouby et al. 2009; Gottfried 2 006; Winston et al. 2005). Odor quality Odor quality is the perceptual identity of an odor that emanates from a complex odor mixture, such as coffee, or chocolate (Howard et al. 2009; Gottfried 2008; Gottfried et al. 2006; Li et al. 2006; Rawson 2000). The dis tinct quality of a particular odor is thought to arise from the differential sensitivity of receptor neurons and the learning of their response patterns. Processing of odor qualit y begins in the olfactory bulb (OB), where information from the olfactory epithelium is collected and edited. This processing involves feedback inhibition upon receptor neurons in the OB as well as feedback responses from higher neural centers. In the OB od or quality information is encoded as ensembles of odorant structural features, which is sent posterior to the PC. Mitral cells from various glomeruli in the OB converge on PC neu rons, thereby combining impulses from multiple receptor types (Jackson 2009). Evide nce strongly suggests that this convergence is enhanced by the extensive interconne ctions within the PC in a manner that allows odorant mixtures to stimulate neurons i n the PC that are not activated by the
58 odorants individual components (Jackson 2009). Ac cordingly, the PC is the likely cortical location for the encoding of odor quality (Howard et al. 2009; Gottfried 2008; Gottfried et al. 2006; Gottfried 2006; Savic 2002; Sobel et al. 2000). Research demonstrates that the PC is able to combine and syn thesize odor feature ensembles into perceptually whole odors. Observations from functi onal imaging studies of activity in the posterior PC have implicated it with a role in basic odor perception (Gottfried 2006). Recent studies demonstrate that the perceptual iden tity of an odor is represented via activity in distributed neuron ensembles in the pos terior PC (Howard et al. 2009). Gottfried et al. (2006) compared perceptually diff erent to perceptually similar odor pairs to categorize neural representations of odor quality. Imaging data demonstrated activity in the posterior PC as respon ses selectively tuned to the qualitative features of odor ensembles. Also, the neurons appe ared to be responsive to categorical aspects of odor quality, or, the perceived similari ty of odors. Other studies show that neurons of the PC can discriminate between odorant mixtures, and their components, as well as familiar odors (Wilson and Sullivan 2003; S obel et al. 2000). Additionally, Gottfried et al. (2006) examined the neural represe ntation of odor structure, independent of qualitative features and revealed activity in th e anterior PC in response to the comparison of structurally similar and dissimilar o dors. These results suggest that fundamental molecular features of an odorant drive the activity in the anterior PC. The anterior PC, the initial recipient of odor-str ucture information from the OB, likely serves as the neural substrate for establish ing odorant structure codes that are subsequently processed into a neural representation of odor quality in the posterior PC (Gottfried et al. 2006; Wilson and Sullivan 2003). Such cortical access to odorant
59 structural information would allow detection of dif ferences in odorant molecular features (Gottfried et al. 2006), and thus an ability to dis criminate among various odor identities. Odor Memory and Olfactory learning In general, the most important mechanisms by which the environment alters behavior are learning and memory (Kandel et al. 200 0). Learning is the means through which humans acquire knowledge about the world, whi le memory is the process in which knowledge is encoded, stored and later retrieved. In the bounds of this chapter, olfactory learning and odor memory are the processes by which knowledge about odors is stored and later retrieved. Through these two processes h umans are capable of retrieving odor memories used to discriminate, recognize and identi fy (semantic labeling) various smells present in their environment (Zelano et al. 2009; W ilson and Stevenson 2003a; Royet et al. 1999) creating a connection between olfactory p rocessing and language (Shepherd 2004; Petrulis and Eichenbaum 2003). The formation of odor memories is a distributed pr ocess that entails the activation of a distinct set of pathways (Petrulis and Eichenb aum 2003). Multiple systems are involved in odor memory formation including the hip pocampal formation, OFC, amygdala system, POC, and OB. Each of these system s is involved in particular aspects of odor memory formation. Acetylcholine (ACh) and norepinephrine (NE) are the two neurotransmitters most intimately involved in modul ating the dynamics of odor memory formation. These two neurotransmitters operate by reducing intrinsic activity and allowing new afferent input to the mitral cells of the OB and the pyramidal cells in the piriform cortex. This regulatory activity reduces interference between stored odor
60 representations (odor memory) and the attainment of new olfactory information if the neuronal ensembles encoding the odors overlap (Petr ulis and Eichenbaum 2003). Many studies have presented data that shows olfact ory neurons are extremely plastic, which would mean our odor perceptions are not systematically fixed (Rouby et al. 2009). In fact, the human olfactory system shows a n extreme capacity for olfactory learning, the process of building an odor memory, t hrough experience-dependent plasticity (Li et al. 2006). Experience with odors allows for the establishment of adaptive changes between the synaptic transmissions of neuro ns. These findings imply that odor perception relies on synthetic processing of olfact ory information, sub-served by cortical and neocortical brain areas (Li et al 2006; Wilson and Stevenson 2003b). Functional imaging studies demonstrate that odor processing in the human brain is reworked by sensory, emotional, associative, and cognitive expe riences of an individual (Gottfried 2008; Gottfried 2006; Li et al. 2006; Shepherd 2004 ;Wilson and Stevenson 2003a; Wilson and Stevenson 2003b; Rawson 2000). In human s, the interconnected components of the central olfactory system are all involved in olfactory memory; however, each has a unique function. The olfactory PC has multiple synaptic connections which are thought to facilitate the development and encoding of odor mem ories (Gottfried 2006). Odorant feature identification takes place in the anterior PC, while qualitative grouping, such as floral or fruity, spurs activity in the posterior P C (Jackson 2009; Gottfried et al. 2006). From the POC, odor signals pass to the thalamus whe re information is integrated. From the thalamus information is sent on to the amygdala to be associated with emotional odor memories, to the EC for memory consolidation, and t o the OFC. In the OFC odor
61 responsive neurons as well as gustatory responsive neurons (and neurons responsive to other sensory modalities) converge and interact to create multisensory (multimodal) perceptions (Jackson 2009). Experience-dependent s ynaptic plasticity has also been observed in the OFC such that neurons there develop expanded synaptic connections based on repeated, coincident, activation. Through these modifications when an odor pattern is recognized, the OFC will simultaneously recall other memories that it was originally developed with, for instance the pairing of strawberry with sweetness, or coffee with bitterness (Gottfried 2006; Wilson and Stevens on 2003a; Zatorre and Jones-Gotman 2000). Activity in rostral areas of the OFC has been link ed with associative learning, working memory, and shortand long-term odor recog nition memory (Gottfried 2006; Dade et al. 2002). Additionally, because the OFC i s a major recipient of projections from the primary olfactory areas, as well as from gustat ory, and thalamic centers, it is evident that it participates in complex olfactory functions dealing with multimodal integration, reward processing, and goal-directed learning and b ehavior (Gottfried 2006). Sensory convergence has been frequently documented in the O FC across a variety of sensory modalities including, but not limited to, odor and taste. Semantic association between odors and tastes increased activity in the OFC. Su ch observations highlight the notion that prior learning and experience are capable of m odulating central processing of sensory information (Gottfried 2006; De Araujo et a l. 2003; Wilson and Stevenson 2003). Maintenance of odor memories for long periods of t ime appears to require the posterior PC and or the EC (Gottfried 2006; Petruli s and Eichenbaum 2003). JonesGotman and Zatorre (1993) demonstrated evidence fro m lesion studies of the importance
62 of the right temporal and frontal lobs in odor memo ry. Zatorre and Jones-Gotman (2000) state that the temporal and frontal lobes are invol ved in odor memory, quality discrimination and odor identification. Zelano et al. (2009) studied olfactory working memory, a function of short-term memory, to identif y activity in response to novel and familiar odors. Activity was observed in the infer ior frontal gyrus, when odors were novel, whereas activity in the frontal piriform cor tex was associated with more familiar odors. The PC has direct and indirect projections to the OFC, which allow association of odors with a sensory context, memory, and hedonic r eaction (Wilson and Sullivan 2003). Odorant coding in the OFC demonstrate that response s to stimuli represent not only the sensory qualities of the stimulus, but also the cur rent and past context of the stimulus, including sensory and hedonic associations and biol ogical significance (Wilson and Sullivan 2003). The OFC appears to be differential ly activated when human subjects were making judgments about the presence of odors, their familiarity, as well as their intensity. Activations in response to these judgme nt tasks are accompanied by responses in the frontal, temporal, parietal, and occipital c ortex, indicating that non-olfactory networks work to mediate higher-level olfactory dec ision-making (Gottfried 2006; Wilson and Sullivan 2003). Odor Discrimination Odor discrimination has been described as the perc eptual differentiation between odorants, and complex odor mixtures, sharing signif icant qualitative or structural characteristics (Li et al. 2006). In the context o f this chapter, odor discrimination refers to an individuals ability to differentiate among o dor qualities present at a given time. In
63 the bottom-up view of olfactory processing, neura l representations of odor quality are believed to relate to the odorants structural comp osition. This view is contested, however, because in humans higher-order cognitive p rocesses deeply modify individual perceptions of odor quality, suggesting top-down pr ocessing (Gottfried 2008; Li et al. 2006). There also appears to be significant prefer ential plasticity in the posterior PC (Wilson and Sullivan 2003). This evidence suggests that previous experience with specific odors allows for odorant feature ensembles to become more readily combined and salient when they are familiar. This synthetic approach of processing of odor ensembles occurs through olfactory experience-depen dent neural plasticity, also known as perceptual learning (Wilson and Sullivan 2003). PC olfactory neurons rapidly habituate during pres entation of a odor stimulus (Gottfried 2008; Petrulis and Eichenbaum 2003; Wils on and Sullivan 2003; Sobel et al. 2000). Habituation is a type of learning in which there is a progressive diminution of neural response probability with repeated exposure to a stimulus. Habituation in the PC likely assists with odor discrimination (Gottfried 2006). Gottfried (2008) stated that experience with specific odors to the point of habi tuation, enhanced the discriminative capacity of an individual for those odors at a late r point in time. In this study, both the piriform and orbitofrontal cortices displayed exper ience-dependent response enhancement, followed by behavioral changes in odor discrimination ability. PC olfactory neurons encode associations between n on-olfactory and olfactory cues that underlie odor discrimination, suggesting that the PC is the locus for long-term odor memories (Petrulis and Eichenbaum 2003). Odor quality discrimination involves a complex of olfactory regions including PC, OFC, and mediodorsal (MD) thalamus
64 (Petrulis and Eichenbaum 2003). Damage to the PC s ignificantly impairs discrimination of odor mixtures, and prevent olfactory learning. The posterior PC and EC may be critical for long-term odor memories, while the ant erior PC is necessary for short-term odor memories (Petrulis and Eichenbaum 2003). Dama ge to the MD thalamus impairs discrimination of qualitatively similar and novel o dors. Likewise, damage to the OFC impairs odor discrimination, but deficits following damage to the OFC are more severe than those after MD damage (Cleland and Linster 200 3; Petrulis and Eichenbaum 2003). Odor recognition and identification Generally, odor recognition describes the identific ation of previously experienced and novel odors, judging the familiarity those odor s, and being able to accurately label odors (Wilson and Sullivan 2003; Zatorre and JonesGotman 2000; Royet et al. 1999). To wine experts, odor recognition involves the abil ity to correctly recognize wine relevant odors that they have been previously expos ed to, while odor identification requires that experts discriminate between and verb ally label the wine odors present (Hughson 2008). Regions of the piriform and right orbitofrontal co rtex were activated during odor recognition and identification tasks (Gottfried et al. 2004; Dade et al. 2002; Zatorre and Jones-Gotman 2000; Jones-Gotman and Zatorre 1993). Activity in these olfactory regions was observed during both long-term and shor t-term odor recognition tasks (Dade et al. 2002). Activity in the PC increases as a fu nction of long-term recognition tasks and odor familiarity. Evidence from previous work sugg ests that the POC acts as a type of associative memory system that allows for the assoc iation of an odor stimulus with memory traces of previously experienced smells (Got tfried 2006; Dade et al. 2002).
