Ivan Petrovich Pavlov. Conditioned reflex There is no need to prove that I.P. Pavlov was an outstanding scientist. During his long life (1849–1936) he achieved enormous success thanks to great diligence, purposeful work, keen insight, theoretical clarity,

Conditional abbreviations aa-t-RNA - aminoacyl (complex) with transport RNAATP - adenosine triphosphoric acidDNA - deoxyribonucleic acid-RNA (i-RNA) - matrix (information) RNANAD - nicotinamide adenine dinucleotide NADP -

Conventional abbreviations AG - Golgi apparatus ACTH - adrenocorticotropic hormone AMP - adenosine monophosphate ATP - adenosine triphosphate VND - higher nervous activity GABA - β-aminobutyric acid GMP - guanosine monophosphate GTP - guanine triphosphoric acid DVP -

UNCONDITIONED REFLEX (specific, innate 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 I.P. Pavlov while studying 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 occurring reflex, I.P. Pavlov discovered a category of reflexes, for the formation of which a number of conditions must be met - a conditioned reflex (see).

A physiological feature of the unconditioned reflex is its relative constancy. An unconditioned reflex always occurs with corresponding external or internal stimulation, manifesting itself on the basis of innate nerve 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 is 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 nervous activity in animals and humans, which were clearly distinguished by I. P. Pavlov. The totality of the unconditioned reflex constitutes lower nervous activity, while the totality of acquired, or conditioned, reflexes constitutes higher nervous activity (see).

From this definition it follows that the unconditioned reflex, in its physiological meaning, 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 total direct the internal life of the organism. I. P. Pavlov attached especially great importance to this last property of the unconditioned reflex. Thanks to innate nerve connections that ensure the interaction of organs and processes within the body, animals and humans acquire an accurate and stable course of basic vital functions. The principle on the basis of which these interactions and integration of activities within the body are organized is self-regulation of physiological functions (see).

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

1. Food, the causative agent of which is the action of nutrients 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, excitation of branched innate nervous structures occurs, which generally constitute 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. For example, applying painful stimulation to a limb causes the limb to be withdrawn, which protects it from further destructive effects.

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

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

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

5. Reflexes from internal organs, reflexes during irritation of muscles and 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, lead to the formation of conditioned reactions very quickly, often after just one combination of any external stimulus with painful reinforcement. The ability of other unconditioned reflexes, for example, blinking or knee reflexes, to form temporary connections with an indifferent external stimulus is less pronounced.

It should also be taken into account that the speed 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 secretion is in strict accordance with the physical and chemical properties of the food taken. If the food is dry, then watery saliva is released, 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 quality of food: saliva will contain a large amount of mucous glucoprotein - mucin, which prevents food injury ways.

Fine receptor assessment is associated with a lack of a particular 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 developing bones, eventually its amount becomes below a constant level. This factor is a selective irritant of some specific cells of the hypothalamus, which in turn keeps the receptors of the tongue in a state of increased excitability. This is how children develop a desire to eat plaster, whitewash and other minerals containing calcium.

Such an appropriate correspondence of the unconditioned reflex to the quality and strength of the stimulus that acts depends on the extremely differentiated effect of nutrients 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 occurrence of movements. In fact, the composition of saliva can be easily changed through a relative change in the production of its main ingredients: water, proteins, salts. It follows from this that the central salivary apparatus can vary the quantity and quality of excited elements depending on the quality of excitation coming from the periphery. The correspondence of an unconditioned response to the specificity of the applied stimulation can go very far. I.P. Pavlov developed the idea of ​​the so-called digestive warehouse of certain unconditioned reactions. For example, if you feed an animal a certain type of food for a long time, the digestive juices of its glands (stomach, pancreas, 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 indicate that the stability, or immutability, of the unconditioned reflex is only relative. There is reason to think that already in the first days after birth, the specific “mood” of the tongue 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 in the mother’s milk that a newborn baby is fed on is increased, then the baby’s sucking movements are immediately inhibited, and in some cases the baby actively throws out the formula that has already been taken. This example convinces us that the innate properties of food receptors, as well as the properties of intranervous relationships, accurately reflect the needs of the newborn.

Methodology for using 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 techniques for using the unconditioned reflex becomes especially important. In experiments on conditioned reflexes, the use of an unconditioned food reflex is based on feeding the animal with certain nutrients from an automatically fed feeder. With this method of using an unconditioned stimulus, the direct effect 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 certainly produces some kind of noise or knocking 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 technique 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 (sight, smell of food, etc.). Therefore, the method of directly introducing food into the mouth has some abnormal conditions and the animal’s reaction to the unusual nature of such a procedure.

