There are several basic conditions for the successful development of a conditioned reflex:
- 1. Coincidence in time (combination) of an indifferent (previously indifferent) signal, which causes only weak excitation in the cortex, with unconditional reinforcement.
- 2. Repeated combination of an indifferent stimulus with reinforcement is necessary.
- 3. Sufficient physiological strength (significance) of the unconditional signal (in any case, it should be greater than the physiological strength of the indifferent signal).
- 4. Absence of extraneous stimuli (there should be no strong external interference).
The formation of a classical conditioned reflex occurs in several stages (Fig. 3.1).
Rice. 3.1.
A - unconditioned salivation reflex in response to food; b - unconditional (indicative) reaction to a light bulb; V - combination of conditioned (light bulb) and unconditional (food) signals; G - conditioned response of salivation in response to the lighting of a light bulb
So, the formation of a conditioned reflex is based on the closure of the temporary connection between the centers of the conditioned and unconditioned stimuli in the bp cortex, which occurs as a result of the interaction between excited centers in the cortex (Fig. 3.2).
The formation of a conditioned reflex occurs in three stages: pregeneralization, generalization and specialization.
Rice. 3.2.
A - cortical zone of one unconditioned reflex (blinking); b - cortical zone
second unconditioned reflex (food); c, d - subcortical centers of the first and second unconditioned reflexes (blinking and food); I - direct temporary connection; II - time feedback
Pregeneralization (.patent stage). At this stage, behavioral reactions are not yet observed, but the BEA of the brain changes significantly - the activity of neurons in the projection zones of the cortex, corresponding to conditioned and unconditioned stimuli, increases. This is a short stage of concentration of excitation.
Generalization. At this stage, a diffuse spread (irradiation) of excitation occurs throughout the brain, various shifts of BEA are widely distributed throughout the cortex and subcortical structures (desynchronization of alpha activity, theta rhythm, the appearance of distant synchronization of different zones, evoked potentials). During this period, conditioned reactions appear, not only to the conditioned signal, but also to other signals, as well as in the intervals between stimuli.
Specialization. At this time, intersignal reactions fade, and a conditioned response occurs only to the corresponding (conditioned) signal. BEA changes are limited only to the projection area of the conditioned stimulus. This is the stage of fine discrimination of stimuli, the specialization of a conditioned reflex skill.
The procedure for developing an associative (classical) conditioned reflex can be expressed graphically. The learning curve in Pavlov's classic experiment has a 5-shape (Figure 3.3). This means that at the beginning of the procedure for developing a conditioned reflex, there are almost no reactions to the stimulus. Then, a connection is quickly established in the nervous system between the conditioned signal and unconditional reinforcement (turning on the light bulb and serving food), as a result of which the intensity of salivation quickly increases.
1 Danilova N. N., Krylova A. L. Physiology of higher nervous activity. 1997.
Rice. 3.3.
By the 8-10th combination, the amount of saliva reaches a relatively constant high level (plateau), and this means that the skill has been developed and a new reflex has been formed.
At this time, at the neurophysiological level, at first only innate nerve connections are involved (indicative reflex to a light bulb and salivation when food is served). Repeated repetition and combination of these two stimuli leads to the formation of a new, previously unused connection. This connection is formed between the cortical representations of the visual signal (light bulb) and food reinforcement (Fig. 3.4). It is this temporary connection that is the basis of the conditioned reflex: first, the signal from the visual receptors (activated when the light bulb is turned on) reaches the visual cortex, then through this connection it reaches the food cortical center, and then goes to the salivary glands.
Rice. BEHIND.Scheme of the formation of the classical conditioned reflex of salivation in response to the turning on of a light bulb:
- 1 - taste center in the medulla oblongata; 2 - salivary center; 3 - salivary gland; 4 - taste center in bp cortex; 5 - visual center in the bp cortex;
- 6 - innate (unconditioned) neural connections; 7 - formed temporary
connection (conditioned reflex) 2
- 1 Comp. from: Regulatory systems of the human body / V. A. Dubynin [etc.].
- 2 Ibid.
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* Crystallizing polymers can also be obtained in these states.
* Sometimes, for example, when rubber swells in benzene, the main effect of the interaction is to increase the freedom of movement of chain links, leading to an increase in the number of possible conformations (T∙ΔS > ΔH > 0).
* Some jellies have thixotropic properties. Under mechanical action, the bonds between macromolecules can be destroyed and the system becomes fluid. Over time, these connections are restored and jelly is formed again.
* In the coacervate phase
General characteristics of unconditioned reflexes, their classification.
Unconditioned reflexes are an innate species-specific reaction of the body, reflexively arising in response to the specific influence of a stimulus, to the influence of a biologically significant (pain, food) stimulus adequate for a given type of activity.
Unconditioned reflexes are associated with vital biological needs and are carried out within a stable reflex pathway.
Unconditioned reflexes are innate, species-specific and develop in the process of evolution of a given species; they arise in response to a specific/adequate stimulus that affects a certain receptor field.
Unconditioned reflexes are relatively constant and persist throughout life.
The centers of unconditioned reflexes are located at the level of the spinal cord and lower parts of the brain, i.e. without the obligatory participation of the cerebral cortex. But with age, a person develops representations of the unconditioned reflex in the cerebral cortex.
General concept of SD, their classification and meaning.
Conditioned reflex (CR)- this is an individually acquired reaction of the body to a previously indifferent stimulus, reproducing an unconditioned reflex. SD is based on the formation of new or modification of existing neural connections that occur under the influence of changes in the external and internal environment. These are temporary connections that are inhibited when reinforcement is canceled or the situation changes. SDs are formed under certain conditions of the individual life of the organism and are inhibited in the absence of appropriate conditions, thereby differing from innate forms of adaptation.
Formation of conditioned reflexes.
Let's consider an example of a conditioned reflex and its development: the formation of a salivation reaction at the sight of a lemon (natural conditioned reflex).
A person who has never tasted lemon does not have any reactions other than curiosity - an indicative reflex. Salivation, as an unconditional reflex act, occurs when the receptors in the oral cavity are irritated by food - when lemon enters the oral cavity.
When forming a conditioned salivary reflex, lemon, its type, acts as a conditioned stimulus (signal). As an unconditional stimulus (reinforcer) – the taste of lemon.
The sight of a lemon leads to the appearance of a focus of excitation in the cortical center of the visual analyzer (occipital region). The unconditioned stimulus is stronger; the excitation of the cortical center under the action of the unconditioned stimulus is dominant. The dominant focus attracts excitation from the visual center. A temporary connection is established between the two cortical centers. If this combination “the sight of lemon - the taste of lemon” is repeated several times, then the excitation in the visual center will quickly pass along the “beaten path” of temporary communication to the food center and from there along the efferent nerve fibers to the salivary glands.
Thus, conditions for the formation of a conditioned reflex are:
1. The presence of a conditioned stimulus (signal) and an unconditioned stimulus (reinforcement),
2. The conditioned stimulus is weaker than the reinforcement in terms of the strength of its impact.
3. Combined or with a lag of 1-5 seconds, repeated action of the signal and reinforcement.
4. Normal, active functional state of the nervous system, especially the brain.
5. There must be a corresponding dominant in the cerebral cortex (the mood to develop this reflex)
6. Lack of extraneous irritants
In a child under 3 years of age, food reinforcement is also of key importance for the development of useful reflexes. In the future, verbal encouragement becomes more important. In the process of training and education, the role of biological factors (food reinforcement, pain stimulation) should not be exaggerated; it is also necessary to take into account the role of social factors in the process of personality formation.
