Neurophysiological mechanisms of memory

In the structural organization of the nervous system, it is customary to distinguish the central nervous system (CNS) and the peripheral. The CNS, in turn, includes the spinal cord and brain. All other nervous structures are included in the peripheral system. The highest part of the CNS - the brain consists of the brain stem, cerebrum and cerebellum. The large brain is represented by two hemispheres, the outer surface of which is covered with gray matter - the cortex. The cortex is the most important part of the brain, being the material substrate of higher mental activity and the regulator of all vital functions of the body.

A.R. Luria identified three main functional blocks of the brain, the participation of which is necessary for the implementation of any kind of mental activity.

The first block - activation and tone. Anatomically, it is represented by a network formation in the brain stem regions - the reticular formation, which regulates the level of cortical activity from the waking state to fatigue and sleep. A full-fledged activity implies an active state of a person, only in conditions of optimal wakefulness can a person successfully perceive information, plan his behavior and implement the planned action programs.

The second block is receiving, processing and storing information. It includes the posterior regions of the cerebral hemispheres. The occipital zones receive information from the visual analyzer - sometimes they are called the visual cortex. The temporal regions are responsible for the processing of auditory information - this is the so-called auditory cortex. The parietal regions of the cortex are associated with general sensitivity, touch. The block has a hierarchical structure and consists of three types of cortical fields: the primary ones receive and process impulses from the peripheral parts, the secondary ones carry out analytical processing of information, the tertiary ones carry out analytical and synthetic processing of information coming from different analyzers - this level provides the most complex forms of mental activities.

Third block - programming, regulation and control. The block is located mainly in the frontal lobes of the brain. Here goals are set, programs of one's own activity are formed, their progress and success are monitored.

The joint work of all three functional blocks of the brain is a necessary condition for the implementation of any human mental activity.

In presenting the brain mechanisms of mental activity, one should dwell on the question of interhemispheric asymmetry of the brain. The work of the cerebral hemispheres is built according to the contralateral principle, i.e. the left hemisphere is responsible for the right side of the human bodily organization, the right hemisphere - for the left. It has been established that both hemispheres are functionally unequal. Functional asymmetry, which is understood as the different participation of the left and right hemispheres in the implementation of mental activity, is one of the fundamental patterns of the brain of humans and animals.

The entire brain as a whole is involved in the implementation of any mental activity, however, different hemispheres perform a different differentiated role in the implementation of each mental function. For example, as a result of experimental and clinical studies, it was found that the right and left hemispheres differ in the strategy of information processing. The strategy of the right hemisphere consists in a holistic simultaneous perception of objects and phenomena, this ability to perceive the whole before its parts is the basis of creative thinking and imagination. The left hemisphere carries out sequential rational processing of information. The problem of interhemispheric asymmetry and interhemispheric interaction is far from being solved and requires further experimental and theoretical studies.

The study of brain mechanisms that provide mental processes does not lead to an unambiguous understanding of the nature of the mental. A simple indication of the brain and nervous system as the material substratum of mental processes is not enough to resolve the question of the nature of the relationship between the mental and the neurophysiological.

Russian physiologist I.P. Pavlov set himself the task of revealing the essence of the mental by objective physiological methods of research. The scientist came to the conclusion that the units of behavior are unconditioned reflexes as reactions to strictly defined stimuli from the external environment and conditioned reflexes as reactions to an initially indifferent stimulus, which becomes indifferent due to its repeated combination with an unconditioned stimulus. Conditioned reflexes are carried out by the higher parts of the brain and are based on the temporary connections formed between the nervous structures.

An important contribution to solving the problem of neurophysiological mechanisms of the psyche is the work of domestic scientists ON THE. Bernstein And PC. Anokhin .

ON THE. Bernstein studied natural human movements and their physiological basis. Before N.A. Bernshtein, the movement mechanism was described by the reflex arc scheme: 1) reception of external influences; 2) the process of their central processing; 3) motor reaction. ON THE. Bernstein proposed a new principle of neurophysiological control of movements, which was called the principle of sensory correction. It was based on the position that movements are controlled not only and not so much by efferent impulses (commands emanating from the central departments to the periphery), but first of all by afferent impulses (signals about the outside world that enter the brain at every moment of movement). ). It is the afferent signals that make up the "tracking device" that provides continuous correction of movement, selecting and changing the necessary trajectories, adjusting the system of stresses and accelerations in accordance with the changing conditions for performing the action.

But afferent impulses are only part of what constitutes the mechanism for organizing voluntary movements. The essential fact is that human movements and actions are not "reactive" - ​​they are active, purposeful and change depending on the intention. The principle of activity is opposed to the principle of reactivity, according to which one or another act, movement, action is determined by an external stimulus and is carried out according to the model conditioned reflex, and overcomes the understanding of the process of life as a process of continuous adaptation to the environment. The main content of the life process of an organism is not adaptation to the environment, but the implementation of internal programs. In the course of such realization, the organism inevitably transforms the environment.

PC. Anokhin created the theory of functional systems, which was one of the first models of genuine psychologically oriented physiology. According to the provisions of this theory, the physiological basis of mental activity is formed by special forms of organization of nervous processes. They are formed when individual neurons and reflexes are included in integral functional systems that provide integral behavioral acts.

The researches of the scientist have shown that the individual's behavior is determined not by a single signal, but by the afferent synthesis of all the information reaching him at the moment. Afferent syntheses launch complex behaviors. As a result, P.K. Anokhin came to the conclusion that it was necessary to revise the classical ideas about the reflex arc. He developed the doctrine of the functional system, which was understood as the dynamic organization of the structures and processes of the body. According to this doctrine, the driving force of behavior can be not only directly perceived impacts, but also ideas about the future, about the purpose of the action, the expected effect of a behavioral act. At the same time, the behavior does not end with the response of the body. The response creates a system of "reverse afferentation", signaling the success or failure of the action, is action result acceptor.

The process of comparing the model of the future with the effect of the performed action is an essential mechanism of behavior. Only if they completely coincide, the action stops. If the action turns out to be unsuccessful, then there is a “mismatch” between the model of the future and the result of the action. Therefore, the action continues, appropriate adjustments are made to it. Reflex arc P.K. Anokhin replaced it with a more complex scheme of the reflex ring, which explains the self-regulating nature of behavior.

Theory of functional systems P.K. Anokhina created a new - systemic - methodology for studying holistic behavioral acts. In the works of the scientist, it was shown that any integral activity of the body is carried out only with the selective integration of many particular physiological mechanisms into a single functional system.

Despite the undeniable fact that the brain is an organ of mental reflection, the relationship between the mental and neurophysiological should be considered from the standpoint of the independence and specificity of each of these processes. The psychic cannot be reduced to the morphological and functional structures that provide it, the work of the brain is not the content of the psyche. Mental reflects not the physiological processes occurring in the human body, but an objective reality. The specific content of the mental lies in the representation of the images of the world and the subjective attitude towards it. As the philosopher A.G. Spirkin, “in the cerebral cortex, the neurosurgeon sees not bright thoughts like a spiritual flame, but just gray matter.”

Attention is one of the most important psychological functions. It is a prerequisite for the effectiveness of any activity, whether it is the perception of real objects and phenomena, the development of a motor skill or operations with numbers, words, images performed in the mind.

Two types of attention are distinguished - voluntary (active), aimed at a consciously chosen goal, and involuntary (passive), arising from unexpected changes in the external environment - novelty, uncertainty.

