Reflex- This is the body's response to irritation from the external or internal environment, carried out with the help of the central nervous system. There are unconditioned and conditioned reflexes.

Unconditioned reflexes- these are congenital, permanent, hereditarily transmitted reactions inherent in representatives of this type of organisms. For example, pupillary, knee, Achilles and other reflexes. Unconditioned reflexes ensure the interaction of the organism with the external environment, its adaptation to environmental conditions and create conditions for the integrity of the organism. Unconditioned reflexes arise immediately after the action of the stimulus, since they are carried out according to ready-made, inherited, reflex arcs, which are always constant. Complex unconditioned reflexes are called instincts.
The unconditioned reflexes include sucking and motor reflexes, which are already inherent in an 18-week-old fetus. Unconditioned reflexes are the basis for the development of conditioned reflexes in animals and humans. In children, with age, they turn into synthetic complexes of reflexes, which increases the adaptability of the organism to the external environment.

Conditioned reflexes- reactions are adaptive, temporary and strictly individual. They are inherent only to one or several representatives of the species, subjected to training (training) or exposure to the natural environment. Conditioned reflexes are developed gradually, in the presence of a certain environment, and are a function of the normal, mature cortex of the cerebral hemispheres and lower parts of the brain. In this regard, conditioned reflexes are associated with unconditioned ones, since they are the response of the same material substrate - the nervous tissue.

If the conditions for the development of reflexes are constant from generation to generation, then reflexes can become hereditary, that is, they can turn into unconditional ones. An example of such a reflex is the opening of the beak by blind and fledgling chicks in response to the shaking of the nest by a bird that comes to feed them. Since the shaking of the nest is followed by feeding, which was repeated in all generations, the conditioned reflex becomes unconditioned. However, all conditioned reflexes are adaptive reactions to a new external environment. They disappear when the cerebral cortex is removed. Higher mammals and humans with damage to the cortex become severely disabled and die in the absence of the necessary care.

Numerous experiments conducted by IP Pavlov showed that the basis for the development of conditioned reflexes is the impulses coming through the afferent fibers from the extero- or interoreceptors. For their formation, the following conditions are necessary: ​​1) the action of an indifferent (in the future conditioned) stimulus must precede the action of an unconditioned stimulus. In a different sequence, the reflex is not developed or is very weak and quickly fades; 2) for a certain time, the action of the conditioned stimulus must be combined with the action of the unconditioned stimulus, i.e., the conditioned stimulus is reinforced by the unconditioned one. This combination of stimuli should be repeated several times. In addition, a prerequisite for the development of a conditioned reflex is the normal function of the cerebral cortex, the absence of disease processes in the body and extraneous stimuli.
Otherwise, in addition to the generated reinforced reflex, there will also be an indicative, or reflex of the internal organs (intestines, bladder, etc.).

The active conditioned stimulus always causes a weak focus of excitation in the corresponding zone of the cerebral cortex. The unconditioned stimulus that is connected (after 1-5 s) creates a second, stronger focus of excitation in the corresponding subcortical nuclei and a section of the cerebral cortex, which diverts the impulses of the first (conditioned) weaker stimulus. As a result, a temporary connection is established between both foci of excitation of the cerebral cortex. With each repetition (i.e., reinforcement), this connection becomes stronger. The conditioned stimulus turns into a signal of a conditioned reflex. To develop a conditioned reflex, a conditioned stimulus of sufficient strength and high excitability of the cells of the cerebral cortex are required, which must be free from third-party stimuli. Compliance with the above conditions accelerates the development of a conditioned reflex.

Depending on the method of development, conditioned reflexes are divided into secretory, motor, vascular, reflexes of changes in internal organs, etc.

A reflex developed by reinforcing a conditioned stimulus with an unconditioned stimulus is called a first-order conditioned reflex. Based on it, you can develop a new reflex. For example, by combining a light signal with feeding, a dog has developed a strong conditioned salivation reflex. If you give a call (sound stimulus) before the light signal, then after several repetitions of this combination, the dog begins to salivate in response to the sound signal. This will be a reflex of the second order, or secondary, reinforced not by an unconditioned stimulus, but by a conditioned reflex of the first order. When developing conditioned reflexes of higher orders, it is necessary that a new indifferent stimulus be turned on 10-15 seconds before the start of the action of the conditioned stimulus of the previously developed reflex. If the stimulus acts at intervals that are closer or combined, then a new reflex will not appear, and the previously developed one will fade away, since inhibition will develop in the cerebral cortex. Repeated repetition of jointly acting stimuli or a significant overlap of the time of action of one stimulus on another causes the appearance of a reflex to a complex stimulus.

A certain period of time can also become a conditioned stimulus for developing a reflex. In humans, the time reflex is the feeling of hunger during the hours when they usually eat. Intervals can be quite short. In school-age children, the time reflex is a weakening of attention before the end of the lesson (1-1.5 minutes before the bell). This is the result of not only fatigue, but also the rhythmic work of the brain during training sessions. The reaction to time in the body is the rhythm of many periodically changing processes, for example, respiration, cardiac activity, awakening from sleep or hibernation, animal molting, etc. It is based on the rhythmic sending of impulses from the corresponding organs to the brain and back to the effector devices.

Conditioned reflexes are complex adaptive reactions of the body, carried out by the higher parts of the central nervous system by forming a temporary connection between the signal stimulus and the unconditional reflex act that reinforces this stimulus. Based on the analysis of the patterns of formation of conditioned reflexes, the school created the doctrine of higher nervous activity (see). Unlike unconditioned reflexes (see), which ensure the adaptation of the body to the constant influences of the external environment, conditioned reflexes enable the body to adapt to changing environmental conditions. Conditioned reflexes are formed on the basis of unconditioned reflexes, which requires the coincidence in time of some stimulus from the external environment (conditioned stimulus) with the implementation of one or another unconditioned reflex. The conditioned stimulus becomes a signal of a dangerous or favorable situation, enabling the body to respond with an adaptive reaction.

Conditioned reflexes are unstable and are acquired in the process of individual development of the organism. Conditioned reflexes are divided into natural and artificial. The first ones arise in response to natural stimuli in the natural conditions of existence: the puppy, which received meat for the first time, sniffs it for a long time and timidly eats it, and this act of eating is accompanied. In the future, only the sight and smell of meat causes the puppy to lick and excrete. Artificial conditioned reflexes are developed in an experimental setting, when the conditioned stimulus for the animal is an impact that is not related to unconditioned reactions in the natural habitat of animals (for example, flashing light, the sound of a metronome, sound clicks).

Conditioned reflexes are divided into food, defensive, sexual, indicative, depending on the unconditioned reaction that reinforces the conditioned stimulus. Conditioned reflexes can be named depending on the recorded response of the body: motor, secretory, vegetative, excretory, and can also be designated by the type of conditioned stimulus - light, sound, etc.

For the development of conditioned reflexes in an experiment, a number of conditions are necessary: ​​1) the conditioned stimulus must always precede the unconditioned stimulus in time; 2) the conditioned stimulus should not be strong so as not to cause its own reaction of the organism; 3) as a conditional stimulus is taken, usually found in the surrounding conditions of the habitat of a given animal or person; 4) the animal or person must be healthy, vigorous and have sufficient motivation (see).

There are also conditioned reflexes of various orders. When a conditioned stimulus is reinforced with an unconditioned stimulus, a first-order conditioned reflex is developed. If some stimulus is reinforced by a conditioned stimulus, to which a conditioned reflex has already been developed, then a second-order conditioned reflex is developed to the first stimulus. Conditioned reflexes of higher orders are developed with difficulty, which depends on the level of organization of a living organism.

In a dog, it is possible to develop conditioned reflexes up to 5-6 orders, in a monkey - up to 10-12 orders, in a person - up to 50-100 orders.

The works of I. P. Pavlov and his students established that the leading role in the mechanism of the emergence of conditioned reflexes belongs to the formation of a functional connection between the centers of excitation from conditioned and unconditioned stimuli. An important role was assigned to the cerebral cortex, where the conditioned and unconditioned stimuli, creating foci of excitation, began to interact with each other, creating temporary connections. Later, using electrophysiological research methods, it was found that the interaction between conditioned and unconditioned excitations can first occur at the level of the subcortical structures of the brain, and at the level of the cerebral cortex, the formation of an integral conditioned reflex activity is carried out.

However, the cerebral cortex always keeps the activity of subcortical formations under control.

Studies of the activity of single neurons of the central nervous system by the microelectrode method showed that both conditioned and unconditioned excitations come to one neuron (sensory-biological convergence). It is especially pronounced in the neurons of the cerebral cortex. These data made it necessary to abandon the idea of ​​the presence of foci of conditioned and unconditioned excitation in the cerebral cortex and create the theory of convergent closure of the conditioned reflex. According to this theory, a temporary connection between conditioned and unconditioned excitation arises in the form of a chain of biochemical reactions in the protoplasm of the nerve cell of the cerebral cortex.