Of particular importance are reflexes for time, which underlies the organization of the daily routine of a child and schoolchild. These reflexes can be classified as trace reflexes.
When forming imitation reflexes, it is not necessary to be a participant; it is enough to be its “spectator” (for example, the formation of motor skills, speech, social behavior). Thanks to extrapolation reflexes, the ability is formed to foresee the results of one’s activities or events based on an analysis of the environment.
Stages of development of a conditioned reflex:
1st stage generalization(generalizations) – at first the reflex may not manifest itself very accurately (the kitten hunts for any moving object).
2nd stage specializations– the properties of the signal are clarified, which is associated with the phenomena of irradiation and concentration of the processes of excitation and inhibition.
Thus, conditioned reflexes provide a more perfect adaptation of the body to changing living conditions (avoidance of danger, orientation in time and space, etc.)
The constant presence of some stimulus (this could be a methodological guide or teacher’s explanations) gradually leads to the consolidation of temporary connections in the cerebral cortex. These conditioned reflex connections can be both unconsciously and consciously consolidated and reproduced by a person either under the influence of certain stimuli (situations), unconsciously (automatic movements, for example, when driving a car), or consciously as necessary to perform learned movements in general and their individual phases
To maintain conditioned reflex connections, training is of great importance, during which these connections are improved, which is expressed in the increasing accuracy of movements, their optimization in strength, amplitude, direction, and time relationships of individual phases of movements.
5.3. Phases of motor skill formation.
In humans, a motor skill is an acquired form of a conditioned reflex motor reaction, formed through the interaction of the first and second signaling systems.
When a person performs motor actions, due to muscle contraction and excitation of the motor, as well as visual, auditory and other analyzers, a number of nerve impulses enter the cerebral cortex. As a result, a number of excitation foci are created in the cortical centers, between which temporary connections are formed. In this case, a new, very complex coordination arises in the activity of the nerve centers involved in the regulation of contraction of various muscle groups. At the same time, the motor nerve centers of the cortex interact with the centers that regulate blood circulation, breathing, metabolism, etc.
When, thanks to the constant repetition of movements, this relationship is strengthened, then motor actions become possible to perform together. In this case, each previous movement (muscle contraction, visual, auditory and other stimuli) will be a conditioned stimulus that prepares the body for the next phases of motor action. Therefore, all parts of motor actions (postures, movements, directions of gaze) enter into an organic relationship with each other due to the formation of conditioned reflexes.
A complex balanced system of internal processes is created in the cerebral cortex (dynamic stereotype). When performing motor actions, this mosaic of excited and inhibitory points (a system of conditioned reflexes) is rearranged in a certain order with each subsequent movement, ensuring contraction and relaxation of certain muscles and changes in the activity of internal organs.
Thus, a dynamic stereotype is characterized both by a certain combination of inhibitory and excited points, and by a fixed sequence in the change in the nature of this mosaic in the process of performing motor actions. In this case, the implementation of each previous conditioned reflex serves as a conditioned stimulus for the phase of movement that follows it.
Stereotyping in the activity of nerve centers, which is formed during the formation of a motor skill, underlies a relatively constant technique for performing motor actions. Due to this, a firmly established motor skill is difficult to restructure. However, the constancy of temporary connections created by repetitions (training), and therefore movements, is not absolute - it can be changed. Therefore, Pavlov I.P. and called the emerging systematicity not just a stereotype, but a dynamic stereotype. This emphasizes the possibility of changing it.
The formation of conditioned reflexes - the basis of a motor skill (dynamic stereotype) goes through two main stages: generalization and concentration.
In the first stage, the resulting conditioned reflexes capture excessively large foci in the subcortical areas and in the cerebral cortex. This is due to the fact that the paths of movement of the excitatory process in the cortex have not yet been fully formed and capture adjacent centers.
Subsequently, during repetitions, thanks to processes associated with differentiated inhibition, excitation processes are concentrated. Nerve centers that do not take part in movements are inhibited. However, it is impossible to establish the boundaries between the first and second stages in the formation of conditioned reflexes during repetitions, and the transition from one to the other occurs gradually.
Like conditioned reflexes, which are an integral part of a motor skill, the latter as a whole is formed sequentially through several phases that do not depend on the type and characteristics of motor activity (this can be learning to read and write, jumping, throwing, swimming, working with various tools and so on.).
Phases motor skill education:
1. Irradiation - excessive distribution of foci of excitation in the cerebral cortex, involving neighboring areas (outwardly manifested in the presence of chaotic, poorly ordered movements along inconsistent trajectories; more muscles are involved in movements than necessary).
2. Concentration - localization of foci of excitation and inhibition (movements are ordered by trajectories, number and degree of contraction of muscle groups, excessive tension in the muscles of antagonists and synergists is relieved).
3. Automation - a motor action begins to be performed without focusing on its phases and elements, a person becomes able to concentrate his attention on solving “tactical” problems, can be distracted from controlling his motor actions (while riding a bicycle or a car, a person can think about objects not associated with the motor actions performed).
Conditions for the formation of motor skills:
Preliminary familiarization with:
The equipment and equipment used (skis, skates, bicycles, parachute, control system for a car, plane, computer, etc.).
Equipment (submariner’s suit, diver’s, cosmonaut’s spacesuit, pilot’s gravity suit, etc.).
The environment for performing motor actions (water environment for swimming and diving, air environment for a parachutist, weightlessness for an astronaut, snow or ice surface for a skier and skater).
4. Study of motor action in parts (isolating the basic components of movements) and their subsequent combination into a holistic motor act.
5. Step-by-step consolidation of the learned components of the taught motor skill and their connection according to the principle - from simple to complex, from known to unknown.
Conditioned reflexes
But the behavior of higher animals and humans is characterized not only by innate, i.e., unconditioned reactions, but also by such reactions that are acquired by a given organism in the process of individual life activity, i.e. conditioned reflexes. The biological meaning of the conditioned reflex is that numerous external stimuli that surround the animal in natural conditions and in themselves do not have vital significance, preceding in the animal’s experience food or danger, the satisfaction of other biological needs, begin to act as signals, by which the animal orients its behavior (Fig. 15).
So, the mechanism of hereditary adaptation is an unconditioned reflex, and the mechanism of individual variable adaptation is a conditioned reflex, developed by combining vital phenomena with accompanying signals.
Rice. 15. Scheme of formation of a conditioned reflex
§ a - salivation is caused by an unconditioned stimulus - food;
§ b - excitement from a food stimulus is associated with a previous indifferent stimulus (light bulb);
§ c - the light of the light bulb became a signal of the possible appearance of food: a conditioned reflex was developed to it
A conditioned reflex is developed on the basis of any of the unconditioned reactions. Reflexes to unusual signals that do not occur in a natural environment are called artificial conditioned. In laboratory conditions, it is possible to develop many conditioned reflexes to any artificial stimulus.
I. P. Pavlov associated with the concept of a conditioned reflex principle of signaling of higher nervous activity, the principle of synthesis of external influences and internal states.
Pavlov's discovery of the basic mechanism of higher nervous activity - the conditioned reflex - became one of the revolutionary achievements of natural science, a historical turning point in the understanding of the connection between the physiological and the mental.
Understanding the dynamics of formation and changes in conditioned reflexes began the discovery of complex mechanisms of human brain activity and the identification of patterns of higher nervous activity.
