We see a lot of everything around us – houses, trees, other people, cats, dogs, cars, buses, fields, forests, laptops, smartphones, and so on and so forth. What we pay attention to, what we don’t, it all depends on what we are doing and what we have in our thoughts. But among everything that hits our retina, there are things that are especially important – so important that there are special groups of neurons in the cerebral cortex for them. These are faces, bodies and body parts, words and, in general, any sequence of symbols, as well as places (territories, spaces where something happens). When we have a face in our field of view, a specific group of neurons reacts to it, tuned specifically to faces in general. In the same way, the brain distinguishes human arms, legs, torsos from any other objects. In the same way, there are neurons that hold the visual representation of a piece of space – a part of the street, a square, an office room, an open field with a flock of crows, etc. There is nothing to say about words.
Employees Massachusetts Institute of Technology added to this list the fifth object of special importance – food. That is, we have special neurons that react to food, which is all the more surprising, because food can be very, very different: after all, there is much more in common between two human physiognomies than between pizza and a banana. We found these neurons using functional magnetic resonance imaging (fMRI).
However, as the authors of the work themselves say, if they simply showed people pictures with food in the fMRI machine and then looked at which parts of the cortex reacted to them, then there would be big questions about such results. For example, how do we know that a group of neurons that we have identified as food-specific are actually food-specific?
The researchers did a different thing: they used an open database of fMRI data, from which they took images of the brains of eight people – these people looked at ten thousand different pictures, and for each picture their brain activity was determined. In the cerebral cortex, they did not specifically look for “food” activity, they looked for such activity in it that would be more or less the same in relation to any class of objects. And here one more algorithmic trick was needed, related to the features of the fMRI itself.
An fMRI image is made up of many voxels (the so-called three-dimensional pixels). Each voxel shows the activity of hundreds of thousands of neurons – this is the resolution of the method so far. Among the hundreds of thousands of neurons in one voxel, there may well be a group of neurons that work differently than all the others, but it is impossible to determine them directly from an fMRI image. But with the help of a special method, it is possible to “see” different populations of neurons in the same voxel, which is analyzed at once on multiple images.
The authors of the work confirmed that in the visual analyzer of the cerebral cortex there are groups of neurons for faces, bodies, places and words. But along the way, it turned out that there is a fifth group of neurons – for food. In an article in Current Biology it is said that visual neurons for food are distributed in populations of other neurons tuned to other objects – therefore, they could not be detected for a long time, other neurons simply obscured them.
The researchers tried to mimic food’s visual neurons in a computer model, and the model eventually worked so well that it distinguished a banana from a crescent moon. Probably, such specialization in neurons does not appear from birth, but develops gradually, as, for example, it happens with neurons that recognize faces. But how exactly the “food section” is formed in the visual cortex will become clear only after further experiments.
Source: Автономная некоммерческая организация "Редакция журнала «Наука и жизнь»" by www.nkj.ru.
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