Modern ideas about conditioned reflexes have been significantly expanded and deepened due to the study of the higher nervous activity of animals in the conditions of their free natural behavior. It has been established that the environment, along with the time factor, plays an important role in the behavior of the animal. Any stimulus from the external environment can become conditional, allowing the body to adapt to environmental conditions. As a result of the formation of conditioned reflexes, the body reacts some time before exposure to an unconditioned stimulus. Consequently, conditioned reflexes contribute to the successful finding of food by animals, help to avoid danger in advance and most perfectly navigate in the changing conditions of existence.

UNCONDITIONED REFLEX (species, natural reflex) - a constant and innate reaction of the body to certain influences of the external world, carried out with the help of the nervous system and does not require special conditions for its occurrence. The term was introduced by IP Pavlov in the study of the physiology of higher nervous activity. An unconditioned reflex occurs unconditionally if adequate stimulation is applied to a certain receptor surface. In contrast to this unconditionally emerging reflex, IP Pavlov discovered the category of reflexes, for the formation of which a number of conditions must be met - a conditioned reflex (see).

The physiological feature of the unconditioned reflex is its relative constancy. An unconditioned reflex always occurs with the corresponding external or internal stimuli, manifesting itself on the basis of innate neural connections. Since the constancy of the corresponding unconditioned reflex is the result of the phylogenetic development of a given animal species, this reflex received the additional name "species reflex".

The biological and physiological role of the unconditioned reflex lies in the fact that, thanks to this innate reaction, animals of a given species adapt (in the form of expedient acts of behavior) to the constant factors of existence.

The division of reflexes into two categories - unconditioned and conditioned - corresponds to two forms of the nervous activity of animals and humans, which were clearly distinguished by IP Pavlov. The totality of the unconditioned reflex is the lower nervous activity, while the totality of acquired, or conditioned, reflexes is the higher nervous activity (see).

From this definition it follows that the unconditioned reflex, in its physiological significance, along with the implementation of constant adaptive reactions of the animal in relation to the action of environmental factors, also determines those interactions of nervous processes that, in sum, direct the internal life of the organism. IP Pavlov attached particular importance to this last property of the unconditioned reflex. Thanks to the innate neural connections that ensure the interaction of organs and processes within the body, the animal and the person acquire an accurate and stable course of basic vital functions. The principle on the basis of which these interactions and the integration of activities within the body are organized is the self-regulation of physiological functions (see).

The classification of unconditioned reflexes can be built on the basis of the specific properties of the acting stimulus and the biological meaning of the responses. It was on this principle that the classification was built in the laboratory of IP Pavlov. In accordance with this, there are several types of unconditioned reflex:

1. Food, the causative agent of which is the action of food substances on the receptors of the tongue and on the basis of the study of which all the basic laws of higher nervous activity are formulated. Due to the spread of excitation from the receptors of the tongue towards the central nervous system, the branched innate nervous structures are excited, which in general make up the food center; as a result of such a fixed relationship between the central nervous system and the working peripheral apparatuses, responses of the whole organism are formed in the form of an unconditioned food reflex.

2. Defensive, or, as it is sometimes called, protective reflex. This unconditioned reflex has a number of forms, depending on which organ or part of the body is in danger. So, for example, the application of pain irritation to a limb causes a withdrawal of the limb, which protects it from further destructive action.

In a laboratory setting, as an irritant that causes a defensive unconditioned reflex, they usually use electric current from the corresponding devices (Dubois-Reymond induction coil, city current with a corresponding voltage drop, etc.). If air movement directed at the cornea of ​​the eye is used as an irritant, then the defensive reflex is manifested by the closing of the eyelids - the so-called blinking reflex. If the irritants are potent gaseous substances that are passed through the upper respiratory tract, then the delay in respiratory excursions of the chest will be a protective reflex. The most commonly used in the laboratory of IP Pavlov is a kind of protective reflex - an acid protective reflex. It is expressed by a strong rejection reaction (vomiting) in response to the infusion of hydrochloric acid solution into the animal's oral cavity.

3. Sexual, which certainly arises in the form of sexual behavior in response to an adequate sexual stimulus in the form of an individual of the opposite sex.

4. Approximate-exploratory, which is manifested by a rapid movement of the head towards the external stimulus that has acted at the moment. The biological meaning of this reflex consists in a detailed examination of the acting stimulus and, in general, of the external environment in which this stimulus arose. Due to the presence in the central nervous system of the innate pathways of this reflex, the animal is able to expediently respond to sudden changes in the external world (see Orienting-exploratory reaction).

5. Reflexes from internal organs, reflexes during irritation of muscles, tendons (see Visceral reflexes, Tendon reflexes).

A common property of all unconditioned reflexes is that they can serve as the basis for the formation of acquired, or conditioned, reflexes. Some of the unconditioned reflexes, for example, defensive ones, lead to the formation of conditioned reactions very quickly, often after one combination of some external stimulus with pain reinforcement. The ability of other unconditioned reflexes, for example, blinking or knee, to form temporary connections with an indifferent external stimulus is less pronounced.

It should also be taken into account that the rate of development of conditioned reflexes is directly dependent on the strength of the unconditioned stimulus.

The specificity of unconditioned reflexes lies in the exact correspondence of the body's response to the nature of the stimulus acting on the receptor apparatus. So, for example, when the taste buds of the tongue are irritated by a certain food, the reaction of the salivary glands in terms of the quality of the discharged secret is in exact accordance with the physical and chemical properties of the food taken. If the food is dry, then watery saliva is separated, but if the food is sufficiently moistened, but consists of pieces (for example, bread), the unconditioned salivary reflex will manifest itself in accordance with this food quality: saliva will contain a large amount of mucous glucoprotein - mucin, which prevents injury to food ways.

A fine receptor assessment is associated with a lack of one or another substance in the blood, for example, the so-called calcium starvation in children during the period of bone formation. Since calcium selectively passes through the capillaries of the developing bones, eventually its amount becomes below the constant. This factor is a selective stimulus of some specific cells of the hypothalamus, which in turn keeps the tongue receptors in a state of increased excitability. This is how the desire for children to eat plaster, whitewash and other mineral substances containing calcium is formed.

Such an expedient correspondence of the unconditioned reflex to the quality and strength of the acting stimulus depends on the extremely differentiated action of food substances and their combinations on the receptors of the tongue. Receiving these combinations of afferent excitations from the periphery, the central apparatus of the unconditioned reflex sends efferent excitations to the peripheral apparatuses (glands, muscles), leading to the formation of a certain composition of saliva or the appearance of movements. Indeed, the composition of saliva can be easily changed through a relative change in the production of its main ingredients: water, proteins, salts. From this it follows that the central apparatus of salivation can vary the quantity and quality of the excited elements depending on the quality of the excitation that came from the periphery. The correspondence of the unconditioned response to the specificity of the applied stimulus can go quite far. IP Pavlov developed the concept of the so-called digestive warehouse of certain unconditioned reactions. For example, if an animal is fed a certain type of food for a long time, then the digestive juices of its glands (gastric, pancreatic, etc.) eventually acquire a certain composition in terms of the amount of water, inorganic salts, and especially the activity of enzymes. Such a "digestive warehouse" cannot but be recognized as an expedient adaptation of innate reflexes to the established constancy of food reinforcement.

At the same time, these examples show that the stability, or immutability, of the unconditioned reflex is only relative. There is reason to believe that already in the first days after birth, the specific "tuning" of the language receptors is prepared by the embryonic development of animals, which ensures the successful selection of nutrients and the planned course of unconditioned reactions. So, if the percentage of sodium chloride content in the mother's milk, which a newborn child eats, is increased, then the child's sucking movements are immediately inhibited, and in some cases the child actively throws out the already taken mixture. This example convinces us that the innate properties of food receptors, as well as the properties of intranervous relationships, most accurately reflect the needs of the newborn.

Methodology for applying unconditioned reflexes

Since in the practice of work on higher nervous activity the unconditioned reflex is a reinforcing factor and the basis for the development of acquired, or conditioned, reflexes, the question of methodological methods for using the unconditioned reflex becomes especially important. In experiments on conditioned reflexes, the use of the alimentary unconditioned reflex is based on feeding the animal certain food substances from an automatically supplied feeder. With this method of using the unconditioned stimulus, the direct action of food on the receptors of the animal's tongue is inevitably preceded by a number of side irritations of the receptors related to various analyzers (see).

No matter how technically perfect the feeding of the feeder is, it will certainly produce some kind of noise or knock and, therefore, this sound stimulus is the inevitable precursor of the truest unconditioned stimulus, that is, the stimulus of the taste buds of the tongue. To eliminate these defects, a method was developed for the direct introduction of nutrients into the oral cavity, while irrigation of the taste buds of the tongue, for example, with a sugar solution, is a direct unconditioned stimulus, not complicated by any side agent.

It should be noted, however, that under natural conditions, animals and humans never receive food into the oral cavity without preliminary sensations (the sight, the smell of food, etc.). Therefore, the method of direct introduction of food into the mouth has some abnormal conditions and the reaction of the animal to the unusualness of such a procedure.

In addition to this use of an unconditioned stimulus, there are a number of methods in which the animal itself receives food with the help of special movements. These include a wide variety of devices with the help of which an animal (rat, dog, monkey), by pressing the appropriate lever or button, receives food - the so-called instrumental reflexes.

The methodological features of reinforcement with an unconditioned stimulus have an undoubted influence on the experimental results obtained, and, therefore, the evaluation of the results should be made taking into account the type of unconditioned reflex. This is especially true for the comparative evaluation of the alimentary and defensive unconditioned reflexes.