Mechanisms of formation of a conditioned reflex, its functional basis
Conditioned reflexes are formed when two foci of excitation appear in the cerebral cortex: one in response to the action of a conditioned stimulus, and the other in response to the action of an unconditioned stimulus. When the action of these stimuli is combined, a temporary connection is established between the emerging foci of excitation, which becomes stronger from experience to experience. Such a connection in the cerebral cortex of I.P. Pavlov called it closure and explained to him the mechanism of formation of a conditioned reflex. 
Description of the picture:
a - cortical center of the blink reflex;
b - cortical center of the food reflex;
c, d - subcortical centers of blinking and food reflexes, respectively;
I - direct temporary connection;
II - time feedback
The formation of a temporary connection occurs according to the dominant principle. The source of excitation from an unconditioned stimulus is always stronger than from a conditioned one, since the unconditioned stimulus is always biologically more significant for the animal. This focus of excitation is dominant. A stronger focus of excitation from unconditioned stimulation attracts excitation from the focus of conditioned stimulation. The degree of his excitement will increase.
The dominant focus has the property of a long, stable existence. Consequently, conditioned and unconditioned excitations will interact with each other for a long time.
If the excitation has passed through some nerve centers, then next time it will pass through these paths much easier. This is based, firstly, on the phenomenon of summation of excitations, and secondly, on the phenomenon of “blazing a path”, accompanied by:
1. long-term increase in the excitability of synaptic formations;
1. changes in protein chains, accumulation of RNA, changes in the amount of mediator in synapses, activation of the formation of new synapses.
Consequently, structural prerequisites are created for the movement of excitation along certain paths. Now the excitation from the zone of the cortical representation of the conditioned reflex will go along the beaten path and cause the manifestation of a conditioned reflex reaction.
There is another idea about the mechanism of formation of a temporary connection. This idea is based on the ability of neurons to respond to stimulation from different modalities, i.e., the phenomenon of polysensory convergence. The existence of neurons on which excitations from different analyzers converge suggests that the process of establishing temporary connections does not occur due to the unification of different parts of the cortex, but through the integration of excitations at the level of one neuron - cortical neurons can integrate conditioned and unconditioned excitations. Conditioned and unconditioned excitations, reaching neurons, are recorded in them in the form of strong chemical compounds, the formation of which is a mechanism for closing the conditioned reflex connection. This theory of the mechanism of temporary connection closure is called convergent theory.
Stages and mechanism of the conditioned reflex. The process of formation of a classical conditioned reflex goes through three main stages:
1. · The pregeneralization stage is a short-term phase, which is characterized by a pronounced concentration of excitation in the projection zones of the cortex of conditioned and unconditioned stimuli and the absence of conditioned behavioral reactions.
2. The stage of generalization, which is based on the process of “diffuse” spread (irradiation) of excitation. This is a phenomenon that occurs in the initial stages of developing a conditioned reflex. The required reaction in this case is caused not only by the reinforced stimulus, but also by others, more or less close to it. During the generalization stage, conditioned reactions occur to signal and other stimuli (the phenomenon of afferent generalization), as well as in the intervals between presentations of the conditioned stimulus.
The initial stage of the formation of a conditioned reflex consists of the formation of a temporary connection not only to this specific conditioned stimulus, but also to all stimuli related to it in nature. The neurophysiological mechanism consists in the irradiation of excitation from the center of the projection of the conditioned stimulus to the nerve cells of the surrounding projection zones, which are functionally close to the cells of the central representation of the conditioned stimulus, to which the conditioned reflex is formed. The farther from the initial initial focus caused by the main stimulus, reinforced by the unconditioned stimulus, the zone covered by the irradiation of excitation is located, the less likely it is to activate this zone. Consequently, at the initial stage of generalization of conditioned excitation, characterized by a generalized generalized reaction, a conditioned reflex response is observed to similar stimuli that are close in meaning as a result of the spread of excitation from the projection zone of the main conditioned stimulus.
1. Specialization stage. As the conditioned stimulus is reinforced, the intersignal reactions fade and the conditioned response occurs only to the signal stimulus. The volume of distribution of biopotentials is decreasing.
As the conditioned reflex strengthens, the processes of irradiation of excitation are replaced by processes of concentration, limiting the focus of excitation only to the zone of representation of the main stimulus. As a result, clarification and specialization of the conditioned reflex occurs. At the final stage of a strengthened conditioned reflex, a concentration of conditioned excitation occurs: the conditioned reflex reaction is observed only to a given stimulus, and to secondary stimuli that are close in meaning, it stops. At the stage of concentration of conditioned excitation, the excitatory process is localized only in the zone of the central representation of the conditioned stimulus (a reaction is realized only to the main stimulus), accompanied by inhibition of the reaction to side stimuli. The external manifestation of this stage is the differentiation of the parameters of the current conditioned stimulus - the specialization of the conditioned reflex.
The rate of formation of the UR depends on the individual characteristics of the animal, on the frequency of stimulation, on the functional state of the cortex itself and its areas, on the ratio of the strength of unconditioned and conditioned stimuli, on the environment and the changes occurring in it.
Initially, I.P. Pavlov assumed that the conditioned reflex is formed at the level of “cortex-subcortical formations”. In later works, he explained the formation of a conditioned reflex connection by the formation of a temporary connection between the cortical center of the unconditioned reflex and the cortical center of the analyzer. In this case, the main cellular elements of the mechanism for the formation of a conditioned reflex are the intercalary and associative neurons of the cerebral cortex, and the closure of the temporary connection is based on the process of dominant interaction between excited centers. Data from modern neurophysiology indicate the possibility of different levels of closure: “cortex-cortex”, “cortex-subcortical formations”, “subcortical formations-subcortical formations”. E.A. Asratyan, studying the unconditioned reflex, put forward a hypothesis about the structure of the conditioned reflex as a process of synthesis of unconditioned reflexes.
To develop conditioned reflexes, the following conditions are necessary:
1. The action of the conditioned stimulus must precede the influence of the unconditioned one.
2. A repeated combination of conditioned and unconditioned stimuli is necessary.
3. Indifferent and unconditioned stimuli must have superthreshold strength.
4. At the moment of developing a conditioned reflex, there should be no extraneous external stimulation.
3) Types of higher nervous activity (HNA) - a set of innate (genotype) and acquired (phenotype) properties of the nervous system that determine the nature of the organism’s interaction with the environment and are reflected in all functions of the body. The specific significance of congenital and acquired - a product of the interaction of genotype and environment - may vary depending on conditions. In unusual, extreme conditions, predominantly innate mechanisms of higher nervous activity come to the fore. Various combinations of the three main properties of the nervous system allowed I.P. Pavlov identified four sharply defined types, differing in adaptive abilities and resistance to neurotic agents.
3 properties of the nervous system: strength of the nervous system, poise (balance) of the nervous system, mobility.
Nervous System Strength- this is its resistance to prolonged exposure to a stimulus, both exciting and inhibitory. A weak nervous system is a highly sensitive nervous system, and this is its advantage over a strong one.
Equilibrium- the ability to move from one reaction to another. For example, from excitation reactions to inhibition reactions in critical situations.
Mobility- this is the rate of formation of new conditional connections.
Types of higher nervous activity:
- Strong, unbalanced, mobile - characterized by a strong irritability process and a lagging inhibitory process, so a representative of this type in difficult situations is easily susceptible to violations of the IRR. Capable of training and greatly improving insufficient braking. In accordance with the doctrine of temperaments, this is a choleric type.
- Strong, balanced, mobile - has equally strong processes of excitation and inhibition with good mobility, which ensures high adaptive capabilities and stability in difficult life situations. In accordance with the doctrine of temperaments, this is a sanguine type.
