Neurogastronomy

Over dinner at Bobby Flay’s Mesa Grill, I was recommending Gordon Shepherd’s book, Neurogastronomy, to a friend, who is a foodie. He seemed really interested in it, having read Herve This’s Molecular Gastronomy and other books like it. I’ll say here what I told my friend.

Shepherd brings with him both expertise and experience on the subject, having actually worked in olfaction for many years. The people he works with are my friends and peers, as I have also worked in olfaction until recently.  The way this book is presented is a model I wish to emulate; it is a  synthesis of both scientific findings and their meaning to us. By combining these elements with clear descriptions of the experiments involved, Shepherd is able to place the mechanics of smell within the context of odor and flavor perception. How the system works, how quality of life can be impaired, possible evolutionary consequences, and ultimately how we can subvert human flavor perception to improve our diet, nutrition, and yes, pleasure. 

Gordon Shepherd has made a huge impact in neurophysiology and in the field of olfaction. I think it is wonderful that he has written this book, to emphasize that olfaction is an important sense, playing a role in shaping human culture by its role in flavor perception. This is a direct counter to the notion that the human (and primate) olfactory system compares “poorly” against other sensory systems because the amount of brain space devoted to processing olfactory data seem so small. It also counters the perception from an olfactory detector consideration, such as that other mammals have both a greater number and variety of odor sensors, and thus as a result that they are better smellers than humans.

For me, I also had the vicarious thrill of seeing people I know depicted in a book meant for a wider audience.

***

From the standpoint of a neuroscientist, it was refreshing to see how a distinguished scientists view as the most important pieces of neurophysiological evidence fitting into the concept of flavor perception.  This is the bit of curation that I am such an enthusiast for. We have a wealth of data, and often, scientific reviews are a great place to being reading about a field. Reviews are as much about synthesis of existing scientific threads as much as about historical perspective and charting future research directions (i.e. what hasn’t been yet addressed).  With so much great writing today, having forty or fifty years of experience may not be necessary to provide proper context for a given research environment.

With that said, it is always nice to see someone with the stature of Gordon Shepherd present such a broad picture of the field and to hew closely to underlying research.

He spends the first chapters discussing some anthropology findings, laying the groundwork for the importance of flavor in shaping human culture. It seems that cooking – with its transformation of food at the molecular level and in the unlocking of huge stores of nutrition – provides a huge impetus in humans retaining a strong smell sense. The rest of the book recounts both his own and others’ contributions to the field of olfaction.

His presentation of neural activity is that brain works by encoding and extracting information that can be described as literal, physical patterned activity. Evidence from open brain surgery, to anatomical tracing, to functional imaging supports this idea. In each case,  patterns arise from ephemeral neural activity, grouped into physically discrete locations on the brain. Hence one hears about the visual and audio cortices, the somatosensory cortex, the hippocampus as a site of early memory formation, and so forth.

For the olfactory system, this is also true: at increasing levels of topologic precision, we can say that the main olfactory processing structures include the olfactory bulb, the olfactory cortex, and the orbitofrontal cortex. As we progress to more microscopic descriptions, we can describe groups of active neurons within these structures. The whole point of the brain’s wiring is to funnel external stimuli into combinations of activated neurons.

The connections between these neurons tend to lead to reactivation of the same groups of neurons to the same stimulus. Brain centers located downstream than operate on these patterns, recognizing them, storing them, retrieving them, and matching them. At some point, this stream of information is combined with other sensory inputs (aural, visual, taste, smell, and touch), resulting in higher order, conscious thoughts.

What I say next is not meant as a criticism but as a way to understand why Shepherd is so effective at presenting the science behind “neurogastronomy”. He left out a significant area of research, that of timing. A full description of how the brain works will have to include not only which neurons are active, but when they are active. There is not enough space in such a book to detail the underlying mechanism of smell: the identity of active neurons, how they are connected, and the timing of their activity.

My old boss (among others) was combining smell discrimination-decision making behavior task with simultaneous neural recordings. He, and others, have shown that within a sniff a rat can gain sufficient information to make a decision. This is on the order of a quarter of a second. Such a system likely functions as a time-based code. This is a huge part of understanding how the brain works.

Yet I have to say, it isn’t necessary to Shepherd’s story. Shepherd paints a compelling picture by simply presenting neuronal activity as a pattern, allowing him to describe a huge arc in a few strokes. But this stroke does reveal his thinking; he clearly places a central role in the anatomical organization of the brain, which groups neural activity into patterns. At ever more minute levels, the specific connections underlie the feature extraction processes going on in the brain. In a sense, the fact that neurons, at some point, activate represents the mechanics of actualizing information processing that we had already determined to take place in these neurons, based simply on how they are connected.

Depending on your viewpoint, when the neurons activate may prove important in these processes. Is timing then a peripheral phenomenon, since the most important observation is how these neurons are wired, or could the same wires actually transmit different “information”, depending on the sequence of activity? These are questions researchers continue to spend entire careers answering.

I can imagine a different investigator may have written the same book, but emphasize the ephemeral nature of neural ensembles where the real significance may lie in timing of the activity. In this case, the sequence of neurons firing, how their activity coincide, and the precise synapses activated in downstream neurons are just a few of the parameters that affect perception.

It isn’t a matter of discrediting one versus the other; it is just a point about presentation. In no way am I suggesting that the viewpoint put forth by Shepherd as deficient, merely that he probably made an editorial decision to provide a coherent framework for the edification of non-scientists. I really admire this book, as an exemplar of a rigorous book meant for popular consumption. Most importantly, I feel that he has described the wealth of experimental detail about how current theories of olfaction and flavor perception were arrived at.

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