Structural and functional organization of attention. The mechanism of involuntary attention is close to that of an orienting response; it arises in response to a new or unexpected presentation of a stimulus. The initial situation of uncertainty requires the mobilization readiness of the cerebral cortex, and the main mechanism that triggers involuntary attention is the involvement of the reticular modulating system of the brain in this process (see Fig. 55). The reticular formation by ascending connections causes generalized activation of the cerebral cortex, and the structures of the limbic complex, which evaluate the novelty of incoming information, mediate either the extinction of the reaction as the signal is repeated, or its transition to attention aimed at perception or organization of activity.

Arbitrary attention, depending on specific tasks, needs, motivation, facilitates, “optimizes” all stages of implementation cognitive activity: initial - input of information, main central - its analysis and assessment of significance and the final result - fixation of new knowledge in individual experience, behavioral response, necessary motor actions.

At the stage of input and primary analysis of the stimulus, its allocation in space, an important role belongs to the motor components of attention - eye movements. Processes occurring at the level of the midbrain (the quadrigemina) provide saccadic eye movements that place the object in the region of best vision on the retina. The implementation of this mechanism occurs with the participation of the posterior associative parietal cortex, which receives multimodal information from sensory zones (information component) and from the cortical part of the limbic system (motivational component). The descending influences of the cortex, which are formed on this basis, control the structures of the midbrain and optimize the initial stage of perception.

The processing of information about a stimulus that is of certain significance for the organism requires the maintenance of attention and the regulation of activation influences. The control effect (local activation) is achieved by the regulatory influences of the frontal cortex. The implementation of local activating influences is carried out through the associative nuclei of the thalamus. This is the so-called fronto-thalamic attention system. In the mechanisms of local activation, a significant role also belongs to the structures of the limbic system (hippocampus, hypothalamus, amygdala, limbic cortex) and their connections with the frontal neocortex (see Fig. 56).

The activation of executive mechanisms, including motor programs and programs of innate and acquired behavior, is carried out with the participation of the frontal regions and basal ganglia, which are under double control - the cortex and the limbic brain.

Thus, arbitrary selective attention is provided by whole complexes of hierarchically organized structures. As a result, activating influences become mediated by the results of situation analysis and significance assessment, which contributes to the formation of a system of activated brain centers that is adequate to the conditions of the task being performed.

EEG analysis of the brain organization of attention. In the EEG with generalized tonic activation in response to the presentation of a new stimulus that caused involuntary attention, desynchronization of the main rhythm occurs (Fig. 62) - blockade of the mid-frequency alpha component, which dominates at rest, and an increase in the representation of high-frequency oscillations of the alpha range, beta and gamma activity.

Rice. 62. Alpha-rhythm blockade - desynchronization reaction in the cortex

hemispheres at the first presentation of a new stimulus -

tone (marked on the top line). Leads are labeled to the left of

curves (here and in subsequent figures, odd numbers - left,

even numbers - right hemisphere). GSR - galvanic skin response

The significance of functional associations of structures in selective attention was demonstrated in the study of the brain organization of directed modally specific attention in a situation of expectation of a certain perceptual task. Information about the modality of the stimulus subjected to binary classification, which the subject received in advance, led to the formation in the cortex of the left hemisphere of functional associations at the frequency of the alpha rhythm in the period immediately preceding perceptual activity, with the center of integration in the area of ​​the cortical projection zone of the corresponding modality - in the temporal zone when waiting for an auditory task, in the sensorimotor cortical zone with a tactile one, in the occipital zone with a visual one. It is significant that it was precisely this organization of pre-stimulus attention that contributed to the correct solution of the problem (Fig. 63). The activity of the right hemisphere in this situation is not related to providing the correct answer while waiting for the task.

Age features of the structural and functional organization of attention. Signs of involuntary attention are detected already in the neonatal period in the form of an elementary orienting reaction to the emergency use of a stimulus. This reaction is still devoid of a characteristic research component, but it is already manifested in certain changes in the electrical activity of the brain, vegetative reactions (changes in breathing, heart rate).

At the age of 2-3 months, the orienting reaction acquires the features of an exploratory character. In infancy, as well as at the beginning of preschool age, cortical generalized activation is not represented by blockade of the alpha rhythm, but by an increase in the theta rhythm, reflecting the increased activity of limbic structures associated with emotions. Features of activation processes determine the specifics of voluntary attention at this age: the attention of a small child is attracted mainly by emotional stimuli. As the speech perception system matures, a social form of attention is formed, mediated by speech instruction. However, up to the age of 5, this form of attention is easily pushed aside by involuntary attention arising in response to new attractive stimuli.

GROWTH OF THE COHERENCE OF ALPHA OSCILLATIONS IN THE SITUATION OF PRE-STIMULAL ATTENTION

Rice. 63. Specificity of the functional organization of the structures of the left and right hemispheres in a situation of pre-stimulus selective attention. Leads are marked on the diagrams. The lines connect the areas of the cortex, in the activity of which there is a significant increase in the values ​​of Cog of the alpha rhythm before the correct answer compared to the wrong one. LP - left, PP - right hemisphere

Significant changes in the cortical activation underlying attention were noted at the age of 6-7 years. A mature form of cortical activation is found in the form of a generalized blockade of the alpha rhythm. The role of speech instruction in the formation of voluntary attention is growing significantly. At the same time, the importance of the emotional factor is still great at this age.

Qualitative changes in the formation of neurophysiological mechanisms of voluntary attention are associated with the structural and functional maturation of the frontal cortex, which ensures the organization of local regulated activation processes in accordance with decision making based on the analyzed information, motivation, or verbal instructions. As a result, certain brain structures are selectively included in the activity, the activity of others is inhibited, and conditions are created for the most economical and adaptive response.

The most important stage in the organization of voluntary attention is the primary school age. At the age of 7-8 years, the insufficient maturity of the frontal-thalamic system of regulation of activation processes determines a greater degree of their generalization and a less pronounced selectivity of the association of cortical zones into working functional constellations in a situation of pre-stimulus attention that precedes a concretely implemented activity. By the age of 9-10, the mechanisms of voluntary regulation are being improved: activation processes become more manageable, determining the improvement in the performance of the organization of activities.

The role of various brain structures in the need-emotional sphere

needs and motivations. Needs are an internal source of active interaction of the organism with the external environment and are considered as the main determinant of behavior aimed at achieving a specific goal. IP Pavlov introduced the concept of "goal reflex" as an expression of the desire of a living organism to possess something - food, various objects. The scope of human needs is very wide. It includes both biological and social and spiritual needs.

Biological needs are associated with the activity of the nerve centers of the hypothalamus. In experiments on animals with electrodes implanted in various nuclei of the hypothalamus, it was noted that in a hungry animal, the electrical activity of certain parts of the hypothalamus sharply increased. Upon saturation, the amplification of the electrical activity of these structures ceased. Their irritation was caused by food search behavior. When other nuclei were stimulated, food refusal, sexual arousal, and aggressive-defensive behavior were observed.

Human biological needs are different from animals. Their implementation is not immediate and is largely determined by social and cultural factors. This indicates that even the biological needs of a person are under the control of the regulatory structures of the cerebral cortex. The need that is being updated, the most significant at the moment, acquiring all the properties of the dominant, is called motivation. According to the theory of the dominant by A.A. Ukhtomsky, it subjugates the activity of the organism, ensuring the priority of this behavioral act and suppressing other types of activity.

