Higher nervous activity. Unconditioned and conditioned reflexes. Formation of the reflex theory

Human behavior is associated with conditionally unconditioned reflex activity and is a higher nervous activity, the result of which is a change in the ratio of the organism with the external environment.

In contrast to higher nervous activity, lower nervous activity consists of a set of reactions aimed at unification, integration of functions within the body.

Higher nervous activity manifests itself in the form of complex reflex reactions, carried out with the obligatory participation of the cerebral cortex and the subcortical formations closest to it.

For the first time, the idea of ​​the reflex nature of the activity of the brain was widely and in detail developed by the founder of Russian physiology, I. M. Sechenov, in his book "Reflexes of the Brain". The ideological setting of this classic work is expressed in the original title, changed under the influence of censorship: "An attempt to introduce physiological basis into mental processes. Before I. M. Sechenov, physiologists and neurologists did not even dare to raise the question of the possibility of an objective, purely physiological analysis of mental processes. The latter remained completely at the mercy of subjective psychology.

The ideas of I. M. Sechenov were brilliantly developed in the remarkable works of I. P. Pavlov, who opened the way for an objective experimental study of the functions of the cerebral cortex and created a coherent theory of higher nervous activity.

I.P. Pavlov showed that while in the lower parts of the central nervous system- subcortical nuclei, brain stem, spinal cord - reflex reactions are carried out along innate, hereditarily fixed nerve pathways, in the cerebral cortex, nerve connections are developed and created in the process of individual life of animals and humans, as a result of a combination of countless stimuli acting on the body.

The discovery of this fact made it possible to divide the entire set of reflex reactions occurring in the body into two main groups: unconditioned and conditioned reflexes.

Conditioned reflexes

• These are reactions acquired by the body in the process individual development based " life experience"
• are individual: some representatives of the same species may have them, while others may not
• are unstable and, depending on certain conditions, they can develop, gain a foothold or disappear; this is their property and is reflected in their very name
• can form in response to a wide variety of stimuli applied to various receptive fields
• closed at the level of the cortex. After the removal of the cerebral cortex, the developed conditioned reflexes disappear and only unconditioned reflexes remain.
• carried out through functional temporary connections

Conditioned reflexes are developed on the basis of unconditioned reflexes. For the formation of a conditioned reflex, it is necessary to combine the time of any change in the external environment and the internal state of the organism, perceived by the cerebral cortex, with the implementation of one or another unconditioned reflex. Only under this condition does a change in the external environment or the internal state of the organism become an irritant of the conditioned reflex - a conditioned stimulus, or signal. The stimulus that causes an unconditioned reflex - an unconditioned stimulus - must, during the formation of a conditioned reflex, accompany the conditioned stimulus, reinforce it.

For the formation of conditioned reflexes, it is necessary to create a temporary connection, a circuit between the cortical cells that perceive the conditioned stimulation, and the cortical neurons that make up the arc of the unconditioned reflex.

With the coincidence and combination of conditioned and unconditioned stimuli, a connection is established between various neurons in the cortex of the cerebral hemispheres, and a closure process occurs between them.

Unconditioned reflexes

• these are congenital, hereditary reactions of the body
• are specific, i.e. characteristic of all representatives of a given species
• relatively constant, usually persisting throughout life
• carried out in response to adequate stimuli applied to one specific receptive field
• closed at the level spinal cord and brain stem
• are carried out through a phylogenetically fixed, anatomically expressed reflex arc.

It should be noted, however, that in humans and monkeys, which have a high degree of corticalization of functions, many complex unconditioned reflexes are carried out with the obligatory participation of the cerebral cortex. This is proved by the fact that its lesions in primates lead to pathological disturbances of unconditioned reflexes and the disappearance of some of them.

It should also be emphasized that not all unconditioned reflexes appear immediately at the time of birth. Many unconditioned reflexes, for example, those associated with locomotion, sexual intercourse, occur in humans and animals a long time after birth, but they necessarily appear under the condition of normal development of the nervous system.

The whole set of unconditional and conditioned reflexes formed on their basis is accepted according to their functional value divided into a number of groups.

