The study of neurochemical and molecular mechanisms of neurological memory has been conducted in recent decades with great intensity. However, despite the huge amount of experimental material, the constant improvement of experimental equipment and the undoubted successes achieved by various researchers, a wide range of questions remains unclear and attempts to create a single harmonious theory that exhaustively and consistently explain all aspects of this most complicated phenomenon face significant difficulties.
It is known that almost all, or at least the vast majority of animal species, are capable, one way or another, of adapting to the circumstances they have to face during their lifetime. The reaction of the animal’s organism to the same circumstances during their repeated manifestation often turns out to be quite different than that which occurs when they first collide with them. This is due to the ability of living systems to learn, i.e. the presence of such a specific feature as memory, the existence of which largely determines the individuality of the behavior of each animal and man, conditioned by his personal experience.
1. Spatial-temporal organization of memory
The set of changes in the CNS associated with fixing a trace of memory is usually called an engram, and one of the main issues of interest to researchers in this field is to identify and locate the engram’s location in the brain. As is known, the brain is organized in such a way that the main functions associated with the perception of the external world and with motor responses to external influences have a representation in certain, rather strictly localized sections of its cortex.This was the basis of the concept of memory, created within the framework of the classical theory of conditioned reflexes, where the processes of elaborating acquired reactions were considered as a “closure” of the connection between certain centers of the cerebral cortex. In this case, damage to the center, of course, should disrupt the memorization associated with the implementation of this function.
Long-term memory is a complex process that begins with the level of a single neuron, then a neural population, individual structures, and the brain as a whole. Therefore, a holistic view of this function of the brain can be compiled only by generalizing the experimental data obtained with the help of mathematical, analog, biophysical, neurophysiological, neurochemical and neuropharmacological methods of investigation. Regardless of the specialty, most researchers believe that the key mechanism providing long-term trace storage in an ensemble of neurons is a steady increase in conductivity in the region of specific synapses.
At the initial stage, the neurophysiological mechanisms of long-term trace storage may not in principle differ from those in short-term memory (prolonged undamped reverberation in closed neuronal circuits).
In this monograph we tried to focus on the neurophysiological and neurochemical analysis of the role of synaptic mechanisms in the formation and long-term storage of engrams and related phenomena. In particular, they considered it necessary to consider in detail the ways of implementing intracellular and synaptic mechanisms of neuron activity, since the synapse is the first link where the integration of external signals triggers the synthesis of information macromolecules and the formation of impulse code specific for a given neuron or group of neurons.
Types of biological memory:
4. Neurological (it is sometimes called mental or individual).
At present, neurological memory is divided into three stages:
1. Short-term memory (duration from several milliseconds to several minutes).
2. Intermediate (from a few seconds to several hours).
3. Long-term memory (years, decades and throughout life).
Neurological memory has a complex system organization and does not have strict localization in certain areas of the brain. According to modern ideas, traces of memory (engrams) are fixed in the brain in the form of changes in the state of the synaptic apparatus, as a result of which the preferential excitation of certain neural pathways arises.
After the perception of information, in the process of its capture and fixation, a series of successively changing neurochemical processes occur in the brain. At the first stages, in the stage of short-term memory, there are changes in the “fast” synapse functions associated with the release and shift of the concentration of “classical” and peptide mediators. In the future, for a period of several seconds to several days, a wide range of neurochemical processes involving changes in the composition and structure of neurospecific proteins, in particular changes in the degree of their phosphorylation, and modification of the synthesis of RNA are involved.
For the formation of lifelong long-term memory, a constant synthesis of new biopolymers is necessary, which can be implemented in the case of stable rearrangements in the functioning of the genome sites. The latter can occur as a result of either structural changes in DNA, or the formation of stable cycles for the continuous synthesis of repressors or derepressors of transcripts. It is also possible that immunological mechanisms are involved in the formation of long-term memory, thanks to which antibody-like compounds are synthesized in the brain that can for a long time modify the activity of synapses in certain nerve pathways. In the mechanisms of memory formation, both “classical” mediators and a large number of neuropeptides that function as mediators and neuromodulators participate.