Experiments with the creation of an artificial dominant have shown that, against its background, the sensitivity of neural systems in structures covered by the dominant state, the speed of the processes occurring in them, and convergent abilities increase. Motivation acts as a trigger mechanism for the formation of a functional system, activating the structures involved in afferent synthesis, decision making, program development and its correction based on the results of action.

Motivation is realized with the direct participation of the hypothalamus and other parts of the limbic system, where, along with the main centers associated with biological needs, there are structures involved in the assessment and regulation of the stages of behavior aimed at satisfying the need. The cerebral cortex, which organizes active search behavior, is also involved in the general multilevel system for the implementation of motivation.

Emotions, their physiological basis. Emotions are closely connected with the motivational-need sphere. Emotions are considered as a mental process that is actively involved in the modulation of the functional state of the brain and the organization of behavior aimed at meeting actual needs. At the same time, emotions reflect a subjective attitude to the outside world, people around, oneself, one's own activity and its result.

The brain organization of emotions was studied in experiments on animals with the destruction and irritation of various subcortical structures, as well as in the clinic of local brain lesions in humans. The most striking effects were obtained with stimulation of certain nuclei of the hypothalamus, which evoked emotional reactions of various signs. Stimulation of the zones of the lateral hypothalamus led to the desire of animals (rats) to prolong this state by self-irritation. Irritation of other centers of the hypothalamus caused an avoidance reaction. Areas of the brain whose stimulation led to reinforcement and avoidance were called centers of pleasure and displeasure, with positive and negative emotional coloring, respectively. Emotional reactions of different signs were also obtained with stimulation of other parts of the limbic system.

As mentioned above, the limbic structures are part of the modulating system of the brain, and this determines the important role of emotions in the regulation of activation processes - generalized and local activation, and, consequently, in the organization of behavioral reactions.

The brain organization of emotions, like others mental functions, multilevel. The limbic system has connections with association areas of the neocortex.

IN clinical research revealed the specific role of the frontal and temporal cortex in the manifestation of emotions. With different types of damage to the frontal lobes, deep disturbances of the emotional sphere were noted, affecting mainly higher emotions associated with social relations, arbitrary activity, creativity. There was a disinhibition of drives, instability of the emotional background from depression to euphoria.

With temporal lesions, especially on the right, the recognition of the emotional intonation of speech is impaired.

The unequal role of associative departments in emotional regulation is revealed. So, it is shown that with right-sided lesions, a state of euphoria and carelessness arises. Left-sided lesions lead to a predominance of concern and anxiety: patients are restless and often cry.

Based on these data, an idea arose about the predominant connection of the right hemisphere with a negative emotional background, and the left hemisphere - with a positive one.

Age features of the need-emotional sphere of the child. From the first months of life, children have a very great need for novelty. Satisfying the need for novelty causes positive emotions, and those, in turn, stimulate the activity of the central nervous system. According to P.V. Simonov, emotion, compensating for the lack of information necessary to achieve the goal, ensures the continuation of actions, contributes to the search for new information, and thereby increases the reliability of a living system.

The emotions of children due to the weakness of control by the higher parts of the central nervous system are unstable, their external manifestations are unrestrained. The child cries easily and quickly, and just as quickly can go from crying to laughter. With joy, the child laughs loudly, screams, waves his arms. With age, as the cerebral cortex matures and its influence on the underlying subcortical structures intensifies, the restraint of emotional manifestations increases. The close connection of emotions with needs determines the need to take into account age features emotional sphere of the child in the process of education. Education can significantly influence even biological, innate needs, change the degree and forms of their manifestation. Even greater is the role of upbringing in the formation of socially conditioned, including cognitive, needs. Expanding the sphere of need with the help of targeted educational activities closely related to emotions at the stage of development, which is characterized by increased emotional activation, will help expand the range of external influences that attract attention, and thereby lead to the improvement of cognitive processes and purposeful activity of the child.

The maturation of the higher parts of the central nervous system at primary school age expands the possibility of forming cognitive needs and contributes to the improvement of the regulation of emotions.

Neurophysiological mechanisms of attention

Attention is one of the most important psychophysiological functions that ensure the optimization of the processes of education and training. Attention increases the level of activation of the cerebral cortex. Signs of involuntary attention are detected already in the neonatal period in the form of an elementary orienting reaction to the emergency use of a stimulus.

The critical period in the formation of involuntary attention is 2-3 months of age - the orienting reaction acquires the features of an exploratory nature. In the chest, as well as in the younger preschool age the attention of a small child is attracted mainly by emotional stimuli. As the speech perception system is formed, a social form of attention is formed, mediated by speech instruction. However, up to the age of five, this form of attention is easily pushed aside by involuntary attention to new attractive stimuli. Significant changes in the cortical activation underlying attention were noted at 6-7 years of age. The role of speech instruction in the formation of voluntary attention is growing significantly. Qualitative shifts in the formation of neurophysiological mechanisms of attention were noted at the age of 9-10 years. At the beginning of adolescence (12-13 years old), neuroendocrine shifts associated with the onset of puberty lead to a change in the cortical-subcortical interaction, a weakening of the cortical regulatory influences on activation processes - attention is weakened, the mechanisms of voluntary regulation of the function are violated. By the end of adolescence, with the completion of puberty, the neurophysiological mechanisms of attention correspond to those of an adult.

Physiological mechanisms of memory

The most important property of the nervous system is the ability to accumulate, store and reproduce incoming information. The accumulation of information occurs in several stages. In accordance with the stages of memorization, it is customary to allocate short-term and long-term memory. If information stored in short-term memory is not transferred to long-term memory, then it is quickly erased. In long-term memory, information is stored for a long time in an accessible form for retrieval. A qualitative feature of human memory, which distinguishes it from the memory of animals, is that a person is able to remember not so much all the details of information as general provisions. This is a human verbal-logical abstract memory.

Mechanisms of memory undergo significant changes with age. The relative simplicity of the memory system in childhood determines the stability and strength of the conditioned reflexes developed in early childhood. With the structural and functional maturation of the brain, a significant complication of the memory system occurs. At primary school age, the amount of memory increases significantly, and the speed of memorization decreases, then increasing by adolescence.

Motivation and emotions

Motivation is an active state of brain structures that induces to perform actions (acts of behavior) aimed at satisfying one's needs. Motivations create the necessary prerequisites for behavior. Motivations can be created both by biological needs and by higher cognitive needs. Emotions are inextricably linked to motivation. Achieving a goal and satisfying a need causes positive emotions. Failure to achieve goals leads to negative emotions. One of the most important human needs is the need for information. This source of positive emotions is inexhaustible throughout a person's life. Emotions change the state of the whole organism. The role of emotions is especially great in childhood, when the processes of cortical emotional activation dominate. Children have a very high need for novelty. Satisfying the need for novelty contributes to positive emotions, and those, in turn, stimulate the activity of the central nervous system. The maturation of the higher parts of the central nervous system at primary school age expands the possibility of forming cognitive needs and contributes to the improvement of the regulation of emotions. The emotions of children due to the weakness of control from the higher parts of the central nervous system are unstable, their external manifestations are unrestrained. With age, restraint of emotional manifestations increases.

