Guide neuron

Publishing houses "Hummingbird" and "ABC-Atticus" represent Michael Bond's book“Guide Neuron. How our brain solves spatial problems ”(translation by Yuri Goldberg).

Navigation skills are deeply rooted in our biology. The ability to find a way over long distances in prehistoric times gave Homo sapiens an evolutionary advantage, allowing you to explore the most remote corners of the planet. The ability to navigate is closely related to other important cognitive functions, such as abstract thinking, imagination and memory. Michael Bond summarizes the results of the latest research in the field of psychology, neurobiology, ethology and anthropology and gives examples from the experience of people whose profession or occupation are somehow related to navigation-masters of sports orientation, pilots, search and rescue volunteers, cartographers, urban planners and others. The result was a fascinating immersion in the topic of orientation of a person in a natural and artificial environment with a special accent on the consideration of the neurobiological foundations of this most important skill.

“The fact that we are not lost so often can be considered a kind of miracle. The world around us is infinitely complex, and yet most of us can navigate it. We are able to walk along unfamiliar streets, adhering to a certain direction, to reduce the way, laying new routes, and after many years to remember the places where we were only once. These are amazing achievements. One of the tasks of this book is to explain how we do it: how our brain makes cognitive cards that help to navigate even in unfamiliar places. But more importantly, the book talks about our relations with the world, how understanding of the world affects psychology and behavior, ”the author writes.

We offer to read a fragment of the book.

Mental cards

In neurobiological laboratories, where researchers devote most of the time to observations of the brain of rats, their favorite food (rats, not scientists) are cereal breakfast rings with chocolate taste. When researchers need something from their furry subjects, they get rings. The hungry rat always does what is required of it. With one exception.

When the rat first finds himself in an unfamiliar place, food does not attract it. Covered by curiosity and fear, the animal sniffs a new territory, clinging to the walls and from time to time jumping into the open space; Studying a new place for a rat is more important than satisfying hunger. Neurobiologist Paul Dudchenko from the University of Sterling studied the process of teaching animals and for a long time observed the behavior of rats in the maze.

“Rats are prone to neophobia, they do not like everything new,” he says. “But if you place them in an unfamiliar environment - and we do it constantly - then they will readily explore it, and always in the same way, until they study the entire space.”

In this regard, rats are no different from other animals. Almost all mammals behave in unfamiliar places in the same way. If you have a cat, try to bring her to the house of your friends and observe how she will examine an unfamiliar place before calm down or eat. People also get used to an unfamiliar environment. The most insatiable researchers are children, if, of course, to allow them. It seems that both people and animals are very important to get acquainted with the new place.

What is this process? What happens in the brain of the rat when she explores the maze, or in our brain, when we walk around the city? These issues occupied neurobiologists and psychologists for more than one decade, but they attracted special attention after 1971, when John O'Kif and Jonathan Prostrovsky, employees of the Department of Anatomy of the University College of London, discovered nervous cells in the brain that were not similar to everything that the researchers saw before. Most nerve cells, or neurons, are excited - that is, they send a message to other parts of the brain - in response to sensory information coming from the body of the animal. And these cells, on the contrary, reacted to the position of the animal in the environment and activated only in certain places. O'Kif called them neurons of the place and suggested that the area of ​​the brain in which they are located - the hippocampus, in shape resembling a sea skate - provides a rat with a spatial coordinate system, or a cognitive map that helps to remember the environment and orient in it.

Since then, neurobiologists studying the brain of rats have discovered several more types of neurons related to the perception of space. There are neurons of head directions that work as an internal compass, informing the animal in which direction it looks; and neurons of gratings indicating the location; and neurons of the boundaries that are excited at a certain distance from the wall or edge. Somehow, all these different types of cells work together so that the animal can understand where it is, and, more importantly, remember where it has already visited.

If the information recorded by these neurons of space really forms a cognitive map - and most researchers describe this that way - then this is not a real map: looking inside the hippocampus, you will not see there nothing reminding Google Maps for those places that you visited or remember. Neurons of places, directions of the head, lattices, borders and other types of neurons of space jointly form a picture of the outside world in us and allow on the basis of this information to make amazing things; Without them, we could never find the way anywhere and would be astraying all the time. But how they do it and in what form they keep memories - all this still remains a mystery that neurobiologists hope to resolve sooner or later.

The study of spatial perception - how the brain receives and uses information about space - has turned into one of the most rapidly developing areas of neurobiology. To a large extent, this was facilitated by the fact that John O'Kif for his research of neurons, which he dedicated four decades, awarded the Nobel Prize in physiology and medicine. Together with him, the prize was received by May-Britt Moser and Edward Moser, discoverers of neurons of the lattice1. This is a very interesting and technologically difficult task.