- Strong, balanced, inert - with strong processes of excitation and inhibition and poor mobility, always experiencing difficulties when switching from one type of activity to another. In accordance with the doctrine of temperaments, this is a phlegmatic type.
- Weak, unbalanced, inert - characterized by weakness of both nervous processes - excitation and inhibition, poorly adapts to environmental conditions, and is susceptible to neurotic disorders. In accordance with the classification of temperaments, this is a melancholic type.
Although the selected three parameters of the nervous system give 2 3 = 8 different combinations, Pavlov believed that considering all of them had no practical application. In his opinion, there is no point in considering balance in an object with a weak nervous system, and mobility in types with a strong and unbalanced one.
According to I.P. Pavlov, temperament is the most important characteristic of the human nervous system, which in one way or another affects all the activities of each individual. I.P. Pavlov understood the type of nervous system as innate, relatively weakly susceptible to changes under the influence of environment and upbringing. He called it genotype.
Based on each type, different systems of conditioned neural connections are formed. The process of their formation depends on the type of nervous system. Thus, the type of nervous system provides uniqueness to human behavior, leaves a characteristic imprint on the entire essence of a person - determines the mobility of mental processes and their stability. However, it is not a decisive factor in behavior, actions, and beliefs that are formed in the process of a person’s individual life and in the process of upbringing.
IP Pavlov's typology has become the source of many studies of temperament. So, at the end of the 50s of the XX century. Laboratory studies were carried out under the leadership of B. M. Teplov, V. D. Nebilitsin, V. S. Merlin, who supplemented I. P. Pavlov’s typologies with new elements. Many techniques have been developed for studying the human nervous system, which have made it possible to better understand the role of individual temperamental characteristics in human activity. B. M. Teplov and V. D. Nebilitsin, studying the strength of nervous processes, came to the conclusion that there is a close connection between the strength of the nervous system relative to excitation (work capacity) and sensitivity. They revealed such concepts as lability, dynamism, ability to concentrate and other traits of temperament.
All types of temperament can be characterized by the following basic qualities:
Related information.
FORMATION OF CONDITIONED REFLEXES
The main elementary act of higher nervous activity is the formation of a conditioned reflex. Here these properties will be considered, like all general laws of the physiology of higher nervous activity, using the example of the conditioned salivary reflexes of a dog.
The conditioned reflex occupies a high place in the evolution of temporary connections, which are a universal adaptive phenomenon in the animal world. The most primitive mechanism of individual adaptation to changing living conditions, apparently, is represented by intracellular temporary connections protozoa. Colonial forms develop rudiments of intercellular temporary connections. The emergence of a primitive nervous system with a mesh structure gives rise to temporary connections of the diffuse nervous system, found in coelenterates. Finally, the centralization of the nervous system into the nodes of invertebrates and the brain of vertebrates leads to rapid progress temporary connections of the central nervous system and the emergence of conditioned reflexes. Such different types of temporary connections are obviously carried out by physiological mechanisms of different natures.
There are countless conditioned reflexes. If the appropriate rules are followed, any perceived stimulus can be made a stimulus that triggers a conditioned reflex (signal), and any activity of the body can be its basis (reinforcement). Depending on the type of signals and reinforcements, as well as on the relationships between them, different classifications of conditioned reflexes have been created. As for studying the physiological mechanism of temporary connections, researchers have a lot of work to do.
General signs and types of conditioned reflexes
Using the example of a systematic study of salivation in dogs, general signs of a conditioned reflex, as well as specific signs of different categories of conditioned reflexes, have emerged. The classification of conditioned reflexes was determined according to the following particular characteristics: 1) circumstances of formation, 2) type of signal, 3) composition of the signal, 4) type of reinforcement, 5) relationship in time of the conditioned stimulus and reinforcement.
General signs of conditioned reflexes. What signs are common and obligatory for all conditioned reflexes? The conditioned reflex a) is the highest individual adaptation to changing living conditions; b) carried out by the higher parts of the central nervous system; c) is acquired through temporary neural connections and is lost if the environmental conditions that caused it have changed; d) represents a warning signal reaction.
So, a conditioned reflex is an adaptive activity carried out by the higher parts of the central nervous system through the formation of temporary connections between signal stimulation and the signaled reaction.
Natural and artificial conditioned reflexes. Depending on the nature of the signal stimulus, conditioned reflexes are divided into natural and artificial.
Natural called conditioned reflexes that are formed in response to the influence of agents that are natural signs of signaled unconditional stimulation.
An example of a natural conditioned food reflex is the salivation of a dog to the smell of meat. This reflex inevitably develops naturally throughout the dog's life.
Artificial called conditioned reflexes that are formed in response to the influence of agents that are not natural signs of signaled unconditional stimulation. An example of an artificial conditioned reflex is the salivation of a dog to the sound of a metronome. In life, this sound has nothing to do with food. The experimenter artificially made it a food intake signal.
Nature develops natural conditioned reflexes from generation to generation in all animals according to their lifestyle. As a result natural conditioned reflexes are easier to form, are more likely to be strengthened and turn out to be more durable than artificial ones. A puppy who has never tasted meat is indifferent to its type. However, it is enough for him to eat meat once or twice, and the natural conditioned reflex is already fixed. At the sight of meat, the puppy begins to salivate. And in order to develop an artificial conditioned reflex of salivation in the form of a flashing light bulb, dozens of combinations are needed. From here the meaning of the “biological adequacy” of the agents from which the stimuli of conditioned reflexes are made becomes clear.
Selective sensitivity to environmentally adequate signals is manifested in the reactions of nerve cells in the brain.
Exteroceptive, interoceptive and proprioceptive conditioned reflexes. Conditioned reflexes to external stimuli are called exteroceptive, to irritants from internal organs - interoceptive, to irritants of the musculoskeletal system - proprioceptive.
Rice. 1. Interoceptive conditioned reflex of urination during the “imaginary infusion” of physiological solution (according to K. Bykov):
1 - initial curve of urine formation, 2 - urine formation as a result of infusion of 200 ml of physiological solution into the stomach, 3 - urine formation as a result of an “imaginary infusion” after 25 true
Exteroceptive reflexes are divided into reflexes caused by distant(acting at a distance) and contact(acting upon direct contact) irritants. Next, they are divided into groups according to the main types of sensory perception: visual, auditory, etc.
Interoceptive conditioned reflexes (Fig. 1) can also be grouped by organs and systems that are sources of signaling: gastric, intestinal, cardiac, vascular, pulmonary, renal, uterine, etc. A special position is occupied by the so-called reflex for a while. It manifests itself in various vital functions of the body, for example, in the daily frequency of metabolic functions, in the secretion of gastric juice when it is time for lunch, in the ability to wake up at the appointed hour. Apparently, the body “keeps time” mainly based on interoceptive signals. The subjective experience of interoceptive reflexes does not have the figurative objectivity of exteroceptive ones. It gives only vague “dark feelings” (I.M. Sechenov’s term), which form the general state of health, which affects mood and performance.
Proprioceptive conditioned reflexes underlie all motor skills. They begin to be developed from the first flaps of the chick’s wings, from the first steps of the child. They are associated with mastery of all types of locomotion. The coherence and accuracy of movement depends on them. The proprioceptive reflexes of the hand and vocal apparatus in humans are receiving a completely new use in connection with labor and speech. The subjective “experience” of proprioceptive reflexes consists mainly in the “muscular feeling” of the position of the body in space and its members relative to each other. At the same time, for example, signals from the accommodative and oculomotor muscles have a visual nature of perception: they provide information about the distance of the object in question and its movements; signals from the muscles of the hand and fingers make it possible to evaluate the shape of objects. With the help of proprioceptive signaling, a person reproduces with his movements the events occurring around him (Fig. 2).