Neurophysiological mechanisms of sleep

Necessary condition The life of the human body is the alternation of wakefulness and sleep. In the waking state, a person actively interacts with the external environment, perceives the signals of the surrounding world and responds with adequate reactions. Sleep is a state characterized by a significant weakening of ties with the outside world. Sleep plays the role of a recovery process. Sleep is essential for normal mental activity. I.P. Pavlov regarded sleep as a protective inhibition that spread in the higher parts of the nervous system.

The sleep state can be divided into three functional types:

1. Falling asleep (drowsiness).

2. Slow sleep - sleep is light, of medium depth (very important for rest, lasts 80-90 minutes) and deep, accompanied by a decrease in muscle tone, general level of activity, and activity of internal organs.

3. REM or paradoxical sleep - dreams appear, vegetative functions are activated. This stage of sleep is associated with the restoration of brain metabolism, processing of information, fixing it in long-term memory, stimulation of nervous growth and development. REM sleep in adults takes 25% of the total sleep period, in newborns - 65-85%.

Basic concepts

Perception- a complex active process, including the analysis and synthesis of incoming information.

Motivation- active states of brain structures that encourage to perform actions (acts of behavior) aimed at satisfying one's needs.

Mobility of excitation and inhibition processes- the speed at which excitation can be replaced by inhibition, and vice versa.

Dream- protective inhibition, spread in the higher parts of the nervous system.

Equilibrium- the ratio of the strength of the processes of excitation and inhibition.

Test 3

1. What does not apply to indicators of types of higher nervous activity?

A. the strength of the processes of excitation and inhibition

B. balance of excitation and inhibition processes

C. mobility of the processes of excitation and inhibition

D. regularity of excitation and inhibition processes

2. What type of higher nervous activity is characterized as

strong but unbalanced?

A. unrestrained

C. calm

D. inert

3. At what age do the first signs of the development of the second

signal system?

A. in primary school age

B. aged 1 to 3 years

C. in the second half of the first year of life

D. in early preschool years

4. What type of children are characterized by high emotional excitability?

A. strong, balanced, fast

B. strong, unbalanced, unrestrained

C. strong, balanced, slow

D. weak with reduced excitability

5. In what zones does the synthesis of information into sensory

complexes?

A. in primary projection areas

B. in secondary projection areas

C. in different cortical areas

D. in analyzer coverage areas

6. What age is the sensitive period for the development of visual

perception?

A. juvenile

B. preschool

C. junior school

D. adolescent

7. At what age are there qualitative changes,

underlying neurophysiological mechanisms of attention?

8. What characterizes primary school age in terms of memory?

a. simplicity of memory system

B. increasing the speed of memorization

C. memory growth

D. instability of conditioned reflexes

9. What improves emotion regulation?

A. dominance of cortical emotional activation processes

B. meeting the need for information

C. having a need for novelty

D. maturation of the higher parts of the central nervous system

10. At what stage of sleep do dreams appear?

A. REM sleep

B. light sleep

C. deep sleep

D. slow sleep

Similar information.

Orientation response (OR) was first described by I.P. Pavlov as a motor reaction of an animal to a new, suddenly appearing stimulus. It included a turn of the head and eyes in the direction of the stimulus and was necessarily accompanied by inhibition of the current conditioned reflex activity. Another feature of the OR was the extinction of all its behavioral manifestations upon repetition of the stimulus. The extinguished EP was easily restored at the slightest change in the situation (see Reader 6.2).

Physiological indicators of OR. The use of polygraphic registration showed that OR causes not only behavioral manifestations, but also a whole range of vegetative changes. Reflection of these Generalized - widespread.");" onmouseout="nd();" href="javascript:void(0);"> generalized changes are the various components of OR: motor (muscular), cardiac, respiratory, galvanic skin, vascular, pupillary, sensory and electroencephalographic (see topic 2). As a rule, when a new stimulus is presented, the Muscle tone is a weak muscle tension that exists almost all the time, preventing complete relaxation of the body and helping to maintain a certain posture.");" onmouseout="nd();" href="javascript:void(0);">muscle tone, the frequency of respiration, pulse changes, the electrical activity of the skin increases, the pupils dilate, sensory thresholds decrease. In the electroencephalogram, at the beginning of the orienting reaction, a generalized activation occurs, which manifests itself in the blockade (suppression) Alpha rhythm - the main rhythm of the electroencephalogram in a state of relative rest, with a frequency in the range of 8 - 14 Hz and an average amplitude of 30 - 70 μV. ");" onmouseout="nd();" href="javascript:void(0);">rhythm alpha and change it with high-frequency activity. At the same time, it becomes possible to unite and synchronize the work of nerve cells not according to the principle of their spatial proximity, but according to the functional principle. Thanks to all these changes, a special state of mobilization readiness of the body arises.
More often than others, in experiments aimed at studying OR, indicators of the galvanic skin response (GSR (galvanic skin response)) are used - a change in the electrical activity of the skin; it is measured in two versions based on an assessment of the electrical resistance or conductivity of various skin areas; it is used in the diagnosis of functional conditions and emotional reactions of a person. onmouseout="nd();" href="javascript:void(0);">GSR ). It has a special sensitivity to the novelty of the stimulus; it is modally nonspecific, i.e. does not depend on what kind of stimulus causes the OR. In addition, GSR quickly fades, even if the RR is caused by a painful stimulus. However, GSR is closely related to the emotional sphere, so the use of GSR in the study of OR requires a clear separation of the actual indicative and emotional components of response to a new stimulus.

Nervous stimulus model. The mechanism of occurrence and extinction of OR was interpreted in the concept of the nervous model of the stimulus proposed by E.N. Sokolov. According to this concept, as a result of the repetition of a stimulus, a "model" is formed in the nervous system, a certain configuration of the trace, in which all the parameters of the stimulus are fixed. Orienting reaction - (reflex) - a type of unconditioned reflex caused by any unexpected change in the situation. ");" onmouseout="nd();" href="javascript:void(0);"> Approximate reaction occurs in those cases when a mismatch is detected between the current stimulus and the formed trace, i.e. "neural model". If the current stimulus and the neural trace left by the previous stimulus are identical, then OR does not occur. If they do not coincide, then the orienting reaction arises and becomes, to a certain extent, the stronger, the more the previous and new stimuli differ. Since the OR arises as a result of a mismatch between the afferent stimulus and the "nervous model" of the expected stimulus, it is obvious that the OR will last as long as this difference exists.
In accordance with this concept, the RR should be fixed at any appreciable discrepancy between two sequentially presented stimuli. There are, however, numerous facts that indicate that OR does not always necessarily arise when the parameters of the stimulus change.

The importance of the stimulus. The orienting reflex is associated with the adaptation of the body to changing environmental conditions, therefore, the "law of force" is valid for it. In other words, the more the stimulus changes (for example, its intensity or degree of novelty), the greater the response. However, insignificant changes in the situation can cause no less, and often a greater reaction, if they are directly addressed to the basic needs of a person.
It seems that a stimulus that is more significant and, therefore, in some way already familiar to a person, should, other things being equal, cause a smaller RR than an absolutely new one. The facts, however, speak otherwise. The significance of the stimulus is often decisive for the occurrence of OR. A highly significant stimulus can produce a powerful orienting response with little physical intensity.

