Shepard Neurogastronomy

Gordon Shepherd, Neurogastronomy Chapters 2, 7, 11, 18, 19, 21, 27

C2: Dogs, Humans, and Retronasal Smell

• comparison of dog’s snout and sniffing with human. Important how motor functions and anatomy are integrated to behavior. Dogs can sniff 6-8 times a second. Mice sniff up to 10x a second!
• Inside the snout: modern mammals engage in ortho and retronasal olfaction. Receptors in nasal bulb direct to brain.

• Evolution of the Human Nose: Why we don’t have snouts....bipedalism or diet. Argued in evo theory that decline of the snout led to ascendency of vision. Stereoscopic vision only possible without the snout. Human olfaction favors retronasal vs. Dogs. Retro-nasal more emphasis on what we put in our mouths. 25-26: mechanics of chewing, sampling by taste buds, air flow, heating, humidification, retronasal olfaction,
• Why would retronasal olfaction be favored in humans?

• 1. Bipedalism increased our range and exposure to food varieties.
• 2. Cooking. Origins of “cuisine” in emergence of cooking 400,000 years ago. (Note both are food explanations and they connect become “omnivores” with evolving retronasal olfaction.

• Conclusion: The evolution of humans as upright omnivores with retro-nasal olfaction puts more emphasis on the brain in processing and remembering flavor and odor.

C7: Images of Smell

• The Olfactory Bulb: molecular and neural pathways at the bulb. Glomerulus (glom) - convergence site of receptor cells. Interneurons: often specialized processors. Periglomeral cells, Mitral cells, tufted cells. Granule cells.

• How does olfactory bulb represent smell? Story of discovery: 1930s Edgar Adrian, hedgehogs, noticed how patterns of excitation could create an “image” of the smell, using electrophysiology techniques.
• Sokoloff method for tracking energy used by the brain with a marker for glucose uptake. Important work that led to PET and fMRI. Follows his own research from 70s in using this method to track energy use in the olfactory bulb as it is exposed to odors.
• Confirms idea of a “smell image” or pattern of activation in the glomeruli. Started to fill in a “map” of the receptor sites on the bulb. 1990s.
• Some “odor images” from the work of Michael Leon and Brett Johnson. [1]
• Final point: The olfactory pathways are heavily modulated - sensitive to behavioral state: appetite, aversion, openness to experience, all affect flavor perception.

C11 Creating, Learning, and Remembering Smell

• lateral olfactory tract — context output from the bulb to the olfactory cortex in the brain. Long in humans. What is its role?
• importance of pyramidal cells. 100: capable of feedback excitation to stimulating cells. Thought important to memory. Damaged in dimentia patients.
• 101: Olfactory cortex “serves as content-addressable memory for association of odor stimuli with memory traces of odors. “. Structures that support this claim. Herb rule - identifies activity that suggest memory and learning. Interesting parallels between odor recognition and face recognition.
• 103: summary of functions of olfactory cortex. Not clear if perception of smell itself arises in ol. Cortex. Some research suggesting that it can detect the absence of the essential amino acids.

• key ideas: knowledge of mechanisms for understanding memory and flavor; learning mechanism, may even detect amino acids.

• [Point: Reinforcement learning takes place immediately in the olfactory cortex. Our experience of food is not a “passive awareness”. Because food is essential to survival, and omnivores have complex food / memory needs, learning and memory processes are crucial. The reward structure of the brain is involved. The olfactory cortex is smart.]

C18 Putting it all Together: The Human Brain Flavor System

• Opening summary of the "human brain flavor system."
• Reference and quote from Brillat-Savarin, the first “gastronome” . Nice continuity between early language and neurogastronomy. “The human brain has specific capabilities that makes the appreciation of flavor of unique importance to humans.”
• Sensory system vs action system
• Sensory system:

• Flavor also produced by smell, taste, mouth-sense, sight, sound. Not just “volatile molecules reaching the olfactory bulb.
• Multi-sensory integration, or “Supra-addivtivity” involves congruent repetition of combinations of stimuli. “internal brain image” of the flavor object.
• read summary sentence, p. 160: “A consensus is emerging that simultaneous activation by a food of a common set of regions, including the orbitofrontal cortex, anterior insula and operculum, frontal operculum, and anterior cingulate Byrd’s, constitutes the distributed representation in our minds of a flavor object” [Think about this a minute....]

