Humans can distinguish around 10,000 separate smells, estimates Linda Buck. We walk into the house and instantly know that someone is cooking roast chicken for supper and that they decided to stuff it with rosemary instead of thyme. Our olfactory systems have an immense power to discriminate between different flavours. Molecules that look near-identical to a specialist chemist in a lab will be easily distinguished by an ordinary person who smells them. Our brains will also interpret the same chemical in radically different ways depending on how concentrated it is. Buck and colleagues note that a ‘striking example is a substance called thioterpineol, whose odor is described as “tropical fruit” at a low concentration, as “grapefruit” at a higher concentration, and as “stench” at a still higher concentration’.28
Once we move beyond smell to consider flavour, however, the images processed in our brains become vastly more complex. In addition to the odour signals from our noses – this coffee is good! – there will be taste signals from the mouth – oh, but it’s bitter! – as well as feelings of texture – smooth crema! – and temperature – that burned my tongue! The experience of tasting food is far more multi-sensory than is the case with hearing, sight or touch, which is why it requires the most sophisticated part of our brain to process it. In fact, eating is influenced by hearing, sight and touch as well as flavour: we prefer apples that crunch loudly, steaks that look blood-red, sauces so smooth they seem to caress the inside of our throats.
If there are 10,000 smells, the number of different flavours that our brains can potentially create is infinite. Professor Gordon M. Shepherd, a biologist based at Yale University, has coined the term ‘neurogastronomy’ to explain our brain’s unique flavour system.29 In Shepherd’s view, complex flavour recognition is at the core of human identity, separating us from other mammals. Cats cannot even detect something as basic as sugar – they lack a taste receptor for sweetness. Humans, on the other hand, can differentiate fake maple syrup from real maple syrup; Coke from Diet Coke. Shepherd notes that the images humans build up of different flavours are processed in the prefrontal cortex, the area of the brain that is most important for decision-making and abstract thought; but also memory. Shepherd’s work has shown that the human brain can potentially generate any number of flavours ‘since every soluble body has a special flavor which does not wholly resemble any other’.30
The way our brains interpret flavours speaks to the human love of patterns. Professor Shepherd and colleagues have done experiments using fMRI and other brain scanning technologies to show that different flavours register as different patterns in the brain. It is startling to see scans of these flavour maps and realize that there is a separate place in our brains for bananas and Cheddar cheese or that strawberries and sugar show up as dots in similar locations. The way our brains map flavour is similar to the way that we perceive visual images. When we ‘see’ something, what we are actually doing is creating an abstract 2D representation of it, with some features enhanced and others suppressed. By the same token, when we put food in our mouths, the flavour molecules that drift to our nose are turned into abstract patterns in the brain. These patterns help us to recognize the food when we taste it again. Our olfactory receptors give different patterns to the sweet and the savoury; the rotten and the fresh. The receptors also modify the patterns depending on what is happening in the rest of the body: whether we are happy or depressed or nauseous.
Through these patterns, our brains make sense of the bewildering world of flavour. Take umami, the so-called fifth taste, which corresponds to the savoury qualities in meat, cheese and certain vegetables such as tomatoes or broccoli. Umami is what gives mushrooms their oomph and the reason it’s so hard to stop pouring gravy on your potatoes. We all have neurons that are specifically tuned to umami. Yet by itself, umami – which is made in artificial form as MSG – doesn’t really taste of much. It is only in conjunction with other flavours that it becomes delicious. We can see this from neuroimaging studies. When glutamates are tasted in conjunction with a savoury vegetable odour, they generate far more brain activity than when the two flavours are tasted separately. The whole is more than the sum of its parts. This makes sense. Our brains are smart enough to see that a dish of Asian greens with soy sauce warrants a more sizeable flavour image than the same greens and soy sauce eaten separately.
What is most significant about our flavour images is the way that they lead to what scientists call ‘images of desire’. Once we have a memory in our heads of a flavour we love, we build up ‘images of desire’ as we seek to acquire it again. In 2004 researchers put subjects on a bland diet and asked them to imagine their favourite foods. Just thinking about these beloved dishes created a response signal in the hippocampus, insula and caudate – the same areas of the brain that are activated during drug craving. Canadian researchers found that people who described themselves as ‘chocolate cravers’ showed different brain activity when eating chocolate than self-diagnosed non-cravers. The cravers’ brains continued to respond favourably to pictures of chocolate long after their bodies had reached a point of fullness. Neuroscience confirms that chocolate means more to some people than others.
To anticipate pleasure in the next meal – something that can take up the greater part of the day, in my experience – is always a form of memory. And each mouthful recalls other mouthfuls you’ve eaten in the past. It stands to reason, therefore, that the flavour patterns in each of our brains are highly dependent on all the things we’ve tasted in the past, especially during childhood. Among North Africans settled in France, fresh mint tea, often served in ornate teapots, is a way of life. Children grow up with that familiar herbal steam rising from the table as adults sit and talk. A particularly refreshing mint tea is served in the courtyard of the Mosque in Paris, a tranquil place to retreat on sweltering days in the city.
For French Algerians, mint tea is imprinted on the mind, in a way that doesn’t hold true for the non-African French population. In 2009 a group of subjects, half of them ‘Algerian-French’ and half of them ‘European-French’ were asked to smell mint and say what they thought of it. All of them – French or Algerian – found it pleasant and all of them correctly identified it as mint. But when gold electrodes were attached to the scalp, the Algerians showed a significantly greater level of neural activity in response to the mint than the Europeans. Because of the mint tea they drank at home, the smell induced a different cortical pattern in the brain. Put simply, mint was a flavour that resonated more with Algerians than the non-Algerians. This was an image their brains had already recognized many times before. If mint were a sound instead of a taste, you could say that the French heard the notes; but only the Algerians appreciated the music of it. Because their memories of it were more expansive, mint actually took up more of their brain.
When we are unable to obtain the flavours we remember from childhood, it can give rise to longings so intense it is hard to think of anything else. The anosmia sufferers we met at the start of the chapter such as Marlena Spieler would confirm this: she hankers for the flavours that would make her feel ‘like Marlena’ again.
Some of the most poignant examples of this flavour-yearning are the food obsessions of prisoners of war. When Primo Levi was imprisoned in a work camp near to Auschwitz called Buna, he remembered that fellow prisoners not only groaned in their sleep, but licked their lips: ‘They are dreaming of eating; this is also a collective dream … you not only see the food, you feel it in your hands, distinct and concrete, you are aware of its rich and striking smell.’
Among memoirs by POWs of the Second World War, a common theme is not just hunger but the fevered memories it gave rise to of all the things they would eat again once they were free. Very seldom did they build these dreams about the grown-up food of sophisticated restaurants, but the food of childhood and of home: stodgy, filling and safe. One British ex-POW remembered dreaming two nights in a row about ‘omelettes and treacle pudding’. He also remembered his bitter disappointment on waking up, since ‘Either was as obtainable as a slice of the moon’.31
Food obsession reached a particularly feverish pitch among European, American and Australian POWs in the Far East, where the mismatch between their rations of rice and the food they longed for was enough to make them slightly unhinged. Food historian Sue Shephard writes that most of the men in the Japanese camps ‘regressed to a childish state’. They all hallucinated