Almost all incentives pass the first level of evaluation, the second and third registers work in parallel. After passing through any of these two registers, the stimulus enters the last one and its significance is evaluated there. Only after this final act of evaluation does the whole complex of the orienting reaction develop.
Thus, the OR does not arise for any new stimulus, but only for one that is preliminarily assessed as biologically significant. Otherwise, we would experience OR every second, since new stimuli act on us constantly. When evaluating OR, therefore, it is necessary to take into account not the formal amount of information contained in the stimulus, but the amount of semantic, meaningful information.
Something else is also essential: perception meaningful incentive often accompanied by the formation of a response Adequate - equal, identical, appropriate.");" onmouseout="nd();" href="javascript:void(0);">adequate reactions. The presence of motor components indicates that the OR provides a unity of perceiving and executive mechanisms. Thus, OR, traditionally considered as a reaction to a new stimulus, is a special case of orienting activity, which is understood as the organization of new types of activity, the formation of activity in changed environmental conditions (see Reader 6.1).

6.2. Neurophysiological mechanisms of attention

One of the most outstanding achievements Neurophysiology is a branch of physiology whose object of study is the nervous system. onmouseout="nd();" href="javascript:void(0);"> neurophysiology in the twentieth century was the discovery and systematic study of the functions of the nonspecific system of the brain, which began with the appearance in 1949 of the book by G. Moruzzi and G. Magun "The reticular formation of the brain stem and the activation reaction in the EEG."
The reticular formation, along with the limbic system, form a block. The modulating system of the brain - specific activating and inactivating structures localized at different levels of the central nervous system and regulating the functional states of the body, in particular, activation processes in activity and behavior. ");" onmouseout="nd();" href="javascript:void(0);"> modulating systems of the brain, the main function of which is the regulation of the functional states of the body (see topic 3 p. 3.1.3). Initially, only reticular formations of the brain stem were classified as a non-specific system of the brain, and their main task was considered diffuse Generalized - widespread.");" onmouseout="nd();" href="javascript:void(0);"> generalized activation of the cerebral cortex. By modern ideas, the ascending nonspecific activating system extends from the medulla oblongata to the thalamus.

Functions of the thalamus. The thalamus, which is part of the diencephalon, has a nuclear structure. It consists of specific and non-specific nuclei. Specific nuclei process all sensory information entering the body, therefore the thalamus (visual tubercle) is a subcortical structure formed by two large groups of nuclei located on both sides of the 3rd ventricle and interconnected by a gray commissure. The thalamus serves as a kind of distributor for information from receptors, which it integrates, interprets and then transmits to the brain. ");" onmouseout="nd();" href="javascript:void(0);">The thalamus is figuratively called a collector of sensory information. The specific nuclei of the thalamus are mainly associated with the primary projection zones. The analyzer is a functional formation of the central nervous system that perceives and analyzes information about phenomena occurring in the external environment and in the body itself. A. consists of a peripheral receptor, nerve pathways, a central section of the cerebral cortex responsible for the activity of this analyzer. ");" onmouseout="nd();" href="javascript:void(0);">parsers . Non-specific nuclei direct their ascending pathways to Associative zones of the cortex - zones that receive information from receptors that perceive irritation of various modalities, and from all projection zones. ");" onmouseout="nd();" href="javascript:void(0);">associative areas of the cerebral cortex. In 1955, G. Jasper formulated the idea of ​​a diffuse-projective thalamic system. Based on a number of facts, he argued that the diffuse projection thalamic system (nonspecific thalamus), within certain limits, can control the state of the cortex, exerting both excitatory and inhibitory effects on it.
Animal experiments have shown that when the nonspecific thalamus is stimulated, an activation reaction occurs in the cerebral cortex. This reaction is easy to observe when registering an encephalogram, however Activation - excitation or increased activity, transition from a state of rest to an active state. onmouseout="nd();" href="javascript:void(0);">activation of the cortex upon stimulation of the nonspecific thalamus has a number of differences from the activation that occurs upon stimulation of the reticular formation of the brain stem.

Table 6.1.

Activation reactions of brain structures

Functions of frontal zones. The reticular formation is a network-like formation, a set of nerve structures located in the central parts of the brain stem (in the medulla oblongata, midbrain and diencephalon). In the area of ​​R.f. there is an interaction of both ascending - afferent, and descending - efferent impulses entering it. ");" onmouseout="nd();" href="javascript:void(0);"> Reticular formation brainstem and nonspecific thalamus are closely related to the cerebral cortex. A special place in the system of these connections is occupied by the frontal zones of the cortex. It is assumed that the excitation of the reticular formation of the brain stem and nonspecific thalamus spreads along direct ascending pathways to the anterior cortex. Upon reaching a certain level of excitation of the frontal zones along the descending pathways leading to the reticular formation and the thalamus, an inhibitory effect is carried out. In fact, there is a self-regulation circuit here: the reticular formation initially activates the frontal cortex, which, in turn, inhibits (reduces) the activity of the reticular formation. Since all these influences are gradual in nature, i.e. change gradually, then with the help of bilateral connections, the frontal zones of the cortex can provide exactly the level of excitation that is required in each specific case.
Thus, the frontal cortex is the most important regulator of the state of wakefulness in general and attention as a selective process. It modulates the activity of the stem and thalamic systems in the right direction. Thanks to this, we can talk about such a phenomenon as controlled cortical activation.

The attention system in the human brain. The scheme outlined above does not exhaust all ideas about the brain provision of attention. She characterizes general principles neurophysiological organization of attention and is addressed mainly to the so-called modal non-specific attention. A more detailed study allows us to specialize attention by highlighting its modal-specific types. The following types of attention can be described as relatively independent: sensory (visual, auditory, tactile), motor, emotional and intellectual. The clinic of focal lesions shows that these types of attention can suffer independently of each other and different parts of the brain are involved in their provision. In maintaining modal-specific types of attention, the cortical zones directly related to the provision of the corresponding mental functions () take an active part.
The well-known researcher of attention M. Pozner argues that in the human brain there is an independent system of attention, which is anatomically isolated from the systems for processing incoming information. Attention is maintained through the work of different anatomical zones that form a network structure, and these zones perform different functions that can be described in cognitive terms. Moreover, a number of functional subsystems of attention are distinguished. They provide three main functions: targeting sensory events, detecting a signal for focal (conscious) processing, and maintaining vigilance, or the waking state. In providing the first function, the posterior parietal region and some nuclei of the thalamus play an important role, the second - lateral and Medial - median, located closer to the median plane of the body. ");" onmouseout="nd();" href="javascript:void(0);">medial sections of the frontal cortex. Maintaining vigilance is provided by the activity of the right hemisphere.
Indeed, a lot of experimental data testifies to the different contribution of the hemispheres to ensuring not only perception, but also selective attention. According to these data, the right hemisphere mainly ensures the general mobilization readiness of a person, maintains the necessary level of wakefulness and is relatively little associated with the characteristics specific activity. The left is more responsible for the specialized organization of attention in accordance with the characteristics of the task.

6.3. Methods for studying and diagnosing attention

Experimental study of the physiological correlates and mechanisms of attention is carried out at different levels, starting from the nerve cell and ending with the bioelectrical activity of the brain as a whole. Each of these levels of research forms its own ideas about the physiological foundations of attention.

