Where are we? Neurons of places

This year, the Nobel Prize in Physiology and Medicine was awarded to John O'Kif and the spouses of Moser, Edward and May- Britt. According to the wording of the Nobel Committee, the prize was received for " cell opening that form a navigation system in the brain." The neuro- and psychophysiologist Olga Awrik tells .

This story began in 1971, when John O'Kif (together with Jonathan Prostrovski) published a work on the analysis of the activity of individual neurons in Hippocampus at rats in free behavior (O'Keefe & Dostrovsky, 1971). John O'Kif was one of the first to use the possibility of registering the activity of individual neurons in freely mobile animals. That is, not in anesthetized, not mildly fixed, but for freely moving and choosing where to go and why. Registration was carried out both during “spontaneous” behavior (movements in space, nutrition and drinking, grooming, periods of sleep), and during “caused” behavior (when oriented to the object, sniffing, biting). Neurons were also tested upon presentation of auditory, visual, odor and tactile stimuli. Of the seventy -six registered cells, eight, as it turned out, had "preferred spatial orientation." It is important that these cells were not associated with a reaction to "simple" sensory stimuli, or with specific motor behavior.

From the very beginning of these studies, it was assumed that the discovered properties of the hippocampus neurons correspond to the idea of the “cognitive maps” of Edward Tolmen (Tolman, 1948), which showed that the rats who had the opportunity to examine the labyrinth are better trained in the subsequent skills in this labyrinth, which did not have such an opportunity. Since the rats did not receive any reinforcement during the initial examination, Tolmen suggested that such “cognitive maps” are formed as abstract representations, and not as a chain of reinforced motor reactions.

In addition to neurons that activate with a certain orientation of the animal, neurons were later described precisely “Places” (Place Cells) (O'KeFe, 1976), which are activated in a certain place, regardless of the specific orientation of the animal in space; Neurons of the “directions of the head” (Head Direction Cells (Taube et al., 1990); neurons of "Coordinate net" (Grid Cells) (Hafting et al., 2005); Neurons of "borders" (Border Cells) (Solstad et al., 2008). Not so long ago, neurons marking three -dimensional space in bats (YartSev & Ulanovsky, 2013) were described.

The record of the activity of 7 neurons at the rat, running a few hundred circles clockwise closed triangular path, stopping in the middle of each side to eat small pieces of food. Black dots show the position of the rat’s head; Color - the potentials of the action of each of the neurons. Image: "Wikipedia"

For the first time, the descriptions of neurons of the “coordinate grid” and neurons of “borders” were given precisely by the Mozgers and their employees. Each neuron of the “coordinate grid” is activated in several places of the examined space, so that the activation map looks like a hexagonal grill, where each grate knot is activation. And the neurons of “borders” are activated where the boundaries of the space provided for examination end.

The described neurons could be represented by components of the brain navigation system, a certain “internal” navigator informing us where we are. However, there are several points that complicate this picture. Judging by the fact that the sequence of activation of neurons in animals is repeated at the moments of stops (Foster & Wilson, 2006) and in the dream (LouIe & Wilson, 2001), as well as in people when recalling the episode of the movement in the virtual space (Miller et al., 2013), our memory can be reproduced in the form of assembly combinations of certain groups of neurons.

In recent studies by Howard Eichenbaum and his group (Macdonald et al., 2011; Eichenbaum, 2014) the so -called “time” cells of the hippocampus were described. It can be assumed that the neural groups of the hippocampus are the experience of the body, specially organized in space and time. And given that a certain sequence of activation of the hippocampus cells can occur even before the animal falls into this space (Dragoi & Tonegawa, 2011), this should be more likely not navigation, but brain predictions regarding future events based on the experience of the past (Buzzaki, 2013).

The awarded Nobel Prize is important in that it notes the achievements of science in the field of understanding what underlies “higher”, cognitive functions. This demonstrates the connection of the activity of neurons with subjective abstract “concepts”, such as “place”, and once again shows that we can have access to the “inner” world of the body. It is also significant that the emphasis of the study of the “higher” functions of the brain is shifted from the search for structures that carry out certain functions to the search for neural groups distributed by the brain, which are activated in accordance with a particular task solved by the body.

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