65 During short-term recognition tasks, activity was a lso observed in the mid-dorsolateral orbitofrontal cortex and parietal lobe, areas impor tant for working memory functions. Olfactory neurons in the OFC became active during b oth shortand long-term odor recognition, and appeared to respond more selective ly to different odors than neurons in the PC. Royet et al. (1999) conducted a study to identify the functional anatomy of semantic processing for odors. When subjects were asked to judge the familiarity of odors, activity for these tasks was observed in the right orbitofrontal areas, as well as regions of the left frontal lobe, and cingulate gyr us. Because of the activity observed in the right OFC, the authors suggested that this regi on participates in processing of stimulus features necessary for familiarity judgmen ts. In turn, activity in the left inferior frontal cortical regions was suggested to be involv ed in semantic processing of odors. Furthermore, lesion studies demonstrate that defici ts in odor recognition and identification memory are observed after damage to the temporal lobe (Petrulis and Eichenbaum 2003). Central gustatory system Anatomy: Primary gustatory relay Neurons innervating the taste buds stem from one o f three cranial nerves (Jackson 2009; Small et al. 2007; Small 2006; Rolls and Scot t 2003; Witt et al. 2003; Kandel et al. 2000; Smith and Davis 2000; Zatorre and Jones-Gotma n 2000). The geniculate ganglion from the chorda tympani nerve fibers of the facial nerve (C.N. VII) provides neurons to the taste buds on the anterior tongue. Other branc hes of C.N. VII also innervate taste buds in the soft palate. Taste buds on the posteri or and lateral margins of the tongue, as
66 well as the tonsil, pharynx, and posterior palate a re contacted by neurons from the petrous ganglion of the glossopharyngeal nerve (C.N. IX). Lastly, the nodose ganglion of the vagus nerve (C.N. X) supplies taste buds of the epi glottis, larynx, and upper esophagus. The three gustatory cranial nerves innervating the tongue and oral space project afferents to the rostral solitary nucleus and tract (NST) in the upper posterior medulla (Small et al. 2007; Small 2006; Witt et al. 2003; S mith and Davis 2000). Second-order gustatory fibers leave the rostral NST and ascend t he brainstem ipsilaterally through the central tegmental tract (CTT) (Simon et al. 2006; S mall 2006; Rolls and Scott 2003; Smith and Davis 2000; Zatorre and Jones-Gotman 2000 ). As the gustatory fibers travel rostrally, they project directly to the parvocellul ar region of the ventroposterior medial nucleus of the thalamus (VPMpc). Primary and secondary gustatory cortex Neuroanatomical tract-tracing studies identified t wo projections from the gustatory thalamus to the gustatory cortex (Small e t al. 2007). Primarily, gustatory fibers from the VPMpc project ipsilaterally to terminate i n the rostral part of the frontal operculum and bordering anterior insula (FO/AI), re spectively known as the primary gustatory cortex (PGC) (Small 2006; Roll and Scott 2003; Zatorre and Jones-Gotman 2000). This region in located within the cortex of the horizontal ramus of the sylvian fissure (Small 2006). Axons of the FO/AI travel an terior, to the secondary taste cortex (STC) in the caudolateral orbitofrontal cortex (OFC ) (Small 2006; Rolls and Scott 2003; Zatorre and Jones-Gotman 2000). Secondarily, gusta tory fibers from the VPMpc project ipsilaterally to terminate in areas along the later al margins of the precentral gyrus at the base of the central sulcus (Small et al. 2007). Ho wever, because the gustatory system is
67 so closely connected to oral somatosensation, the e xtent to which this secondary projection represents taste opposed to oral somatos ensation is unclear (Small et al. 2007; Roll and Scott 2003; Zatorre and Jones-Gotman 2000) Efferents from the FO/AI and the OFC also project to the lateral, central, and corti comedial nuclei of the amygdala. Connections Various sensory input converge in the FO/AI of the PGC. This reflects the multimodal nature of gustation (Zatorre and Jones-G otman 2000). Afferents to the FO/AI arrive predominantly from the VPMpc. Unlike olfaction, in the gustatory system there is an initial thalamic relay prior to sending taste information to cortical structures. Additionally, fibers from the primary somatosensory cortex, entorhinal cortex, and basolateral amygdala terminate on neurons in the FO /AI. The PGC projects efferents to parts of the frontal cortex including the OFC, and the lateral, central, and corticomedial nuclei of the amygdala (Rolls and Scott 2003). The amygdala receives projections from the primary (FO/AI) and secondary (OFC) gustatory cortices (Rolls and Scott 2003). T he caudolateral OFC largely receives input from the mediodorsal nucleus of the thalamus (MD), but not the VPMpc. The caudolateral OFC also receives afferent input from surrounding OFC areas, as well as the ventral region of the rostral insular cortex, and t he amygdala. The posterior OFC has direct input from caudolateral OFC that travel towa rds the middle OFC. There are also feedback projections from the OFC to the inferior t emporal cortex, EC, and cingulate cortex (Rolls and Scott 2003).
68 Figure. 8: Central gustatory structures. Drawing of a coronal section of the rostral brain and dorsal aspect of the brainstem th at depicts areas in which gustatory information is processed. Image based on Kandel et al. (2000)
69 Figure. 9: Central gustatory pathway. A diagram tha t portrays the central structures gustatory information travels to. Image based on Purves (2001).
70 Function: Neural Processing of gustatory information Although there have been significant advances in t he technology available for studying taste, the representation of gustatory inf ormation in the central nervous system and the associated neural mechanisms responsible fo r taste-guided behavior are still far from being understood. Human neuroimaging and lesi on studies provide insight into our current understandings of gustatory functions. But for the most part, evidence from nonhuman primate studies has proved to be invaluable, and is therefore used to establish and support current hypotheses about cortical represent ations of gustation in humans. Much like the olfactory system, the gustatory system is mediated by parallel and hierarchical processing (Small et al. 2007; Smith and Davis 2000 ). Feedback projections from higher gustatory levels impinge upon various points in the ascending pathway to modify gustatory perceptions. The rostral NST is first neural structure in the g ustatory system with taste responsive neurons (Smith and Davis 2000). Presuma bly, the ascending pathway in the rostral NST is responsible for coding and perceptio n of the quality, intensity, and valence of a taste stimulus, as well as the integration of sensory activity associated with eating and drinking. Findings from primate and human neur oimaging studies of taste clearly demonstrate that there are multiple taste-responsiv e regions in the FO/AI and OFC (Small et al. 2007). The central gustatory system infrequ ently functions independent of other sensory modalities. Primary and secondary gustator y areas receive a range of projections from somatosensory, olfactory, visual, and auditory brain areas (Small 2006; Rolls and Scott 2003; Smith and Scott 2003; Breslin 2001; Zat orre and Jones-Gotman 2000). Some gustatory neurons identified in cortical areas are finely tuned to single specific taste
71 qualities, while other neurons are more broadly tun ed and respond to more than one or two taste qualities (Smith and Davis 2000). In man y instances, gustatory neurons are multimodal, responding not only to taste stimuli, b ut olfactory, and oral somatosensory stimuli as well (Zatorre and Jones-Gotman 2000). Like olfaction, basic gustatory information proces sing entails encoding taste quality, intensity and valence (Small 2006; Breslin 2001). Beyond studying basic gustatory processes, the majority of research has e xplored how cortical taste centers respond to chemical stimuli during complex cognitiv e processes like motivational feeding behaviors (Okamoto and Dan 2007; Small 2006; Smith and Davis 2000; Zatorre and Jones-Gotman 2000). The cortical gustatory system is also capable of learning through experience-dependent plasticity (Jones et al. 2006) Cortical and peripheral gustatory areas are interconnected through feedforward and fe edback projections, and therefore modulate individual perceptions of tastes. The exp eriential changes that facilitate gustatory learning and taste memory create and shap e unimodal gustatory associations (taste-taste), as well as bimodal and multimodal as sociations between taste stimuli and other sensory stimuli, including odor stimuli (odor -taste) (Small 2006; Rolls and Scott 2003). Gustatory memories transpire as a result of these sensory associations, such that humans are capable of memorizing, recollecting, and imaging tastes they have encountered before (Okamoto and Dan 2007; Jones et al. 2006; Smith and Davis 2000; Zatorre and Jones-Gotman 2000). Although progress has been made in revealing aspec ts of cortical gustatory functions, the neural mechanisms that underlie tast e perceptions are still not well understood (Landis et al. 2009; Small 2006; Kringel bach et al. 2004; Schoenfeld et al.
72 2004). Using conventional functional imaging techn iques to study human gustation are limiting because they require that subjects are lyi ng down, that head movement be severely restricted during the scan, and that taste stimuli are introduced via tubes or straws (Jackson 2009; Okamoto and Dan 2007). Addit ionally, the anatomical location of, as well as the presence of multimodal neurons in co rtical gustatory structures impedes these conventional imaging techniques as mentioned earlier (Zatorre and Jones-Gotman 2000). During the taste procedure, wine experts ev aluate the quality of the wines tastes, i.e. the sweetness, sourness and bitterness, and th e intensity of those tastes (Jackson 2009). Therefore, in the confines of this chapter, I will only discuss the neural structures known to be associated with taste quality processin g and recognition, as well as taste intensity coding. Taste quality Taste qualities are broken into the five perceptua l categories of: salty, sour, bitter, sweet, and umami (also known as savory) (Jackson 20 09; Small 2006; Breslin 2001). In the NST, different neurons have best responses to p articular taste qualities. However, the tuning of these NST gustatory neurons is broad (Rol ls and Scott 2003). The broadly tuned nature of the NST gustatory neurons suggests that the afferent code for taste quality is translated across more than one neuron type, as a pattern of activity (Simon et al. 2006; Small 2006; Smith and Davis 2000). Taste quality coding evidence, primarily from rode nts, has led researchers to conclude that in the periphery, classes of taste ce lls respond to taste quality in a particular pattern of activity across a population of cells (J ackson 2009; Small 2006; Breslin 2000; Smith and Davis 2000). Researchers then investigat ed the responses of gustatory neurons
73 in the insular and opercular cortices and saw that similar patterns of neuronal activity arose during taste stimulation (Small 2006; Rolls a nd Scott 2003). Thus, it was proposed that centrally, taste quality maybe represented by the similarity between the patterns of activity generated across all gustatory neurons in the PGC (Rolls and Scott 2003; Smith and Davis 2000). Schoenfeld et al. (2004) used fMR I techniques to examine the role of the PGC in gustatory information processing. The s tudy revealed that each taste quality had different but overlapping representations in th e PGC. Additionally, primate studies suggest that the taste-responsive neurons in the FO /AI as well as the OFC are more finely tuned to taste quality than neurons in the gustator y NST. Therefore, the FO/AI and OFC have also been implicated as regions necessary for taste quality coding (Small 2006; Small et al. 1997). Taste quality recognition is a more complex cognit ive process that deals with the identification of sour, bitter, sweet, salty, and u mami taste identities. Quality recognition accounts for the behavioral differentiation between various taste qualities present at a given instant (Okamoto and Dan 2007). The anterior temporal lobe and frontal operculum are associated with taste quality recogni tion (Zatorre and Jones-Gotman 2000; Small et al. 1997b). Previous non-human primate st udies demonstrated a close relationship between the PGC and taste quality reco gnition (Small et al. 1997a). A neuroimaging study conducted by Small et al. (1997a ) investigated taste quality recognition in humans, and revealed activity in the caudolateral OFC, gyrus rectus, frontal operculum, basal forebrain and lingual gyru s. Cognitive processing of sensory information involves the lateral portion of the pre frontal association cortex (LPFC) (Okamoto and Dan 2007; Kringelbach et al. 2004). S tudies have suggested that activity
74 the dorsal LFPC is evoked by food-related stimulati on, and that these areas are engaged during the recognition of taste and other food or b everage attributes. Taste intensity Intensity of a taste describes the magnitude of th e qualitative gustatory sensation at any point in time. Generally, the perceived int ensity of a chemical stimulus increases exponentially with increases in the physical concen tration of the stimulus (Breslin 2001). Like other sensory systems, intensity and valence o f taste are closely tied and difficult to tease apart. Small et al. (2003) dissociated the n eural representations of intensity and affective value of tastants. Activity observed in the amygdala was associated with intensity of the tastant irrespective of its valenc e (Small et al. 2003). In this study, the cerebellum, pons, amygdala, and middle insula were also reported to be responsive to the intensity of pleasant and unpleasant taste stimuli. The insular and opercular gustatory corticies seem to be critical for suprathreshold (stimulus of sufficient strength/quantity to induce physiologically change) taste intensity perception (Small 2006). Taste responsive cells in the insular and opercular gustatory regions were reported to generate intensity-respons es that correspond to human psychophysical data of intensity perceptions (Small 2006; Small et al. 2003). Human lesions studies documented deterioration in taste i ntensity perception after damage to the insula. Furthermore, Faurion et al. (1999) reporte d in a fMRI study, intensity processing resulted in activations in the superior part of the anterior and medial insula, and in the frontal operculum, the lower preand post-central gyri, and the first temporal gyrus, cited in Zatorre and Jones-Gotman (2000). Additional act ivity was observed in the temporal
75 and frontal lobes, anterior cingulate gyrus, and th e MD thalamus (Zatorre and JonesGotman 2000). Flavor Perception As humans, we experience flavor when we eat food a nd drink a beverage. Flavor, a product of olfactory, gustatory, and oral somatosensory systems, has a powerful influence over human eating and drinking behavior ( Shepherd 2004; de Araujo et al. 2003; Liang and Jinks 1996). Flavor perceptions ar ising from the olfactory and gustatory senses are often confused, such that the sensations experienced when consuming things like chocolate or coffee, are mistakenly ascribed t o the gustatory system as being tastes (Hummel 2008; Small 2008; Small 2006; Small and Pre scott 2005; Liang and Jinks 1996). The five qualities sweet, sour, bitter, sal ty, and umami, represent taste sensations, which are mediated by distributions of taste buds t hroughout the oral cavity. In contrast to taste, odor sensations involve a vastly larger c ollection of diverse odorous qualities. Retronasal odor sensations arise from volatiles in the foods and beverages we consume and reach olfactory receptors embedded in the olfac tory epithelium in the upper nasal cavity by travelling up the nasal pharynx. The neural correlates of flavor perception in huma ns are beginning to be unraveled. Flavor perception studies reveal how re tronasal odor, taste, and oral tactile sensations are perceived as a unified sensation in the oral space, and have also sought to identify the neural structures responsible for the integration of these sensations into whole flavor perceptions. Non-human primate studies laid the foundations for flavor research in humans (Rolls and Rolls 1997). Primate research ha s revealed multimodal neurons in secondary cortical gustatory areas that are finely tuned to taste quality, but also
76 responsive to both odor and taste components of a s timulus (Rolls and Scott 2003). Functional imaging studies in human have localized brain areas with multimodal neurons that integrate odor and taste stimuli (as well as o ther sensory stimuli) for flavor perception (de Araujo et al. 2003; Rolls and Rolls 1997). An important caveat to this research was the discovery that retronasal odors ar e processed differently than orthonasal odors in the central nervous system (Welge-Lssen e t al. 2009; Hummel 2008; Small 2008; Small and Prescott 2005; de Araujo et al. 200 3). In the following section I discuss the neural subs trates of flavor perception. I begin by briefly addressing how retronasal odors ar e processed in the central nervous systems (Welge-Lssen 2009; Hummel 2008). Then, I present data from functional imaging studies, which have localized the neural st ructure involved in the integration of olfactory and gustatory modalities for flavor perce ption (Small et al. 2007; Small and Prescott 2005; Small et al. 2004; de Araujo et al. 2003; Zatorre and Jones-Gotman 2000), and review findings from a study that looked at fla vor processing in sommeliers (Castriota-Scanderbeg et al. 2004). Central representation of retronasal olfaction Mentioned previously, odors reach the olfactory ep ithelium by one of two routes: orthonasally when smells occur in the external envi ronment and retronasally when smells arise in the oral cavity from food or beverage (She pherd 2006). Odors are released in the mouth, and are therefore perceived as if they are s ensed within the mouth (Small 2008; Liang and Jinks 1996). Studies demonstrate that re tronasal odor perception is distinct from orthonasal perception due to its intimate asso ciation with taste and touch perceptions occurring simultaneously in the mouth. Imaging research has uncovered a
77 network of regions consisting of the orbitofrontal cortex, frontal operculum, ventral insula, amygdala, and anterior cingulate cortex act ivated by retronasal odors (WelgeLssen et al. 2009; Small and Prescott 2005; Small et al. 2004; de Araujo et al. 2003). Hummel (2008) used electrophysiological, and imagi ng techniques to examine the differences between orthoand retronasal perceptio n of food and non-food related odors in humans. Electrophysiological results demonstrat ed that olfactory information processing was dependent on the route of odor prese ntation. Moreover, imaging techniques revealed differential response patterns to orthoand retronasal stimulation. Retronasal presentation of food odors evoked prefer ential activation in the medial orbitofrontal cortex (OFC), perigenual cingulate, s uperior temporal gyrus, and posterior cingulate cortex (Hummel 2008). These differences in neural activation may relate to differential circuits for food and non-food related odors. In a similar study, WelgeLssen et al. (2009) examined the influence of a si multaneous gustatory stimulus on orthonasal and retronasal olfaction. Subjects were presented with food and non-food odors and concurrently had a gustatory stimulus app lied to the tongue to create congruent (vanilla-sweet) and incongruent (vanilla-sour) odo r-taste pairings. Results demonstrate that congruent olfactory-gustatory stimuli (food re lated odors) are processed more rapidly in the brain than incongruent stimuli (non-food rel ated odors). The evidence was consistent with prior research demonstrating activa tion of the same structures during retronasal perception. Moreover, this research hig hlights the notion that congruency and familiarity play an important role in stimulus proc essing, particularly during perception of flavor (Welge-Lssen et al. 2009; Hummel 2008).