While reinforcement with a food unconditioned stimulus is a factor of positive biological significance for the animal (I. P. Pavlov), on the contrary, reinforcement with a painful stimulus is a stimulus for a biologically negative unconditioned reaction. It follows from this that "non-reinforcement" of a well-hardened conditioned reflex by an unconditioned stimulus in either case will have an opposite biological sign. While non-reinforcement of the conditioned stimulus with food leads to a negative and often aggressive reaction in the experimental animal, on the contrary, non-reinforcement of the conditioned signal with an electric current leads to a completely distinct biological positive reaction. These features of the animal's attitude to the non-reinforcement of the conditioned reflex by one or another unconditioned stimulus can be well identified by such a vegetative component as respiration.

Composition and localization of unconditioned reflexes

The development of experimental techniques made it possible to study the physiological composition and localization of the unconditioned alimentary reflex in the central nervous system. For this purpose, the very action of the unconditioned food stimulus on the receptors of the tongue was studied. An unconditioned stimulus, regardless of its nutritional properties and consistency, primarily irritates the tactile receptors of the tongue. This is the fastest type of excitation, which is part of the unconditioned irritation. Tactile receptors produce the fastest and highest-amplitude type of nerve impulses, which are the first to propagate along the lingual nerve to the medulla oblongata and only after a few fractions of a second (0.3 seconds) do nerve impulses from temperature and chemical irritation of the tongue receptors arrive there. This feature of the unconditioned stimulus, which manifests itself in the successive excitation of various receptors of the tongue, is of great physiological importance: in the central nervous system, conditions are created for signaling each previous stream of impulses about subsequent stimuli. Owing to such correlations and characteristics of tactile excitation, which depend on the mechanical properties of the given food, in response to these excitations alone, salivation can occur before the chemical properties of the food act.

Special experiments carried out on dogs and a study of the behavior of newborns have shown that such correlations between individual parameters of the unconditioned stimulus are used in the adaptive behavior of the newborn.

So, for example, in the first days after birth, the chemical qualities of the child's food intake are the decisive stimulus. However, after a few weeks, the leading role passes to the mechanical properties of food.

In the life of adults, information about the tactile parameters of food is faster than information about chemical parameters in the brain. Due to this pattern, the sensation of “porridge”, “sugar”, etc. is born before the chemical signal arrives in the brain. According to the teachings of I. P. Pavlov about the cortical representation of the unconditioned reflex, each unconditioned irritation, along with the inclusion of subcortical apparatuses, has its own representation in the cerebral cortex. Based on the above data, as well as oscillographic and electroencephalographic analysis of the distribution of unconditioned excitation, it was found that it does not have a single point or focus in the cerebral cortex. Each of the fragments of unconditioned excitation (tactile, temperature, chemical) is addressed to different points of the cerebral cortex, and only almost simultaneous excitation of these points of the cerebral cortex establishes a systemic connection between them. These new data correspond to IP Pavlov's ideas about the structure of the nerve center, but require a change in existing ideas about the "cortical point" of the unconditioned stimulus.

Studies of cortical processes with the help of electrical devices have shown that the unconditioned stimulus comes to the cerebral cortex in the form of a very generalized stream of ascending excitations, and, obviously, to each cell of the cortex. This means that not a single excitation of the sense organs that preceded the unconditioned stimulus can "escape" its convergence with the unconditioned excitation. These properties of the unconditioned stimulus reinforce the idea of ​​the "convergent closure" of the conditioned reflex.

Cortical representations of unconditioned reactions are such cellular complexes that take an active part in the formation of a conditioned reflex, that is, in the closing functions of the cerebral cortex. By its nature, the cortical representation of the unconditioned reflex must have an afferent character. As you know, I. P. Pavlov considered the cerebral cortex "an isolated afferent section of the central nervous system."

Complex unconditioned reflexes. I. P. Pavlov singled out a special category of the unconditioned reflex, in which he included innate activities that have a cyclic and behavioral character - emotions, instincts and other manifestations of complex acts of innate activity of animals and humans.

According to the initial opinion of IP Pavlov, complex unconditioned reflexes are a function of the "nearest subcortex". This general expression refers to the thalamus, hypothalamus, and other parts of the diencephalon and midbrain. However, later, with the development of ideas about the cortical representations of the unconditioned reflex, this point of view was also transferred to the concept of complex unconditioned reflexes. Thus, a complex unconditioned reflex, for example, an emotional discharge, has a specific subcortical part in its composition, but at the same time, the very course of this complex unconditioned reflex at each individual stage has a representation in the cerebral cortex. This point of view of IP Pavlov was confirmed by recent studies using the method of neurography. It has been shown that a number of cortical regions, for example, the orbital cortex, the limbic region, are directly related to the emotional manifestations of animals and humans.

According to I.P. Pavlov, complex unconditioned reflexes (emotions) are "blind force" or "the main source of force" for cortical cells. The statements made by I. P. Pavlov about complex unconditioned reflexes and their role in the formation of conditioned reflexes at that time were only at the stage of the most general development, and only in connection with the discovery of the physiological characteristics of the hypothalamus, the reticular formation of the brain stem, it became possible to study this Problems.

From the point of view of IP Pavlov, the instinctive activity of animals, which includes several different stages of animal behavior, is also a complex unconditioned reflex. The features of this type of unconditioned reflex are that the individual stages of the performance of any instinctive action are connected with each other according to the principle of a chain reflex; however, later it was shown that each such stage of behavior must necessarily have a reverse afferentation) from the results of the action itself, that is, to carry out the process of comparing the actually obtained result with the previously predicted one. Only then can the next stage of behavior be formed.

In the process of studying the pain unconditioned reflex, it was revealed that pain excitation undergoes significant transformations at the level of the brain stem and hypothalamus. Of these structures, unconditioned excitation generally covers all areas of the cerebral cortex simultaneously. Thus, along with the mobilization in the cerebral cortex of the systemic connections inherent in a given unconditioned excitation and forming the basis of the cortical representation of the unconditioned reflex, unconditioned stimulation also produces a generalized effect on the entire cerebral cortex. In electroencephalographic analysis of cortical activity, this generalized effect of an unconditioned stimulus on the cerebral cortex manifests itself in the form of desynchronization of cortical wave electrical activity. The conduction of pain unconditional excitation to the cerebral cortex can be blocked at the level of the brain stem with the help of a special substance - chlorpromazine. After the introduction of this substance into the blood, even a strong damaging (nociceptive) unconditional excitation (hot water burn) does not reach the cerebral cortex and does not change its electrical activity.

Development of unconditioned reflexes in the embryonic period

The innate nature of the unconditioned reflex is especially clearly revealed in studies of the embryonic development of animals and humans. At different stages of embryogenesis, each stage of the structural and functional formation of the unconditioned reflex can be traced. The vital functional systems of the newborn are fully consolidated by the time of birth. Separate links of a sometimes complex unconditioned reflex, such as the sucking reflex, include various parts of the body, often at a considerable distance from each other. Nevertheless, they are selectively combined by various connections and gradually form a functional whole. The study of the maturation of the unconditioned reflex in embryogenesis makes it possible to understand the constant and relatively unchanging adaptive effect of the unconditioned reflex when an appropriate stimulus is applied. This property of the unconditioned reflex is associated with the formation of interneuronal relationships based on morphogenetic and genetic patterns.

The maturation of the unconditioned reflex in the embryonic period is not the same for all animals. Since the maturation of the functional systems of the embryo has the most important biological meaning in preserving the life of a newborn of a given animal species, then, depending on the characteristics of the conditions for the existence of each animal species, the nature of structural maturation and the final formation of the unconditioned reflex will exactly correspond to the characteristics of this species.

Thus, for example, the structural design of the spinal coordination reflexes is different in birds, which immediately become completely independent after hatching from the egg (chicken), and in birds that, after hatching from the egg, are helpless for a long time and are in the care of their parents (rooks). While the chick stands on its feet immediately after hatching and uses them completely freely every other day, in the rook, on the contrary, the forelimbs, that is, the wings, are the first to come into action.

This selective growth of the nervous structures of the unconditioned reflex takes place even more clearly in the development of the human fetus. The very first and clearly manifested motor reaction of the human fetus is a grasping reflex; it is detected as early as the 4th month of intrauterine life and is caused by the application of any solid object to the palm of the fetus. The morphological analysis of all links of this reflex convinces us that before it is revealed, a number of nervous structures differentiate into mature neurons and unite with each other. Myelination of the nerve trunks related to the flexors of the fingers begins and ends before this process unfolds in the nerve trunks of other muscles.

Phylogenetic development of unconditioned reflexes

According to the well-known position of I.P. Pavlov, unconditioned reflexes are the result of fixing by natural selection and heredity those reactions acquired over millennia that correspond to repeated environmental factors and are useful for a given species.

There is reason to believe that the fastest and most successful adaptations of an organism may depend on favorable mutations, which are subsequently selected by natural selection and are already inherited.

