The brain combines memories 22.07.2015

About 10 years ago, neuroscientists discovered a strange phenomenon: certain neurons in the human brain only fired in response to a particular image. Those studies were performed on patients with epilepsy, who were injected with electrodes into the cerebral cortex to find out which area is responsible for the disease. At the same time, it was possible to perform scientific experiments (of course, on a voluntary basis).

When a person with an electrode in their head was shown a photo of some celebrity, like actresses Jennifer Aniston or Julia Roberts, or a certain scene from a cartoon, then in response one could see the activity of certain nerve cells, and the "Jennifer Aniston" neuron was silent in the photo of Julia Roberts . Such nerve cells were located in the region of the brain that captures the hippocampus, which, as you know, serves as our main memory center.

Further experiments showed that there are indeed cells in the brain that are responsible for recognizing various objects, human faces, etc. Not one or two, but about a thousand, if not more, have been identified for each object, but they can defend each other from each other. friend is too far away for neuroscientists to notice them all at once.

Moreover, what is important, these cells distinguish important features from minor ones: for example, they react to a famous person regardless of what the celebrity is wearing and what hairstyle she has. However, in some cases, when a familiar object was shown to a person in a new context, such neurons were silent.

At the same time, our memories never consist of separate objects. For example, we can remember our friend in a situation where he came to visit us, or when we met him on the street - it is obvious that there are two different places here, the street and the house, for which their neurons are allocated, and they must somehow then interact with the cells responsible for the image of a person. In general, we remember whole chains of events in which something happens all the time with a variety of objects - this kind of information is called episodic memory.

Itzhak Fried (one of those who discovered such cells) from the University of California, Los Angeles and his colleagues from the University of Leicester tried to find out how the specific neurons described above behave with such a memory. Volunteers in their experiments again served as epileptic patients who had electrodes inserted into the cerebral cortex - they were shown from one hundred to two hundred very different images: among them there were places that the most participants in the experiment liked, and portraits of celebrities, and famous architectural structures, such as the Leaning Tower of Pisa , and other elements of the landscape.

In each person (and there were 14 of them), it was possible to record the activity of 600 cells, and among them groups from 2 to 28 could be distinguished, which together responded to at least one image. Then the pictures were changed so that the character and background did not match in terms of neural activity, for example, the actor Clint Eastwood was combined with the Leaning Tower of Pisa - knowing that the neurons responsible for a famous person do not react in any way to a famous architectural structure.

After the participants in the experiment looked at such collages, they had to pass a series of memory tests: for example, they had to assemble a collage they had seen from separate photos - that is, to match a photo of Clint Eastwood with a photo of the Leaning Tower of Pisa.

The goal of the researchers was to understand what would happen to the neurons of a specific response. In an article in Neuron, they write that after the first time, the cells understood that they had “their object” in front of them, just under new conditions, and even responded to its new, modified version with greater activity. "From the first time" means that it was enough to show the combined picture once for special neurons to remember their object in relation to the new environment.

In fact, one would expect the brain to have a way of turning individual objects into a continuous chain of memories. The peculiarity of the new work is that the authors managed to show changes in the work of the higher nervous system at the neuronal level - and the main thing here is that the emergence of a new association, the need to associate a familiar object with new conditions affects the activity of single neurons.

Obviously, by combining the activity of various groups of special neurons, each responsible for its own image, the brain is able to remember a unique event in our life, which did not happen in the past and which will not be repeated in the future.