In addition to this use of an unconditioned stimulus, there are a number of techniques 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) receives food by pressing the corresponding lever or button - 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 assessment of the results should be made taking into account the type of unconditioned reflex. This especially applies to the comparative assessment of the food and defensive unconditioned reflex.

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

Composition and localization of unconditioned reflexes

The development of experimental technology has made it possible to study the physiological composition and localization of the unconditioned food reflex in the central nervous system. For this purpose, the very effect of an 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 that is part of unconditioned stimulation. Tactile receptors produce the fastest and highest-amplitude type of nerve impulses, which first spread along the lingual nerve to the medulla oblongata, and only after a few fractions of a second (0.3 seconds) nerve impulses from temperature and chemical stimulation of the tongue receptors arrive there. This feature of the unconditioned stimulus, manifested in the sequential excitation of various receptors of the tongue, has enormous physiological significance: conditions are created in the central nervous system for signaling with each previous stream of impulses about subsequent stimuli. Thanks to such relationships and characteristics of tactile excitation, depending on the mechanical qualities of a given food, in response only to these excitations, salivation can occur before the chemical qualities of the food act.

Special experiments carried out on dogs and studies of the behavior of newborn children have shown that such relationships between individual parameters of the unconditioned stimulus are used in the adaptive behavior of the newborn.

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

In the lives of adults, information about the tactile parameters of food is faster than information about chemical parameters in the brain. Thanks 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 on the cortical representation of the unconditioned reflex, each unconditioned irritation, along with the inclusion of the subcortical apparatuses, has its own representation in the cerebral cortex. Based on the above data, as well as oscillographic and electroencephalographic analysis of the spread of unconditioned excitation, it was established that it does not have a single point or focus in the cerebral cortex. Each of the fragments of unconditional excitation (tactile, temperature, chemical) is addressed to different points of the cerebral cortex, and only the almost simultaneous stimulation of these points of the cerebral cortex establishes a systemic connection between them. These new data correspond to I. P. 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 using electrical devices have shown that an unconditioned stimulus comes to the cerebral cortex in the form of a very generalized flow of ascending excitations, and, obviously, to every cell of the cortex. This means that not a single excitation of the sensory organs that preceded the unconditioned stimulus can “escape” its convergence with the unconditioned excitation. These properties of the unconditioned stimulus strengthen the idea of ​​“convergent closure” of the conditioned reflex.

Cortical representations of unconditioned reactions are 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 be afferent in nature. As is known, I.P. Pavlov considered the cerebral cortex “an isolated afferent section of the central nervous system.”

Complex unconditioned reflexes. I.P. Pavlov identified a special category of unconditioned reflex, into which he included innate activities that are cyclical and behavioral in nature - emotions, instincts and other manifestations of complex acts of innate activity of animals and humans.

According to the initial opinion of I.P. Pavlov, complex unconditioned reflexes are a function of the “proximal subcortex”. This general expression refers to the thalamus, hypothalamus and other parts of the interstitial and midbrain. However, later, with the development of ideas about the cortical representations of the unconditioned reflex, this point of view was transferred to the concept of complex unconditioned reflexes. Thus, a complex unconditioned reflex, for example, an emotional discharge, has a specific subcortical part, but at the same time the very course of this complex unconditioned reflex at each individual stage is represented in the cerebral cortex. This point of view of I.P. Pavlov was confirmed by research in recent years using the neurography method. It has been shown that a number of cortical areas, for example, the orbital cortex, the limbic area, are directly related to the emotional manifestations of animals and humans.

According to I.P. Pavlov, complex unconditioned reflexes (emotions) represent a “blind force” or “the main source of strength” for cortical cells. The propositions expressed 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, did a more in-depth study of this problems.

From the point of view of I.P. 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 performing any instinctive action are connected with each other according to the principle of a chain reflex; however, it was later shown that each such stage of behavior must necessarily have a reverse afferentation) from the results of the action itself, that is, carry out the process of comparing the actually obtained result with the previously predicted one. Only after this can the next stage of behavior be formed.