Bibliography: Anokhin P.K. Biology and neurophysiology of the conditioned reflex, M., 1968, bibliogr.; Afferent link of interoceptive reflexes, ed. Edited by I. A. Bulygina. Moscow, 1964. Vedyaev F. P. Subcortical mechanisms of complex motor reflexes, JI., 1965, bibliogr.; Vinogradova O. S. Orienting reflex and its neurophysiological mechanisms, M., 1961, bibliogr.; Groysman S. D. and Dekush P. G. Attempt of a quantitative research of intestinal reflexes, Pat. physiol. and Experiment, ter., v. 3, p. 51, 1974, bibliogr.; Orbeli JI. A. Questions of higher nervous activity, p. 146, M.-JI., 1949; Pavlov I.P. Complete works, vol. 1-6, M., 1951 - 1952; Petukhov BN Closing after the loss of the main unconditioned reflexes, Proceedings of the Center, Institute of Improvements. doctors, t. 81, p. 54, M., 1965, bibliography; Salch e n to about IN The latent periods of the myotatic reflexes providing motive interactions of people, Fiziol. man, vol. 1, Jvft 2, p. 317, 197 5, bibliography; Sechenov I. M. Reflexes of the brain, M., 1961; Slonim AD Fundamentals of general economic physiology of mammals, p. 72, M, -JI., 1961, bibliogr.; Human Physiology, ed. E. B. Babsky, p. 592, M., 1972; Frank Stein S. I. Respiratory reflexes and mechanisms of shortness of breath, M., 1974, bibliogr.; Shu with t and NA N. Analysis of unconditioned reflexes in the light of the doctrine of the dominant, Fiziol, zhurn. USSR, vol. 61, JSft 6, p. 855, 1975, bibliography; Human reflexes, pathophysiology of motor systems, ed. by J. E. Desment, Basel a. o., 1973; Mechanisms of orienting reaction in man, ed. by I. Ruttkay-Nedecky a. o., Bratislava, 1967.

The outstanding Russian physiologist I.M. Sechenov was the first to express the idea of ​​the connection between the consciousness and thinking of a person with the reflex activity of his brain. This idea was developed and convincingly confirmed in numerous experiments by I.P. Pavlova. Therefore, I.P. Pavlov is considered the creator of the doctrine of higher nervous activity.

Higher nervous activity- these are the functions of the cerebral cortex and the nearest subcortical formations, where temporary nerve connections (conditioned reflexes) are developed anew, providing the most subtle and perfect individual adaptation of the body to changing environmental conditions.

UNCONDITIONAL AND CONDITIONAL REFLEXES

Higher nervous activity is reflex in nature. Unconditioned and conditioned reflexes are inherent in higher animals and man. Their specifics are as follows.

unconditioned reflexes, ensuring the maintenance of life in relatively constant environmental conditions, inherent in man from birth. These include food (sucking, swallowing, salivation, etc.), defensive (coughing, blinking, hand withdrawal, etc.), reproduction (feeding and caring for offspring), respiratory, etc.

Conditioned reflexes are produced on the basis of unconditioned when exposed to a conditioned stimulus. They provide a more perfect adaptation of the body to changing environmental conditions. They help to find food by smell, get away from danger, navigate, etc.

Meaning of the word. In humans, conditioned reflexes can be formed not only as in animals, on the basis of the first signal system, when the conditioned stimuli are directly objects of the outside world, but also on the basis of the second (speech) signal system, when the conditioned stimuli are words expressing concepts of objects and phenomena . Conditioned reflexes are the physiological basis of technical processes, the basis of thinking. The word is a kind of stimulus for many conditioned reflexes. For example, just talking about food or describing it can cause a person to salivate.

Features of conditioned and unconditioned reflexes

Unconditioned reflexes	Conditioned reflexes (temporary connections)
Congenital, hereditarily transmitted reflex reactions of this type	Acquired in the process of individual development based on unconditioned reflexes
Reflex centers are located in the subcortical nuclei, brain stem and spinal cord	Reflex centers are located in the cerebral cortex
Racks. They persist throughout life. Their number is limited	Changeable. New reflections arise, and the old ones fade away when the environmental conditions change. Quantity is unlimited
Carry out the relationship of parts of the body, reflex self-regulation and maintaining the constancy of the internal environment	Carry out a reflex reaction of the body to a stimulus (conditioned), signaling the upcoming action of an unconditioned stimulus

The consciousness of people is connected with the activity of the cerebral cortex. This has been convincingly proven by numerous experiments by IP Pavlov, as well as by the study of diseases and disorders of the brain.

The teachings of IP Pavlov on the higher nervous activity of a person convincingly proved the inconsistency and anti-science of religious ideas about the "soul".

Inhibition of conditioned reflexes. When environmental conditions change, previously developed conditioned reflexes fade away, new ones are formed. IP Pavlov distinguished two types of inhibition of conditioned reflexes.

External braking occurs when the body is exposed to an irritant that is stronger than the previous one. At the same time, a new focus of excitation is formed in the cerebral cortex. For example, in a dog, a conditioned salivary reflex developed to light (see "Digestion") is inhibited under experimental conditions by a stronger stimulus - the sound of a bell. The latter causes a strong excitation in the auditory zone of the cerebral cortex. At first, it generates inhibition of neighboring areas, and then spreads to the visual zone. Therefore, excitation through the neurons located in it cannot be carried out and the arc of the former conditioned reflex is interrupted.

Internal braking occurs in the arc of the conditioned reflex when the conditioned stimulus ceases to receive reinforcement from the unconditioned stimulus and the temporary connections formed in the cortex are gradually inhibited. When conditioned reflexes are repeated in the same sequence, dynamic stereotypes are formed that make up habits and skills.

Hygiene of physical and mental labor. The activity of the body depends on the state of the central nervous system. Its overwork leads to a breakdown of the vital functions of the body, reduces perception, attention, memory and performance.

With monotonous physical labor, only one muscle group works and only one section of the central nervous system is excited, which leads to its fatigue.

To avoid overwork, it is useful to carry out industrial gymnastics during breaks, in which other muscles participate. This, in turn, leads to the excitation of new areas of the cerebral cortex, inhibition of previously working areas, their rest and restoration of working capacity.

Mental labor also causes fatigue of the central nervous system. The best rest in this case is gymnastics or other physical activity.

Of great importance in the formation of conditioned reflexes is the regime of the day. If it is observed, a person develops many important conditioned reflexes that stimulate the better functioning of various organ systems and prevent their overwork.

The alternation of physical and mental labor, rationalization of labor, observance of the daily routine, active rest are of paramount importance for protecting the central nervous system from overwork.

Sleep gives the most complete rest to the central nervous system. The alternation of sleep and wakefulness is a necessary condition for human existence. I.P. Pavlov proved experimentally that sleep is an inhibition that covers the cerebral cortex and other parts of the brain. During sleep, metabolism, hearing, smell, and the intensity of activity of a number of organ systems decrease, muscle tone decreases, and thinking is turned off. Sleep is a protective device against overwork of the nervous system. Babies sleep 20-22 hours, schoolchildren - 9-11 hours, adults - 7-8 hours. With lack of sleep, a person loses his ability to work. In order for the body to get the most complete rest during sleep, it is necessary to go to bed at the same time, eliminate bright lights, noise, ventilate the room, etc.

Unconditioned and conditioned reflexes.

An element of higher nervous activity is a conditioned reflex. The path of any reflex forms a kind of arc, consisting of three main parts. The first part of this arc, which includes the receptor, sensory nerve and brain cell, is called the analyzer. This part perceives and distinguishes the whole complex of various external influences that enter the body.

The cerebral cortex (according to Pavlov) is a collection of cerebral ends of various analyzers. Stimuli from the external world come here, as well as impulses from the internal environment of the organism, which leads to the formation of numerous foci of excitation in the cortex, which, as a result of induction, cause points of inhibition. Thus, a kind of mosaic arises, consisting of alternating points of excitation and inhibition. This is accompanied by the formation of numerous conditional connections (reflexes), both positive and negative. As a result, a certain functional dynamic system of conditioned reflexes is formed, which is the physiological basis of the psyche.

Two main mechanisms carry out higher nervous activity: conditioned reflexes and analyzers.

Each animal organism can exist only if it constantly balances (interacts) with the external environment. This interaction is carried out through certain connections (reflexes). I.P. Pavlov singled out permanent connections, or unconditioned reflexes. With these connections, an animal or a person will be born - these are ready-made, constant, stereotyped reflexes. Unconditioned reflexes, such as the reflex to urinate, defecate, the sucking reflex in a newborn, salivation, are various forms of simple defensive reactions. Such reactions are the constriction of the pupil to light, the closing of the eyelid, the withdrawal of the hand in case of sudden irritation, etc. Complex unconditioned reflexes in humans include instincts: food, sexual, orienting, parental, etc. Both simple and complex unconditioned reflexes are innate mechanisms, they operate even at the lowest levels of development of the animal world. So, for example, the weaving of a web by a spider, the construction of honeycombs by bees, the nesting of birds, sexual desire - all these acts do not arise as a result of individual experience, learning, but are innate mechanisms.

However, the complex interaction of animal and man with the environment requires the operation of a more complex mechanism.

