What makes a dish stand out? On the face of it, this question does not lend itself to an objective or scientific answer. Of course, we could talk about the quality of the products used, the chef’s expertise, an urge to take a calculated risk to surprise guests but not baffle them, or about a pleasant atmosphere in a tasteful decor... But in the end, as with aesthetic preferences, it is pretty clear that it is not easy to rationalise our culinary pleasures either, as they are often based on a je ne sais quoi or some sort of ‘alchemy in cooking’. In other words, science and gastronomy do not necessarily go hand in hand.
The origins of neurogastronomy
Yet, the connection between these two disciplines has never been stronger. It is nothing new either, as illustrated in the widely read Physiologie du goût (The Physiology of Taste) by Jean Anthelme Brillat-Savarin, first published in 1825 and still in print today. This book is regarded as the precursor to what we now call ‘neurogastronomy’, as Brillat-Savarin, a town lawyer, theorised on the growing interest in a scientific approach to taste, based on the premise that the human diet went far beyond its restorative role necessary for survival. The pleasure derived from a good meal not only helps unite societies, but also brings this activity akin to carnal desire and a predilection for discovery. Brillat-Savarin made no mention of psychology, nor of course of neurosciences as they barely existed at that time, but his observations brought to light a very simple fact that we all may well have noticed from time to time: Eating influences our way of thinking. “[Gastronomy] also considers the action of food or aliments on the moral of man, on his imagination, his mind, his judgment, his courage, and his perceptions, whether he is awake, sleeps, acts, or reposes.”1
From the oven to the brain
The fact that eating (well, poorly, a lot, a little or not at all) influences our behaviour, our mood and our decisions seems so self-evident that very few people have actually taken the trouble to evaluate the consequences. A study of the sentences handed out in an Israeli court, for example, found that judges were much more lenient after their lunch break than just before it2, for which the obvious explanation lies in another quote from Brillat-Savarin: “They saw that a full stomached individual was very different from a fasting one.”3
In fact, other researchers have been able to measure the impact of food on the brain simply by showing pictures of enticing dishes to famished volunteers lying in a scanner or by wafting appetising smells around them. The results are spectacular: It is as if the mere thought of eating brings the entire brain to the boil! Under any other circumstances, we would expect such signals to cause metabolic activity to vary by 1 to 2% at most, yet here researchers observed an almost immediate increase of up to 24%.4 This could partly explain the new trend for ‘food porn’ or ‘gastropornography’, which involves taking photos of food and sharing them with the community of foodies on social media!
So, what exactly is ‘taste’? We generally use this term in its emotional, hedonistic sense, to describe the tendency of food or drink to produce a pleasant sensation, to be delicious. Here, researchers had to contend with this everyday use of the word ‘taste’, albeit somewhat ambiguous. On the one hand, we think of taste as one of the five distinct senses Aristotle classified alongside smell, touch, sight and hearing. On the other hand, the ‘taste’ of food seems to go beyond the simple activation of taste receptors embedded in our tongues, enabling us to distinguish between sweetness, saltiness, bitterness and sourness, the four ‘primary tastes’ to which we now add umami, a taste typical of Japanese food with a high glutamate content. In reality, as Brillat-Savarin rightly noted, it seems that this second aspect of ‘taste’ is primarily a result of our sense of smell, and that these two senses are inextricably linked in our appreciation of food and drinks. So as not to get bogged down in linguistics, specialists use the term ‘flavour’ when referring to the perception of food based on olfaction and gustation (among others things... as we will see below).
The birth of modern neurogastronomy
This observation led Gordon Shepherd, a neurobiologist, to suggest the term neurogastronomy in 20065 to refer to the specific study not of the senses as such and of how the brain depicts them, but more globally of all the neurobiological mechanisms involved in the detection and appreciation of flavours, what these mechanisms teach us about human behaviour, and how we can apply them in the kitchen.
