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Neurogastronomy: How the Brain Creates Flavor and Why It Matters

Gordon M. Shepherd
Copyright Date: 2012
Pages: 288
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  • Book Info
    Book Description:

    Leading neuroscientist Gordon M. Shepherd embarks on a paradigm-shifting trip through the "human brain flavor system," laying the foundations for a new scientific field: neurogastronomy. Challenging the belief that the sense of smell diminished during human evolution, Shepherd argues that this sense, which constitutes the main component of flavor, is far more powerful and essential than previously believed.

    Shepherd begins Neurogastronomy with the mechanics of smell, particularly the way it stimulates the nose from the back of the mouth. As we eat, the brain conceptualizes smells as spatial patterns, and from these and the other senses it constructs the perception of flavor. Shepherd then considers the impact of the flavor system on contemporary social, behavioral, and medical issues. He analyzes flavor's engagement with the brain regions that control emotion, food preferences, and cravings, and he even devotes a section to food's role in drug addiction and, building on Marcel Proust's iconic tale of the madeleine, its ability to evoke deep memories.

    Shepherd connects his research to trends in nutrition, dieting, and obesity, especially the challenges that many face in eating healthily. He concludes with human perceptions of smell and flavor and their relationship to the neural basis of consciousness. Everyone from casual diners and ardent foodies to wine critics, chefs, scholars, and researchers will delight in Shepherd's fascinating, scientific-gastronomic adventures.

    eISBN: 978-0-231-53031-6
    Subjects: Biological Sciences, Ecology & Evolutionary Biology, Psychology

Table of Contents

  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-viii)
  3. Preface
    (pp. ix-x)
  4. Acknowledgments
    (pp. xi-xvi)
  5. INTRODUCTION Retronasal Smell and the New Age of Flavor
    (pp. 1-8)

    The origins of this book are the cooked meal around the family dinner table that my wife, Grethe, and I have shared at the end of each day beginning when we were students together.

    Her interests run to food (as a gourmet cook), books (as a reference librarian and an avid reader), flowers and gardens (at our homes in the United States and Denmark), travel, friends, opera, and keeping tabs on our growing family. My life has been in the laboratory, studying the part of the brain responsible for the sense of smell. Through the years—from England to Washington,...

  6. PART I Noses and Smells

    • CHAPTER ONE The Revolution in Smell and Flavor
      (pp. 11-18)

      I met a man from Denmark who had been to Disney World in Florida for a week with his friends.

      “How did it go?” I asked. “Did you enjoy American culture?”

      “Oh yes,” he said. “We had a great time.”

      My wife is Danish, and I know how much a Dane loves food, so I kidded him by asking, “Did you enjoy eating hamburgers and hot dogs every day?”

      “We never touched them,” he said.

      “What in the world did you live off?” I asked.

      “We brought with us a week’s supply of rugbrod [Danish pumpernickel] and Danish salami and...

    • CHAPTER TWO Dogs, Humans, and Retronasal Smell
      (pp. 19-27)

      To appreciate how humans are adapted for retronasal smell, it is useful to compare us with one of the acknowledged champions of smell: man’s best friend, the dog. To compare the two, it is necessary to understand how each is engineered to serve its functions best. It will be no surprise that the dog’s nose is an engineer’s dream. But what about the human’s? Are we as poor as Aristotle believed? The take-home message is that dogs are adapted primarily for sniffing in smells of the environment, whereas humans are adapted primarily for sensing smell as the main feature of...

    • CHAPTER THREE How the Mouth Fools the Brain
      (pp. 28-32)

      I have claimed that smell is the main component of flavor, and that it is stimulated through the retronasal route. What is the proof?

      Psychologists and food scientists answer this question by devising sophisticated methods to introduce food volatiles at the back of the mouth, synchronized with expiration, to show activation of smell responses by the retronasal route. But there is a simpler test, one that is often used by psychologists when visiting schools and giving demonstrations of scientific principles in science class. It’s called the nose-pinch test, usually done with a piece of candy, but you can use any...

    • CHAPTER FOUR The Molecules of Flavor
      (pp. 33-44)

      As Jean Anthelme Brillat-Savarin predicted,

      The number of tastes is infinite, since every soluble body has a special flavor which does not wholly resemble any other…. Up to the present time there is not a single circumstance in which a given taste has been analyzed with stern exactitude…. Men who will come after us will know much more than we of this subject, and it cannot be disputed that it is chemistry which will reveal the causes or the basic elements of taste.