1. According to the receptor
   1. Exteroceptive reflexes
      • visual
      • olfactory
      • taste, etc.
   2. Interoreceptive reflexes- reflexes, in which the conditioned stimulus is irritation of the receptors of internal organs by a change chemical composition, temperature of internal organs, pressure in hollow organs and vessels
2. According to effector, i.e. by those effectors that respond to stimulation
   1. autonomic reflexes
      • food
      • cardiovascular
      • respiratory, etc.
   2. somato-motor reflexes- manifested in the movements of the whole organism or its individual parts in response to the action of the stimulus
      • defensive
3. By biological significance
   1. food
      • reflex act of swallowing
      • reflex act of chewing
      • reflex act of sucking
      • reflex act of salivation
      • reflex act of secretion of gastric and pancreatic juice, etc.
   2. defensive- elimination reactions from damaging and painful stimuli
   3. Sexual- reflexes associated with the implementation of sexual intercourse; the so-called parental reflexes associated with feeding and rearing offspring can also be included in this group.
   4. Stato-kinetic and locomotor- reflex reactions to maintain a certain position and movement of the body in space.
   5. Reflexes of maintaining homeostasis
      • thermoregulation reflex
      • respiratory reflex
      • cardiac reflex
      • vascular reflexes that contribute to maintaining the constancy of blood pressure, etc.
   6. Orienting reflex- a reflex to novelty. It occurs in response to any sufficiently fast occurring oscillation environment and is expressed outwardly in alertness, listening to a new sound, sniffing, turning the eyes and head, and sometimes the whole body in the direction of the light stimulus that has appeared, etc. The implementation of this reflex provides a better perception of the acting agent and has an important adaptive value.

      IP Pavlov figuratively called the orienting reaction the reflex "what is it?" This reaction is innate and does not disappear with the complete removal of the cerebral cortex in animals; it is also observed in children with underdeveloped cerebral hemispheres - anencephaly.

The difference between the orienting reflex and other unconditional reflex reactions is that it fades relatively quickly with repeated applications of the same stimulus. This feature of the orienting reflex depends on the influence of the cerebral cortex on it.

The above classification of reflex reactions is very close to the classification of various instincts, which are also divided into food, sexual, parental, defensive. This is understandable due to the fact that, according to IP Pavlov, instincts are complex unconditioned reflexes. Their distinctive features is the chain nature of the reactions (the end of one reflex serves as the causative agent of the next) and their dependence on hormonal and metabolic factors. Thus, the emergence of sexual and parental instincts is associated with cyclic changes in the functioning of the gonads, and the food instinct depends on those metabolic changes that develop in the absence of food. One of the features of instinctive reactions is also that they are characterized by many properties of the dominant.

The reflex component is a reaction to irritation (movement, secretion, change in breathing, etc.).

Most unconditioned reflexes are complex reactions, which include several components. So, for example, with an unconditioned defensive reflex evoked in a dog by strong electrical stimulation of the limb, along with protective movements, there is also increased and increased respiration, acceleration of cardiac activity, voice reactions appear (screeching, barking), the blood system changes (leukocytosis, platelets and etc.). In the food reflex, its motor (grasping, chewing, swallowing), secretory, respiratory, cardiovascular and other components are also distinguished.

Conditioned reflexes, as a rule, reproduce the structure of the unconditioned reflex, since the conditioned stimulus excites the same nerve centers, which is unconditional. Therefore, the composition of the components of the conditioned reflex is similar to the composition of the components of the unconditioned reaction.

Among the components of the conditioned reflex, the main reflexes specific to this type and secondary components are distinguished. In the defensive reflex, the motor component is the main one, in the food reflex, the motor and secretory ones.

Changes in respiration, cardiac activity, and vascular tone accompanying the main components are also important for the integral response of the animal to a stimulus, but, as IP Pavlov said, they play a "purely auxiliary role." Thus, increased and increased respiration, increased heart rate, increased vascular tone, caused by a conditioned defensive stimulus, contribute to an increase in metabolic processes in the skeletal muscles and thereby create optimal conditions for the implementation of protective motor reactions.