In the process of adaptation to living conditions in the cerebral cortex, another type of connection with the external environment is formed - temporary connections, or conditioned reflexes. The conditioned reflex, according to Pavlov, is an acquired reflex, developed under certain conditions, subject to fluctuations. If not reinforced, it can weaken, lose its direction. Therefore, these conditioned reflexes are called temporary connections.

The main conditions for the formation of a conditioned reflex in an elementary form in animals are, firstly, the combination of a conditioned stimulus with an unconditioned reinforcement and, secondly, the combination of the conditioned stimulus that preceded the action of the unconditioned reflex. Conditioned reflexes are developed on the basis of unconditioned or on the basis of well-developed conditioned reflexes. In this case, they are called conditioned or conditioned reflexes of the second order. The material basis of unconditioned reflexes are the lower levels of the brain, as well as the spinal cord. Conditioned reflexes in higher animals and humans are formed in the cerebral cortex. Of course, in each nervous act it is impossible to clearly distinguish between the action of unconditioned and conditioned reflexes: undoubtedly, they will represent a system, although they differ in the nature of their formation. The conditioned reflex, being at first generalized, is then refined and differentiated. Conditioned reflexes as neurodynamic formations enter into certain functional relationships with each other, forming various functional systems, and are thus the physiological basis of thinking,

knowledge, skills, labor skills.

To understand the mechanism of formation of a conditioned reflex in its elementary form in a dog, the well-known experiment of I.P. Pavlov and his students (Fig. 56).

The essence of the experiment is as follows. It is known that during the act of feeding in animals (in particular, in dogs), saliva and gastric juice begin to stand out. These are natural manifestations of the unconditioned food reflex. Similarly, when acid is poured into a dog's mouth, saliva is abundantly secreted, washing away acid particles that irritate it from the mucous membranes of the mouth. This is also a natural manifestation of the defensive reflex, which is carried out in this case through the salivary center in the medulla oblongata. However, under certain conditions it is possible to make a dog salivate in response to an indifferent stimulus, such as the light of a light bulb, the sound of a horn, a musical tone, and so on. To do this, before giving the dog food, light a lamp or give a call. If you combine this technique one or more times, and then act only with one conditioned stimulus, without accompanying it with food, then you can cause the dog to release saliva in response to the action of an indifferent stimulus. What explains this? In the dog's brain, during the period of action of the conditioned and unconditioned stimulus (light and food), certain areas of the brain come into a state of excitation, in particular the visual center and the center of the salivary gland (in the medulla oblongata). Being in a state of excitation, the food center forms a point of excitation in the cortex as a cortical representation of the center of the unconditioned reflex. The repeated combination of indifferent and unconditioned stimuli leads to the formation of a lightened, "beaten" path. Between these points of excitation a chain is formed in which a series of irritated points is closed. In the future, it is enough to stimulate only one link in a closed chain, in particular the visual center, as the entire developed connection is activated, which will be accompanied by a secretory effect. Thus, a new connection was established in the dog's brain - a conditioned reflex. The arc of this reflex closes between the cortical foci of excitation, arising as a result of the action of an indifferent stimulus, and the cortical representations of the centers of unconditioned reflexes. However, this relationship is temporary. Experiments have shown that for some time the dog will salivate only in response to the action of a conditioned stimulus (light, sound, etc.), but soon this reaction will cease. This will indicate that the connection has died out; True, it does not disappear without a trace, but only slows down. It can be restored again by combining feeding with the action of a conditioned stimulus; again salivation can be obtained only on the action of light. This experience is elementary, but it is of fundamental importance.

The point is that the reflex mechanism is the main physiological mechanism in the brain of not only animals, but also humans. However, the ways of formation of conditioned reflexes in animals and humans are not the same. The fact is that the formation of conditioned reflexes in humans is regulated by a special second signaling system peculiar only to humans, which does not exist in the brain of even higher animals. The real expression of this second signaling system is the word, speech. Hence, the mechanical transfer of all laws obtained on animals to explain the entire higher nervous activity of man will not be justified. I.P. Pavlov suggested observing "the greatest caution" in this matter. However, in general terms, the principle of the reflex and a number of basic laws governing the higher nervous activity of animals retain their significance for humans as well.

Pupils of I.P. Pavlova N.I. Krasnogorsky, A.G. Ivanov - Smolensky, N.I. Protopopov and others did a lot of research on conditioned reflexes in people, in particular in children. Therefore, material has now been accumulated that makes it possible to make an assumption about the features of higher nervous activity in various acts of behavior. So, for example, in the second signaling system, conditioned connections can be formed quickly and more firmly held in the cerebral cortex.

Take for example such a process close to us as teaching children to read and write. It used to be assumed that the basis of literacy (learning to read and write) is the development of special centers for reading and writing. Now science denies the existence in the cerebral cortex of some local areas, anatomical centers, as if specializing in the area of ​​these functions. In the brain of people who have not mastered literacy, such centers naturally do not exist. But how do these skills develop? What are the functional mechanisms of such completely new and real manifestations in the mental activity of a child who has mastered literacy? This is where the most correct idea will be that the physiological mechanism of literacy skills are nerve connections that form specialized systems of conditioned reflexes. These connections are not laid down by nature, they are formed as a result of the interaction of the student's nervous system with the external environment. In this case, such an environment will be a class - a literacy lesson. The teacher, starting to teach literacy, shows the students on the appropriate tables or writes individual letters on the board, and the students copy them in their notebooks. The teacher not only shows letters (visual perception), but also pronounces certain sounds (auditory perception). As you know, writing is carried out by a certain movement of the hand, which is associated with the activity of the motor-kinesthetic analyzer. When reading, there is also a movement of the eyeball, which moves in the direction of the lines of text being read. Thus, during the period of learning to read and write, numerous stimuli enter the cerebral cortex of the child, signaling the optical, acoustic and motor appearance of letters. All this mass of irritations leaves nerve traces in the cortex, which are gradually balanced, reinforced by the speech of the teacher and the student's own oral speech. As a result, a specialized system of conditional connections is formed, reflecting sound-letters and their combinations in various verbal complexes. This system - a dynamic stereotype - is the physiological basis of school literacy skills. It can be assumed that the formation of various labor skills is a consequence of the formation of neural connections that arise in the process of learning a skill - through vision, hearing, tactile and motor receptors. At the same time, one must keep in mind the importance of innate inclinations, on which the nature and results of the development of one or another ability depend. All these connections, arising as a result of nervous stimuli, enter into complex relationships and form functional-dynamic systems, which are also the physiological basis of labor skills.

As is known from elementary laboratory experiments, a conditioned reflex that is not reinforced by food fades, but does not disappear completely. We see something similar in people's lives. There are known facts when a person who learned to read and write, but then, due to life circumstances, did not deal with a book, to a large extent lost the once acquired literacy skills. Who does not know such facts when the acquired skill in the field of theoretical knowledge or labor skills, not supported by systematic work, is weakened. However, it does not disappear completely, and a person who has studied this or that skill, but then left it for a long time, only feels very insecure at first if he again has to return to his former profession. However, it will relatively quickly restore the lost quality. The same can be said about people who once studied a foreign language, but then thoroughly forgot it due to lack of practice; undoubtedly, it is easier for such a person, with appropriate practice, to re-learn the language than for another who will learn a new language for the first time.

All this suggests that traces of past stimuli remain in the cerebral cortex, but, not reinforced by exercise, they fade away (slow down).

Analyzers

Analyzers are understood as formations that carry out the knowledge of the external and internal environment of the body. These are, first of all, taste, skin, olfactory analyzers. Some of them are called distant (visual, auditory, olfactory), because they can perceive irritation at a distance. The internal environment of the body also sends constant impulses to the cerebral cortex.

1-7 - receptors (visual, auditory, skin, olfactory, taste, motor apparatus, internal organs). I - area of ​​the spinal or medulla oblongata where afferent fibers enter (A); impulses from which are transmitted to the neurons located here, forming ascending paths; the axons of the latter go to the region of the visual tubercles (II); the axons of the nerve cells of the thalamus ascend to the cerebral cortex (III). At the top (III), the location of the nuclear parts of the cortical sections of various analyzers is outlined (for the internal, gustatory and olfactory analyzers, this location has not yet been accurately established); scattered cells of each analyzer scattered over the cortex are also indicated (according to Bykov)

One of these analyzers is the motor analyzer, which receives impulses from the skeletal muscles, joints, ligaments and informs the cortex about the nature and direction of movement. There are other internal analyzers - interoreceptors that signal to the cortex about the state of internal organs.

Each analyzer consists of three parts (Fig. 57). Peripheral end, i.e. The receptor is directly exposed to the external environment. These are the retina of the eye, the cochlear apparatus of the ear, sensitive devices of the skin, etc., which are connected to the brain end through the conducting nerves, i.e. specific area of ​​the cerebral cortex. Hence, the occipital cortex is the cerebral end of the visual, temporal - auditory, parietal - skin and musculo-articular analyzers, etc. In turn, the cerebral end, already in the cerebral cortex, is divided into a nucleus, where the most subtle analysis and synthesis of certain stimuli is carried out, and secondary elements located around the main nucleus and representing the analyzer periphery. The boundaries of these secondary elements between individual analyzers are fuzzy and overlap. In the analyzer periphery, a similar analysis and synthesis is carried out only in the most elementary form. The motor area of ​​the cortex is the same analyzer of the skeletal-motor energy of the body, but its peripheral end is turned into the internal environment of the body. Characteristically, the analyzer apparatus acts as a holistic formation. Thus, the cortex, including in its composition numerous analyzers, is itself a grandiose analyzer of the external world and the internal environment of the organism. The stimuli that have entered certain cells of the cortex through the peripheral ends of the analyzers produce excitation in the corresponding cellular elements, which is associated with the formation of temporary nerve connections - conditioned reflexes.