      There are indeed men and women who have come after, who definitely do know about the chemistry...

  7. PART II Making Pictures of Smells

    • CHAPTER FIVE Smell Receptors for Smell Molecules
      (pp. 47-58)

      Most explanations of the brain systems involved in flavor start with the sense of taste. However, we have made the case that, paradoxically, smell is more important for taste than taste is, so we start with smell and give most of our attention to it. This is the first step toward a scientifically based neurogastronomy.

      The sense of smell begins with the action of smell molecules on the receptor molecules in our nose. Here lies a second paradox. Smell molecules in our food, as described in the previous chapter, have been the subject of study for many years. Companies producing...

    • CHAPTER SIX Forming a Sensory Image
      (pp. 59-65)

      How does the brain represent our sensory world in order to serve as the basis for perception? This is one of the oldest questions in philosophy and a central question for modern psychology and neuroscience. It is also central for neurogastronomy.

      Modern neuroscience has shown that other sensory systems construct spatial representations of their stimuli. The body surface is represented by a body map, also called a homunculus. The visual world is represented by visual images. In audition, different frequencies are represented in spatial “tonotopic” maps. In all these cases, the spatial representations start with the sheet of sensory receptor...

    • CHAPTER SEVEN Images of Smell: An “Aha” Moment
      (pp. 66-75)

      From the olfactory receptor cells, the pathway to smell perception in the brain passes through a series of regions: the olfactory bulb, the olfactory cortex, and the orbitofrontal olfactory cortex. The first processing steps take place in the olfactory bulb. Because of its critical role in forming the smell image that is the major component of flavor, we will take several chapters to explain how it works.

      As its name implies, the olfactory bulb is shaped like an incandescent light bulb, sticking out in front of the frontal lobe of the brain. In comparison with the visual pathway, which starts...

    • CHAPTER EIGHT A Smell Is Like a Face
      (pp. 76-84)

      If you have had a brain or body scan for functional magnetic resonance imaging (fMRI), you know that it is done with your body inserted into a large circular magnet. This technology was developed in the 1990s. Like the use of 2-deoxyglucose (2DG), fMRI is based on local changes in blood flow within the brain that are related to the energy demands of locally active nerve cells. The magnets for humans must have wide internal chambers to receive the human body. Initially they were limited to modest magnetic strengths of 1 to 2 Tesla (the unit for measuring magnetic strength),...

    • CHAPTER NINE Pointillist Images of Smell
      (pp. 85-91)

      The neural basis of our ability to perceive a rich palette of smells can be compared with the neural basis of our ability to perceive a rich palette of colors. The best way to illustrate this is by comparison with pointillist art.

      There are two ways to put colored paint on a canvas to elicit the perception of color in the mind of the observer. One is to mix the paints to achieve a particular color impression: red and white to achieve pink, blue and yellow to achieve green, and so on.

      The other is to place different colors in...

    • CHAPTER TEN Enhancing the Image
      (pp. 92-98)

      There are two levels of processing in the olfactory bulb. The first, described in chapter 9, consists of the glomerular layer, which forms an image representing the smell molecules and performs signal-to-noise operations and lateral interactions to begin the processing of the image. The image is then sent to the second level within the olfactory bulb. The connection between levels is by means of a large cell, the mitral cell, and its smaller companion, called a tufted cell (see figure 7.1). These cells collect the input in their dendritic branches in the glomerulus, transfer the processed signal to the next...

    • CHAPTER ELEVEN Creating, Learning, and Remembering Smell
      (pp. 99-106)

      In all mammals, the output fibers from the olfactory bulb gather in a bundle called the lateral olfactory tract, which connects to the next stage, the olfactory cortex. The tract is relatively short in most animals, but very long in humans, an inch or so (up to 30 mm), in order to reach from the olfactory bulbs, sitting in front over the nasal cavity, to the olfactory cortex on the underside of the brain. The length reflects the expansion of the brain as the neocortex grew in size during mammalian and especially primate evolution. As in the case of the...

  8. PART III Creating Flavor

    • CHAPTER TWELVE Smell and Flavor
      (pp. 109-116)

      We have seen that the olfactory cortex begins the task of creating the brain’s representation, not of individual smell molecules, but of “smell objects” representing the food we are consuming. What more is needed? The main need is someone to “read” the smell object in a way that gives it meaning in a human context. This requires the neocortex, in evolutionary terms the newest type of cortex, that dominates the mammalian brain.