In the study of conditioned reflexes, the experimenter often chooses any one of its main components as an indicator. Therefore, they speak of conditioned and unconditioned motor or secretory or vasomotor reflexes. However, it must be taken into account that they are only separate components of the integral reaction of the organism.

The biological significance of conditioned reflexes lies in the fact that they make it possible to adapt much better and more accurately to the conditions of existence and survive in these conditions.

As a result of the formation of conditioned reflexes, the body reacts not only directly to unconditioned stimuli, but also to the possibility of their action on it; reactions appear some time before unconditional irritation. This very organism turns out to be prepared in advance for the actions that it has to carry out in a given situation. Conditioned reflexes help to find food, avoid danger in advance, eliminate harmful influences, etc.

The adaptive significance of conditioned reflexes is also manifested in the fact that the precedence of a conditioned stimulus to an unconditioned one strengthens the unconditioned reflex and accelerates its development.

The behavior of animals is different forms of external, mainly motor activity, aimed at establishing vital connections between the organism and the environment. Animal behavior consists of conditioned, unconditioned reflexes and instincts. Instincts include complex unconditioned reactions that, being innate, appear only at certain periods of life (for example, the instinct of nesting or feeding offspring). Instincts play a leading role in the behavior of lower animals. However, the higher an animal is at the evolutionary level, the more complex and diverse its behavior, the more perfect and subtle it adapts to the environment, and the greater the role of conditioned reflexes in its behavior.

The environment in which animals exist is very variable. Adaptation to the conditions of this environment by means of conditioned reflexes will be subtle and precise only if these reflexes are also changeable, i.e., conditioned reflexes that are unnecessary in new environmental conditions disappear, and new ones are formed in their place. The disappearance of conditioned reflexes occurs due to the processes of inhibition.

Distinguish between external (unconditioned) inhibition of conditioned reflexes and internal (conditioned) inhibition.

External inhibition of conditioned reflexes arises under the influence of extraneous stimuli that cause a new reflex reaction. This inhibition is called external because it develops as a result of processes occurring in areas of the cortex that are not involved in the implementation of this conditioned reflex.

Superstrong or long-acting extraneous stimuli can cause prohibitive inhibition of reflexes.

Internal inhibition of conditioned reflexes occurs in the absence of reinforcement by an unconditioned stimulus of the received signal.

In this case, internal inhibition does not appear immediately. As a rule, repeated application of an unreinforced signal is required.

The fact that this is inhibition of the conditioned reflex, and not its destruction, is evidenced by the restoration of the reflex the next day, when the inhibition has passed. Various diseases, overwork, overstrain causes a weakening of internal inhibition.

If the conditioned reflex is extinguished (not reinforced with food) for several days in a row, then it may disappear altogether.

There are several types of internal inhibition. The form of inhibition considered above is called extinctive inhibition. This inhibition underlies the disappearance of unnecessary conditioned reflexes.

Another variety is differentiated (distinctive) inhibition.

An unreinforced conditioned stimulus causes inhibition in the cortex and is called an inhibitory stimulus. With the help of the described technique, it was possible to determine the distinctive ability of different sense organs in animals.

The phenomenon of disinhibition. It is known that extraneous stimuli cause inhibition of conditioned reflexes. If an extraneous stimulus occurs during the action of an inhibitory stimulus, for example, when a metronome is used with a frequency of 100 times per minute, as in the previous case, then this will cause the opposite reaction - saliva will flow. I. P. Pavlov called this phenomenon disinhibition and explained it by the fact that an extraneous stimulus, causing an orienting reflex, inhibits any other process that occurs in this moment in the centers of the conditioned reflex. If the inhibition process is inhibited, then all this leads to the excitation and implementation of a conditioned reflex.

The phenomenon of disinhibition also indicates the inhibitory nature of the processes of discrimination and extinction of conditioned reflexes.

The value of conditional inhibition very large. Thanks to inhibition, a much better correspondence of the reaction of the organism to external conditions is achieved, and its adaptation to the environment is more perfect. The combination of two forms of a single nervous process - excitation and inhibition - and their interaction enable the body to orient itself in various complex situations, are the conditions for the analysis and synthesis of stimuli.