78 Functional neuroimaging data of flavor perception Investigations that explore the cortical structures involved in both human olfactory and gustatory processing have been the fo cus of research for many years. Up until a few years ago, very little was known about the brain structures responsive to information from both chemosensory systems, or how they interact to design flavor perceptions. However, recent functional neuroimagi ng techniques have made vast contributions to our current understanding of chemo sensory integration and the representation of flavor in the human brain (Small 2008; Small et al. 2007; Small and Prescott 2005; Small et al. 2004; de Araujo et al. 2003; Gottfried et al. 2002; Small et al. 1997a). Taste and smell neuroimaging studies demonstrate t hat unimodal representation of a tastant or odorant produces overlapping activa tion in regions of the insula, amygdala, orbitofrontal cortex, and anterior cingulate cortex (Small et al. 2007; Small 2006; Kringelbach et al. 2004; de Araujo et al. 2003; Rol ls and Scott 2003; Gottfried et al. 2002; Savic et al. 2000; Zald and Pardo 2000; Zator re and Jones-Gotman 2000; Small et al. 1997a). Likewise, bimodal neurons exist in the se cortical chemosensory structures. Several researchers have examined the responses of bimodal neurons in these cortical areas (Welge-Lssen et al. 2009; Small and Prescott 2005; Small et al. 2004; de Araujo et al. 2003). Subjects are typically presented with t wo flavors, made up of incongruent or congruent odor-taste pairs. The goal of these elec trophysiological and neuroimaging studies was to identify differences in neural proce ssing when either the congruent or incongruent odor-taste pair was presented. The res ults have demonstrated that congruent odor-taste pairs activated regions different than i ncongruent pairs. Both unimodal
79 neurons that independently respond to taste or odor information, and bimodal neurons responsive to congruent odor-taste combinations are observed in the anterior cingulate cortex, frontal operculum, dorsal insula, anterior ventral insula extending into the caudal OFC, ventral lateral prefrontal cortex, and post-pa rietal cortex (Small 2008; Small 2006; Small and Prescott 2005; Small et al. 2004; Shepher d 2004; de Araujo et al. 2003; Rolls and Scott 2003). The data reflected supra-additive responses in those areas, in that the activity was greater for the odor-taste combination s, than the sum of the neural activation evoked by unimodal stimulation (Small and Prescott 2005; Small et al. 2004; de Araujo et al. 2003). The occurrence of both unimodal and bimodal neurons in these areas underscores that these neural structures deal with integration of odors and tastes for flavor processing in humans. The occurrences of multimodal neurons that receive converging sensory information, reflects integration across sensory mo dalities (Small and Prescott 2005; de Araujo et al. 2003). Multimodal neurons are able t o respond to specific combinations of varying sensory input, to encode information about the sensory properties of complex combinations of stimuli. In the case of flavor, th is includes smell-taste-touch sensory combinations. Multimodal neurons responsive to olf actory, gustatory, and other sensory stimuli, have been documented in regions of the OFC (Small et al. 2007; Shepherd 2006; Small and Prescott 2005; Small et al. 2004; de Arau jo et al. 2003; Rolls and Scott 2003). The convergence of these two chemosensory modalitie s in the OFC suggests that it is an anatomical locus for the representation of flavor. Notably, corresponding stimulation across modalities drives multimodal neurons in the OFC, such that a cell that responds to
80 sweet also responds to fruity but not fishy odor, t hereby highlighting a role for these neurons in the representation of flavor. Castriota-Scanderbeg et al. (2004) used fMRI to st udy sensory integration in the brain of sommeliers. This study explored differenc es in neural representations of flavor in sommeliers compared to nave subjects. It was a ssumed that judging a wine expertly is a complex process that requires higher cognitive fu nctions such as memory and an ability to integrate sensory modalities. Additionally, dur ing wine tasting sommeliers, compared to nave individuals, use specific strategies to cl assify and recognize the qualities of a particular wine, and how they combine to form the c omplex beverage. The results of the study provided evidence for substantial difference in the neural representation of the flavor of wine in sommeliers compared to untrained participants. In sommeliers, response to wine activated a network of regions inv olving the left insula, including its most anterior region, the adjoining caudolateral or bitofrontal cortex, left putamen, right inferior frontal gyrus, as well as bilateral activa tion in the inferior portion of the middle frontal gyrus of the dorsolateral prefrontal cortex The larger and better-defined cerebral network elicited by wine tasting in sommeliers appe ared to be modulated by expertise. These observations indicated a more refined sensiti vity to combined olfactory and taste perceptions in sommeliers and that more analytical or cognitive evaluation strategies are likely to account for observed differences. Conclusion The review of central olfactory, gustatory and fla vor systems helps to identify the neural substrates that contribute to the skill of w ine experts. Although, the majority of
81 the evidence presented was gathered through general human studies, it is applicable to our current understanding of the central events rel ative to wine sensory evaluations.
82 Chapter 4 The Psychology of Wine Expertise Introduction Wine is a complex beverage made up of hundreds of c hemical compounds that contribute either directly or indirectly to the odo r and flavor of wine. Wine stimulates more than just the olfactory and gustatory receptor s. Tactile sensations are part of the inmouth sensations of the wine and give the wine its texture (Jackson 2009). Additionally, most tasters use a number of visual cues, including the wines color, clarity, hue and depth, during wine evaluation. Wine sensory evalua tion relates to the judgment of a wines appearance, fragrance, flavor, mouth-feel an d acceptability. The assessment of wine happens over an extended period of time so tha t the taster may identify and appraise the duration and development of the wines chemosen sory components (Jackson 2009; Hughson 2008). It is questioned whether expertise in any domain i s the outcome of an innate and genetically predetermined capacity, training and ex perience, or the combination of both (Hughson 2008; Parr 2008). For some researchers, a n innate capacity was believed to generate superior performance. However, since de G root (1948; 1976) and Chase and Simon (1973) demonstrated that experience is requir ed to acquire expertise in a domain, research turned to the realm of cognitive psycholog y to explain experts, as cited by Hughson (2008). Studies have been limited to domai ns that appear to be based on cognitive processes, such as chess, physics, medica l diagnostics, and bridge (Hughson 2008). Domain related experiences result in the de velopment of long-term memory structures, which provide the foundations for the a dvanced level of performance.
83 Expertise research in cognitive domains, such as ch ess, put forward long-term memory models to highlight the proposition that performanc e is based on higher cognitive processes (Hughson 2008). Wine expertise is believed to be a perceptually dr iven domain, and was regarded to be an example of perceptual learning by Gibson a nd Gibson (1955). Generally, sophisticated perceptual skills rather than any cog nitive ones, such a categorical knowledge or episodic memory, is believed to primar ily establish wine expertise (Hughson and Boakes 2002; Hughson and Boakes 2001). However, Gawel (1997) and Solomon (1997) described theories of wine expertise that emphasize the importance of experience and long-term memory for such advanced p erformance in the domain of wine. Superior knowledge and experience in the domain of wine tasting, as with other domains, is inherent to expertise. But what changes when an individual develops wine expertise? To begin to understand what underlies wine expertis e, one must be able to delineate between different levels of skill relative to wine. Investigators have used a wine knowledge test to assess level of expertise, so wha t are the criteria for an individual to be regarded as a non-expert (novice), intermediate or expert wine taster? In reading the literature, I noticed that each res earcher presented a particular set of qualities to classify the expertise level of taster s. The novices, or non-expert, tasters are generally described as individuals who rarely consu me wine and know very little about it (Hughson 2008). This is typically an individual th at does consume wine on occasion, but has had no formal training in wine tasting or winem aking experience (Ballester et al. 2008). Additionally, non-experts have minimal perc eptual and verbal expertise (Melcher and Schooler 1996). Intermediate tasters are those individuals who have drunk wine
84 regularly over an extended period of time, but have had no training, and possess a limited knowledge of wine (Parr et al. 2002; Hughson and Bo akes 2001). These individuals have moderate perceptual expertise but do not know how t o describe wines with much precision and therefore lack verbal expertise (Melc her and Schooler 1996). Hughson (2008) defines a wine expert as someone wh o knows a great deal about the production of wine, has received formal trainin g in enology (the science and study of wine and winemaking) and whose profession requires frequent wine tasting. In many studies, wine experts are individuals with 7+ years of professional tasting experience in the wine industry and include wholesale buyers, win e makers, retail managers, sommeliers and wine educators (Parr et al. 2004; Hu ghson and Boakes 2002; Parr et al. 2002; Solomon 1997). Gawel (1997) categorized expe rts as 4th year enology students having received intensive structured training in ad dition to their considerable experience with wine. One thing that is consistent throughout these defi nitions is that in order to be qualified an expert one must have extensive experie nce with wine and have completed formal training in enology. In this thesis, formal training is defined as a uniform and directed program of instruction. Experience relate s to the familiarity with a product class resulting from long-term exposure to a wide variety of members representative of that product class. Additionally, experience is the res ult of exposure to a product class that occurs in combination with verbal labeling of the p roducts sensory characteristics. Wine experts have developed an extensive vocabulary spec ific for olfactory and gustatory sensations that substantially improves their descri ptive abilities (Melcher and Schooler 1996). Presumably, those individuals deemed to be wine experts have acquired richer,
85 domain-specific cognitive processes as a result of their training and experience. Herdenstam et al. (2009) examined how training affe cts the way wine is experienced by holding open discussions with wine professionals. The professionals stated that training determines the understanding and description of cer tain attributes in wine, increasing the number of terms used, the use of specific descripti ons and their ability to discriminate between attributes. A wine expert is an individual with sophisticated discriminative and descriptive skills with respect to wine, as they need to be abl e to recognize and identify specific notes in a wine even when those notes are subtle componen ts of an extremely complex mixture (Parr 2008; Hughson and Boakes 2001). Wine notes r efer to the various fragrant characteristics that shape the wines aroma and bou quet. The fragrance, aroma and bouquet, of a wine are the by-product of the type o f grape (aroma) and the maturation process (bouquet) with which the wine was produced. Wine experts make claims regarding to their olfact ory and gustatory perceptual acuity. But, in spite of these claims, there remai ns a lack of experimental evidence that clearly demonstrates the sources that underlie such expert advantage. Only a few researchers have investigated the differences in ab ility between expert, intermediate and non-expert wine tasters to understand the psycholog ical basis of expert ability by measuring detection threshold, discriminative perfo rmance, aptitude for odor recognition and identification, and descriptive skill (Ballest er et al. 2008; Hughson 2008; Parr 2008; Parr et al. 2004; Parr et al. 2002; Hughson and Boa kes 2001; Hughson and Boakes 2001; Brochet and Dubourdieu 2001; Gawel 1997; Solomon 19 97; Solomon 1990; Lawless 1984).