Rice. 2. Study of proprioceptive components of human visual representation:
A- image previously shown to the subject, b- Light source, V- reflection of a light beam from a mirror mounted on the eyeball, G- trajectory of eye movement when remembering an image
A special category of conditioned reflexes consists of model experiments with electrical stimulation of the brain as a reinforcement or signal; using ionizing radiation as reinforcement; creation of a dominant; the development of temporary connections between points of the neuronally isolated cortex; study of the summation reflex, as well as the formation of conditioned reactions of a nerve cell to a signal, reinforced by local electrophoretic application of mediators.
Conditioned reflexes to simple and complex stimuli. As has been shown, a conditioned reflex can be developed to any one of the listed extero-, intero- or proprioceptive stimuli, for example, to turning on a light or to a simple sound. But in life this rarely happens. More often, the signal becomes a complex of several stimuli, for example, smell, warmth, the soft fur of the mother cat becomes an irritant of the conditioned sucking reflex for the kitten. Accordingly, conditioned reflexes are divided into simple And complex, or complex, irritants.
Conditioned reflexes to simple stimuli do not require explanation. Conditioned reflexes to complex stimuli are divided based on the relationships between members of the complex (Fig. 3).
Rice. 3. Relationship in time between members of complexes of complex conditioned stimuli. A- simultaneous complex; B- total stimulus; IN- sequential complex; G- chain of stimuli:
single lines show indifferent stimuli, double lines show previously developed signals, dotted lines show reinforcement
Conditioned reflexes developed on the basis of various reinforcements. The basis for the formation of a conditioned reflex is its reinforcements- can be any activity of the body carried out by the nervous system. Hence the limitless possibilities of conditioned reflex regulation of almost all vital functions of the body. In Fig. Figure 4 schematically presents various types of reinforcements, on the basis of which conditioned reflexes can be developed.
Rice. 4. Classification of reinforcements to which conditioned reflexes can be formed
Each conditioned reflex, in turn, can become the basis for the formation of a new conditioned reflex. A new conditioned reaction developed by reinforcing a signal with another conditioned reflex is called conditioned reflex of the second order. The second-order conditioned reflex, in turn, can be used as a basis for developing conditioned reflex of the third order etc.
Conditioned reflexes of the second, third and further orders are widespread in nature. They constitute the most significant and perfect part of natural conditioned reflexes. For example, when a she-wolf feeds a wolf cub with the meat of torn prey, it develops a natural conditioned reflex of the first order. The sight and smell of meat becomes a food signal for him. Then he "learns" to hunt. Now these signals - the sight and smell of the meat of caught prey - play the role of the basis for developing hunting techniques for lying in wait and pursuing live prey. This is how various hunting signs acquire their secondary signal meaning: a bush gnawed by a hare, traces of a sheep straying from the herd, etc. They become stimuli of second-order conditioned reflexes, developed on the basis of natural ones.
Finally, an exceptional variety of conditioned reflexes, which are reinforced by other conditioned reflexes, is found in the higher nervous activity of man. They will be discussed in more detail in Chap. 17. Here it is only necessary to note that, unlike the conditioned reflexes of animals human conditioned reflexes are formed not on the basis of unconditioned food, defensive and other similar reflexes, but on the basis of verbal signals, reinforced by the results of joint activities of people. Therefore, a person’s thoughts and actions are guided not by animal instincts, but by the motives of his life in human society.
Conditioned reflexes developed at different timings of signal and reinforcement. Based on how the signal is located in time relative to the reinforcing reaction, they distinguish cash And trace conditioned reflexes(Fig. 5).
Rice. 5. Options for the temporal relationship between signal and reinforcement. A- cash matching; B- cash set aside; IN- cash lagging; G- trace conditioned reflex:
The solid line indicates the duration of the signal, the dashed line indicates the time of reinforcement.
Cash are called conditioned reflexes, during the development of which reinforcement is used during the action of a signal stimulus. Depending on the timing of the addition of reinforcement, existing reflexes are divided into coinciding, delayed and delayed. Matching reflex is produced when, immediately after the signal is turned on, reinforcement is attached to it. For example, when working with salivary reflexes, dogs turn on the bell, and after about 1 s they begin to feed the dog. With this method of development, the reflex is formed most quickly and is soon strengthened.
Retired the reflex is developed in cases where a reinforcing reaction is added only after some time has passed (up to 30 s). This is the most common method of developing conditioned reflexes, although it requires a larger number of combinations than the coincidence method.
Delayed reflex produced when a reinforcing reaction is added after a long isolated action of the signal. Typically, this isolated action lasts 1–3 minutes. This method of developing a conditioned reflex is even more difficult than the previous two.
Followers are called conditioned reflexes, during the development of which a reinforcing reaction is presented only some time after the signal is turned off. In this case, the reflex is developed in response to the action of the signal stimulus; use short intervals (15–20 s) or long ones (1–5 min). The formation of a conditioned reflex using the trace method requires the largest number of combinations. But trace conditioned reflexes provide very complex acts of adaptive behavior in animals. An example would be hunting for hidden prey.
Conditions for the development of temporary connections
What conditions must be met so that the activity of the higher parts of the central nervous system can culminate in the development of a conditioned reflex?
Combination of a signal stimulus with reinforcement. This condition for the development of temporary connections was revealed from the very first experiments with salivary conditioned reflexes. The steps of the servant carrying food only caused “psychic salivation” when they were combined with food.
This is not contradicted by the formation of trace conditioned reflexes. Reinforcement is combined in this case with a trace of excitation of nerve cells from a previously switched on and switched off signal. But if the reinforcement begins to precede the indifferent stimulus, then the conditioned reflex can be developed with great difficulty, only by taking a number of special measures. This is understandable, since if you first feed the dog and then give a food signal, then, strictly speaking, it cannot even be called a signal, since it does not warn about upcoming events, but reflects the past. In this case, the unconditioned reflex suppresses signal excitation and prevents the formation of a conditioned reflex to such a stimulus.
Indifference of the signal stimulus. The agent chosen as a conditioned stimulus for the food reflex should not itself have any relation to food. He must be indifferent, i.e. indifferent, for the salivary glands. The signal stimulus should not cause a significant orienting reaction that interferes with the formation of a conditioned reflex. However, each new stimulus evokes an indicative reaction. Therefore, for it to lose its novelty, it must be reused. Only after the indicative reaction is practically extinguished or reduced to an insignificant value does the formation of a conditioned reflex begin.
The predominance of the strength of excitation caused by reinforcement. The combination of the sound of the metronome and the feeding of the dog leads to the rapid and easy formation of a conditioned salivary reflex to this sound. But if you try to combine the deafening sound of a mechanical rattle with food, then such a reflex is extremely difficult to form. For the development of a temporary connection, the ratio of signal strength and reinforcing reaction is of great importance. In order for a temporary connection to form between them, the focus of excitation created by the latter must be stronger than the focus of excitation created by the conditioned stimulus, i.e. a dominant must arise. Only then will there be a spread of excitation from the focus of the indifferent stimulus to the focus of excitation from the reinforcing reflex.
The need for a significant intensity of excitation of a reinforcing reaction has a deep biological meaning. In fact, a conditioned reflex is a warning reaction to a signal about upcoming significant events. But if the stimulus that they want to make a signal turns out to be an event even more significant than those that follow it, then this stimulus itself causes a corresponding reaction in the body.
