Although the molecular mechanisms of the functioning of a single nerve cell have been studied in many of their manifestations and the principles of organization of interneuronal connections have been formulated, it is still not clear how the molecular properties of neurons provide storage, reproduction and analysis of information-memory.
The fact that acquired knowledge (like moral principles) is not inherited, and new generations have to be taught again, allows us to consider that learning is the process of creating new inter-neural connections and remembering information is provided by the ability of the brain to reproduce these links as necessary (activate their). However, modern neurochemistry is not yet able to provide a consistent theory describing how the analysis of the factors of the external world takes place in the living brain. One can only outline the problems that scientists of different areas of neurobiology are working on intensively.
Almost all kinds of animals are capable of analyzing changes in the external environment to a greater or lesser degree and responding adequately to them. In this case, the repeated reaction of the body to external effects is often different than in the first collision. This observation shows that living systems have the ability to learn. They have memory that preserves the personal experience of the animal, which forms behavioral reactions and can differ from the experience of other individuals.
Biological memory is diverse. It is inherent not only in brain cells. Memory of the immune system, for example, for a long time (often for life) keeps information about an alien antigen that once got into the body. When you re-meet, the immune system triggers an antibody reaction that allows you to quickly and effectively defeat the infection. However, the immune system “knows” how to respond to a known factor, and when encountering an unknown agent, it must develop an behavior strategy anew. The nervous system, unlike the immune system, can be trained to create a strategy of behavior in the new circumstances, based on the “life experience”, which makes it possible to develop an effective response to an unknown stimulus.
The main questions to be answered in the study of molecular mechanisms of memory are: what metabolic changes occur in neurons when they meet with an external stimulus, which allow the stored information to be preserved for a certain (sometimes long) time; in what form the received information is stored; how is it analyzed?
In the process of active learning, occurring at an early age, there are changes in the structure of neurons, the density of synaptic contacts increases, the ratio of glial and nerve cells increases. It is difficult to distinguish the process of maturation of the brain and structural changes, which are molecular carriers of memory. However, it is clear that for the full development of intelligence it is necessary to solve the tasks posed by the external environment (recall the phenomenon of Mowgli or the problems of adaptation to life in nature of animals grown in captivity).
In the last quarter of the XX century. attempts were made to study in detail the morphological features of the brain of A. Einstein. However, the result was rather disappointing – no features that distinguish it from the average modern brain were revealed. The only exception was a certain (insignificant) excess of the ratio of glial and nerve cells. Does this mean that the molecular processes of memory leave no visible traces in the nerve cells?
On the other hand, it has long been established that DNA synthesis inhibitors do not affect memory, while inhibitors of transcription and translation impair memory processes. Does this mean that certain proteins in brain neurons are memory carriers?
The organization of the brain is such that the main functions associated with the perception of external signals and reactions to them (for example, with motor reaction) are localized in certain parts of the cerebral cortex. Then the development of the acquired reactions (conditioned reflexes) should be a “closure of the bonds” between the corresponding centers of the cortex. The experimental damage to this center must destroy the memory of this reflex.
However, experimental neurophysiology has accumulated a lot of evidence that the memory of acquired skills is distributed to different parts of the brain, and not concentrated only in the area responsible for the function in question. Experiments with partial disturbance of the cortex in rats trained to orientate themselves in the maze showed that the time required to restore the disrupted skill is proportional to the volume of destruction and does not depend on its localization.
Probably, the development of behavior in the labyrinth involves the analysis of a whole set of factors (olfactory, taste, visual), and the brain regions responsible for this analysis can be located in different areas of the brain. Thus, although for each component of the behavioral response there is a certain part of the brain, the general reaction is realized when they interact. Nevertheless, in the brain, departments have been found whose function is directly related to memory processes. It is a hippocampus and an amygdaloid complex, as well as nuclei of the midline of the thalamus.
A set of changes in the CNS, associated with the fixation of information (image, type of behavior, etc.), neuroscientists are called an engram. Modern ideas about the molecular mechanisms of memory suggest that the involvement of individual brain structures in the process of memorizing and storing information does not consist of storing specific engrams, but in regulating the creation and functioning of neural networks that capture, record and reproduce information.
In general, the data accumulated in the study of behavioral reflexes and electrical activity of the brain indicate that both behavioral and emotional manifestations of vital activity are not localized in a certain group of neurons of the brain, but are expressed in a change in the interactions of a large number of nerve cells that reflect the functioning of the entire brain as of an integrated system.
To describe the flow of the process of remembering new information over time, the terms short-term memory and long-term memory are often used. In the short-term memory, information can be stored from fractions of a second to tens of minutes, while in long-term memory, information is sometimes contained throughout life. To convert the first type of memory into a second one, a so-called consolidation process is needed. Sometimes it is allocated to a separate stage of intermediate memory. However, all these terms, probably reflecting the obvious processes, are not yet filled with real biochemical data.