86 In relation to wine expertise, detection threshold is the concentration of an odor stimulus necessary for it to be sensed while discri mination refers to an individuals capacity to discern between wines, as well as featu res that comprise the wines fragrance and flavor. In turn, odor recognition involves the ability of subjects to correctly identify wine-relevant odors that they have been exposed to on some previous occasion, whereas odor identification entails discriminating among an d accurately verbally labeling odor mixtures that emanate from the wine. Lastly, descr iptive skill reflects ones capability for generating detailed accounts of their chemosens ory perceptions consistently. The major focus of much of the research has been w ine-relevant verbal abilities, namely semantic memory and language (Brochet and Du bourdieu 2001; Gawel 1997; Solomon 1997). Other cognitive investigations have explored human conceptual behavior (Ballester et al. 2008) and types of memor y (Parr et al. 2004; Parr et al. 2002) including perceptual, also called sensory-based, me mory. Currently, two main theories have been presented to examine the basis of wine ex pertise (Hughson 2008). The first theory states that expertise is based on low-level perceptual advantage. The second theory puts indicates that knowledge, both implicit and explicit, gained through extensive training and experience underlies the development o f wine expertise (Ballester et al. 2008; Hughson and Boakes 2002; Gawel 1997; Solomon 1997; Solomon 1990). I hypothesize that the superior skill of wine expe rts to discriminate, recognize, and describe the fragrance, flavor and overall qual ity of wine, develops as the result of formal training and experience in the domain of win e. Formal training and experience spur the processes of perceptual learning so that e xperts learn about and construct memories for the critical olfactory and gustatory a ttributes in wine. I propose that
87 perceptual learning with wine enables experts to de velop superior perceptual skill that helps experts establish a better system of classifi cations, and categorization, resulting in a sophisticated conceptual knowledge of wine. Percep tual skill and conceptual knowledge are further strengthened with a specific lexicon of wine terminology. In the following sections I present studies that p ropose that the experts superior discrimination is developed through enhanced percep tual skill (the more effective perceptual encoding of wines chemosensory attribut es) as well as studies that identify perceptual memory to be the basis of greater olfact ory recognition performance of wine experts (Hughson 2008; Parr 2008; Parr et al. 2004; Parr et al. 2002; Hughson and Boakes 2001; Bende and Nordin 1997; Livermore and L aing 1996). Additionally, I look at studies, which assert that expertise in the doma in of wine is shaped by an individuals conceptual knowledge and vocabulary of wine charact eristics (Ballester et al. 2008; Hughson and Boakes 2002; Gawel 1997; Solomon 1997; Solomon 1990; Lawless 1984). Lastly, I present literature that addresses wine de scriptive language, and the necessity of training for the effective use of this tool (Hughso n and Boakes 2002; Brochet and Dubourdieu 2001; Gawel 1997; Solomon 1997; Solomon 1990; Lawless 1984). Understanding wine expertise: Perceptual Learning Wine expertise is frequently referred to as an exa mple of perceptual learning (Gottfried 2008; Wilson and Stevenson 2003a; Wilson and Stevenson 2003b; Gibson and Gibson 1955) Psychologists J. J Gibson and E. J. G ibson (1955) stated that perceptual learning involves extracting previously un-noticed perceptual information from a stimulus array, such that past experiences enriches accurate perception. Later, Gibson (1963) described perceptual learning as any relativ ely enduring and consistent change in
88 the perception of a stimulus array; a phenomenon th at followed practice and experience with the array. Wine expertise is thought to be a domain that develops from perceptual learning within the chemical senses. But how does perceptual learning occur? In the previous chapter, olfactory learning was presented as an example of perceptual learning (Wilson and Stevenson 2003a; Wilson and Stevenson 2 003b). The human olfactory system has an extreme capacity for learning, a proc ess also known as experiencedependent synaptic plasticity that leads to the for mations of memories. At the neuronal level, perceptual learning occurs when a stimulus i s repeatedly experienced, resulting in the establishment of adaptive changes between the s ynaptic transmissions of neurons. At the behavioral level, perceptual learning manifests as better discrimination and recognition of a stimulus. In relation to wine exp erts, perceptual learning would result in better discrimination and recognition of wines. Goldstone (1998) proposed that mechanisms such as attentional weighting, differentiation and unitization play a role in perc eptual learning. Through attentional weighting individuals are able to focus their atten tion on more salient dimensions and features of a stimulus, while ignoring those that a re irrelevant. Thus, if only the important features are attended to, only the releva nt dimensions are used for the identification of differences (discrimination) betw een stimuli. Differentiation is the process by which two stimuli, originally perceived inseparable, become psychologically independent (Goldstone 1998). Once the two stimuli are separate from one another, discriminations can be made between percepts that w ere initially psychophysically indistinct. At the neuronal level, experience with a stimulus creates specialized receptors for stimulus components or wholes to improve percep tion. Moreover, this mechanism
89 directs learned discrimination of complex stimuli t hat differ along many dimensions, as well as the differentiation of entire categories an d the separation of the perceptual dimensions that comprise a single stimulus. The last mechanism, unitization, refers to recogni tion of a previously experienced complex stimulus that is subsequently treated as a single functional unit (Goldstone 1998). Unitization entails the development of sing le functional units that can be triggered when a complex configuration occurs. By unitizatio n, components of often-presented stimuli become processed as a single functional uni t when they consistently occur together. This mechanism does not appear to facili tate finer discrimination since features that frequently co-occur are unitized so that all c omponents together evoke a similar response. Although this mechanism appears to funct ion in a manner that opposes differentiation, both mechanisms are declared neces sary for the development of accurate representations for the perceptions at hand. In ot her words, unitization and differentiation work together within a model of perceptual learning that begins with a specific feature description of objects, and generates units for com binations of features if features appear together, and divides features into sub-features if independent sources of dissimilarity within the original features are detected. In relation to wine expertise, perceptual learning mechanisms like attentional weighting, differentiation, and unitization, work t ogether to bring about better perceptual skill. The mechanism of attentional weighting is u seful to wine experts since it would give them increased attention for features of a win e that are critical to identifying grape type and the methods used to produce it (Hughson 20 08). Additionally, attentional weighting would improve discrimination and descript ive performance by allowing
90 experts to attend to those more salient features of wines. Differentiation is also a process constructive to wine experts as it presents a means for the discernment of various wine varieties (differentiation of categories) and the m ultitude of olfactory and gustatory components that compose an individual wine (differe ntiation of perceptual dimensions). Unitization is a mechanism that appears to be a hin drance to wine expertise since experience appears to decrease discrimination betwe en similar stimuli, with related wines being treated as a single perception. However, evi dence from conceptual knowledge studies (Hughson and Boakes 2002; Brochet and Dubou rdieu 2001) suggests that wine experts employ unitization to their advantage by de veloping prototypes of wine samples to aid in discrimination and description. Perceptual skill In many domains, experts are able to make perceptu al judgments that are seemingly mysterious to the everyday untrained huma ns. In the domain of wine, expert tasters are capable of discriminating between chara cteristics of wines that are critical to the accurate identification and description of the wine. Researchers have sought to explore whether experts do in fact have better perc eptual skill (detection and discrimination) than non-experts because wine exper tise is largely regarded as perceptually based. To examine the influence of ol factory perceptual learning among professional wine tasters and non-experts, Bende an d Nordin (1997) had participants complete detection, discrimination and identificati on tasks. In this study, absolute detection thresholds were measured for the odorant 1-butonal. The olfactory sensitivity to this odorant was no different between professional wine tasters and a group of nonexperts. As mentioned earlier, learning and experi ence do not influence a humans basic
91 sensitivity (detection threshold) to chemosensory s timuli. Therefore, it is not surprising that this and other studies, have found that wine e xperts do not have a greater sensitivity for wine relevant chemosensory stimuli or chemosens ory stimuli in general, implying that perceptual learning processes do not modify the inh erent sensitivity of the olfactory receptors to odorants (Parr et al. 2004; Parr et al 2002; Hughson and Boakes 2001; Bende and Nordin 1997; Livermore and Laing 1996). Expert tasters have demonstrated superior supra-th reshold discrimination for chemosensory stimuli over non-experts, as they are typically observed to have more accuracy when judging the similarity, or lack there of, between wine samples (Wilson and Stevenson 2003a; Hughson and Boakes 2001). Dis crimination skill in experts and novices has been measured using a triangle test. In this test, three wine samples are given to an individual, two of which are identical, and participants are asked to determine which sample is different. In the Solomon (1990) s tudy, experts display finer discrimination performance (capacity to identify th e chemosensory differences between wine samples) than novices on this task. Matching tasks have also assess the precision of discrimination in experts and novices (Solomon 1997 ; Melcher and Schooler 1996; Solomon 1990). Participants are given a set of win es to sample and are subsequently asked to match the wine to the appropriate sensory description. Melcher and Schooler (1996) observed that experts were more accurate tha n non-experts at matching a wine from a set of alternatives to the correct descripti on. Likewise, Solomon (1990; 1997) observed that experts were superior at matching win es to descriptions. In matching tasks, discrimination is measured as a function of descrip tive ability and expertise; more
92 accuracy in identifying and matching a wine to its description reflects better discriminative performance. A study conducted by Parr et al. (2002) investigat ed detection threshold, and recognition and identification of wine-relevant odo rs as a function of domain-specific expertise to explore the perceptual skill of wine e xperts and intermediates. Expert and intermediates participated in tasks that assessed o lfactory sensitivity, odor recognition, odor identification and consistency of odor naming. These experiments were used to measure whether experts are more accurate than inte rmediates at recognizing and identifying wine relevant odors. Additionally, Par r and colleagues hoped to reveal the locus of the greater ability observed in experts. This study aimed to simulate the odordiscrimination tasks that occur within the typical wine evaluation situation. Odor identification was employed as measure of explicit, semantic memory, while odor recognition was used as a measure of explicit, epis odic memory. Semantic memory is defined as being based on a persons general knowle dge and experience with an odor, while episodic memory has its basis in perceptual a nd possibly imaging processes, but is not necessarily based on a verbal representation. Parr and co-workers employed a two-alternative for ced-choice procedure to determine odor detection threshold (olfactory sensi tivity). Participants were presented with bottles containing a solution of 1-butonal (of some concentration) in distilled water and bottles containing distilled water and asked to determine which bottle contained 1butonal. The concentration at which 1-butonal was s ensed was taken as an estimate of a participants detection threshold. To assess odor recognition and identification, participants smelled various wine-relevant odors an d asked to remember the smells.
93 After a delay, participants were presented with mor e odorants, half of which they had previously experienced (old) and half of which were new, and asked to judge whether each odorant was new or old, give a confidence rati ng for the recognition judgment, name the odorant as specifically as possible, and lastly give a confidence rating for the verbal labeling. Experts identified more old odorants (those previo usly experienced) among the new ones, demonstrating superior odor recognition p erformance compared to that of intermediates. These findings established superior explicit recognition (episodic memory) by wine experts for wine-relevant odorants. The results did not demonstrate the effect of expertise on olfactory identification or consistency of labeling the wine relevant odorants. Experts ability to correctly label the odors they identified was better than intermediates, however not by much. Furthermore, P arr and colleagues did not observe a relationship between recognition (episodic memory) and identification and labeling performance (semantic memory). Thus, it was conclu ded that experts enhanced performance, as measured by odor identification and naming consistency, was not rooted in sensitivity (detection threshold) or semantic me mory. The authors suggest that differences in performance between experts and inte rmediates are due to some type of superior wine-related perceptual (sensory-based) me mory system that functions independently of semantic memory processes. In lin e with an accumulating body of evidence, this study suggests that verbal codes are not essential, or automatically activated for successful odor-guided cognition. In stead, data implies that perceptual skill in relation to olfaction, is fundamental to wine ex pertise. The authors concluded that the
94 locus of superior recognition of wine-relevant odor s is perceptual memory, such as olfactory imaging. In 2004, Parr and co-workers re-investigated what underlies wine experts olfactory recognition memory. In this study the pe rformance of novice tasters (instead of intermediate) was tested against that of experts. As in their previous experiment (Parr et al. 2002), experts and novice participated in olfac tory sensitivity, odor recognition, and odor identification tasks. Parr and colleagues als o investigated whether verbalization in general (employing speech to comment on an odor) or the specific verbalization involved in naming an odor (semantic memory), influenced acc uracy of odor recognition. Additionally, this study incorporated an incidental recognition memory task to explore whether experts are better than novices at recogniz ing recently sampled odors when they are not expecting their memories of their smells to be tested. Parr and colleagues employed methods similar to t he ones used in their previous study (Parr et al. 2002) to test olfactory sensitiv ity and odor recognition memory. However, the memory task was incidental rather than intentional; participants were unaware that theyd be tested on their memory for p reviously experienced odors. In the olfactory identification test, the verbalization wi thout forced naming task, participants were required make an affective judgment concerning each odorant by commenting on whether the odorant they smelled was pleasant, unpl easant or neutral. In the forced naming verbalization task participants were asked t o identify and verbally label odorants theyd previously been exposed to. Again, data demonstrated that experts and novices do not differ in their detection thresholds (Parr et al. 2002). Thus, enhanced sens itivity is not major factor that
95 contributes to the ability to recognize or identify wine relevant odors. As previously observed (Parr et al. 2002) experts displayed super ior recognition performance for wine relevant odors. Moreover, experts recognition mem ory is superior to that of novices irrespective of whether the memory task was intenti onal or incidental. This study demonstrated superior olfactory explicit recognitio n memory for domain specific odorant compounds by wine experts. Although odor identific ation performance of wine experts was similar to that of novices, olfactory recogniti on memory was improved when subjects were asked to verbally label, rather than rate for pleasantness, the wine odorants they had been presented. This observation suggests that semantic memory does play an important role in odor recognition, even though it is not the locus of domain-specific, superior olfactory recognition memory demonstrated by wine experts. The results of the present study support previous findings, that the l ocus of superior olfactory recognition memory is perceptual (sensory-based) memory, which is the memory for the smell itself, and olfactory imaging. The evidence presented thus far demonstrates that experts demonstrate a discriminative advantage (perceptual skill) over no vices yet the mechanisms that bring about this effect are unclear. Hughson and Boakes (2001) inquired whether the superior discrimination observed in wine experts reflects mo re effective perceptual encoding (bottom-up processing) that is most likely implicit or more conceptually-driven encoding (top-down processing), that may be implicit, explic it or both. They restrict their analysis to perceptual judgments made on the basis of olfact ory and gustatory stimulation, noting that experts possess a great amount of explicit kno wledge of wine, notably about grape varieties and wine production. How can such knowle dge then be used to inform