Excitation and inhibition of nervous processes

The formation of conditioned reflexes is possible only in an active, active state of the cerebral cortex. This activity is determined by the flow in the cortex of the main nervous processes - excitation and inhibition.

Excitation is an active process that occurs in the cellular elements of the cortex when it is exposed to certain stimuli of the external and internal environment through the analyzers. The process of excitation is accompanied by a special state of nerve cells in a particular area of ​​the cortex, which is associated with the active activity of the coupling apparatus (synapses) and the release of chemicals (mediators) such as acetylcholine. In the area of ​​occurrence of foci of excitation, there is an increased formation of nerve connections - here the so-called active working field is formed.

Braking(delay) is also not a passive, but an active process. This process, as it were, forcibly restrains excitement. Braking is characterized by varying degrees of intensity. I.P. Pavlov attached great importance to the inhibitory process, which regulates the activity of excitation, "holds it in his fist." He singled out and studied several types, or forms, of the inhibitory process.

External inhibition is an innate mechanism based on unconditioned reflexes, acts immediately (from the spot) and can suppress conditioned reflex activity. An example illustrating the action of external inhibition was the fact, not uncommon in the laboratory, when the established conditioned reflex activity in dogs to the action of a conditioned stimulus (for example, salivation to light) suddenly ceased as a result of some extraneous strong sounds, the appearance of a new face, etc. d. The orienting unconditioned reflex to novelty that arose in the dog inhibited the course of the developed conditioned reflex. In people's lives, we can often encounter similar facts, when intense mental activity associated with the performance of a particular job may be disturbed due to the appearance of some extra irritants, for example, with the appearance of new faces, loud conversation, some sudden noises and etc. External inhibition is called extinguishing, because if the action of external stimuli is repeated many times, then the animal already, as it were, "gets used" to them and they lose their inhibitory effect. These facts are well known in human practice. So, for example, some people get used to working in a difficult environment, where there are many external stimuli (work in noisy workshops, work of cashiers in large stores, etc.), causing a beginner to feel confused.

Internal inhibition is an acquired mechanism based on the action of conditioned reflexes. It is formed in the process of life, upbringing, work. This type of active inhibition is inherent only in the cerebral cortex. Internal inhibition has a twofold character. During the day, when the cerebral cortex is active, it takes a direct part in the regulation of the excitatory process, is of a fractional nature and, mixing with foci of excitation, forms the basis of the physiological activity of the brain. At night, this same inhibition radiates through the cerebral cortex and induces sleep. I.P. Pavlov in his work "Sleep and internal inhibition - one and the same process" emphasized this feature of internal inhibition, which, participating in the active work of the brain during the day, delays the activity of individual cells, and at night, spreading, radiating through the cortex, causes inhibition of the entire cerebral cortex that determines the development of physiological normal sleep.

Internal inhibition, in turn, is subdivided into extinction, retardation and differentiation. In well-known experiments on dogs, the mechanism of extinctive inhibition causes a weakening of the effect of a developed conditioned reflex when it is reinforced. However, the reflex does not disappear completely, it can reappear after a while and is especially easy with appropriate reinforcement, such as food.

In humans, the process of forgetting is due to a certain physiological mechanism - extinctive inhibition. This type of inhibition is of very significant importance, since the inhibition of currently unnecessary connections contributes to the emergence of new ones. Thus, the desired sequence is created. If all educated connections, both old and new, were at the same optimal level, then rational mental activity would be impossible.

Delayed inhibition is due to a change in the order in the supply of stimuli. Usually, in an experiment, the conditioned stimulus (light, sound, etc.) somewhat precedes the unconditioned stimulus, such as food. If, however, the conditioned stimulus is set aside for some time, i.e. lengthen the time of its action before giving the unconditioned stimulus (food), then as a result of such a change in the regimen, the conditioned salivary reaction to light will be delayed by approximately the time for which the conditioned stimulus was set aside.

What is the reason for the delay in the appearance of the conditioned reaction, the development of inhibition of delay? The mechanism of delayed inhibition underlies such properties of human behavior as endurance, the ability to restrain one or another type of mental reactions that are inappropriate in the sense of rational behavior.

Of exceptional importance in the work of the cerebral cortex is differential inhibition. This inhibition can dismember conditional connections to the smallest detail. So, in dogs, a salivary conditioned reflex was developed for 1/4 of the musical tone, which was reinforced by food. When they tried to give 1 / 8 of the musical tone (the difference in acoustic terms is extremely insignificant), the dog did not salivate. Undoubtedly, in the complex and subtle processes of human mental and speech activity, which have chains of conditioned reflexes in their physiological basis, all types of cortical inhibition are of great importance, and differentiation should be especially singled out among them. The development of the finest differentiations of the conditioned reflex determines the formation of higher forms of mental activity - logical thinking, articulate speech and complex labor skills.

Protective (outrageous) braking. Internal inhibition has various forms of manifestation. During the day, it is of a fractional nature and, mixing with foci of excitation, takes an active part in the activity of the cerebral cortex. At night, irradiating, it causes diffuse inhibition - sleep. Sometimes the cortex can be exposed to superstrong stimuli, when the cells work to the limit and their further intense activity can lead to their complete exhaustion and even death. In such cases, it is advisable to turn off weakened and depleted cells from work. This role is played by a special biological reaction of the nerve cells of the cortex, which is expressed in the development of an inhibitory process in those areas of the cortex whose cells were weakened by superstrong stimuli. This type of active inhibition is called healing-protective or transcendental and is predominantly innate. During the period of coverage of certain areas of the cortex by transcendent protective inhibition, weakened cells are switched off from active activity, recovery processes take place in them. As diseased areas normalize, inhibition is removed, and those functions that were localized in these areas of the cortex can be restored. The concept of protective inhibition, created by I.P. Pavlov, explains the mechanism of a number of complex disorders that occur in various nervous and mental diseases.

“We are talking about inhibition, which protects the cells of the cerebral cortex from the danger of further damage, and even death, prevents a serious threat that occurs when the cells are overexcited, in cases where they are forced to perform overwhelming tasks, in catastrophic situations, with exhaustion and weakening them under the influence of various factors. In these cases, inhibition occurs not in order to coordinate the activity of the cells of this higher department of the nervous system, but in order to protect and protect them "(EA Asratyan, 1951).

In cases observed in the practice of defectologists, such triggering factors are toxic processes (neuroinfections) or skull injuries that cause weakening of nerve cells due to their exhaustion. A weakened nervous system is fertile ground for the development of protective inhibition in it. “Such a nervous system,” wrote I.P. Pavlov, “when encountering difficulties ... or after unbearable excitement, inevitably passes into a state of exhaustion. And exhaustion is one of the main physiological impulses to the emergence of an inhibitory process, as a protective process.”

Pupils and followers of I.P. Pavlova - A.G. Ivanov-Smolensky, E.A. Asratyan, A.O. Dolin, S.N. Davydenko, E.A. Popov and others - attached great importance to further scientific developments related to clarifying the role of healing and protective inhibition in various forms of nervous pathology, noted for the first time by I.P. Pavlov in the physiological analysis of schizophrenia and some other neuropsychiatric diseases.

Based on a number of experimental works carried out in his laboratories, E.A. Asratyan formulated three main points characterizing the importance of healing and protective inhibition as a protective reaction of the nervous tissue under various harmful influences:

1) healing-protective inhibition belongs to the category of universal coordination properties of all nervous elements, to the category of general biological properties of all excitable tissues;

2) the process of protective inhibition plays the role of a healing factor not only in the cerebral cortex, but also in the entire central nervous system;

3) the process of protective inhibition fulfills this role not only in functional, but also in organic lesions of the nervous system.

The concept of the role of curative-protective inhibition is especially fruitful for the clinical and physiological analysis of various forms of nervous pathology. This concept makes it possible to more clearly imagine some complex clinical symptom complexes, the nature of which has long been a mystery.

Undoubtedly, the role of protective-healing inhibition in the complex system of cerebral compensation is great. It is one of the active physiological components that contribute to the development of compensatory processes.

The duration of the existence of curative-protective inhibition in certain areas of the cortex in the residual stage of the disease, apparently, can have different periods. In some cases, it does not last long. It mainly depends on the ability of the affected cortical elements to recover. E.A. Asratyan points out that in such cases there is a peculiar combination of pathology and physiology. Indeed, on the one hand, the protective inhibitory process is curative, since the exclusion of a group of cells from active working activity gives them the opportunity to "heal their wounds." At the same time, the loss of a certain mass of nerve cells from the general cortical activity, working at a reduced level, leads to a weakening of the cortex's working capacity, to a decrease in individual abilities, to peculiar forms of cerebral asthenia.