Neurons of novelty. The most interesting facts illustrating the functions of neurons in the mechanisms of attention are related to the provision Orienting reaction - (reflex) - a type of unconditioned reflex caused by any unexpected change in the situation. ");" onmouseout="nd();" href="javascript:void(0);"> indicative reaction. Back in the 60s. G. Jasper during neurosurgical operations isolated special neurons in the human thalamus - "detectors" of novelty, or attention, which reacted to the first presentation of stimuli.
Later, nerve cells were isolated in neural networks, called neurons of novelty and identity (). Novelty neurons allow you to highlight new signals. They differ from others in a characteristic feature: their background impulsation increases under the action of new stimuli of different Modality - a kind of sensations (for example, touch, sight, smell, etc.). ");" onmouseout="nd();" href="javascript:void(0);">modalities. With the help of multiple connections, these neurons are connected to the detectors of individual areas of the cerebral cortex, which form plastic excitatory synapses on novelty neurons. Thus, under the action of new stimuli, the impulse activity of novelty neurons increases. As the stimulus is repeated, and depending on the strength of the excitation, the response of the novelty neuron is selectively suppressed, so that additional Activation - excitation or increased activity, transition from a state of rest to an active state. onmouseout="nd();" href="javascript:void(0);">activation only background activity disappears and remains in it.
The identity neuron also has background activity. To these neurons through plastic Synapses are places of functional contacts formed by neurons.");" onmouseout="nd();" href="javascript:void(0);">synapses pulses are received from detectors of different modalities. But unlike novelty neurons, in identity neurons, communication with detectors is carried out through inhibitory synapses. Under the action of a new stimulus, the background activity in identity neurons is suppressed, and under the action of habitual stimuli, on the contrary, it is activated.
So, a new stimulus excites novelty neurons and inhibits identity neurons, thus a new stimulus stimulates the activating system of the brain and suppresses Synchronization - consistency of encephalogram rhythms in frequency or phase during EEG registration from different areas of the cerebral cortex or other brain formations. ");" onmouseout="nd();" href="javascript:void(0);"> synchronizing(brake) system. The habitual stimulus acts in the exact opposite way - by increasing the work of the inhibitory system, it does not affect the activating one.
Features of the impulse activity of human neurons during the performance of psychological tests that require the mobilization of voluntary attention are described in the works of N.P. Bekhtereva and her staff. At the same time, in the anterior parts of the thalamus and a number of other structures of the nearest subcortex, rapid emerging bursts of impulse activity were recorded, the frequency of which was 2–3 times higher than the background level. Characteristically, the described changes in the impulse activity of neurons persisted throughout the entire test, and only upon its completion did the level of activity of these neurons return to the initial one.
In general, these studies found that various forms of human cognitive activity, accompanied by a strain of voluntary attention, are characterized by a certain type of neuronal activity, clearly comparable with the dynamics of voluntary attention.

Electroencephalographic correlates of attention. It is well known that upon presentation of a stimulus, the encephalogram exhibits suppression (blockade) Alpha rhythm - the main rhythm of the electroencephalogram in a state of relative rest, with a frequency in the range of 8 - 14 Hz and an average amplitude of 30 - 70 μV. ");" onmouseout="nd();" href="javascript:void(0);">rhythm alpha and is replaced by an activation reaction. However, this does not exhaust changes in the electrical activity of the brain in a situation of attention.
The study of the total electrical activity during the mobilization of intellectual attention revealed regular changes in the nature joint activities different areas of the cortex. When assessing the degree of distant synchronization of biopotentials, it was found that in the anterior zones of the left hemisphere, the level of spatial synchronization significantly increases compared to the background. Similar results are obtained by using another indicator extracted from the encephalogram - coherence (see topic 2, paragraph 2.1.1). In the situation of waiting for a stimulus, regardless of its modality, there is an increase in coherence in the alpha rhythm band, and mainly in the anterior (premotor) cortical zones. High indicators of distant synchronization and coherence indicate how closely the cortical zones, primarily the anterior parts of the left hemisphere, interact in providing voluntary attention.

Studying attention with the help of VP. The first studies of attention using the EP method used simple behavioral models, such as stimulus counting. At the same time, it was found that drawing the attention of the subjects to the stimulus is accompanied by an increase in the amplitude of the EP components and a reduction in their latency. On the contrary, distraction of attention from the stimulus is accompanied by a decrease in the EP amplitude and an increase in latency. However, it remained unclear what caused these changes in EP parameters: a change in the general level of activation, maintenance of vigilance, or mechanisms of selective attention. To breed these processes, it was necessary to design the experiment in such a way that its organization would allow isolating the effect of selective attention mobilization in a "pure" form.
As such a model, one can cite the experiments of S. Hilliard, who received in the 70s. widespread fame. When sound stimuli are presented through headphones to the left and right ears, the subject is asked to mentally respond (count) rare ("target") stimuli coming through one of the channels (only to the right or left ear). As a result, evoked potentials are obtained - bioelectric oscillations that occur in nervous structures in response to receptor stimulation and are in a strictly defined temporal connection with the moment the stimulus is presented. ");" onmouseout="nd();" href="javascript:void(0);"> evoked potentials in response to 4 variants of stimuli: frequently encountered in the relevant (controlled) and irrelevant (ignored) channels and rarely encountered (targeted) in both channels. In this case, it becomes possible to compare the effects of the channel and the stimulus that are the object of attention. In experiments of this type, as a rule, very short intervals between stimuli are used (slightly more or less than one second), as a result, the intensity and stability of the subject's selective attention to rapidly alternating stimuli of different informational significance increases.

Auditory evoked potentials, reflecting the attraction of selective attention to one of the channels in the situation of distinguishing sound signals (700 or 300 Hz) (according to H. Hansen & S. Hillyard, 1982). High- and low-frequency tones were presented in a random order (approximately three times per second). The subjects each time paid attention to only one channel, trying to identify signal stimuli that had a long duration of EP in the channel to which attention was drawn, had a pronounced negative wave. This wave clearly appears when the response to the signal stimulus is subtracted from the response to the non-signal stimulus - in Fig. on right.

It was found that drawing attention to one of the channels leads to an increase in the amplitude of the first negative wave with a latent period of about 150 ms, designated as the N1 component. The target stimuli were accompanied by the appearance of a late positive P3 oscillation in the EP composition with a latent period of about 300 ms. It was suggested that the negative wave N1 reflects the “attitude” to the stimulus, which determines the direction of voluntary attention, and the P3 component reflects the “attitude toward the response”, associated with the choice of the answer option. Subsequently, the P3 component (more often defined as P300) has been the subject of many studies (see Topic 10).
In later studies, using a special technique for subtracting potentials recorded in response to signal and standard stimuli, it was found that the first negative wave N1 is an inhomogeneous cortical phenomenon of complex structure, in which one can distinguish a special negative oscillation, the so-called "negativity, reflecting information processing". This oscillation with a latent period of about 150 ms and a duration of at least 500 ms is recorded when a rarely presented target stimulus does not coincide with the "trace of attention" formed in Associative zones of the cortex - zones that receive information from receptors that perceive irritation of various modalities, and from all projection zones. ");" onmouseout="nd();" href="javascript:void(0);">associative auditory zone and frontal region with frequent repetition and reproduction of a standard stimulus. At the same time, the smaller the difference between these stimuli, the longer the latent period and the longer the negative oscillation that develops in response to the target, non-standard stimulus.
In addition, another negative fluctuation is described, which in some cases accompanies the situation of comparing stimuli. This component, referred to as " Mismatch negativity is a component of evoked or event-related potentials that characterizes the processes of involuntary attention.");" onmouseout="nd();" href="javascript:void(0);"> mismatch negativity", occurs in the auditory cortex with a latent period of 70-100 ms and reflects the automatic process of comparing the physical signs of a sound stimulus with a trace of a standard stimulus stored for 5-10 seconds in sensory memory. physical properties of the stimulus from the trace of the repeatedly presented standard stimulus, "negativity of mismatch" develops.
It is assumed that both components ("negativity associated with information processing" and "negativity of mismatch") can participate in the formation of wave N1. Moreover, the first of these components is associated with a preconscious, involuntary assessment of the signs of an unusual sound stimulus, carried out by comparing them with the nervous model of a frequently repeated stimulus, and the second component reflects the processes of processing sensory information at the conscious level, namely: voluntary attention, focusing the subject's consciousness on certain critical signs of the stimulus and comparing it with the "trace of attention" stored in working memory.
Thus, using the EP method, it was shown that two types of components arise in response to target sound stimuli (in the situation of choosing a stimulus and a channel), one of which reflects the processes of sensory memory, the other reflects selective attention.