Lack of extraneous irritants. Each extraneous irritation, for example, an unexpected noise, causes the already mentioned indicative reaction. The dog becomes alert, turns in the direction of the sound and, most importantly, stops its current activity. The animal is all turned towards the new stimulus. No wonder I.P. Pavlov called the orienting reaction the “What is it?” reflex. In vain at this time the experimenter will give a signal and offer the dog food. The conditioned reflex will be delayed by the more important at the moment for the animal - the orienting reflex. This delay is created by an additional focus of excitation in the cerebral cortex, which inhibits conditioned excitation and prevents the formation of a temporary connection. In nature, many such accidents influence the course of the formation of conditioned reflexes in animals. A distracting environment reduces a person's productivity and mental performance.
Normal functioning of the nervous system. Full closure function is possible provided that the higher parts of the nervous system are in normal working condition. The method of chronic experimentation therefore made it possible to detect and study the processes of higher nervous activity, because at the same time the normal state of the animal was preserved. The performance of nerve cells in the brain sharply decreases due to insufficient nutrition, under the influence of toxic substances, such as bacterial toxins in diseases, etc. Therefore, general health is an important condition for the normal functioning of the higher parts of the brain. Everyone knows how this condition affects a person’s mental functioning.
The formation of conditioned reflexes is significantly influenced by the state of the body. Thus, physical and mental work, nutritional conditions, hormonal activity, the action of pharmacological substances, breathing at high or low pressure, mechanical overload and ionizing radiation, depending on the intensity and timing of exposure, can modify, strengthen or weaken conditioned reflex activity up to its complete suppression.
The formation of conditioned reflexes and the implementation of acts of higher nervous activity are extremely dependent on the body's need for biologically significant agents used as reinforcement. Thus, it is very difficult for a well-fed dog to develop a conditioned food reflex; it will turn away from the food offered, but in a hungry animal with high food excitability it forms quickly. It is well known how a student’s interest in the subject of classes contributes to its better assimilation. These examples show the great importance of the factor of the body’s attitude to the stimuli shown, which is designated as motivation(K.V. Sudakov, 1971).
Structural basis of the closure of temporary conditional connections
The study of the final, behavioral manifestations of higher nervous activity was significantly ahead of the study of its internal mechanisms. To date, both the structural basis of the temporal connection and its physiological nature have not yet been sufficiently studied. There are different views on this matter, but the issue has not yet been resolved. To solve it, numerous studies are being conducted at the systemic and cellular levels; use electrophysiological and biochemical indicators of the dynamics of the functional state of nerve and glial cells, taking into account the results of irritation or shutdown of various brain structures; attract data from clinical observations. However, at the current level of research it is becoming more and more certain that, along with the structural one, it is also necessary to take into account the neurochemical organization of the brain.
Changes in the localization of the closure of temporary connections in evolution. Regardless of whether one considers that conditioned reactions coelenterates(diffuse nervous system) arise on the basis of summation phenomena or real temporary connections, the latter do not have a specific localization. U annelids(nodal nervous system) in experiments with the development of a conditioned avoidance reaction, it was discovered that when a worm is cut in half, the reflex is preserved in each half. Consequently, the temporary connections of this reflex are closed many times, possibly in all nerve nodes of the chain and have multiple localizations. U higher molluscs(the anatomical consolidation of the central nervous system, which already forms a developed brain in the octopus, is sharply expressed) experiments with the destruction of parts of the brain showed that the supraesophageal sections carry out many conditioned reflexes. Thus, after the removal of these sections, the octopus ceases to “recognize” the objects of its hunt and loses the ability to build a shelter out of stones. U insects functions of organizing behavior are concentrated in the cephalic ganglia. The so-called mushroom bodies of the protocerebrum, the nerve cells of which form many synaptic contacts with numerous paths to other parts of the brain, reach particular development in ants and bees. It is assumed that this is where the closure of temporary connections occurs during insect learning.
Already at an early stage of the evolution of vertebrates, the brain, which controls adaptive behavior, is distinguished in the anterior parts of the initially homogeneous brain tube. It develops structures that are of greatest importance for closing harmful connections in the process of conditioned reflex activity. Based on experiments with the removal of parts of the brain from fish it was suggested that in them this function is performed by the structures of the midbrain and diencephalon. Perhaps this is determined by the fact that it is here that the paths of all sensory systems converge, and the forebrain develops only as an olfactory one.
U birds The striatal bodies, which form the bulk of the cerebral hemispheres, become the leading department in brain development. Numerous facts indicate that temporary connections are closed in them. A pigeon with its hemispheres removed serves as a clear illustration of the extreme poverty of behavior, deprived of the skills acquired in life. The implementation of particularly complex forms of behavior in birds is associated with the development of hyperstriatum structures that form an elevation above the hemispheres, which is called the “vulst.” In corvids, for example, its destruction disrupts the ability to carry out complex forms of behavior characteristic of them.
U mammals The brain develops mainly due to the rapid growth of the multilayered cortex of the cerebral hemispheres. The new cortex (neocortex) receives special development, which pushes aside the old and ancient cortex, covers the entire brain in the form of a cloak and, not fitting on its surface, gathers in folds, forming numerous convolutions separated by grooves. The question of the structures that carry out the closure of temporary connections and their localization in the cerebral hemispheres is the subject of a large number of studies and is largely debatable.
Removal of parts and the entire cerebral cortex. If the occipital areas of the cortex are removed from an adult dog, then it loses all complex visual conditioned reflexes and cannot restore them. Such a dog does not recognize its owner, is indifferent to the sight of the most delicious pieces of food, and looks indifferently at a cat running past, which it would previously have rushed to pursue. What used to be called “mental blindness” sets in. The dog sees because it avoids obstacles and turns towards the light. But she “does not understand” the meaning of what she saw. Without the participation of the visual cortex, visual signals remain unrelated to anything.
And yet such a dog can form very simple visual conditioned reflexes. For example, the appearance of an illuminated human figure can be made a food signal, causing salivation, licking, and tail wagging. Consequently, in other areas of the cortex there are cells that perceive visual signals and are able to associate them with certain actions. These facts, confirmed in experiments with damage to the cortical areas of representation of other sensory systems, led to the opinion that projection zones overlap each other (L. Luciani, 1900). Further studies of the issue of localization of functions in the cortex in the works of I.P. Pavlov (1907–1909) showed a wide overlap of projection zones, depending on the nature of the signals and the temporary connections formed. Summarizing all these studies, I.P. Pavlov (1927) put forward and substantiated the idea of dynamic localization cortical functions. The overlaps are traces of the wide representation of all types of reception in the entire cortex that took place before their division into projection zones. Each core of the cortical part of the analyzer is surrounded by its scattered elements, which become less and less as they move away from the core.
Scattered elements are not able to replace specialized cells of the nucleus for the formation of subtle temporary connections. After removal of the occipital lobes, a dog can produce only the simplest conditioned reflexes, for example, to the sight of an illuminated figure. It is not possible to force her to distinguish between two such figures, similar in shape. However, if the occipital lobes are removed at an early age, when the projection zones have not yet been isolated and consolidated, then, as they grow up, these animals exhibit the ability to develop complex forms of conditioned visual reflexes.
The possibility of widespread interchangeability of the functions of the cerebral cortex in early ontogenesis corresponds to the properties of the poorly differentiated mammalian cerebral cortex in phylogenesis. From this point of view, the results of experiments on rats are explained, in which the degree of impairment of conditioned reflexes turned out to depend not on the specific area of the removed cortex, but on the total volume of the removed cortical mass (Fig. 6). Based on these experiments, it was concluded that for conditioned reflex activity all parts of the cortex have the same importance, the cortex "equipotential"(K. Lashley, 1933). However, the results of these experiments can only demonstrate the properties of the poorly differentiated cortex of rodents, while the specialized cortex of more highly organized animals does not reveal “equipotentiality,” but a well-defined dynamic specialization of functions.