      The increase in the area of the neocortex in primate and human evolution has produced many different cortical areas. These areas are of three main types. First are...

    • CHAPTER THIRTEEN Taste and Flavor
      (pp. 117-127)

      The olfactory pathway can act alone when we smell the aromas of food or beverages by inhaling them by the orthonasal route. When smells arise from food in the mouth to make their contribution to flavor, they always act on the brain in concert with other systems. We need to keep reminding ourselves that in addition to the sense of smell being a dual system—orthonasal smell and retronasal smell—retronasal smell is never sensed by itself, but always together with virtually every other sense in the mouth. It is the basis for my claim that flavor is among the...

    • CHAPTER FOURTEEN Mouth-Sense and Flavor
      (pp. 128-134)

      In addition to having a smell and a taste, every kind of food and drink has physical properties that give it a feel in the mouth. This feel is the result of so many senses that it is difficult to summarize in one name, so we call it variously mouth-sense, mouth-feel, or food-texture. This sensation is something we prejudge when we take the food to consume it. We compare this expectation against the actual sensation in the mouth as part of judging the quality of the food. Mouth-sense is mediated by the somatosensory (somato = body) system, which encompasses a...

    • CHAPTER FIFTEEN Seeing and Flavor
      (pp. 135-142)

      We all know that if we are hungry, the sight of a tasty food makes our mouths water. Technically speaking, the sight stimulates our autonomic nerves to activate our salivary glands to secrete saliva into our mouths to prepare to ingest and digest the food. We usually don’t consider that the sight might also have an inluence on the flavor of the food, but much common experience and many experiments have shown this to be the case. So, although sight is not a property of the food once it is in our mouths, it is part of the multisensory sensation...

    • CHAPTER SIXTEEN Hearing and Flavor
      (pp. 143-146)

      The last sensory system we will discuss that contributes to flavor is hearing. Although it seems unlikely, it has its own role to play.

      The auditory pathway starts with the ear, composed of the outer ear and the ear canal leading to the ear drum (tympanic membrane). Inside is the middle ear, with the three little bones that transfer the vibration of the eardrum to the round window of the inner ear, where the cochlea contains the hair cells that respond to the vibrations set up by the sounds.

      The hair cells pass their responses on to the endings of...

    • CHAPTER SEVENTEEN The Muscles of Flavor
      (pp. 147-154)

      When we talk about gastronomy, people usually mean how the food stimulates our senses to give rise to particular flavors. However, this requires moving the food within our mouths in a coordinated manner. We take this part of eating for granted, but closer inspection shows that it is incredibly complicated. I’d like to convince you it is one of our supreme motor acts. The next time you take a bite, think of what is happening in your mouth. There is a complex sequence of movements involving the muscles of the lips, jaw, and tongue and those involved in swallowing; these...

    • CHAPTER EIGHTEEN Putting It Together: The Human Brain Flavor System
      (pp. 155-162)

      We have covered the main sensory and motor systems of the brain that are involved in generating the sensation of “taste,” which we now recognize is really “flavor.” We share these systems with other animals, but there are some big differences that characterize humans. We have fewer olfactory receptors, but we are much more adapted to retronasal smell, and we have much bigger brains, with many more brain areas and connections between them. And we have language. Our overall brain system for flavor therefore varies in quantitative terms from that of other animals, and qualitatively it has new capacities to...

  9. PART IV Why It Matters

    • CHAPTER NINETEEN Flavor and Emotions
      (pp. 165-173)

      In moving from the sensory input to the action output within the human brain flavor system, it is natural to begin with emotions. The word emotions is derived from “to move.” Just as movements of the mouth and tongue make flavor an active sense, so is it also an active sense in that we must be motivated to acquire the food and liquid we put in our mouths. As indicated in the previous chapter, these systems have a close relation to the part of the brain called the amygdala, and their activity can be seen as beginning with the motivation...