Temporal characteristics of attention. Using the EP method, one can assess the dynamics of the development of attention processes in real time. The question is, at what stage of information processing are attention processes activated? Since the beginning of the first negative wave that occurs in response to signal stimuli is mainly timed to 50 ms from the moment of stimulus presentation, the fifty-millisecond boundary was considered for quite a long time as a time limit after which the processes of selective attention unfold.
More detailed studies, however, have shown that in the auditory and, apparently, somatosensory systems, voluntary regulation of the processing of incoming information is switched on no later than after 20-30 seconds. after presentation of the stimulus. The effects of attention in the visual system reveal themselves later, starting from 60 ms. It is possible that these time limits will be changed as the methods of study improve. The bottom line, however, is that the chronometry of information processing processes is a set of methods for measuring the duration of individual stages in the process of information processing based on measuring physiological indicators, in particular, the latent periods of the components of evoked and event-related potentials.");" onmouseout="nd();" href="javascript:void(0);">chronometry of information processing and inclusion of attention as one of the main regulators of this process can be studied with such accuracy only in psychophysiological experiments.

Glossary of terms

1. orienting reaction
2. brain modulating system
3. activation
4. reticular formation
5. evoked potentials
6. mismatch negativity
7. chronometry of information processing processes

Questions for self-examination

1. What are the functions of novelty neurons?
2. How do generalized and local activation differ?
3. How is "setting to a stimulus" and "setting to a response" reflected in the parameters of evoked potentials?
4. What is the function of the frontal lobes of the brain in providing attention?

Bibliography

1. Danilova N.N., Krylova A.L. Physiology of higher nervous activity. M.: MGU, 1989.
2. Dubrovinskaya N.V. Neurophysiological mechanisms of attention. L.: Nauka, 1985.
3. Kochubey B.I. On the definition of the concept of orienting reaction in humans. / Questions of psychology. 1979. N 3.
4. Machinskaya R.M., Machinsky N.O., Deryugina E.I. Functional organization of the right and left hemispheres of the human brain with directed attention // Human Physiology. 1992. T. 18. N 6.
5. Naatanen R., Alho K., Soames M. Brain mechanisms of selective attention // Cognitive Psychology. Moscow: Nauka, 1986.
6. Neurophysiological mechanisms of attention // Ed. E.D. Khomskoy, M.: MGU, 1979.
7. Sokolov E.N. Nervous stimulus model and orienting reflex. / Questions of psychology. 1960. No. 4.
8. Suvorov N.F., Tairov O.P. Psychophysiological mechanisms of selective attention. L.: Nauka, 1985.
9. Khomskaya E.D. The brain and activation. M.: MGU, 1973.

Topics of term papers and essays

1. Studies of the orienting reaction in the school of I.P. Pavlova.
2. Modern psychophysiological models of orienting reaction.
3. Studies of the reticular formation and activation reactions (G. Moruzzi - G. Magun and state of the art question).
4. Comparative analysis of modal-non-specific and modal-specific attention.
5. Electroencephalographic correlates of attention processes.

In the formation and implementation of the higher functions of the brain, the general biological property of fixing, storing and reproducing information, united by the concept of memory, is very important. Memory as the basis of learning and thinking processes includes four closely related processes: memorization, storage, recognition, reproduction. Throughout a person's life, his memory becomes a receptacle for a huge amount of information: over 60 years of active creative activity, a person is able to perceive 1013-10 bits of information, of which no more than 5-10% is actually used. This indicates a significant redundancy of memory and the importance of not only memory processes, but also the process of forgetting. Not everything that is perceived, experienced or done by a person is stored in memory, a significant part of the perceived information is forgotten over time. Forgetting manifests itself in the inability to recognize, recall something or in the form of erroneous recognition, recall. The reason for forgetting can be various factors associated both with the material itself, its perception, and with the negative influences of other stimuli acting immediately after memorization (the phenomenon of retroactive inhibition, memory suppression). The process of forgetting largely depends on the biological significance of the perceived information, the type and nature of memory. Forgetting in some cases can be positive character, such as memory for negative signals, unpleasant events. This is the truth of the wise oriental saying: “Fortunately, memory is a joy, oblivion, friend, burns.”

As a result of the learning process, physical, chemical and morphological changes occur in the nervous structures, which persist for some time and have a significant impact on the reflex reactions carried out by the body. The totality of such structural and functional changes in nerve formations, known as the "engram" (trace) of acting stimuli, becomes an important factor that determines the whole variety of adaptive adaptive behavior of the body.

Types of memory are classified according to the form of manifestation (figurative, emotional, logical, or verbal-logical), according to a temporal characteristic, or duration (instant, short-term, long-term).

Figurative memory is manifested by the formation, storage and reproduction of a previously perceived image of a real signal, its nervous model. Emotional memory is understood as the reproduction of some previously experienced emotional state upon repeated presentation of a signal that caused the initial occurrence of such an emotional state. Emotional memory is characterized by high speed and strength. This, obviously, is the main reason for the easier and more stable memorization of emotionally colored signals and stimuli by a person. On the contrary, gray, boring information is much more difficult to remember and quickly erased from memory. Logical (verbal-logical, semantic) memory is memory for verbal signals denoting both external objects and events, and the sensations and representations caused by them.

Instantaneous (iconic) memory consists in the formation of an instant imprint, a trace of the current stimulus in the receptor structure. This imprint, or the corresponding physical and chemical engram of an external stimulus, is distinguished by high information content, completeness of features, properties (hence the name "iconic memory", that is, a reflection clearly worked out in detail) of the active signal, but also by a high rate of extinction (it is not stored more than 100-150 ms if not reinforced, not reinforced by repeated or continued stimulus).

The neurophysiological mechanism of iconic memory obviously consists in the processes of reception of the current stimulus and the immediate aftereffect (when the real stimulus is no longer active), expressed in trace potentials formed on the basis of the receptor electrical potential. The duration and severity of these trace potentials is determined both by the strength of the current stimulus and by the functional state, sensitivity and lability of the perceiving membranes of receptor structures. Erasing the memory trace occurs in 100-150 ms.

biological significance iconic memory is to provide the analyzer structures of the brain with the ability to highlight individual features and properties of the sensory signal, image recognition. Iconic memory stores not only the information necessary for a clear idea of ​​sensory signals coming within fractions of a second, but also contains an incomparably larger amount of information than can be used and is actually used at the subsequent stages of perception, fixation and reproduction of signals.