Rice. 6. Interchangeability of parts of the cerebral cortex after their removal in rats (according to K. Lashley):
the removed areas are blackened, the numbers under the brain indicate the amount of removal as a percentage of the entire surface of the cortex, the numbers under the bars indicate the number of errors when testing in the maze
The first experiments with the removal of the entire cerebral cortex (<…пропуск…>Goltz, 1982) showed that after such an extensive operation, apparently affecting the immediate subcortex, the dogs could not learn anything. In experiments on dogs with removal of the cortex without damaging the subcortical structures of the brain, it was possible to develop simple conditioned salivation reflex. However, it took more than 400 combinations to develop it, and it was not possible to extinguish it even after 130 applications of the signal without reinforcement. Systematic studies on cats, which tolerate decortication surgery more easily than dogs, have shown the difficulty of forming in them simple generalized food and defensive conditioned reflexes and the development of some gross differentiations. Experiments with cold shutdown of the cortex demonstrated that full-fledged integral brain activity is impossible without its participation.
The development of an operation for cutting all ascending and descending pathways connecting the cortex with other brain structures made it possible to carry out decortication without direct injury to subcortical structures and to study the role of the cortex in conditioned reflex activity. It turned out that in these cats it was possible with great difficulty to develop only crude conditioned reflexes of general movements, and defensive conditioned flexion of the paw could not be achieved even after 150 combinations. However, after 20 combinations, a reaction to the signal appeared: changes in breathing and some conditioned vegetative reactions.
Of course, with all surgical operations it is difficult to exclude their traumatic effect on subcortical structures and to be sure that the lost ability for subtle conditioned reflex activity was a function of the cortex. Convincing evidence was provided by experiments with temporary reversible shutdown of cortical functions, which manifests itself in a spreading depression of electrical activity when KCI is applied to its surface. When the rat's cerebral cortex is turned off in this way and the animal's reaction to conditioned and unconditioned stimuli is tested at this time, one can see that unconditioned reflexes are completely preserved, while conditioned ones are disrupted. As can be seen from Fig. 7, more complex defensive and especially food conditioned reflexes with maximum depression are completely absent during the first hour, and the simple defensive reaction of avoidance suffers to a lesser extent.
Thus, the results of experiments with partial and complete surgical and functional decortication indicate that higher In animals, the function of forming precise and subtle conditioned reflexes capable of ensuring adaptive behavior is mainly performed by the cerebral cortex.
Rice. 7. The effect of temporary shutdown of the cortex through spreading depression on nutritional (1) and defensive (2) conditioned reflexes, unconditioned avoidance response (3) and EEG severity (4) rats (according to J. Buresh and others)
Cortical-subcortical relations in the processes of higher nervous activity. Modern research confirms the statement of I.P. Pavlov that conditioned reflex activity is carried out by the joint work of the cortex and subcortical structures. From a consideration of the evolution of the brain as an organ of higher nervous activity, it follows that the ability to form temporary connections that ensure adaptive behavior was demonstrated by the structures of the diencephalon in fish and the striatal bodies in birds, which are phylogenetically the youngest parts of it. When the phylogenetically youngest neocortex, which carried out the most subtle analysis of signals, arose in mammals above these parts of the brain, it assumed the leading role in the formation of temporary connections that organize adaptive behavior.
Brain structures that turn out to be subcortical retain, to some extent, their ability to close temporary connections that provide adaptive behavior characteristic of the level of evolution when these structures were leading. This is evidenced by the behavior of animals described above, which, after turning off the cerebral cortex, could hardly develop only very primitive conditioned reflexes. At the same time, it is possible that such primitive temporary connections have not completely lost their significance and form part of the lower level of the complex hierarchical mechanism of higher nervous activity, headed by the cerebral cortex.
The interaction of the cortex and subcortical parts of the brain is also carried out by tonic influences, regulating the functional state of nerve centers. It is well known how mood and emotional state influence the efficiency of mental activity. I.P. Pavlov said that the subcortex “charges” the cortex. Neurophysiological studies of the mechanisms of subcortical influences on the cortex have shown that reticular formation the midbrain has an effect on her upward activating action. Receiving collaterals from all afferent pathways, the reticular formation participates in all behavioral reactions, determining the active state of the cortex. However, its activating influence during a conditioned reflex is organized by signals from the projection zones of the cortex (Fig. 8). Irritation of the reticular formation causes a change in the electroencephalogram in the form of its desynchronization, characteristic of a state of active wakefulness.
Rice. 8. Interaction of the reticular formation of the midbrain and cortex (according to L.G. Voronin):
thick lines indicate afferent specific paths with collaterals to the reticular formation, intermittent lines - ascending paths to the cortex, thin lines - the influence of the cortex on the reticular formation, vertical shading - facilitating zone, horizontal - inhibitory zone, cellular shading - thalamic nuclei
A different effect on the functional state of the cortex is exerted by specific nuclei of the thalamus. Their low-frequency irritation leads to the development of inhibition processes in the cortex, which can lead to the animal falling asleep, etc. Irritation of these nuclei causes the appearance of peculiar waves in the electroencephalogram - "spindle", which turn into slow ones delta waves, characteristic of sleep. The spindle rhythm can be determined inhibitory postsynaptic potentials(IPSP) in hypothalamic neurons. Along with the regulatory influence of nonspecific subcortical structures on the cortex, the reverse process is also observed. Such bilateral cortical-subcortical mutual influences are mandatory in the implementation of mechanisms for the formation of temporary connections.
The results of some experiments were interpreted as evidence of the inhibitory effect of striatal structures on the behavior of animals. However, further research, in particular experiments with the destruction and stimulation of the caudate bodies, and other facts led to the conclusion about the presence of more complex cortical-subcortical relationships.
Some researchers consider the facts about the participation of subcortical structures in the processes of higher nervous activity as a basis for considering them a place of closure of temporary connections. This is how the idea of "centrencephalic system" as a leader in human behavior (W. Penfield, G. Jasper, 1958). As evidence of the closure of the temporary connection in the reticular formation, observations were cited that during the development of a conditioned reflex, the first changes in the electrical activity of the brain occur precisely in the reticular formation, and then in the cerebral cortex. But this only indicates a completely understandable early activation of the ascending cortical activation system. Finally, a strong argument in favor of the subcortical localization of closure was considered to be the possibility of developing a conditioned, for example, visual-motor, reflex, despite repeated dissection of the cortex to its full depth, interrupting all cortical pathways between the visual and motor areas. However, this experimental fact cannot serve as proof, since the closure of the temporary connection in the cortex is multiple in nature and can occur in any part of it between the afferent and effector elements. In Fig. 9 thick lines show the path of the conditioned visual-motor reflex when cutting the cortex between the visual and motor areas.
Rice. 9. Multiple closure of temporary connections in the cortex (shown by the dotted line), which are not prevented by its cuts (according to A.B. Kogan):
1, 2, 3 - central mechanisms of defensive, food and orientation reactions, respectively; the path of the conditioned food reflex to the light signal is shown in thick lines
As numerous studies have shown, the participation of subcortical structures in the processes of higher nervous activity is not limited to the regulatory role of the reticular formation of the midbrain and limbic structures. After all, already at the subcortical level, the analysis and synthesis of existing stimuli and the assessment of their biological significance take place, which largely determines the nature of the connections formed with the signal. The use of indicators of the formation of the shortest paths along which the signal reaches various subcortical structures of the brain revealed the most pronounced participation in the learning processes of the posterior parts of the thalamus and field CA 3 of the hippocampus. The role of the hippocampus in memory phenomena is confirmed by many facts. Finally, there is no reason to assume that the ability for primitive closure activity of brain structures, which was acquired in evolution when they were leading, has now completely disappeared in them when this function has passed to the neocortex.