In the process of studying the unconditioned pain reflex, it was revealed that pain excitation undergoes significant transformations at the level of the brain stem and hypothalamus. From these structures, unconditioned excitation generally covers all areas of the cerebral cortex simultaneously. Thus, along with the mobilization in the cerebral cortex of systemic connections that are characteristic of a given unconditional excitation and form 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 unconditioned painful excitation to the cerebral cortex can be blocked at the level of the brain stem using a special substance - aminazine. After the introduction of this substance into the blood, even a strong damaging (nociceptive) unconditioned 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 a newborn are completely consolidated at the time of birth. Individual links of a sometimes complex unconditioned reflex, such as the sucking reflex, involve different parts of the body, often at a considerable distance from each other. Nevertheless, they are selectively united 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 unchangeable adaptive effect of the unconditioned reflex upon application of the corresponding stimulus. This property of an 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 species of animal, then, depending on the characteristics of the conditions of existence of each species of animal, the nature of structural maturation and the final formation of the unconditioned reflex will exactly correspond to the characteristics of the given species.

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

This selective growth of the nervous structures of the unconditioned reflex occurs even more clearly in the development of the human fetus. The very first and clearly visible motor reaction of the human fetus is the grasping reflex; it is detected already in the 4th month of intrauterine life and is caused by the application of any hard object to the palm of the fetus. Morphological analysis of all links of this reflex convinces us that, before it is revealed, a number of nerve structures differentiate into mature neurons and unite with each other. Myelination of the nerve trunks related to the finger flexors begins and ends earlier than 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 a consequence of the consolidation by natural selection and heredity of those reactions acquired over thousands of years that correspond to repeated environmental factors and are useful for a given species.

There is reason to assert that the most rapid and successful adaptations of the 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. I. A. Bulygina, M., 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. An attempt at a quantitative study 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 B. N. Closure after loss of basic unconditioned reflexes, Proceedings Center, Institute of Improvements. doctors, vol. 81, p. 54, M., 1965, bibliogr.; S a l h e nko I. N. Hidden periods of myotatic reflexes that ensure motor interactions of people, Physiol. human, vol. 1, Jvft 2, p. 317, 197 5, bibliography; Sechenov I. M. Reflexes of the brain, M., 1961; Slonim A.D. Fundamentals of general economic physiology of mammals, p. 72, M,-JI., 1961, bibliogr.; Human Physiology, ed. E. B. Babsky, p. 592, M., 1972; Frankstein S.I. Respiratory reflexes and mechanisms of shortness of breath, M., 1974, bibliogr.; Sh u s t i n N. A. Analysis of unconditioned reflexes in the light of the doctrine of the dominant, Physiol, journal. USSR, vol. 61, JSft 6, p. 855, 1975, bibliogr.; Human reflexes, pathophysiology of motor systems, ed. by J. E. Desment, Basel a. o., 1973; Mechanisms of orienting reactions in man, ed. by I. Ruttkay-Nedecky a. o., Bratislava, 1967.

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 a signal stimulus and an unconditioned reflex act that reinforces this stimulus. Based on an 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 body’s adaptation to constant environmental influences, 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, allowing 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 natural conditions of existence: a puppy, having received meat for the first time, sniffs it for a long time and timidly eats it, and this act of eating is accompanied by. In the future, only the sight and smell of meat causes the puppy to lick and eliminate. Artificial conditioned reflexes are developed in an experimental setting, when the conditioned stimulus for an animal is an influence that is not related to unconditioned reactions in the animals’ natural habitat (for example, flickering light, the sound of a metronome, sound clicks).

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

To develop 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 the body’s own reaction; 3) a conditioned stimulus is taken that is usually found in the environmental conditions of the given animal or person; 4) the animal or person must be healthy, cheerful and have sufficient motivation (see).

There are also conditioned reflexes of various orders. When a conditioned stimulus is reinforced by 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 the living organism.

A dog can develop conditioned reflexes of up to 5-6 orders, in a monkey - up to 10-12 orders, in humans - up to 50-100 orders.

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

However, the cerebral cortex always controls the activity of subcortical formations.

By studying the activity of single neurons of the central nervous system using the microelectrode method, it was established that both conditioned and unconditioned excitations come to one neuron (sensory-biological convergence). It is especially clearly expressed in the neurons of the cerebral cortex. These data forced us 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 expanded and deepened significantly thanks to the study of the higher nervous activity of animals in 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 conditioned, allowing the body to adapt to environmental conditions. As a result of the formation of conditioned reflexes, the body reacts some time before the impact of unconditioned stimulation. Consequently, conditioned reflexes contribute to the successful finding of food by animals, help to avoid danger in advance and to most perfectly navigate the changing conditions of existence.