96 perceptual judgments? Hughson and Boakes state that the perceptual and cognitive skills associated with wine experts can be measured in a h ierarchical manner and present a ranking that reflects how explicit knowledge of win e is likely to be important to such skills. The first and second levels account for detection and discrimination between compounds, and the detection of elements in a compo und (Hughson and Boakes 2001). The authors state that knowledge is not required fo r skills involving detection and discrimination of absolute thresholds and differenc e threshold for wine and non-wine compounds or the ranking of wines along sensory dim ensions. Additionally, knowledge is not required for detection of a single element w ithin a compound or the detection of different levels of a given element. Verbal descri ptions are ranked third on Hughson and Boakes (2001) hierarchy of perceptual and cognitive skill. At this level knowledge is needed to help tasters consistently use verbal labe ls for wines features and configural properties, and also helps in the matching of wines to feature and configural descriptions. Lastly, categorical judgments (level four) require that experts have explicit knowledge about wine, knowledge that facilitates the identifi cation of types and subtypes of wine, as well as faults in production. Conceptual change It has become widely accepted that the superior pe rformance of experts largely relies on domain-specific knowledge (Hughson 2008; Parr 2008; Ballester et al. 2008; Hughson and Boakes 2002; Hughson and Boakes 2001; S olomon 1997; Solomon 1990). Research in other domains reveals that experts use different criteria to categorize the domain specific samples than the criteria used by n on-experts. Classification is a basic
97 means of judging the relationship between objects w ithin the same category (Solomon 1997). During classification, exemplars of a class are judged to be, at some level, identical. A class involves a certain set of featur es that are weighted in importance according to some standard that is theoretical in n ature or due to characteristics of processing. By this definition, objects classified together have similarities in a set of salient features, such that when an individual clas sifies an object, they use the standard by which similarity can be assessed and by which class is defined. One of the most basic ways to organize our knowled ge is through categorizing our perceptions (Ballester et al. 2008). Categoriz ation is the mechanism by which objects are recognized, differentiated and understood. Cat egories are organized along a typicality gradient from best to worse representati ve objectstypical objects share a lot of features while non-typical objects share few featur es. Humans distinguish among categories on the basis of interrelated properties (Rosch and Mervis 1975) and that features co-vary by classes of objects, instead of varying continuously in the perceived world (Rosch et al. 1976), as cited by Solomon (199 7). Solomon (1997) also cites the work of Malt and Smith (1984), which demonstrated t hat correlated clusters of properties exist within basic level categories. This evidence led to the implication that experts further divide categories in ways that maintain tho se clusters of properties and therefore differ from novices in the manner they conceptualiz e their domain specific experiences. Relative to wine, expert tasters possess explicit knowledge of the set of qualities that tend to cluster together in wine from a given variety of grape. This knowledge of grape variety is thought to affect experts percept ion and descriptions of a given wine sample (Gawel 1997; Solomon 1997) since it is belie ved to contain information about the
98 range of sensations associated with wines made from relevant grape varieties. Parallels can be drawn between expertise in other domains and the domain of wine given that wine experts appear to categorize wines according to gra pe variety while novices use basic perceptual features such as bitterness, or sweetnes s to group wines (Solomon 1997). It has been proposed that wine experts undergo a conce ptual change during acquisition of their expertise (Hughson and Boakes 2002; Gawel 199 7; Solomon 1997). Kitcher (1988) defined conceptual change as a reordering of which concepts in a domain are considered fundamental and which are derivative, as cited by S olomon (1997). Conceptual change in the acquisition of expertise is reflected as a reweighting of features considered to be salient in determining or characterizing membership in a class, a reweighting that manifests as a different understan ding of a domain. Solomon (1997) specifies that expertise in a domain requires a reo rganization of the grosser classes distinguished by novices and a restructuring of the conceptual framework within which such classifications and understandings of salient features are surrounded. With knowledge of more specific categories, expert taste rs are able to take advantage of these correlated features and, guided by deductions from more apparent features, search the perceptual array splashing across their palates for less obvious features. For instances, when tasting a Reisling, experts are likely to sear ch for notes of flower, lime and citrus, features typical to wines of that grape type. Solomon (1997) explored conceptual change and wine expertise by inquiring whether experts and novices describe wines using si milar features (at different levels of specificity), and if they understand these features to determine similar systems of classification. The first experiment, explored how knowledge of wine influenced
99 descriptions generated by experts and novices. Par ticipants were presented a set of white wines to taste and then describe with the aid of th e Wine Wheel (a verbal tool developed by enologists). The second experiment assessed whe ther experts and novices differed in their systems of classification and whether those c lasses corresponded to grape type. Tasters were asked to explicitly sort wines into cl asses, give explanations for their groupings, and subsequently interviewed to clarify their beliefs about what causes a wine to have the features it does. Results from experiment 1 support the claim of inc reased differentiation associated with greater expertise. Expert tasters described wines using more specific features. As has been observed in other domains, w ine experts appear to identify more features with greater specificity than do non-exper ts. It appears that wine experts describe the wines in a manner that reflects the na tural division of grape type. A difference in the conceptual organization of wines between experts and non-experts may be the result of experts ability to distinguish th is covariation, a skill that novices lack. In experiment 2, results demonstrate that experts c ategorize wines differently than do intermediate and novice tasters. In the justificat ion of their sorting, experts indicated that they based their classification judgments on suppos ed grape type (variety), whereas nonexperts never mentioned grape type when explaining their judgments. It was concluded that expert and non-experts differed in how they un derstood their perceptions to relate to their organizing of the wine world. Solomons findings support the idea that the acqui sition of wine expertise entails a change in the tasters systems of classification. In the course of training, experts learn a framework that organizes and explains the feature i mportant to their domains. Many
100 experts study grape type (variety) as an essential factor underlying a wines observable features. Greater conceptual knowledge appears to be associated with a difference between expert and non-experts in how they assigned importance to observed features in a determining class membership. Moreover, the expe rts system of classification is associated with their having explicit causal explan ations, a conceptual basis, for why wines have the features they do. Experts are there fore better able to capture the range of classification in their descriptions because they h ad a fundamental model (varietal scheme) of wine that supported the generation of su ch feature descriptions. Ballester et al. (2008) carried out a study in whi ch differences in wine categorization between wine experts and novices was explored. Previous investigations with wine demonstrate that experts organize wine ar omas along a typicality gradient, suggesting that wine categories have a graded struc ture. However, Ballester et al. (2005) observed that boundaries between the Chardonnay win e category and neighboring white wine categories are not definite suggesting some ov erlap in perceptual features constituting each category. This study employed tw o similar varieties of wine (Melon de Bourgogne and Chardonnay) and chose 10 different wi nes that were representative of each wine variety, respectively. Researchers belie ved that the odors of these wines were similar enough to partially overlap with each other Experts and novices were asked to sort the wine samples into groups according to odor similarity. Additionally, participants were asked to complete a typicality-rating task whe re they rated how representative each wine type was to its respective category. Experts were able to more clearly distinguish the two varieties of wine, while novices had some difficulty in separating the two v arieties. Ballester et al. (2008) suggest
101 that experts enhanced performance in the sorting t ask is the result of superior discriminative abilities, possibly due to a more ef ficient wine tasting procedure. Likewise, the authors suggest that experts use topdown processes in which knowledge of different wine styles and varieties influences simi larity assessment. This deeper knowledge of wine styles would enable experts to fo cus on individual features that differentiate the samples best, a finding consisten t with the observations of Solomon (1997) in which experts appeared to sort wine by gr ape variety. The results of the rating task demonstrate that experts shared a common senso ry concept whereas novices did not. Ultimately, these results were inferred to show tha t wine varietal knowledge structures change with level of expertise, such that novices w ere unable to accurately organize the two wines along typicality gradients. Hughson and Boakes (2002) investigated the role of knowledge and linguistic skill relative to wine expertise to explore some of the cognitive processes involved in wine expertise. These authors emphasize the signif icance of experience and long-term memory for advanced discriminative and descriptive abilities in the domain of wine for wine expertise. This study was intended to further explore theories of knowledge put forward by Gawel (1997) and Solomon (1997). In par ticular, how high-level knowledge influences percepts of wines character and directs the search for relevant labels by bringing about expectations that are likely to enha nce component identification. The first two experiments were designed to address whether wi ne experts are able to remember domain-relevant information better than novices in intentional and incidental memory tasks.
102 The first experiment sought to test whether the ef fect of intentional memory occurred in expert and novice tasters in a verbal m emory task with commonly used wine relevant descriptors. Both varietal (combination o f words consistent with description of a wine) and shuffled (meaningless combination of word s inconsistent with description of a wine) wine color, nose and palate descriptions were presented. The varietal condition contained descriptors like inky-crimson; blackberr y and leather; and full-bodied with prune to describe the color, nose and palate respe ctively. The shuffled condition used meaningless words like bright green-gold; straw an d vanilla oak; plum and full-bodied as descriptors for the color, nose and palate respe ctively. Participants were shown the list of descriptors and after a brief delay asked to rec all these sets of descriptors to measure intentional memory. The goal of the second experim ent was to explore whether the superior recall by experts of domain-relevant infor mation would occur when the request to recall information was not expected (incidental recall). Participants completed two tasks, an incidental followed by an intentional sho rt-term verbal memory task. In the incidental task subjects viewed wine descriptions t hat they were unexpectedly asked to recall, while in the intentional task participants were informed that they would be required to recall details from the descriptions. Results of experiment 1 demonstrate that experts c an recall more varietal than shuffled descriptions than novices. However, exper ts recalled less shuffled descriptions than novices. The poorer performance by experts in the shuffled configuration condition was thought to indicate that lack of meaning in the shuffled descriptions interfered with experts short-term memory. These findings were un derstood in terms of wine expertise relying on a knowledge base that included descripti on of typical wine styles stored in
103 memory. Results from experiment 2 show that even u nder incidental conditions experts can recall more wine related words grouped in a mea ningful way than novices. As previously demonstrated (Gawel 1997; Solomon 1997), this evidence helps to establish that wine experts refer to long-term memory structu res when performing wine-related tasks. This suggests that wine experts automatical ly bring to bear their conceptual knowledge about typical features of particular vari eties of wines that incorporates appropriate vocabulary for describing wines. Findings from Hughson and Boakes (2002) provide st rong evidence for the notion that knowledge of wine styles makes and important c ontribution to an experts ability to discriminate between different wines and match them to a description. Evidence appears to illustrate that experts identify the attributes of a wine by comparing it with models and by searching for only those features previously ass ociated with a model. Each of these studies (Ballester et al. 2008; Hughson and Boakes 2002; Solomon 1997) suggests that the learning processes of wine experts results in t he construction of a specific reference framework that especially concerns the verbalizatio n of sensory perceptions. This and the above-mentioned study provide strong empirical evidence that wine expertise, a domain seemingly based in perceptual skill, also re lies heavily on conceptual knowledge and descriptive language. Descriptive skill One of the major goals of wine sensory evaluation is to provide an objective description of the product in terms of its perceive d sensory characteristics. Expert wine tasters most frequently use written descriptions to convey their sensory experiences. These qualitative sensory descriptions commonly ref er to the perceived attributes of the
104 wine and their intensities perceived during evaluat ion (Jackson 2009; Gawel 1997). Wine descriptions reflect this sensory assessment a s well as the relative intensities of the wines appearance, aroma, taste and textural attrib utes. It also contains comments about how those attribute relate to each other, referred to as balance and structure of the wine. This information is expressed in the framework of a n individuals semantic style and use of lexicon of varying specificity (Herdenstam et al 2009). Synthetic descriptive terms describe several attri butes of the wine holistically and are recognized to have greater communicative value for evaluating a wines quality. Synthetic descriptions reflect assessment of the ba lance, complexity, development, and duration of a wine (Herdenstam et al. 2009; Jackson 2009). Analytical aroma descriptive terms are used to express only specific attributes found in the wine and usually describe an odor in terms of other aromatic objects (e.g. li me, raspberry, violet, almond). Specific analytical aroma descriptive terms exist for variet al white and red wines (Jackson 2009). White wine aroma descriptors include (but are not l imited to): apple, citrus, vanilla, melon, and fruity. Red wine descriptors typically i nclude terms like: cherry, bell pepper, rose, spice, and blackcurrant. The language of wine experts hints at a conceptual organization not immediately apparent to novices (S olomon 1997). Rabin and Cain (1984) found that learning to attac h labels to unfamiliar odors can improve ones ability to discriminate between them. In relation to wine, a key component to wine expertise is that of possessing a specific lexicon for labeling the numerous sensory properties of wine. Wine experts appear to have superior descriptive skill, seen in their ability produce more accurate descriptions and to match wines to descriptions produced by themselves or other. Howe ver, the basis for this advanced
105 discriminative skill is poorly understood. The maj ority of the experimental work exploring wine expertise and cognitive processes ha s investigated expertise in relation to knowledge and language. Researchers have therefore examined the influence of formal training and experience on the use of wine tasting vocabulary by expert, intermediate and novice tasters (Hughson and Boakes 2002; Brochet an d Dubourdieu 2001; Gawel 1997; Solomon 1997; Melcher and Schooler 1996; Solomon 19 90; Lawless 1984). In Lawless (1984) and Solomon (1990) the ability o f a wine to be recognized from its written description was used as an indirec t measure of the communicative value of the descriptors provided. Expert wine tasters w ere found to be better than non-expert tasters at matching wines to its descriptors. Lawl ess and Solomon demonstrated that experience influences the use of wine tasting langu age, such that the communicative value of the description is affected. Both found t hat experts are able to write descriptions that they themselves or other experts can later mat ch to the appropriate samples, while novices cannot. Solomon also found that novices we re poorer at identifying wines using the sensory descriptions created by experts and nov ices. Novices inability to correctly match wines to experts descriptions may reflect th e fact that experts frequently use descriptors that are foreign and misunderstood by n ovices. The descriptions that experts constructed consisted of more noticeable sensory di mensions and more concrete associations, such as floral or citrus, than those of novices, while those of novices were confined to a few dimensions such as bitterness and sweetness. The findings tend to suggest that experts and novices find different cha racteristics of the wine salient, resulting in the use of different labels for identi cal samples (Hughson and Boakes 2001).