Thus, cortical-subcortical relationships are determined regulation of the functional state of the cortex by the activating system - the reticular formation of the midbrain and the inhibitory system of the nonspecific nuclei of the thalamus, as well as possible participation in the formation of primitive temporary connections at the lower level of complex hierarchical mechanisms of higher nervous activity.
Interhemispheric relations. How do the cerebral hemispheres, which are a paired organ, participate in the processes of formation of conditioned connections? The answer to this question was obtained in experiments on animals that underwent brain “splitting” surgery by cutting the corpus callosum and anterior commissure, as well as longitudinal division of the optic chiasm (Fig. 10). After such an operation, it was possible to develop different conditioned reflexes of the right and left hemispheres, showing different figures to the right or left eye. If a monkey operated in this way develops a conditioned reflex to a light stimulus presented to one eye, and then applies it to the other eye, then no reaction will follow. “Training” one hemisphere left the other “untrained.” However, if the corpus callosum is preserved, the other hemisphere also turns out to be “trained.” The corpus callosum carries out interhemispheric transfer of skill.
Rice. 10. Studies of learning processes in monkeys subjected to brain splitting surgery. A- a device that sends one image to the right eye and another to the left eye; B- special optics for projecting visual images into different eyes (according to R. Sperry)
Using the method of functional switching off the cerebral cortex in rats, the conditions of a “split” brain were reproduced for some time. In this case, temporary connections could be formed by one remaining active hemisphere. This reflex also manifested itself after the cessation of the spreading depression. It persisted even after inactivation of the hemisphere that was active during the development of this reflex. Consequently, the “trained” hemisphere transferred the acquired skill to the “untrained” one through the fibers of the corpus callosum. However, this reflex disappeared if such inactivation was carried out before the activity of the hemisphere included during the development of the conditioned reflex was completely restored. Thus, in order to transfer an acquired skill from one hemisphere to the other, it is necessary that both of them are active.
Further studies of interhemispheric relations during the formation of temporary connections of conditioned reflexes showed that inhibition processes play a specific role in the interaction of the hemispheres. Thus, the hemisphere opposite to the side of reinforcement becomes dominant. It first carries out the formation of the acquired skill and its transfer to the other hemisphere, and then, by slowing down the activity of the opposite hemisphere and exerting a selective inhibitory effect on the structure of temporary connections, it improves the conditioned reflex.
Thus, each hemisphere, even when isolated from the other, is capable of forming temporary connections. However, in natural conditions of their pair work, the side of reinforcement determines the dominant hemisphere, which forms the subtle excitatory-inhibitory organization of the conditioned-reflex mechanism of adaptive behavior.
Assumptions about the location of the closure of temporary connections in the cerebral hemispheres. Having discovered the conditioned reflex, I.P. Pavlov first suggested that the temporary connection is a “vertical connection” between the visual, auditory or other parts of the cerebral cortex and the subcortical centers of unconditioned reflexes, for example food - cortical-subcortical temporal connection(Fig. 11, A). However, numerous facts of further work and the results of special experiments then led to the conclusion that the temporary connection is a “horizontal connection” between foci of excitation located within the cortex. For example, during the formation of a conditioned salivary reflex to the sound of a bell, a short circuit occurs between the cells of the auditory analyzer and the cells that represent the unconditioned salivary reflex in the cortex (Fig. 11, B). These cells were called representatives of the unconditioned reflex.
The presence of unconditioned reflexes in the dog’s cerebral cortex is proven by the following facts. If you use sugar as a food irritant, salivation in response to it is produced only gradually. If any conditioned stimulus is not reinforced, then the “sugar” salivation that follows it decreases. This means that this unconditioned reflex has nerve cells located in the sphere of cortical processes. Further research has shown that if the dog's cortex is removed, its unconditioned reflexes (salivation, secretion of gastric juice, limb movements) undergo permanent changes. Consequently, unconditioned reflexes, in addition to the subcortical center, also have centers at the cortical level. At the same time, the stimulus, which is made conditional, also has a representation in the cortex. Hence the assumption arose (E.A. Asratyan, 1963) that the temporary connections of the conditioned reflex are closed between these representations (Fig. 11, IN).
Rice. 11. Various assumptions about the structure of the temporal connection of the conditioned reflex (for explanation, see the text):
1 - conditioned stimulus, 2 - cortical structures, 3 - unconditional irritant, 4 - subcortical structures, 5 - reflex reaction; broken lines show temporary connections
Consideration of the processes of closure of temporary connections as central links in the formation of a functional system (P.K. Anokhin, 1961) relates closure to the structures of the cortex, where the comparison of the signal content occurs - afferent synthesis- and the result of the conditioned reflex response - action acceptor(Fig. 11, G).
The study of motor conditioned reflexes showed a complex structure of temporary connections formed during this process (L.G. Voronin, 1952). Each movement performed on a signal itself becomes a signal for the resulting motor coordination. Two systems of temporary connections are formed: for a signal and for movement (Fig. 11, D).
Finally, based on the fact that conditioned reflexes are preserved during surgical separation of sensory and motor cortical areas and even after multiple incisions of the cortex, and also given that the cortex is abundantly supplied with both incoming and outgoing pathways, it has been suggested that the closure of temporary connections can occur in each of its microsections between its afferent and efferent elements, which activate the centers of the corresponding unconditioned reflexes that serve as reinforcement (A.B. Kogan, 1961) (see Fig. 9 and 11, E). This assumption corresponds to the idea of the emergence of a temporary connection within the analyzer of a conditioned stimulus (O.S. Adrianov, 1953), the opinion about the possibility of “local” conditioned reflexes that are closed within the projection zones (E.A. Asratyan, 1965, 1971), and the conclusion that in closing a temporary connection, the afferent link always plays a key role (U.G. Gasanov, 1972).
Neural structure of temporal connections in the cerebral cortex. Modern information about the microscopic structure of the cerebral cortex, combined with the results of electrophysiological studies, allows us to judge with a certain degree of probability the possible participation of certain cortical neurons in the formation of temporary connections.
The highly developed mammalian cerebral cortex is known to be divided into six layers of different cellular composition. The nerve fibers coming here end mostly in two types of cells. One of them is interneurons located in II, III and partly IV layers. Their axons go to V And VI layers to large pyramidal cells of the associative and centrifugal type. These are the shortest paths, which may represent innate connections of cortical reflexes.
Another type of cells with which incoming fibers form the greatest number of contacts are bush-like branching round and angular short-processed cells, often stellate in shape. They are located mainly in IV layer. Their number increases with the development of the mammalian brain. This circumstance, along with the fact that stellate cells occupy the position of the final station for impulses arriving in the cortex, suggests that it is the stellate cells that are the main perceptive cortical cells of the analyzers and that the increase in their number in evolution represents the morphological basis for achieving high subtlety and accuracy of reflection of the surrounding peace.
The system of intercalary and stellate neurons can enter into countless contacts with large associative and projection neurons of a pyramidal shape located in V And VI layers. Association neurons, with their axons passing through the white matter, connect different cortical fields with each other, and projection neurons give rise to pathways connecting the cortex with the lower parts of the brain.