Food on the brain
The brain is one of the most complex structures in the universe. It contains about 100 billion neurones, about the same number of stars in all the galaxies of the known universe. It takes in everything relating to the body’s external and internal environments and gives signals to act accordingly.
When we eat and drink, different zones in our brain respond to the taste and smell of food as well as other sensory properties. Scientists in the Perception Physiology Group at the Nestlé Research Center (NRC) use a technique called electro-encephalography (EEG) to record exactly where and when the flavour of food and other properties are processed in the brain once they enter the oral cavity.
During an EEG, volunteers wear a cap that tightly covers the head with a network of electrodes on the inside. These electrodes pick up brainwave signals from the scalp and are sensitive enough to pinpoint the exact location within the brain where the imprint of a certain food ingredient has landed.
What are brainwaves and what do they do?
Brainwaves are the result of electrical signals given off by neurons when they communicate with each other. They are by nature very complex as they are generated by billions of interconnected neurons sending each other micro-volt range electrical pulses. EEGs measure the sum of simultaneously generated pulses by capturing the signals via electrodes placed on the scalp.
Brainwaves can be classified as slow, moderate or fast waves depending on their speed, measured in Hertz (cycles per second). Although no single brainwave is responsible for a single function, there are some generalities that link specific types of brainwaves to specific states of mind. For example, alpha waves are linked to periods of quiet and calm and can be notably generated during meditation1. Beta waves are linked to moments of cognitive tasks such as decision-making and problem-solving2.
EEGs pick up these brainwaves while volunteers sample specific kinds of food and will generate an electrical image of the impact of each foodstuff on the brain, which proves extremely helpful in identifying how our bodies and minds react to certain kinds of food.
Message from the brain: Wake up!
In a test, Dr Julie Hudry at the Nestlé Research Center compared the stimulating feeling of eating an ice cube with that of drinking a glass of cold water. The ice cube gives off a cold, juicy, tingling delicious sensation that refreshes the mouth and head. Why? Because the refreshing stimulus sets off a myriad of tiny electrical impulses all over the scalp! Dr Hudry used EEG to compare the brainwaves related to both these actions. The ‘cool’ refreshing feeling in the mouth was measured as it increased the amplitude of the brain’s α-waves. The figure on the right shows a comparatively greater increase in α-wave activity over the whole scalp with ice than with water alone, interpreted as a tingling sensation of increased alertness.
LABBE D., MARTIN N., LE COUTRE J., HUDRY J., 2011. Impact of refreshing perception on mood, cognitive performance and brain oscillations: An exploratory study. Food Quality and Preference, 22, 92-100
Sending messages to the brain
When we eat, all five of our senses - taste, smell, sight, touch and sound - send messages to the brain. Each sense plays a key role in our overall perception of food.
Tongues have thousands of taste receptors, or taste buds, which pick up the five basic elements of taste: sweet, sour, salty, bitter and umami. The taste we perceive is a combination of all five.
Our taste buds have evolved over thousands of years, from when our hunter-gatherer ancestors could only rely upon taste to know which kinds of food were safe to eat. Over time, these were identified by trial and error, mainly using the senses of touch, taste and smell, often at great risk to the person trying new and potentially toxic food.
Bitterness was often a sign that a plant was toxic. Our taste buds evolved to be able to better process this information and even today we still have 25 different types of receptors (taste buds) on our tongues to pick up bitter flavours and send ‘warning’ messages to our brains. Compare this to the single receptor we have to pick up ‘sweet’ tastes!
The nose refines this experience even further by picking up aromas. There are about 1000 different olfactory receptors in the retro-nasal cavity. According to the human genome project, we have about 400 functional genes coding for olfactory receptors, around 1.3% of the total human genome.
All these olfactory receptors provide a system to differentiate between a multitude of odours and each can detect more than one odour. Compared to the tongue, the olfactory system can distinguish between an almost infinite number of odorant molecules, alone or combined in food. So, even when we think we are tasting something, 80% of the time we are actually perceiving it through our nose, i.e. we are actually smelling it.
"The first taste is always with the eyes"
What we see definitely has an impact on our perception of our food. We know that our tongues and noses play a key role in tasting food, but so do our eyes! Chefs traditionally say "the first taste is with the eyes", yet the science behind this is still unknown. How food looks can impact our expectations and even pre-define if we are going to accept or reject it.
In order to test how sight could impact someone's perception of taste, Dr Johannes le Coutre and Dr Julie Hudry from the NRC gathered 14 volunteers for an EEG. The hypothesis was that seeing high-calorie food would make something taste better and vice-versa, as low-calorie food would negatively impact perception3.
The volunteers were shown images of either high-calorie or low-calorie food like pizza or watermelon. They were then given an electric taste test from an electrode on the tongue that would emit a neutral flavour, neither pleasant nor unpleasant, and were asked to rate the taste on its ‘pleasantness’ and ‘intensity’.
Dr Johannes le Coutre concluded that “Our findings indicate that when the volunteers saw the high-calorie images they enjoyed the taste more than with the low-calorie images. Images of high-calorie food appear to heighten the personal expectation and liking of subsequently presented tastes.”
Dr Julie Hudry added “The brain images shed light on how sight and taste are processed to procure food enjoyment. The challenge for the future is to find out how much the brain regions we have identified in visual-gustatory interactions could account for regulation of appetite and food intake control in real-world settings.”
When we eat, all of our five senses work together in order for our brain to know exactly what is going on. When one of our five senses is not working properly - think about the last time you had a cold - then our brain is at a disadvantage and even if we eatsomething we have eaten before, it just doesn't seem the same!