Applying this provision to our cases, we can assume that some forms of unformed individual abilities in students who have had a brain disease, for example, in reading, writing, counting, as well as some types of speech deficiencies, memory impairment, shifts in the emotional sphere, are based on the presence of stagnant inhibitory process, causing a violation of the mobility of general neurodynamics. Improvement in development, activation of weakened abilities, which is witnessed by the school, comes gradually, as individual areas of the cortical mass are released from inhibition. However, it would be an attempt at simplification to explain the noticeable improvements that occur in the condition of children who have suffered trauma, encephalitis, only by the gradual removal of protective inhibition.

Based on the very nature of this type of healing process, which is a kind of self-treatment of the body, it should be assumed that the removal of protective inhibition from certain areas of the cerebral cortex is associated with the simultaneous development of a whole complex of recovery processes (resorption of foci of hemorrhage, normalization of blood circulation, reduction of hypertension and a number of others). ).

It is known that sleep usually does not come immediately. Between sleep and wakefulness, there are transitional periods, the so-called phase states, which cause drowsiness, which is a certain threshold of sleep. Normally, these phases can be very short-term, but in pathological conditions they are fixed for a long time.

Laboratory studies have shown that animals (dogs) during this period react differently to external stimuli. In connection with this, special forms of phase states were singled out. The equalizing phase is characterized by the same reaction to both strong and weak stimuli; in the paradoxical phase, weak stimuli have a noticeable effect, and strong ones have an insignificant effect, and in the ultraparadoxical phase, positive stimuli do not work at all, and negative ones cause a positive effect. Thus, a dog in the ultra-paradoxical phase turns away from the food offered to it, but when the food is removed, it reaches for it.

Patients with certain forms of schizophrenia sometimes do not answer the questions of others, asked in a normal voice, but they give an answer to the question addressed to them, asked in a whisper. The emergence of phase states is explained by the gradual spread of the inhibitory process over the cerebral cortex, as well as by the strength and depth of its effect on the cortical mass.

Natural sleep in the physiological sense is diffuse inhibition in the cerebral cortex, which extends to part of the subcortical formations. However, inhibition may be incomplete, then sleep will be partial. This phenomenon can be observed during hypnosis. Hypnosis is a partial sleep in which certain areas of the cortex remain excited, which causes a special contact between the doctor and the person undergoing hypnosis. Various types of sleep and hypnosis treatments have entered the arsenal of therapeutic agents, especially in the clinic of nervous and mental diseases.

Irradiation, concentration and mutual induction of nerve

processes

Excitation and inhibition (delay) have special properties that naturally arise during the implementation of these processes. Irradiation - the ability of excitation or inhibition to spread, spread over the cerebral cortex. Concentration is the opposite property, i.e. the ability of nervous processes to gather, to concentrate in any one point. The nature of irradiation and concentration depends on the strength of the stimulus. I.P. Pavlov pointed out that with a weak stimulus, irradiation of both the irritable and inhibitory processes occurs, with stimuli of medium strength - concentration, and with strong irradiation again.

Under the mutual induction of nervous processes is meant the closest connection of these processes with each other. They are constantly interacting, conditioning each other. Emphasizing this connection, Pavlov figuratively said that excitation will give birth to inhibition, and inhibition - excitation. Distinguish between positive and negative induction.

These properties of the basic nervous processes are distinguished by a certain constancy of action, which is why they are called the laws of higher nervous activity. What do these laws, established on animals, give for understanding the physiological activity of the human brain? I.P. Pavlov pointed out that it can hardly be disputed that the most general foundations of higher nervous activity, confined to the large hemispheres, are the same both in higher animals and in humans, and therefore the elementary phenomena of this activity should be the same in both. . Undoubtedly, the application of these laws, adjusted for that special specific superstructure that is peculiar only to man, namely, the second signaling system, will help in the future to better understand the basic physiological laws that also operate in the human cerebral cortex.

The cerebral cortex is integrally involved in certain nervous acts. However, the degree of intensity of this participation in various parts of the cortex is not the same and depends on which analyzer is mainly associated with active human activity in a given period of time. So, for example, if this activity for a given period is by its nature predominantly associated with the visual analyzer, then the leading focus (working field) will be localized in the region of the brain end of the visual analyzer. However, this does not mean that only the visual center will work during this period, and all other areas of the cortex will be turned off from activity. Everyday life observations prove that if a person is engaged in activities that are mainly associated with the visual process, for example, reading, then he simultaneously hears the sounds reaching him, the conversation of others, etc. However, this other activity - let's call it secondary - is carried out inactively, as if in the background. The areas of the cortex that are associated with side activities are, as it were, covered with a "haze of inhibition", the formation of new conditioned reflexes there is limited for some time. When switching to activities associated with another analyzer (for example, listening to a radio broadcast), the active field, the dominant focus, moves from the visual analyzer to the auditory, etc. in the cerebral cortex. More often, several active foci are formed simultaneously in the cortex, caused by various external and internal stimuli. At the same time, these centers enter into interaction with each other, which may not be established immediately ("struggle of centers"). The active centers that have entered into interaction form the so-called constellation of centers "or a functional-dynamic system, which for a certain period will be the dominant system (dominant, according to Ukhtomsky). When activity changes, this system slows down, and in other areas of the cortex another system is activated, which occupies the position of a dominant in order to give way again to other functional-dynamic formations that have come to replace, again associated with new activity, due to the entry into the cortex of new stimuli from the external and internal environment.This alternation of points of excitation and inhibition, due to the mechanism of mutual induction, is accompanied by the formation of numerous chains of conditioned reflexes and represents the basic mechanisms of the physiology of the brain.The dominant focus, the dominant, is the physiological mechanism of our consciousness. However, this point does not remain in one place, but moves along the cerebral cortex, depending on the nature of human activity, mediated by the influence of external and internal stimuli.

Systemicity in the cerebral cortex

(dynamic stereotype)

The various stimuli acting on the cortex are diverse in the nature of their influence: some have only an indicative value, others form nerve connections, which are initially in a somewhat chaotic state, then are balanced by the inhibitory process, are refined and form certain functional-dynamic systems. The stability of these systems depends on certain conditions of their formation. If the complex of active stimuli acquires some kind of periodicity and the stimuli arrive in a certain order for a certain time, then the system of conditioned reflexes developed is more stable. I.P. Pavlov called this system a dynamic stereotype.

Thus, a dynamic stereotype is a developed
balanced system of conditioned reflexes that perform

specialized functions. The development of a stereotype is always associated with a certain nervous labor. However, after the formation of a certain dynamic system, the performance of functions is greatly facilitated.

The significance of the developed functional-dynamic system (stereotype) is well known in the practice of life. All our habits, skills, sometimes certain forms of behavior, are due to a developed system of neural connections. Any change, violation of a stereotype is always painful. Everyone knows from life how difficult it is sometimes perceived by a change in lifestyle, habitual forms of behavior (breaking a stereotype), especially by older people.

The use of systemic cortical functions is extremely important in the upbringing and education of children. A reasonable, but steady and systematic presentation of a number of specific requirements to the child determines the stable formation of a number of general cultural, sanitary-hygienic and labor skills.

The question of the strength of knowledge is sometimes a sore point for the school. The teacher's knowledge of the conditions under which a more stable system of conditioned reflexes is formed also provides students with a solid knowledge.

Often one has to observe how an inexperienced teacher, not taking into account the possibilities that the higher nervous activity of students, especially special schools, has, leads the lesson incorrectly. Forming any school skill, he gives too many new irritations, and chaotically, without the necessary sequence, without dosing the material and without doing the necessary repetitions.

So, for example, when explaining to children the rules for dividing multi-digit numbers, such a teacher at the moment of explanation is suddenly distracted and remembers that one or another student did not bring a certificate of illness. Such inappropriate words by their nature are a kind of extra irritants: they interfere with the correct formation of specialized systems of connections, which then turn out to be unstable and are quickly erased by time.

Dynamic localization of functions in the cortex of large

hemispheres

In constructing his scientific concept of localization of functions in the cerebral cortex, I.P. Pavlov proceeded from the basic principles of the reflex theory. He believed that the neurodynamic physiological processes occurring in the cortex necessarily have the root cause in the external or internal environment of the body, i.e. they are always determined. All nervous processes are distributed among the structures and systems of the brain. The leading mechanism of nervous activity is analysis and synthesis, which provide the highest form of adaptation of the organism to environmental conditions.

Without denying the different functional significance of individual areas of the cortex, I.P. Pavlov substantiated a broader interpretation of the concept of "center". On this occasion, he wrote: “And now it is still possible to remain within the limits of the previous ideas about the so-called centers in the central nervous system. To do this, it would only be necessary to attach the physiological point of view to the exceptional, as before, anatomical point of view, allowing association through a special well-trodden connections and paths of different parts of the central nervous system for the performance of a certain reflex act.

The essence of the new additions made by I.P. Pavlov in the doctrine of the localization of functions, consisted primarily in the fact that he considered the main centers not only as local areas of the cortex, on which the performance of various functions, including mental ones, depends. The formation of centers (analyzers, according to Pavlov) is much more complicated. The anatomical region of the cortex, characterized by a unique structure, represents only a special background, the basis on which a certain physiological activity develops, due to the influence of various stimuli from the external world and the internal environment of the organism. As a result of this influence, nerve connections (conditioned reflexes) arise, which, gradually balancing, form certain specialized bathroom systems - visual, auditory, olfactory, gustatory, etc. Thus, the formation of the main centers occurs according to the mechanism of conditioned reflexes, which are formed as a result of the interaction of the organism with the external environment.