The key theory of neurogastronomy is therefore that flavour originates in the brain rather than in the food itself. It also takes a multimodal approach, not only focusing on the senses of taste and smell, but all the other senses too, as well as motricity. Brillat-Savarin had already emphasised this point: Flavour is not imparted passively. We are the ones who spear food on our plates onto our forks, put it in our mouths, chew, savour and swallow it, and then appraise it. According to Gordon Shepherd, this results in the creation of ‘odour images’ in our brains, just like we have visual ‘mental images’ which enable us to recognise faces and imagine places. Furthermore, while neurological damage can impair sight, language and memory, there are also lesser-known clinical examples of brain injuries causing changes in food behaviour.
Nothing could be simpler than deciding if something tastes ‘good’ or ’bad’, yet these impressions are the fruit of an extraordinarily complex process we are only just beginning to understand. This process is based on a strange psychological illusion. We get the impression that we perceive taste, in the broadest sense of the term, in our mouths, yet we do in fact perceive taste in our nasal cavities, via a subconscious mechanism known as retronasal olfaction. When we wish to smell food, we generally place it under our noses and then sniff it, breathing in deeply. This is known as orthonasal olfaction. However, it is after we have chewed food, releasing its juices and molecules into our mouths, that as we breathe out, volatile odorous compounds are sent back to the nasal cavity through the back of the mouth. The roof of the nasal cavity has a mucous membrane called the olfactory epithelium, which comprises neurons that are sensitive to odorous molecules. These neurons are directly connected to a tiny olfactory bulb… inside the cranium, in the brain!
The olfactory bulb gathers the numerous signals sent by the epithelium receptor neurons and integrates them in a cerebral activation pattern, a sort of odour ‘map’ or ‘image’ that represents the particular mix of odorous molecules specific to each morsel of food. The olfactory bulb then projects this map towards various other structures of the brain, including the amygdala, a structure directly involved in our emotions, and the orbitofrontal cortex (located just above our eyes), a major hub grouping together bundles from other sensory systems. These include sight, touch (in our mouths too, with information about the temperature and texture of the food) and taste (which thereby takes a completely different route to that of the sense of smell), together with sensations coming from the viscera, and the homeostatic processes regulating hunger and thirst. They also include bundles from regions controlling memory and emotions, as well as the mechanisms governing inhibition and decision-making. In short, at this stage, as the episode of Marcel Proust’s madeleine so perfectly illustrates, simple odorous molecules reach and become part of an individual’s identity. Consequently, an aroma is never ‘neutral’ as it is always influenced by the context and the visual appearance of dishes, as well as by each person's preferences, appetite, mood, beliefs and memories.
We cannot see this complex layered process, so we get the impression that we perceive everything in our mouths, the place where we have put the food or drink. Yet, an important part of what we are sensing actually comes from our nasal cavities. Quite a handy evolutionary perk! After all, if we want to stay alive, we cannot just eat anything and everything: We rely on our brains sending commands to the muscles in our mouths to either spit something out or swallow it!
From neurogastronomy to gastrophysics
That’s all very well and good, but how exactly does it help us prepare the perfect risotto or choose the best appetisers? This is exactly the kind of criticism some researchers have voiced against Shepherd’s neurogastronomy. In-depth understanding of the neurophysiological processes responsible for our experience of flavours may well provide an essential basis for grasping the mechanisms at play in gastronomy. It reveals, for example, how the sense of smell plays more of a role than taste, even if both remain inextricably linked, and especially how our other senses, the state of our bodies, our moods and even our beliefs can influence flavour. Images of brain activity demonstrate how the price of a bottle of wine can influence our appraisal of it, or why we can be ‘tricked’ by a fizzy drink bearing the label of its competitor.
Miguel Sánchez Romera, part-neurologist, part-chef, briefly ran a restaurant in Manhattan6 showcasing the concept of ‘neurogastronomy’, but this knowledge remains difficult to transpose into delicious recipes.4 Generally speaking, neurosciences have had much less of an impact on gastronomy than physics and chemistry had in their contribution to what was called ‘molecular gastronomy’. This movement emerged during a 1992 congress and focused on the science behind egg mayonnaise. It gave scientific foundation to the little tricks picked up from our grandmothers and helped improve them, and also led to the invention of all sorts of new processes – spherification, fumigation, concentration, distillation and other thermal shock treatments – designed to please, amuse, surprise and impress.7 There’s nothing ‘neuro’ about that.