    • CHAPTER TWENTY Flavor and Memory: Reinterpreting Proust
      (pp. 174-183)

      For many people, the most important parts of smell and flavor are the memories they evoke and the emotions associated with them. To illustrate the impact these have, we can do no better than start with Marcel Proust. An understanding of the brain mechanisms involved throws new light on his classic story:

      But when from a long-distant past nothing subsists, after the people are dead, after the things are broken and scattered, taste and smell alone, more fragile but more enduring, more unsubstantial, more persistent, more faithful, remain poised a long time, like souls, remembering, waiting, hoping, amid the ruins...

    • CHAPTER TWENTY-ONE Flavor and Obesity
      (pp. 184-191)

      Does knowledge of the human brain flavor system give insights into practical problems like the current epidemic of obesity in worldwide populations? Let us consider the case of fast food.

      Suppose you’ve taken a bite of French-fried potatoes. This may not have been the kind of food that Jean Anthelme Brillat-Savarin had in mind when he extolled human flavor, but it is probably as near to a universal food as we have. It was brought to the United States from France by returning soldiers after World War I and gained popularity in the 1920s and 1930s. According to Eric Schlosser,...

    • CHAPTER TWENTY-TWO Decisions and the Neuroeconomics of Flavor and Nutrition
      (pp. 192-199)

      The most important ultimate function of the human brain flavor system is making the right choices in consuming healthy or unhealthy food. The key to making these choices lies in the decision-making mechanisms of our brains, which only recently have begun to be recognized. Interest in these mechanisms has merged with the interests of economists, who for many years have realized that people make economic choices that are based on their value judgments about what they like. I first became aware of this when my father, Geoffrey Shepherd, wrote an article about it in 1956. This merging of interests of...

    • CHAPTER TWENTY-THREE Plasticity in the Human Brain Flavor System
      (pp. 200-206)

      The more we learn about the brain the more we find that it can be changed by activity and experience. At a recent seminar I attended on the subject of critical periods for plasticity of the visual system during development in young animals, the theme was summarized by the speaker in the following way: we traditionally think of the brain as being stable but having limited capacity for being plastic; the new view is that the basic state of brain cells is plastic, and that the brain goes to great lengths to restrain and control this plasticity.

      Plasticity applies especially...

    • CHAPTER TWENTY-FOUR Smell, Flavor, and Language
      (pp. 207-215)

      A New York Times story about a dessert prepared by the French actor Gérard Depardieu brings together several themes of neurogastronomy:

      “The other day we made a fondant of apples with three different kinds of apples—Canada, Granny Smith and Calville,” Depardieu said. “We did a white caramel sauce, put that on the plate. Then in the compote of apples, slightly reduced, I put a bit of butter and an egg yolk, and put that in the oven. It’s not at all like a compote because it’s lightly gratineed on top. We served it with a creme Anglaise and a...

    • CHAPTER TWENTY-FIVE Smell, Flavor, and Consciousness
      (pp. 216-223)

      How much of flavor perception is conscious and how much unconscious? Studies of smell are beginning to provide some intriguing answers. Traditionally, the neural basis of consciousness was ruled out as a subject for scientific study. However, recently it has become a growth industry in neuroscience. Leading the way have been a computational neuroscientist, Christof Koch, and his colleague Francis Crick. Crick, with James Watson, solved the structure of DNA in the early 1950s. He then turned his interest to neuroscience. Beginning in the 1970s, he took on the question of the neural basis of consciousness as a special interest,...

    • CHAPTER TWENTY-SIX Smell and Flavor in Human Evolution
      (pp. 224-232)

      The new evidence regarding how the brain creates smell and flavor that dominate our daily lives suggests the hypothesis that the human brain flavor system may have played a much larger role in human evolution than is appreciated. There has been little discussion of this possibility up to now. Speculations on how evolution occurred are notoriously difficult to make. However, in pursuing this question I have been greatly encouraged by interactions with anthropologists. It will be useful to identify some of the evidence for events in human evolution in which the human brain flavor system may have played a significant...

    • CHAPTER TWENTY-SEVEN Why Flavor Matters
      (pp. 233-242)

      For many readers, the evidence presented in this book will be useful in giving personal insights into how “flavor” exists not in our food but in the way it is created by our brains. It should stimulate new insights for chefs, food critics, consumers of fast food, and families around the dinner table.

      In addition to these personal rewards, knowledge of how the brain creates flavor has important implications for public policies on food and nutrition. A possible advantage of a new term like neurogastronomy is that it can help focus public policy more effectively in applying advances in brain...

  10. Bibliography
    (pp. 243-256)
  11. Index
    (pp. 257-268)