106 Gawel (1997) analyzed the difference in ability of two groups of wine tasters to accurately communicate the sensory properties of wi ne. One group consisted of highly experienced individuals who had not undergone forma l wine training (intermediates), while the second group contained highly experienced individuals who had undergone many years of formal training (experts). Gawel loo ked to address whether trained tasters produced better descriptions of wines than untraine d experienced tasters. Additionally, Gawel looked at whether intermediates would find it easier to recognize a wine from a description produced by experts. Gawel employed two types of matching tasks. In th e first matching task, both expert and intermediates were evenly divided into t wo groups. All participants were aware that the wines were of a single varietal and wine styleChardonnays. One group was asked to taste wines and then produce a written description of their aroma and palate. The other group was given the descriptions and the same set of wines and asked to match the wines to the description generated by the other group. The expert group matched wines to description produced by the other expert g roup, while the intermediate group matched description generated by the other intermed iate group. In the second matching task, a separate group of four professional tasters independently evaluated and described the same wines. These descriptions were then combi ned into consensus descriptions. The intermediate group was asked to match the wines to the consensus descriptions. Results from the first matching experiment demonst rate that trained tasters were significantly better at matching descriptions gener ated for wines than the untrained tasters, however, both groups preformed at a better than chance level when matching wines to descriptions produced by their peers. Thi s observation led Gawel to conclude
107 that formal training was not necessary to distingui sh wines from their descriptions. Matching performance in the second task increased i n intermediate tasters when they were asked to match wines to descriptions generated by professional tasters rather than those produced by their peers. Gawel suggests that because experts possess explicit knowledge of the set of qualities that tend to clus ter together in a wine for a given type of grape, this varietal knowledge affects their percep tion and description of a given wine. Brochet and Dubourdieu (2001) conducted a lexical analysis on expert descriptions of wine to investigate the structure o f language used by experts. The goal of this study was to investigate how experts organize their knowledge and language of wine and how this organization affects their perceptions and descriptions. Researchers used four different collections of writing that containe d extensive wine-tasting notes produced by four different wine professionals. Results refl ect that experts use word associations specific to their knowledge or perceptions. Also, the descriptive field includes sensations and observations outside of olfactory and gustatory sensations that are not strictly related to describing the taste sensations of a wine. This observation led the authors to conclude that experts use an associative system to describe wines. Results were interpreted to suggest that experts largely base their language on prototypes of wine rather than a wines individual chemosensory qualities. That is to say that upon tasting a wine an expert scrutinizes it and then labels it according to a prototypical model constructed from prior experience with similar wines. Experiment 3 in Hughson and Boakes (2002) looked t o answer whether the poor matching performance of novices relative to experts is due to a perceptual disadvantage or lack of knowledge, such as impoverished vocabula ry. The findings indicate when
108 novices direct their search to a specific limited n umber of terms, they are better able to generate descriptions of wine that they themselves can later match to the appropriate samples. Thus, providing novices with knowledge in the shape of a short list of descriptors used to detail the distinctive characte ristics of various wine varieties, resulted in enhanced performance on matching tasks. Further more, this demonstrates that novices do not have inferior perceptual abilities compared to experts, which supports the belief that expertise is not innate. A consistent finding observed in the above-mention ed studies, is that knowledge and language, gained through explicit formal traini ng and experience, enhances performance in wine evaluation tasks. These findin g provide strong support for the notion that knowledge about wine varietal styles ma kes a significant contribution to an experts ability to discriminate between different wines and match them to their own or another experts description (Hughson and Boakes 20 02; Gawel 1997; Solomon 1997). Likewise, these finding demonstrate that experts re fer to knowledge of correlated properties gained through experience during descrip tive tasks. Currently, there are two major theories concerning the role of memory in win e experts descriptive abilities. The varietal schema model suggests that wine experts po ssess varietal-based knowledge structures that direct their search for relevant de scriptive terms (Gawel 1997; Solomon 1997). The global prototype model proposes that ex perts identify which of a number of global prototypes, developed from prior experience of wines, best fits the sample, and then describe the prototype instead of the wine sam ple (Brochet and Dubourdieu 2001). Both Gawel (1997) and Solomon (1997) propose that knowledge of wine varieties and styles (varietal knowledge) influences and dire cts a wine experts search for relevant
109 verbal labels. This knowledge is developed for the normal features of particular varietals and consists of information concerning the range of sensations that arise from wines made from a particular variety of grape. In other words, they propose that once the grape variety of wine has been identified, a search for d escriptors known to be associated with that particular variety can occur Subsequently, high-level knowledge not only directs the search for relevant labels, but also causes expecta tions of typical characters that function to increase the probability of component identifica tion (Gawel 1997). Conversely, Brochet and Dubourdieu (2001) propose that experts compare characteristics of a wine to a set of prototypes, i dentify the most relevant of those structures and then describe the prototype instead of the wine sample itself. In this model a wine taster does not complete an analysis of the wines individual chemosensory properties. Instead, experts appear to make a comp arison of all the cognitive connections they have from a wine with the impressions they hav e previously experienced when tasting other wines. The descriptions generated us e a series of terms that has been previously used for that category of wine and does not reflect a description of the specific wine itself. Thus, in this model experts descript ion is a categorization of wines as an ensemble of sensations. By and large, evidence supports the varietal schem a theory put forth by Gawel (1997) and Solomon (1997) as more accurately encomp assing the manner in which wine experts organize and use their knowledge of wine th an the global prototype theory proposed by Brochet and Dubourdieu (2001). There i s strong support for the proposition that experts descriptive skill relies on a varieta l structure of knowledge (Ballester et al. 2008; Hughson and Boakes 2002; Solomon 1997; Gawel 1997). In experiment 1 of
110 Hughson and Boakes (2002) the observation that alte ring the configuration (from varietal to shuffled) of sensory components results in lower descriptive performance by strongly suggests that experts rely on varietal knowledge. Additionally, if experts do in fact rely on this structure of knowledge, novices should bene fit from the provision of this sort of knowledge in descriptive tasks. In fact, when novi ces are provided with a varietal list of terms for wine samples they are able to perform bet ter on descriptive tasks (Hughson and Boakes 2002; Solomon 1997). Additional evidence th at supports expert use of varietal schema comes from data in Gawel (1997). This study illustrates that both expert and intermediate tasters are able to describe and match a set of wines within a particular varietal style, indicating that during the descript ive task, experts search widely for wines individual chemosensory components, rather than per form a simple search for relevant prototypes. Conclusion Wine experts are not genetically predetermined, an d their perceptual skills are not the result of an innate ability to better detect ch emosensory stimuli. Experts do not possess more sensitive chemosensory systems and thu s do not have lower odorant or tastant detection thresholds (Parr et al. 2004; Par r et al. 2002; Hughson and Boakes 2001; Bende and Nordin 1997; Livermore and Laing 1996). The perceptual skill of wine experts refers to their advanced discriminative abi lity and superior olfactory recognition. Studies of human olfactory perceptual learning demo nstrate that experiencing an odor, even once, can improve ones ability to discriminat e that odor in the future (Wilson and Stevenson 2003a; 2003b). Better perceptual skill ( finer discrimination) and perceptual memory (better recognition) are likely the result o f perceptual learning with wine, since
111 experience is shown to be a critical determinant of perceptual expertise. Although there is not substantial empirical evidence that confirms perceptual learning as the basis of wine expertise, there is definitely strong evidence to suggest its role in the development of expertise (Parr et al. 2004; Parr et al. 2002; B ende and Nordin 1997; Livermore and Laing 1996). The conceptual knowledge of wine experts is seen a s a finer conceptual framework to classify and categorize wines chemose nsory characteristics, and a better understanding of wines similarities and difference s. The organization of conceptual knowledge is shown to be a function of expertise, s uch that individuals with extensive experience and formal training build a superior con ceptual framework for wine. No study specifically states that conceptual knowledge arises with perceptual learning. However, by inference, it can be argued that if an individual is better able to discriminate and recognize features of a wine, they should be ab le to establish more sophisticated conceptual framework with which to organize their p erceptions. Evidence exists in support of wine experts possessing a different conc eptual framework for the world of wine (Ballester et al. 2008; Hughson and Boakes 200 2; Brochet and Dubourdieu 2001; Gawel 1997; Solomon 1997; Solomon 1990). Therefore I propose that this framework is established when experts experience changes in thei r ability to discriminate between and recognize chemosensory perceptions, as a result of training and experience within the domain of wine. The perceptual learning mechanisms of attentional weighting, differentiation and unitization are especially suit ed to improve discrimination and recognition with stimuli (Hughson 2008; Goldstone 1 998). Likewise, it could be argued that these mechanisms also contribute to the concep tual changes that experts undergo
112 during the acquisition of expertise since this chan ge is observed as better discriminative abilities. Knowledge of a standard vocabulary is essential fo r communication, as well as for a high level of discrimination (Hughson and Boa kes 2002; Hughson and Boakes 2001; Gawel 1997; Solomon 1997). The greater preci sion that experts demonstrate in describing wines is associated with their ability t o discriminate more precisely (Herdenstam et al. 2009). It appears that advanced perceptual skill is required for the effective use of vocabulary terms to describe the p erceptions at hand. Parr et al.(2004; 2002) demonstrated that perceptual skill, measured in olfactory recognition memory, did not rely on verbal skill (semantic memory). Thus, although verbal skill is definitely a measure of expertise, it develops independent of pe rceptual skill, another measure of expertise (Melcher and Schooler 1996). Conceptual knowledge of wines is inherent to descriptive skill, since experts conceptual refere nce framework also relates to verbalization of sensory perceptions (Ballester et al. 2008; Hughson and Boakes 2002; Solomon 1997) and as Hughson and Boakes (2001) note d, verbal descriptions are helped by knowledge. Additionally, it was demonstrated th at when novices are provided with a concise list of verbal descriptors they are able to generate more accurate descriptions of wine implicating that knowledge improves descriptiv e performance. The overwhelming finding in many studies is that descriptive perform ance improves with training, which is not surprising considering that conceptual knowledg e of wine enhances with training as well (Ballester et al. 2008; Hughson and Boakes 200 2; Gawel 1997; Solomon 1997) It is evident that expertise in the domain of wine is the result of formal training and formal experience (Herdenstam et al. 2009; Jack son 2009; Hughson 2008; Parr 2008;
113 Hughson and Boakes 2002; Hughson and Boakes 2001; G awel 1997; Solomon 1997; Melcher and Schooler 1996; Solomon 1990; Lawless 19 84). In this chapter I present studies to support my belief that perceptual learni ng (initiated through formal training and experience) in the domain of wine results in the ad vanced discriminative and descriptive performance associated with experts. From the stud ies discussed above it can be concluded that wine experts rely on a combination o f perceptual skill, conceptual knowledge and a specific vocabulary of wine terms, gained in the course of formal training and experience, to effectively complete th eir sensory evaluations of wine.
114 Chapter 5 Conclusion The aim of this thesis was to look at the biology of wine expertise by providing a review of human olfaction, gustation and flavor alo ng with psychological investigations that examined the basis of the advance skills of wi ne experts. The exploratory work of this thesis reveals that gaps exist in our current understandings of how information contained within odor and taste stimuli results in the chemosensory perceptions of smell, taste and flavor. Likewise, the research concernin g the cognitive processes that bring about high-level performance and domain relevant sk ills in wine experts is incomplete. The following section will summarize the informatio n presented in the three body chapters to tie together the contributions of the p eripheral and central chemosensory systems in the development of wine expertise. The second chapter served as an overview of the pe ripheral olfactory and gustatory systems. Here I identify the sensory cel ls of the olfactory and gustatory epitheliums, reviewing our current understanding of the transduction and coding events that occur in the peripheral chemosensory system. This material is presented to highlight what importance the initial chemosensory events hav e in coding smell and taste information that is passed on to the central olfact ory and gustatory structures. Odor molecules are detected by odorant receptors. This interaction elicits a particular pattern of olfactory neuron activity to generate a signal i n which information about the identity of the specific odor stimulus is embedded (Buck 2004; Floriano et al. 2004; Meierhenrich et al. 2004; Rawson 2000). The odor signal is transmi tted along the olfactory nerve to synapse within glomeruli of the olfactory bulb. Th ere is a high degree of convergence
115 between the olfactory receptor neurons and glomerul i, such that olfactory neurons expressing the same odorant receptor terminate on a specific glomerular unit (Johnson and Leon 2007). A combinatorial code of odorant in formation processing explains how information about the quality of an odorant is enco ded by particular patterns of activity among olfactory receptor neurons, glomeruli, and ol factory bulb interneurons (Rawson and Yee 2006; Floriano et al. 2004; Menini et al. 2 004; Meierhenrich et al. 2004; Moon and Ronnett 2003; Schoppa and Urbana 2003; Uchida e t al. 2000). The five sapid tastants (salt, sour, sweet, bitter and umami) interact with taste cells within the taste bud (Roper 2007; Simon et al 2006; Breslin 2001; Kandel et al. 2000; Rawson 2000) Taste receptor cells possess the receptor proteins required for the transduction of sweet, umami and bitter stimuli, in addition to ion channels that conduct salt stimuli. Nevertheless, taste receptor cells a re deficient in synaptic connections (Chandrashekar et al. 2007; Tomchik et al. 2007). Synaptic taste cells also possess ion channels with which to sense sour stimuli. Some fo rm of cell-cell communication occurs between receptor and synaptic cells so that informa tion about the identity of a tastants is able to reach the gustatory nerve fibers that inner vate synaptic cells (Glendinning et al. 2000). Two theories of how gustatory information i s encoded in the periphery are suggested: the across-fiber pattern and labeled-lin e model (Ishimaru 2009; Chandrashekar et al. 2006; Simon et al. 2006; Sugit a 2006; Smith and St. John 1999). The across-fiber pattern theory posits that taste r eceptor cells are broadly tuned to all taste qualities, and that individual receptor cells expre ss distinct classes of tastants receptors (Chandrashekar et al. 2006; Simon et al. 2006). Th us, decoding the combined activity of various classes of the broadly tuned taste receptor cells results in tastant recognition. The
116 labeled line theory is more basic and states that d ifferent taste cells expressing their respective receptors recognize one of the five tast ants (Ishimaru 2009; Roper 2009; Sugita 2006). By this system, coding follows along straightforward labeled lines transforming information about taste quality into a neural signal. The third chapter examined the central olfactory, gustatory and flavor systems. The chapter covers the functional anatomy and infor mation processing regarding olfactory, gustatory and flavor perceptions. Funct ional neuroimaging studies have contributed greatly to the current body of data wit h respect to how chemosensory information, arriving from the periphery, is coded within neural structures (Zald and Pardo 2000; Zatorre and Jones-Gotman 2000). Olfact ory information exits the olfactory bulb and travels to cortical olfactory structures v ia the lateral olfactory tract (Gottfried 2006; Cleland and Linster 2003). Within the pirifo rm cortex, amygdala, and orbitofrontal cortex, information about the quality and intensity of an odor is processed (Gottfried et al. 2006; Anderson et al. 2003; Wilson and Sullivan 200 3; Sobel et al. 2003; Zatorre and Jones-Gotman 2000). Humans have demonstrated a cap acity for olfactory learning and memory that is dependent on the mechanism of experi ence-dependent synaptic plasticity (Li et al. 2006). By this mechanism, olfactory neu rons are able to undergo perceptual learning of odors (Gottfried 2006; Shepherd 2004; W ilson and Stevenson 2003a; Wilson and Stevenson 2003b). At the neural and behavioral level this olfactory perceptual learning is reflected in the development of better discrimination and recognition of odors as a result of the enduring changes within olfactor y cortical structures like the piriform cortex (Gottfried 2008; Li et al. 2006; Wilson and Sullivan 2003; Wilson and Stevenson 2003a).
117 Gustatory information from the periphery travels v ia gustatory cranial nerves VII, IX and X to the brain stem, synapsing within the ro stral solitary nucleus (Jackson 2009; Small 2006; Rolls and Scott 2003; Witt et al. 2003; Kandel et al. 2000; Smith and Davis 2000; Zatorre and Jones-Gotman 2000). Gustatory fi bers ascend the brainstem to terminate in the thalamus; from there they project to the frontal operculum and anterior insula before traveling to the orbitofrontal cortex (Small et al. 2007; Smith and Davis 2000). Due to tastes inherent multimodal nature, gustatory information processing is usually accompanied by retronasal olfactory and ora l somatosensory information processing. This blending of three sensory systems leads to the construction of flavor perceptions within chemosensory cortical areas that possess unimodal, bimodal and multimodal neurons (Small and Prescott 2005; Small et al. 2004; de Araujo et al. 2003). Functional imaging data demonstrate that the orbito frontal cortex is the anatomical locus of flavor representations (Small et al. 2007; Sheph erd 2006). The fourth chapter focuses on the psychological fo undations of wine expertise and the importance of perceptual skill, conceptual knowledge and a specific vocabulary to the development of advance discriminative and de scriptive skill. As was hypothesized, advanced discriminative and descriptive skill devel ops with training and experience. Wine experts do have better perceptual skill seen i n their improved discrimination and recognition performance (Parr et al. 2004; Hughson and Boakes 2002; Parr et al. 2002; Bende and Nordin 1997; Solomon 1997; Livermore and Laing 1996). Additionally, during the acquisition of expertise, experts experi ence changes it their conceptualizations concerning wine (Ballester et al. 2008; Solomon 199 7). These changes in perceptual skill and conceptual knowledge are enhanced by profession al language (Herdenstam et al.