With sufficient strength of the current stimulus, iconic memory passes into the category of short-term (short-term) memory. Short-term memory is a working memory that ensures the implementation of current behavioral and mental operations. The basis of short-term memory is repeated multiple circulation of impulse discharges through circular closed circuits of nerve cells. Ring structures can also be formed within the same neuron by return signals generated by the terminal (or lateral, lateral) branches of the axon process on the dendrites of the same neuron (IS Beritov). As a result of repeated passage of impulses through these ring structures, persistent changes gradually form in the latter, laying the foundation for the subsequent formation of long-term memory. Not only excitatory, but also inhibitory neurons can participate in these ring structures. The duration of short-term memory is seconds, minutes after the direct action of the corresponding message, phenomenon, object. The reverberation hypothesis of the nature of short-term memory allows for the presence of closed circles of circulation of impulse excitation both inside the cerebral cortex and between the cortex and subcortical formations (in particular, thalamocortical nerve circles) containing both sensory and gnostic (trained, recognizing) nerve cells. Intracortical and thalamocortical reverberation circles as the structural basis of the neurophysiological mechanism of short-term memory are formed by cortical pyramidal cells of layers V-VI of predominantly frontal and parietal areas of the cerebral cortex.

The participation of the structures of the hippocampus and the limbic system of the brain in short-term memory is associated with the implementation by these nerve formations of the function of distinguishing the novelty of signals and reading incoming afferent information at the input of the waking brain. The realization of the phenomenon of short-term memory practically does not require and is not actually associated with significant chemical and structural changes in neurons and synapses, since the corresponding changes in the synthesis of matrix (information) RNA require more time.

Despite the differences in hypotheses and theories about the nature of short-term memory, their initial prerequisite is the occurrence of short-term reversible changes in the physicochemical properties of the membrane, as well as the dynamics of neurotransmitters in synapses. Ionic currents across the membrane, combined with short-term metabolic shifts during synapse activation, can lead to a change in the efficiency of synaptic transmission lasting several seconds.

The transformation of short-term memory into long-term memory (memory consolidation) is generally due to the onset of persistent changes in synaptic conduction as a result of re-excitation of nerve cells (learning populations, ensembles of neurons according to Hebb). The transition of short-term memory to long-term memory (memory consolidation) is due to chemical and structural changes in the corresponding nerve formations. According to modern neurophysiology and neurochemistry, long-term (long-term) memory is based on complex chemical processes of the synthesis of protein molecules in brain cells. Memory consolidation is based on many factors that facilitate the transmission of impulses through synaptic structures (enhanced functioning of certain synapses, increasing their conductivity for adequate impulse flows). One of these factors can be the well-known phenomenon of post-tetanic potentiation, supported by reverberant impulse flows: stimulation of afferent nerve structures leads to a fairly long-term (tens of minutes) increase in the conductivity of spinal cord motoneurons. This means that the physicochemical changes in postsynaptic membranes that occur during a persistent shift in the membrane potential probably serve as the basis for the formation of memory traces, which are reflected in changes in the protein substrate of the nerve cell.

Changes observed in the mediator mechanisms that ensure the process of chemical transmission of excitation from one nerve cell to another have a certain significance in the mechanisms of long-term memory. Plastic chemical changes in synaptic structures are based on the interaction of mediators, such as acetylcholine, with receptor proteins of the postsynaptic membrane and ions (Na+, K+, Ca2+). The dynamics of transmembrane currents of these ions makes the membrane more sensitive to the action of mediators. It has been established that the learning process is accompanied by an increase in the activity of the cholinesterase enzyme, which destroys acetylcholine, and substances that inhibit the action of cholinesterase cause significant memory impairment.

One of the widespread chemical theories of memory is Hiden's hypothesis about the protein nature of memory. According to the author, the information underlying long-term memory is encoded and recorded in the structure of the polynucleotide chain of the molecule. The different structure of impulse potentials, in which certain sensory information is encoded in the afferent nerve conductors, leads to a different rearrangement of the RNA molecule, to specific movements of nucleotides in their chain for each signal. Thus, each signal is fixed in the form of a specific imprint in the structure of the RNA molecule. Based on Hiden's hypothesis, it can be assumed that glial cells involved in the trophic provision of neuron functions are included in the metabolic cycle of encoding incoming signals by changing the nucleotide composition of synthesizing RNA. The entire set of possible permutations and combinations of nucleotide elements makes it possible to fix a huge amount of information in the structure of an RNA molecule: the theoretically calculated amount of this information is 10 -1020 bits, which significantly overlaps the real amount of human memory. The process of fixing information in a nerve cell is reflected in protein synthesis, into the molecule of which the corresponding trace imprint of changes in the RNA molecule is introduced. In this case, the protein molecule becomes sensitive to a specific pattern of the impulse flow, thereby, as it were, it recognizes the afferent signal that is encoded in this impulse pattern. As a result, the mediator is released in the corresponding synapse, leading to the transfer of information from one nerve cell to another in the system of neurons responsible for fixing, storing and reproducing information.

A possible substrate for long-term memory is some peptides of a hormonal nature, simple protein substances, and a specific protein S-100. Such peptides that stimulate, for example, the conditioned reflex mechanism of learning, include some hormones (ACTH, somatotropic hormone, vasopressin, etc.).

An interesting hypothesis about the immunochemical mechanism of memory formation was proposed by I. P. Ashmarin. The hypothesis is based on the recognition of the important role of an active immune response in the consolidation and formation of long-term memory. The essence of this idea is as follows: as a result of metabolic processes on synaptic membranes during reverberation of excitation at the stage of formation of short-term memory, substances are formed that play the role of an antigen for antibodies produced in glial cells. The binding of an antibody to an antigen occurs with the participation of stimulators of the formation of mediators or an inhibitor of enzymes that destroy and break down these stimulating substances.

A significant place in the provision of neurophysiological mechanisms of long-term memory is given to glial cells (Galambus, A. I. Roitbak), the number of which in the central nervous formations is an order of magnitude greater than the number of nerve cells. The following mechanism of participation of glial cells in the implementation of the conditioned reflex mechanism of learning is proposed. At the stage of formation and strengthening of the conditioned reflex in the glial cells adjacent to the nerve cell, the synthesis of myelin is enhanced, which envelops the terminal thin branches of the axon process and thereby facilitates the conduction of nerve impulses along them, resulting in an increase in the efficiency of synaptic transmission of excitation. In turn, stimulation of myelin formation occurs as a result of depolarization of the oligodendrocyte (glial cell) membrane under the influence of an incoming nerve impulse. Thus, long-term memory may be based on associated changes in the neuro-glial complex of central nervous formations.

The possibility of selective exclusion of short-term memory without impairment of long-term memory and selective effect on long-term memory in the absence of any impairment of short-term memory is usually considered as evidence of the different nature of the underlying neurophysiological mechanisms. Indirect evidence of the presence of certain differences in the mechanisms of short-term and long-term memory are the features of memory disorders in case of damage to brain structures. So, with some focal lesions of the brain (lesions of the temporal zones of the cortex, structures of the hippocampus), when it is concussed, memory disorders occur, expressed in the loss of the ability to remember current events or events of the recent past (which occurred shortly before the impact that caused this pathology) while maintaining memory for the previous ones, events that happened a long time ago. However, a number of other influences have the same type of influence on both short-term and long-term memory. Apparently, despite some noticeable differences in the physiological and biochemical mechanisms responsible for the formation and manifestation of short-term and long-term memory, their nature has much more in common than different; they can be considered as successive stages of a single mechanism of fixation and strengthening of trace processes occurring in nervous structures under the influence of repetitive or constantly acting signals.