• Flavor-action system

• Chart on p. 161 matching brain structures to aspects of flavor perception and desire, motivation, and action. The action system includes emotional response, memory, decision making, plasticity (how the activity of the body/brain — in this case eating— changes the brain) Language, consciousness. (Each treated in next section. We sample the chapter on emotions.)

C19: Flavor and Emotions

• emotions moves us toward action, but also reflect our internal state of desiring and wanting. What is diff between want and craving?

• research from Monell Chemical Senses Institute. Cravings implicated in eating disorders. Dull diets stimulate craving. Marcia Pelchat and colleagues looked at parallels between food cravings and drug craving. In a study, one group of test subjects were on a monotonous diet and another on a normal diet. In brain imaging, the monotonous eaters produced strong activation when asked to imagine a favorite food. Supports hypothesis that there is a common circuitry to natural and pathological rewards (food and drugs). 168ff: discussion of brain structures implicated in the study. Hippocampus, insula, caudate nucleus. Caudate includes high concentration of dopamine. Also part of the striatum, which involves habits (which probably involve dopamine). When we are hungry, we can activate food memories and emotional responses in anticipation of the food.

• [An implication of this for eating is that hunger plays a key role in satisfaction. The hungrier eater produces stronger anticipatory activation. “Hunger is the best relish.” “Images of desire” maybe be important to satisfaction. But also, this research suggests that an unsatisfied brain (one on a dull diet) is more likely to produce cravings . In a sense the brain demands satisfaction. read at 168. Digression on question: Does the industrial diet produce real satisfactions? Mixed evidence. ]

• chocolate-satiety study (Dana Small) — test subjects eat chocolate to satiety while in imaging. Difference in activation can be thought of as a change in the flavor image (for chocolate) under conditions of craving and satisfaction. Mentions concept of “reward value” current in brain research. cool idea here is that our flavor images change with our hunger states.

C21: Flavor and Obesity

• considers the case of french fries in relation to the flavor perception system. Salt, fat, and sweetness (SFS). Discusses the meat flavor from tallow, now artificially added. Adds in the rest of the typical fast food meal. Chased with coffee and a cookie. Coffee has over 600 volatile molecules. Point: the fast food meal involves sensory overload.

• Overeating:

• sensory overload;
• caloric density; reduced roughage.
• But also “Sensory-specific satiety” . Single flavors diminish appetite while multiple flavors amplify it. You can eat more food if it includes multiple flavors. The complexity of industrial flavors increases our ability to overconsume them. 187
• long-term overstimulation of skin and membranes of the lips and mouth. Interesting research shows obese test subjects have more activation of these areas even while not eating. [this supports the idea of a learned behavior from food conditioning]
• Conditioned overeating: Other research by Dana Small. You can induce extra eating in rats with conditioned stimuli (bell). Humans have wide field of potential conditioning stimuli.
• Other research suggests that ineffective inhibitory circuits play a role in obesity.
• Others speculate that the reward value of food for obese is too low. The brain doesn’t register enough pleasure from a normal diet.
• Kessler: combination of SFS culprit (note that in Kessler’s theory several of the above theories are included.)

C27: Why Flavor Matters

• brief summary.
• Flavor at different life stages:

• In the womb: flavors in amniotic fluid, rat study showing odor preference established pre-natally. Diet studies with pregnant women (using anise or carrot juice for eample) show similar results.
• In infants: flavor and preference also communicated through breast milk
• In childhood: research showing kids are hyper sensitive to SFS foods.
• In adolescents.
• Flavor and dieting in adults. Doesn’t work. 238: “key element missing in most discussions of diet is flavor”. Very important point. Cites Brownell’s “Food Fight” (2004) and Barbara Rolls.
• In old age: research on loss of smell sense.