118 2009; Hughson and Boakes 2002; Gawel 1997; Solomon 1997). I argue that training and experience stimulate the processes of perceptual le arning. With improved discrimination and recognition for chemosensory stimuli individual s are able to build the necessary conceptual framework to arrange their knowledge of the world of wines. A precise language of wine descriptive terms is a necessary f acet of conceptual knowledge. Conceptual knowledge is important for descriptive s kill but not the discriminative aspect of wine expertise (Hughson and Boakes 2001). Throu gh the combination of these three factors, expertise in the domain of wine can be dev eloped. Attainment of expertise entails the maturations of complex skills and strat egies through training, which provides the grounds for high-level performance and domain-r elevant skills. The first and second chapters are presented to pro vide a look at the underpinnings of wine sensory evaluation, by focusing on the sens ory events of peripheral systems that result in the construction of perceptions centrally Unfortunately, there is a relative dearth of experimental studies pertaining to periph eral and central chemosensory events during the wine tasting process. What can be taken away from these is knowledge of how odorants and tastants are sensed by their respe ctive receptors to initiate sensory transduction and encoding of stimulus identity, and subsequently processed by cortical neurons for the construction of perceptions. Conta ined within the signal produced in the peripheral chemosensory systems is information that will be used to depict the quality and intensity of the odor or taste in the central s ystems. Upon reaching the central nervous system, chemosensory information is carried to specific areas to be processed and integrated into whole perceptions of smell, tas te and flavor.
119 With respect to central events during wine tasting one study carried out by Castriota-Scanderbeg et al. (2004) investigated win e experts and novices neural representations of flavor. Assuming that wine expe rtise involves complex processes that require higher cognitive functions, as well as the employment of specific strategies to classify and recognize characteristics in wine, the authors hypothesized that they would observe differences in neural representations of fl avor. Results demonstrated that experts have a larger and better-defined cerebral network e licited during wine sensory appraisal. Thus, it was inferred that experts have a more refi ned sensitivity to the combination of olfactory and gustatory perceptions, and the differ ence in neural representations reflect the use if cognitive strategies. Along with the ge neral human research, this study was presented to indicate the cortical structures activ e during flavor perceptions. These studies demonstrate that although the same cortical structures become active in both novices (general humans) and experts, neural repres entations change with the acquisition of expertise (Small et al. 2007; Small and Prescott 2005; Small et al. 2004; de Araujo et al. 2003). A growing body of research suggests that learning is factor key to understanding how the brain processes and discriminates odors (Go ttfried 2008; Wilson and Stevenson 2003a; Wilson and Stevenson 2003b). Experience pla ys a significant role in odor perception, such that exposure improves odor discri mination. Furthermore, learning and past-experience strongly affect perception of odor quality and discrimination. Thus, learning that a particular combination of features is different from other feature combinations improves object discrimination. Resea rchers believe that odor discrimination and recognition occur through such p rocesses. These olfactory perceptual
120 learning processes are observed as long-term change s in the piriform cortex, olfactory bulb and odorant receptors (Small 2008; Gottfried 2 008; Wilson and Stevenson 2003a; Wilson and Stevenson 2003b; Firestein 2001). The overwhelming finding of chapter four is that perceptual learning with respect to wine expertise needs to be better investigated. Similarly, further exploration of the role of knowledge and language in wine expertise is necessary. Understanding the nature of wine expertise will provide important insight in to the nature of chemosensory perceptual expertise, and expertise in general.
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133 Image. 9: Central gustatory pathway Kandel, E.R., Schwartz, J.H. and Jessell. T. M. Sme ll and taste: The chemical senses. In H. L. John Butler (Ed.), Principles of neural science United States: McGraw-Hill, 2000, 4th edition, pp. 625-647.
134 Appendix I List of abbreviations Chapter. 2 OE: Olfactory epithelium ORN: Olfactory receptor neuron GPCR: G-protein couple receptor OR: Olfactory receptor cNGc: Cyclic nucleotide gated channels MC: Mitral cell TuC: Tufted cell PGC: Periglomerular cell GC: Granule cell C.N.: Cranial nerve TB: Taste bud TC: Taste cell ENaC: Epithelial sodium channel Chapter. 3 AON: Anterior olfactory nucleus AI: Anterior insular cotex CAC: Corticomedial amygdaloid complex CG: Cingulate gyrus CTT: Central tegmental tract DTT: Dorsal tenia tecta EC: Entorhinal cortex fMRI: Functional magnetic resonance imaging FO: Frontal Operculum LOT: Lateral olfactory tract LPFC: Lateral portion of the prefrontal cortex MD: Mediodorsal nucleus of the thalamus NST: Solitary nucleus and tract OB: Olfactory bulb
135 OFC: Orbitofrontal cortex OT: Olfactory tract PAC: Periamygdaloid cortex PC: Piriform cortex PET: Positron emission tomography PGC: Primary gustatory cortex POC: Primary olfactory cortex SG: Supracallosal gyrus STC: Secondary taste cortex VPMpc: Ventroposterior medial nucleus of the thalam us (parvocellular) VTT: Ventral tenia tecta
136 Appendix II Glossary of terms Terms are taken directly from Biological Psychology (Kalat), 9th Edition, 2007; Cellular and Molecular Biology (Karp), 5th Edition, 2007; Cognitive Psychology (Goldstein) 2nd Edition 2008; Cognitive Psychology (Sternberg) 5th Edition, 2009; Mosbys dictionary of medicine, nursing and health professionals, 7th Edition, 2006; Wine Tasting: A Professional Handbook (Jackson) 2nd Edition, 2009, and Neuroscience: exploring the brain (Bear, Connors and Paradiso) 3rd Edition, 2007. Adenylyl cyclase III: An integral transmembrane pro tein that when stimulated activates the production of cAMP. Acetylcholine: Chemical sim ilar to an amino acid, except that the NH2 group has been replaced by an N(CH3) group; a neurotransmitter. Across fiber pattern principle: Notion that each re ceptor responds to a wide range of stimuli and contributes to the perception of every stimulus in its system. Action potential: An electrical impulse consisting of a self-propagating series of polarizations and depolarizations, transmitted acro ss the plasma membranes of a nerve fiber during the transmission of a nerve impulse an d across the plasma membranes of a muscle cell during contraction or other activity. Adaptation: Decreased response to a stimulus as a r esult of recent exposure to it. Adenosine triphosphate (ATP): A compound that store s energy, also used as a neuromodulator. Afferent axon: A neuron that brings information to a structure. Amiloride: Blocks epithelial sodium channels, inhib iting diffusion of sodium. Anosmia: General lack of olfaction. Antagonist: Any agent, such as a drug, that exerts an opposite action to that of another or competes for the same receptor site. Anterior: Towards the front of the brain (above the midbrain). Towards the ventral surface of the body (below the midbrain). Anterior commissure: Bundles of fibers connection l eft and right temporal lobes, and olfactory bulbs. Anterior olfactory nucleus (AON): Located in the po sterior region of each olfactory bulb, receives input signals from mitral and tufted cells and relays them to the contralateral olfactory bulb via the anterior commi ssure. Apical: Of, relating to, or situated at the apex. Ascending: A nervous system pathway that carries im pulses toward the brain. Association fiber: Fibers that unite different port ions of the same cerebral hemisphere. Associative learning: A type of learning in which i deas and experiences reinforce one another and can be linked to enhance the learning p rocess.
137 Aroma: Fragrance of the wine derived from the grape s; typically resembling some complex of fruity, floral, herbaceous, or other aro matic attributes. Attention: The active cognitive processing of a lim ited amount of information from the vast amount of information available through the se nses, in memory, and through cognitive processes; focusing on specific features of the environment. Axon: A single prominent extension of a neuron that emerges from the cell body, capable of conducting action potentials or self-pro pagating nervous impulses away from the cell body. Balance: Wine attribute that refers to the percepti on of harmony, notably between sweet, sour, bitter, and astringent oral sensations. Influ enced by the intensity of the aromatic sensations of the wine. Basal: Of related to or situated towards the base. Basal ganglia: A portion of the brain that consists of the caudate nucleus, the putamen, and the globus pallidus. Basic level: Degree of specificity of concept that seems to be a level within a hierarchy that is preferred to other levels. Bimodal: Pertaining to two sensory modalities Bottom-up processing: Data driven processing where processing starts with information received by receptors. Bouquet: Fragrance derived either from alcoholic fe rmentation (e.g., fruity, yeasty), processing (e.g., buttery, nutty, oaky), or aging ( e.g., oxidized, leathery, cigar-box). Brainstem: The portion of the brain comprising the medulla oblongata, the pons, and the mesencephalon. Categorization: The process by which the common fea tures of a category (e. g. wine) are learned as a result of successive encounters with d ifferent exemplars (Pinot noir, Shiraz, Cabernet ) of the category. The process by which o bjects are placed in categories. Category: A concept that functions to organize or p oints out aspects of equivalence among other concepts based on common features or si milarity to a prototype. Groups of objects that belong together because they belong to the same class of objects. Cation: A positively charged ion. Caudal: Signifying a position towards the distal en d of the body, or an inferior position. Causal inferences: Judgments about whether somethin g causes something else. Central nervous system: One of the two main divisio ns of the nervous system, consisting of the brain and the spinal cord. Central sulcus: Large groove in the surface of the cerebral cortex, separating the frontal and parietal cortex
138 Characteristic features: Qualities that describe (c haracterize and typify) a prototype. Cilia: Hair like motile organelles that project fro m the surface the olfactory epithelium and contain olfactory receptors. Cognitive: Pertaining to the mental processes of co mprehension, judgment, memory, and reasoning, as contrasted with emotional and volitio nal processed. Communication: Exchange of thoughts and feelings. Complexity: A qualitative/quantitative (synthetic) descriptive term referring to the perceptible presence of many aromatic compounds, co mbining to generate pleasure. Concept: An idea about something that provides a me ans of understanding the world. The mental representation for a variety of cognitiv e functions like memory, reasoning and using and understanding language. Conformational change: A predictable movement withi n a molecule that is associated with biological activity. Connexin: Subunit of identical proteins forming a c onnexin, consists of four membrane spanning regions. Connexon: Multi-subunit complex of a gap junction h emichannel, formed by the clustering of the integral membrane protein connexi n. Each connexon is composed of six connexin subunits. Configural learning: Performance of a task in which the meaning of a stimulus depends on what other stimuli are paired with it. Consolidation: Conversion of short-term memories in to long-term memories and strengthening of those memories. Process of integr ating new information into stored information. Contralateral: On the opposite side. Cortex: The outer layer of a body structure or orga n. Cribiform plate: A thin sheet of ethmoid bone under lying the olfactory bulb. Cyclic adenosine monophosphate (cAMP): A second mes senger capable of diffusion to other sites within the cell. Stimulates a variety of cellular activities. Cyclic nucleotide: A nucleotide whose phosphate gro up is bonded to two of the hydroxyl groups on sugar, forming a cyclical or ring structu re. Cyclic nucleotide gated channels: Protiens that ser ve as ion channels across the plasma membrane. Dendrites: Fine extensions from the cell bodies of most neurons that receive incoming information. Dendro-dendritic synapses: Rare class of synapses b etween mitral and granule cells of the olfactory bulb in which both sides of the synap ses are dendrites that release neurotransmitters. Depolarization: The reduction of a membrane potenti al to a less negative value.