It is difficult for neurobiologists to obtain the permission of ethical committees to implant microelectrodes into the brain of healthy people, and therefore most studies of the neurons of space were carried out on rats or mice, whose brain is more similar to ours than at first glance. A considerable skill is required to place the electrodes with the thickness of human hair exactly in the place of the rat’s brain that you intend to study. When the animal recovers after surgery (this takes several days), researchers get the opportunity to record voltage impulses from individual neurons, the so -called “action potentials” that are developed when the neuron reacts to incoming information and transmits it further on its network of connections. In other words, they can look into the “motherboard” of the rat, where its interactions with the outside world are processed. After O'Kif opened the neurons of places in rats, other neurobio logo found these cells in mice, rabbits, bats and monkeys, as well as in epilepsy people who have already implanted electrodes into the brain in the process of treatment. All neurons of places perform the same function.

To understand the role of these nerve cells, imagine for a minute that you are a neuron in the Hippocampus Rat named Roland. When Roland falls into a small compartment, where he was not before, and begins to sniff, nothing happens to you at first. But, when he gets to a certain place in space, the tension you produce suddenly increases sharply and remains at this level until Roland moves on. You remain in a calm state until the rat returns to this special place - and your tension again goes to the peak. Looking at other neurons of places - your neighbors in the hippocamp - you notice that the same thing happens with them, only in other places - everyone produces an impulse in a certain zone, the so -called “field of place”.

A few minutes later, Roland through the door enters another compartment, and you find that everything has changed. Your field is shifted, the fields of the place of neighboring cells are mixed. Roland falls into the third compartment, and everything changes again: here you are not showing any activity. Then Roland, hungry and hoping to find delicious rings, returns to the first compartment, and the field fields in it are located exactly the same as for the first time. Roland's brain obeys a certain logic, although its rules are quite complicated.

We translate this mental experiment into the language of science: when the animal falls into an unfamiliar space and begins to explore it, a unique combination of neurons of the place is activated in the hippocampus, and when it enters the same space again, the same combination is excited, and each neuron is activated in the same place of space as before; This pattern is a cognitive map informing the animal that it was already here. O'Kif found out that in order to get comfortable in a box with an area of ​​one square meter, the rat requires about 32 neurons of places that are excited when the rat is in different parts of the box. The more often the animal returns to one or another area, re -activating the same sequence of neurons of the place, the more stable the connections between neurons, and hence memory. Different spaces are displayed by different combinations of neurons of the place, that is, different cards. Neurobiologists studying the behavior of rats in labyrinths can sometimes determine the location of the rat by signals from neurons with an impressive example of reading animal thoughts.

Be that as it may, the cognitive card differs from those cards that you can see in the royal geographical society in London or in the Congress library in Washington. The hippocampus does not store copies of the sequential activation of neurons of the place; These neurons are excited only when the animal is in the corresponding area2. The brain should keep spatial memory somewhere, but no one knows where it stores it and in what form.

Neurons of places in the hippocampus - unlike their fields, are clearly not like a map: neighboring neurons of places do not necessarily correspond to the neighboring points of space, and the distribution of fields through the neurons looks random. Moreover, this whole scheme is mixed - or “a new map is compiled,” as neurobiologists are expressed - when the animal falls into a new environment. So far, no one has managed to predict how neurons of the place would behave when changing the situation or where the appropriate field fields can be.

“The lack of neurons of the place of topographic structure always confused me,” says O'Kif. - I worked all my life at the Department of Anatomy. If you look at the cerebral cortex, then the cells corresponding to the finger are located next to the cells corresponding to the next finger, that is, we see a kind of topographic display. But when you have a structure in which this is not observed, and two neurons of places displaying neighboring points of space are located far from each other, and all this should be a map ... this is not a map. ”

In 1998, the late Robert Muller, an O'Kif’s colleague, demonstrated the random nature of the location of the neurons of the place, recording the electrical activity of these nerve cells in rats, which studied unfamiliar space. Then he rebooted these cells, erasing the spatial memory of rats, and again placed the animals in the same place to check whether the same neurons of the place will be excited. It turned out not.

The rat’s cognitive map - the scheme of excitation of its neurons of the place - was not at all like the original. This indicates not only the unpredictability of the display in the brain of the location in space, but also in general on the absence of any predetermination. Perhaps there is a serious biological reason for that, but in this case to understand the idea of ​​the hippocampus as a card is even more complicated.

During the time, since O'Kif opened the neurons of the place, it became clear that cognitive cards did not just display information about space. If the rat runs along a certain route, then turns and runs back, the cognitive cognitive cards of travel there and back will be different. In this case, the card records not only the topography of the route, but also the direction of movement. As we will see, cognitive cards display many aspects of the animal’s experience (if this route is already familiar along the road, the map will also look different). We can’t survive without cognitive cards, but no one knows for sure what they are.

1. Edward and May-Brith Moser are married and are still working together.

2. Or, as we will soon see when it thinks about this area or sees it in a dream.