The importance of the environment in the formation of receptors has long been noted by evolutionary scientists. Thus, it was known that in some animals living underground, where the sun's rays do not reach, underdevelopment of the visual organs was noted, for example, in moles, shrews, etc. The mechanical concept of the center as a narrow local area in the new physiology was replaced by the concept of an analyzer - a complex device, providing cognitive activity. This device combines both anatomical and physiological components, and its formation is due to the indispensable participation of the external environment. As mentioned above, I.P. Pavlov singled out the central part at the cortical end of each analyzer - the nucleus, where the accumulation of receptor elements of this analyzer is especially dense and which corresponds to a certain area of ​​the cortex.

The core of each analyzer is surrounded by an analyzer periphery, the boundaries of which with neighboring analyzers are fuzzy and can overlap each other. The analyzers are closely interconnected by numerous connections that cause the closure of conditioned reflexes due to the alternating phases of excitation and inhibition. Thus, the entire complex cycle of neurodynamics, proceeding according to certain laws, is a tuphysiological "outline" on which a "pattern" of mental functions arises. In this regard, Pavlov denied the presence in the cortex of the so-called mental centers (attention, memory, character, will, etc.), as if connected with certain local areas in the cerebral cortex. These mental functions are based on various states of the basic nervous processes, which also determine the different nature of conditioned reflex activity. So, for example, attention is a manifestation of the concentration of the excitatory process, in connection with which the formation of the so-called active, or working field, occurs. However, this center is dynamic, it moves depending on the nature of human activity, hence visual, auditory attention, etc. Memory, which is usually understood as the ability of our cortex to store past experience, is also determined not by the presence of an anatomical center (memory center), but represents a combination of numerous nerve traces (trace reflexes) that arose in the cortex as a result of stimuli received from the external environment. Due to the constantly changing phases of excitation and inhibition, these connections can be activated, and then the necessary images appear in the mind, which, if unnecessary, are inhibited. The same should be said about the so-called "supreme" functions, to which the intellect was usually attributed. This complex function of the brain previously exclusively correlated with the frontal lobe, which, as it were, was considered the only bearer of mental functions (the center of the mind).

In the 17th century the frontal lobes were seen as thought factories. In the 19th century the frontal brain was recognized as the organ of abstract thinking, the center of spiritual concentration.

Intelligence - a complex integral function - arises as a result of the analytical and synthetic activity of the cortex as a whole and, of course, cannot depend on individual anatomical centers in the frontal lobe. However, observations are known in the clinic when damage to the frontal lobe causes lethargy of mental processes, apathy, and motor initiative suffers (according to Lermit). The tracts observed in clinical practice led to the views on the frontal lobe as the main center for the localization of intellectual functions. However, the analysis of these phenomena in the aspect of modern physiology leads to other conclusions. The essence of the pathological changes in the psyche noted in the clinic in case of damage to the frontal lobes is not due to the presence of special "mental centers" that have suffered as a result of the disease. It's about something else. Psychic phenomena have a certain physiological basis. This is a conditioned reflex activity that occurs as a result of alternating phases of excitatory and inhibitory processes. In the frontal lobe there is a motor analyzer, which is presented in the form of a nucleus and scattered periphery. The value of the motor analyzer is extremely important. It regulates motor-motor acts. Violation of the motor analyzer due to various reasons (impaired blood supply, skull trauma, brain tumors, etc.) may be accompanied by the development of a kind of pathological inertia in the formation of motor reflexes, and in severe cases, their complete blocking, which leads to various movement disorders (paralysis, lack of motor coordination ). Disorders of conditioned reflex activity are based on a lack of general neurodynamics, with them the mobility of nervous processes is disturbed, stagnant inhibition occurs. ”All this, in turn, is reflected in the nature of thinking, the physiological basis of which is conditioned reflexes. There is a kind of stiffness of thinking, lethargy, lack of initiative - in a word, the whole complex of mental changes that were observed in the clinic in patients with lesions of the frontal lobe and which were previously interpreted as the result of the disease of individual local points that carry "supreme" functions. The same should be said about the essence of speech centers. The lower parts of the frontal region of the dominant hemisphere, which regulate the activity of the speech organs, are allocated to the speech motor analyzer. However, this analyzer also cannot be mechanically considered as a narrow local center of motor speech. Here only the highest analysis and synthesis of all speech reflexes coming from all other analyzers is carried out.

It is known that I.P. Pavlov emphasized the unity of the somatic and mental in a holistic organism. In the studies of Academician K.M. Bykov, the connection between the cortex and internal organs was experimentally confirmed. Currently, the so-called interoreceptor analyzer is localized in the cerebral cortex, which receives signals about the state of internal organs. This area of ​​the cortex is conditionally reflexively connected with the entire internal structure of our body. Facts from everyday life confirm this connection. Who is not aware of such facts when mental experiences are accompanied by various sensations from the internal organs. So, with excitement, fear, a person usually turns pale, often experiences an unpleasant sensation from the heart ("heart stops") or from the gastrointestinal tract, etc. Corticovisceral connections have two-way information. Hence, the initially disturbed activity of the internal organs, in turn, can have a depressing effect on the psyche, causing anxiety, lowering the mood, and limiting the ability to work. The establishment of corticovisceral connections is one of the important achievements of modern physiology and is of great importance for clinical medicine.

In the same aspect, centers, activities
which was usually associated with the management of individual skills and labor
skills, such as writing, reading, counting, etc. These centers in the past also
were interpreted as local areas of the cortex, with which the graphic
and lexical functions. However, this view from the standpoint of modern
physiology also cannot be accepted. In humans, as mentioned above,
birth, there are no special cortical centers for writing and reading, formed by specialized elements. These acts are specialized systems of conditioned reflexes that are gradually formed in the process of learning.

However, how can we understand the facts that at first glance can confirm the presence of local cortical centers of reading and writing in the cortex? We are talking about observations of writing and reading disorders in the defeat of certain areas of the parietal cortex. So, for example, dysgraphia (writing disorder) often occurs when field 40 is affected, and dyslexia (reading disorder) occurs more often when field 39 is affected (see Fig. 32). However, it is wrong to assume that it is these fields that are the direct centers of the described functions. The modern interpretation of this issue is much more complicated. The center of writing is not only a group of cellular elements on which the specified function depends. The skill of writing is based on a developed system of neural connections. The formation of this specialized system of conditioned reflexes, which is the physiological basis of the skill of writing, occurs in those areas of the cortex where the corresponding junction of pathways occurs that connects a number of analyzers involved in the formation of this function. So, for example, to perform the function of writing, at least three receptor components are required - visual, auditory, kinesthetic and motor. Obviously, in certain points of the cortex of the parietal lobe, the closest combination of associative fibers occurs, connecting a number of analyzers involved in the act of writing. It is here that the closure of the neural connections that form the functional system occurs - a dynamic stereotype, which is the physiological basis of this skill. The same applies to field 39 associated with the read function. As you know, the destruction of this area is often accompanied by alexia.

Thus, the centers of reading and writing are not anatomical centers in a narrow local sense, but dynamic (physiological), although they arise in certain cortical structures. Under pathological conditions, during inflammatory, traumatic and other processes, the systems of conditioned connections can quickly disintegrate. We are talking about aphasic, lexical and graphic disorders developing after brain disorders, as well as about the disintegration of complex movements.

In cases of optimal excitability of one or another point, the latter becomes dominant for some time, and other points that are in a state of less activity are attracted to it. Paths are blazed between them and a kind of dynamic system of working centers (dominant) is formed, which performs one or another reflex act, as mentioned above.

It is characteristic that the modern theory of the localization of functions in the cerebral cortex is based on anatomical and physiological correlations. Now it would seem naive to imagine that the entire cerebral cortex is divided into many isolated anatomical centers that are associated with the performance of motor, sensory and even mental functions. On the other hand, it is also certain that all these elements are united at any given moment in a system where each of the elements is in interaction with all the others.

Thus, the principle of the functional association of centers into certain working systems, in contrast to narrow static localization, is a new characteristic addition to the old doctrine of localization, which is why it was called dynamic localization of functions.

A number of attempts have been made to develop the provisions expressed by I.P. Pavlov, in connection with the problem of dynamic localization of functions. The physiological nature of the reticular formation as a tonic apparatus of cortical processes was subjected to clarification. Finally, and most importantly, ways were determined to explain the connections that exist between higher mental processes (as a complex product of socio-historical development) and their physiological basis, which was reflected in the works of L.S. Vygotsky, A.N. Leontiev, A.R. Luria and others. "If the higher mental functions are complexly organized functional systems, social in their genesis, then any attempt to localize them in special narrowly limited areas of the cerebral cortex, or centers, is even more unjustified than" an attempt to look for narrow limited "centers "for biological functional systems... Therefore, it can be assumed that the material basis of higher mental processes is the entire brain as a whole, but as a highly differentiated system, the parts of which provide different aspects of a single whole."