139 Development: A wine attribute that refers to the c hange in the aromatic quality during the period the wine is sampled. Diacylglycerol: A lipid molecule that remains in th e plasma membrance following formation of PLC b It recruits and activated protein kinase c. Diagonal Band: Cells within the ventral division of the septal area. Differentiation: The process through with unspecial ized cells become more complex in structure and function. Distal: Away from or the farthest from a point of o rigin or attachment. Domain-specific knowledge: A relatively self contai ned collection of knowledge about a particular topic Dorsal: Towards the top of the brain. Towards the back, away from the ventral side. Duration: The length of time the wine maintains its distinctive character before becoming generically wine-like. Ecto-ATPase: Enzymes that hydrolyze extracellular A TP. Effector: A substace that brings about a cellular r esponse to a signal. Efferent axon: neuron that carries information away from a structure. Efflux: An outward flow. Electrophysiological: Pertaining to the study of th e electrical properties of cells and tissues. Engram: Physical representation of what has been le arned. Enology: The science and study of all aspects of wi ne and winemaking. Episodic memory: Memory for events. Epithelial sodium channels (ENaC): Membrane bound i on channel selectively permeable to cations like Na+. Excitatory neurotransmitters: Neurotransmitters tha t cause an excitatory effect on the membrane. This effect causes an increase in firing or in the likelihood of firing. Exemplar: In categorization, members of a category that a person has experienced in the past. Experience-dependent plasticity: A mechanism that c auses neurons to develop so they respond best to the type of stimulation that they e xperience. Expertise: A specific knowledge an expert has about a given domain. Experts: Person who, by devoting a large amount of time to learning about a field and practicing application of that learning, has become acknowledged as being extremely skilled or knowledgeable about that field. Explicit memory: Deliberate recall of information t hat one recognizes as a memory,
140 detectable by direct testing such asking a person t o describe a past event. Memory that involves conscious recollection. Extracellular: Outside of a cell. Feedback inhibition: A mechanism to control signal pathways that results in the inactivation of the signal. Flavor: The integrated percept of taste, oral somat osensation, and odor of food and beverages. Fragrance: Those olfactory perceptions that may com e from sniffing the wine (orthonasally) or vapors that travel up the nasal p assage through the mouth (retronasally). The aromatic aspect of wine includes the aroma and bouquet characters. Frontal lobe: The largest of five lobes constitutin g each of the two cerebral hemispheres. Functional imaging: A method of detecting physiolog ical activity within tissue and the brain. GOLF: G-protein associated with signal cascades in peri pheral olfactory system. Gammaaminobutyric acid (GABA): An amino acid that functi ons as an inhibitory neurotransmitter in the brain and spinal cord. Ganglion: A knot or knot-like mass of nervous tissu e Gap junction: Sites between animal cells that are s pecialize for intercellular communication. Plasma membranes of adjacent cells are separated by a very minimal amount of space, this gap is spanned by connexon he michannels that allow the passage of small molecules. Gap junction channels: Channels that connect neuron s at gap junction: formed by two hemichannels, one on the presynaptic neuron and one on the postsynaptic neuron. Gated channel: An ion channel that can change confo rmation between an form open to its solute ion and one closed to the ion. Such cha nnels can be voltage gated or chemical gated depending on the nature of the process that t riggers the conformational change. Glial cell: Non-neuronal cells forming the intersti tial tissue of the central nervous system. Gluatamate: Major excitatory amino acid neurotransm itter in the central nervous system G-protein: A guanosine-5-triphosphate (GTP)-bindin g protein. Key regulatory roles in many different cellular processes. G-proteins can be present in one of two conformations, an active form containing a bound GT P molecule, and an inactive form containing a bound GDP molecule. Activation of a G-protien by binding of a neurotransmitter to its receptor results in activat ion of a second messanger system that can either act directly on the ion channel to open it, or activate an enzyme that opens the channel by phosphorylating the channel protein. G-protein couple receptors: A group of related rece ptors that span the plasma membrane seven times. The binding of the ligand to its spec ific receptor causes a change in the
141 conformation of the receptor that increases its aff inity for a heterotrimeric G-protein initiating a response within the cell. Granule cell: Axonless GABAergic interneurons of th e olfactory bulb, connected with mitral cells to produce lateral inhibition between mitral cells. Provide negative feedback circuits. Guanosine triphosphate (GTP): A nucleotide of great importance in cellular activities. It binds to a variety of proteins and acts as a switch to turn on their activities. Gustation: Sensation of taste Gustducin: G-protein associated with signal transdu ction in the peripheral gustatory system. Gyrus rectus: Medial aspect of the anterior prefron tal cortex. Habituation: Decrease in response to a stimulus tha t is presented repeatedly and that is accompanied by no change in other stimuli. Hebbian synapes: Synapse that increases in effectiv eness because of simultaneous activity in the presynaptic axon and the post-synap tic neurons. Hedonic value: See valence. Hemichannel: Large pore ion channels that spans gap junctions. Heterodimeric: consisting of two different receptor s Hierarchy: A system with distinctive levels with ma ny systems and lower levels feeding into fewer systems at higher levels. Hippocampal formation: Deep cortical structure situ ated in the medial aspect of the temporal lobe, consisting of the hippocampus and su bicular cortex, associated with short-term memory and regulation of emotion and aut onomic functions. Hippocampus: Large forebrain structure between the thalamus and cortex. Hypothalamus: A portion of the diencephalon of the brain, forming the floor and part of the lateral wall of the third ventricle. Implicit learning: Learning, which does not involve conscious knowledge of the skill or rule that is being learned or acquired. Implicit memory: Influence of recent experience on memory, even if one does not recognize that influence or realize that one is usi ng memory at all. Immuno-staining: The use of an antibody to detect t he presence of a specific protein. Inferior: Located below another part. Influx: An inward flow. Inositol 1,4,5-triphosphate (IP3): A second messenger important to cell signaling, induces the diffusion of calcium into the cell by a cting as a calcium channel. Input neuron: Receives signals from the external en vironment or other neurons.
142 Insula: Cerebral cortex structure deep within the l ateral fissure between the temporal and frontal lobe. Interneuron: A neuron that exclusively signals anot her neuron. Intracellular: Within a cell Intragemmal: Within the taste bud. Intrinsic neurons: Interneurons with very short axo ns, have an inhibitory function. Axons are confined within a given structure. Ion: A charged particle Ion channels: Channels that allow some ions to cros s the membrane in the direction of their concentration gradient. Ipsilateral: Affecting the same side of the body. Labeled Line principle: Concept that each receptor response to a limited range of stimuli and has a direct line to the brain. Lateral: Away from the midline. Lateral inhibition: Restraint of activity in one ne uron by activity in a neighboring neurons. Lateral olfactory tract: Large bundle of axons from the mitral and tufted cells that exit the olfactory bulb to supply the piriform lobe. Lesion: Damage to a structure Lexicon: A persons vocabulary. Ligand: Any molecule that can bind to a receptor be cause it has a complementary structure. Limbic system: A group of structures within the rhi nencephalon of the brain that are associated with various emotions and feelings such as anger, fear, sexual arousal, pleasure, and sadness. Local neuron: Small neuron with no axon, or a very short one. Long-term memory: Memory of an event that is not cu rrently held in attention. Medial: Pertaining to, situated in, or oriented tow ard the midline of the body. Medulla: The most internal part of a structure. Microvilli: Fingerlike projections of taste sensory neurons, rich in taste receptors. Mitral cells: Output neurons of the olfactory bulb that synapse with axons of olfactory receptor neurons within glomeruli. Transmit inform ation from the olfactory bulb to the piriform cortex, entorhinal cortex and amygdala. Morphological: Pertaining to the form, shape and st ructure. Motif: A substructure found among many different pr oteins, such as the ab barrel, which consists of of b strands connected by an a -helical region.
143 Multimodal: Pertaining to two or more sensory modal ities. Myelin: A lipid-rich material wrapped around most n eurons in the vertebrate body. Nerve: One or more bundles or impulse-carrying fibe rs, myelinated or unmyelinated or both, that connect the brain and the spinal cord wi th other parts of the body. Neural adhesion molecule (NCAM): Homophilic binding protein expressed on the surface of neurons that has a role in cell-cell adh esion and synaptic plasticity. Neuroanatomic: Relating to the structure of the ner vous system. Neurobiology: Branch of biology that is concerned w ith the anatomy and physiology of the nervous system. Neurohormone: A hormone produced in neurosecretory cells such as those of the hypothalamus and released into the bloodstream, the cerebrospinal fluid, or intercellular spaces of the nervous system. Neuromodulator: Chemical that has properties interm ediate between those of a neurotransmitter and those of a hormone. Non-vesicular: Does not consist of vesicles. Norepinephrine: An adrenergic hormone (catecholamin e) that acts to increase blood pressure by vasoconstriction but does not affect ca rdiac output. Nucleus: A group of nerve cells of the central nerv ous system having a common function. Olfaction: Sense of smell. Produced by volatile com pound carried by inspiration or expiration to the olfactory epithelium in the nose and able to reach and stimulate receptor neurons. Operculum: The posterior portion of the inferior fr ontal gyrus of the frontal lobe. Output neuron: Sends information to other neurons. Orbitofrontal cortex: Area of the prefrontal cortex in the frontal lobes. The region of the brain where various sensory inputs (olfaction, tast e, oral somatosensation) are integrated in the perception of flavor. Pannexin hemichannel: Protein channels that allow t he release of ATP in taste receptor cells. Papilla (papillae-pl): Structure on the surface of the tongue containing taste buds. Paracellular pathway: Involves the movement of ions through the intercellular spaces between epithelial cells. Practice: Repetition of a task, which eventually re sults in improved performance. Parvocellular: Pertains to regions containing small sized cells. Perception: Concious experience that results from s timulation of the senses. Periamygdaloid cortex: The more posterior regions o f the piriform lobe underlying the amygdala.
144 Periglomerular cell: Interneurons that encircle a g lomerulus and make inhibitory dendrodendritic synapses with mitral cell dendrites Peripheral nervous system: The motor and sensory ne rves and ganglia outside the brain and spinal cord. Perirhinal cortex: Part of the medial temporal lobe located along and dorsal to the rhinal sulcus. Piriform cortex: Region of the temporal cortex adjo ining the amygdala; receives olfactory information and transmits it to the amygd aloid nuclei. Phosphatidylinositol 4,5-bishphosphate (PIP2): A second messenger that binds to proteins to bring the proting to the cytoplasmic fa ce of the membrance where it is able to interact with other membrane bound proteins. Phosphodiesterase (PDE): An enzyme that breaks a ph osphodiester bond such as PLC. Phospholipase C: An enzyme that catalyzes a reactio n that splits PIP2 into inositol 1,4,5triphosphate (IP3) and diacylglycerol (DAG), both of which play impo rtant roles as second messangers in cell signaling. Phospholipase C 2: Phospholipase enzyme specific t o mammalian taste receptor cells. Phosphorylation: The addition of a phosphate group to a protein. Posterior: In the back part of a structure, such as of the dorsal surface of the human body. Pons: Part of the brainstem extending from the midb rain to the medulla. Precentral gyrus: Gyrus of the cerebral cortex just anterior to the central sulcus site of the primary motor cortex. Prefrontal cortex: Anterior portion of the frontal lobe cortex. Protein kinase: An enzyme that transfers phosphate groups to other proteins, often having the effect of regulation the activity of oth er proteins. Protein kinase A (PKA): Enzyme whose activity is de pendent on cAMP levels. Prototypes: The most characteristic exemplars of a category. A standard used in categorization that is formed by averaging the cate gory members an individual has experienced in the past. Pseudogenes: Sequences that are clearly homologous to functional genes, but have accumulated mutations that render them nonfunctiona l. Psychophsyical: Concerns perceptions of various sti muli. Pyramidal cells: Prominent cells of the cerebral co rtex and hippocampal formation that form the main output neurons of these regions. Quality: For specific odor, refers to a descriptive term applied to that odor. For aromatic compounds this refers to the subjective similarity to a known flavor or aroma, such as melon-like. The property of wine showing marked aro matic and flavor complexity, harmony, and development associated with a distinct aroma and aged bouquet.
145 Raphe nucleus: Midline nuclei situated in the brain stem that give rise to serotonin neurons that supply the brain and spinal cord. Recall task: A test in which participants are prese nted with stimuli and then, after a delay, are asked to remember as many of the stimuli as possible. Receptive field: Part of the field to which any one neuron responds. Receptor: Any substance that can bind to a specific molecule (ligand), often leading to the uptake or signal transduction. Recognition task: A procedure for testing memory in which stimuli are presented during a study period and then, later the same stimuli plu s other new stimuli are presented. The task is to pick the stimuli that were originally pr esented. Rostral: Towards the front of the brain (above the midbrain). Towards the cerebral cortex (below the midbrain) Schemas: Organized packets of information about the world, events or people stored in long-term memory. A persons knowledge about what is involved in a particular experience. Schwann cells: Supporting cells of the peripheral n ervous system responsible for the formation of myelin Second messenger: A substance that is formed in the cell as the result of the binding of a first messanger (a hormone or other ligand) to a re ceptor at the outer surface of the cell. Semantic memory: Memory of meanings, understandings and other concept-based knowledge unrelated to specific experiences. Form of long-term memory consisting of general knowledge about the world, language etc. Sensory-based memory: Memory in which the impressio n of sensory information is stored after original stimulus ends. A brief stage of memory that hold information for seconds or fractions of a second. Sensory imaging: The imaging of a stimulus in the b rain using ones sensory channels. Serotonin (5-HT): A naturally occurring derivitaive of tryptophan found in platelets and in cells of the brain and the intestine. It acts a s a potent neurotransmitter. Short-term memory: Memory of an event that just hap pened. Signal transduction: The overall process in which i nformation carried by extracellular messenger molecules is translated into changes that occur inside a cell. Signaling pathways: The information pathways of a c ell. Each consists of a series of distinct proteins that operate in sequences. Each protein in the pathway acts by altering the conformation of the downstream protein in the s eries. Solitary nucleus and tract: Area in the medulla tha t receives input from taste receptors. Somatosensory system: The components of the central and peripheral nervous systems that receive and interpret sensory information from organs in the joints, ligaments, muscles, and skin. This system processes informati on about the length, degree of
146 stretch, tension, and contraction of muscles, pain, temperature, pressure, and joint position. Spatial code: Signal representation of the activity of two or more synapses onto a single neuron. Supra-threshold: Of sufficient strength or concentr ation to produce a perceptible physiological effect. Synapse: The region surround the point of contact b etween two neurons or between a neuron and an effector organ, across which nerve im pulses are transmitted through the action of a neurotransmitter. Synaptosome-associated protein (SNAP 25): Protein t hat is involved in the formation of a tight complex that fuses synaptic vesicles to the plasma membrane. Stylistic: Presence of a fragrance typical to a par ticular winemaking style. Taste: The sensations produced by substances dissol ved or mixed in the saliva that activate receptors in the mouth, includes bitter, s weet, salty, sour, and umami perceptions. Temporal code: The signal representation of repeate d synaptic stimulation within a period of time. Temporal lobe: Lateral portion of each hemisphere, near the temples. Thalamus: One of a pair of large oval nervous struc tures made of gray matter and forming most of the lateral walls of the third vent ricle of the brain and part of the diencephalon. It relays sensory information, exclu ding smell, to the cerebral cortex. Threshold: The amount of activity required to activ ate subsequent stages. Tight junction: Specialized contacts that occur at the very apical end of the junctional complex between adjacent epithelial cells. The adj oining membranes make contact at intermittent points, where integral proteins of the two adjacent membranes meet. Transmembrane domain: The portion of a membrane pro tein that passes through the lipid bilayer, often composed of non-polar amino ac ids in a -helical conformation. Transient receptor potential channel: A family of i on channels that are relatively nonselectively permeable to cations. Tufted cell: Output neurons of the olfactory bulb t hat synapse with olfactory receptor neuron axons within glomeruli. Two-pore domain potassium channel: Known as leak c hannels, regulated by Gproteins. Typicality gradient: The organization objects in te rms of their typicality as a category member. Uncus: Medial extension of the anterior end of the parahippocampal gyrus. Unimodal: Pertaining to one sensory modality.
147 Valence: Refers to the emotional value tied to a st imulus, whether it is pleasant or unpleasant. Varietal: Presence of an aroma distinctive of a sin gle or a group of related grape cultivars. Ventral: Towards the bottom of the brain. Towards the stomach. Ventral posteromedial nucleus: Nucleus situated in the ventrolateral aspect of the posterior thalamus Volatile: In olfaction, it refers to the tendency o f an odor chemical to exist in a vapor state. In wine, it refers to the escape of aromatic compounds from the wine into the air. Voltage gated channel: Membrane channel whose perme ability to ions depends on the voltage difference across the membrane. Working memory: Temporary storage of memories while we are working with them or attending to them. Form of short-term memory requi ring recall of a sequence of events for a few minutes in order to complete the task.