The functional unit of GNI is a conditioned reflex, which is based on a temporary connection between various neuronal structures. For the first time, the idea of ​​​​the reflex principle of the central nervous system was put forward by I.M. Sechenov in his work "Reflexes of the brain", where he first expressed the idea that the basis mental activity is the reflex principle. I.P. Pavlov (figure) presented the first experimental evidence of the reflex principle of the CNS, conducting studies on the so-called "fistula" animals. I.P. Pavlov introduced the concept of a conditioned reflex. The conditioned reflex is higher form reflex activity. A conditioned reflex is not a reaction to a stimulus, but a reaction to a signal that precedes this stimulus, which allows you to avoid the action of the stimulus if it is dangerous, or to rush towards this stimulus if it is necessary. An important role in the study of physiological processes that determine the behavior of animals and humans was played by the methods of classical (IP Pavlov, 1906, 1927) and instrumental (E. Thorndike, 1898) conditioned reflexes.

Drawing - Pavlov I.P.

According to the classical method of developing conditioned reflexes, a conditioned stimulus (indifferent to a given reflex, for example, the light of a light bulb) must precede and be combined with the action of an unconditioned stimulus (for example, food). After several repetitions of these combinations, a conditioned reflex is developed (for example, salivation in response to the light of a light bulb).

The technique for developing an instrumental conditioned reflex involves Active participation animal in a given process, that is, only certain behavior of the animal (for example, movement in a certain direction) leads to a reward. With this approach, learning is faster.

The classical and instrumental methods of developing a conditioned reflex differ in the way the unconditioned stimulus is reinforced and in the degree of extinction of the conditioned reflexes: the instrumental reflex is preserved with partial reinforcement, while the classical reflex fades. Both methods are based on the associative type of behavior.

In addition, I.P. Pavlov (1927) described non-associative types of behavior change:

– habituation(addiction), in which there is a decrease in the strength of reflex reactions with repeated repetition of stimuli;

– sensitization- an increase in the strength of reflex reactions to a given stimulus under the action of another, stronger stimulus.

All reflexes are divided into unconditioned and conditional (table 1). Unconditioned reflexes are congenital, hereditary reactions of the body, conditional- these are reactions acquired by the body in the process of individual development on the basis of "life experience". Unconditioned reflexes are relatively constant, stereotyped in response to adequate stimulation of the corresponding receptive field, and serve as the basis for the formation of conditioned reflexes associated with individual experience. Unconditioned reflexes provide coordinated activity aimed at maintaining the constancy of the internal environment, the interaction of the organism with the external environment, the coordinated activity of somatic and vegetative reactions.

Table 1

Differences between unconditioned and conditioned reflexes

Unconditioned reflexes are specific, i.e. common to all members of this species. Conditioned reflexes are individual. Unconditioned reflexes are permanent, conditioned reflexes are unstable, they can be developed, consolidated and disappear.

Unconditioned reflexes are innate reactions, they were formed and fixed in the process of evolution and are inherited. Unconditioned reflexes do not require special conditions for their occurrence; they arise if certain stimuli act on certain receptors. Unconditioned reflexes can be carried out at the level of the spinal cord and brain stem. Conditioned reflexes can be formed to any signals perceived by the body and are a function of the cerebral cortex, implemented with the participation of subcortical structures.

Unconditioned reflexes can ensure the existence of the organism only at the very early stage of life. Adaptation of the organism to constantly changing environmental conditions is provided by conditioned reflexes developed during life.

Conditioned reflexes provide a more perfect adaptation of the body to changing conditions of life. They help to find food by smell, timely escape from danger, orientation in time and space. The conditioned reflex separation of saliva, gastric and pancreatic juices in appearance, smell, meal time creates the best conditions for the digestion of food even before it enters the body. An increase in gas exchange and an increase in pulmonary ventilation before starting work only when you see the environment in which the work is done contributes to greater endurance and better performance of the body during muscle activity. The activity of the CBP is signaling, since it provides the body with a preliminary preparation for responding to stimuli.

Difficulties in distinguishing between conditioned and unconditioned reflex activity are associated, for example, with the improvement of unconditioned reflex activity in the process of individual development. In addition, when interacting with conditioned reflexes, unconditioned reflexes “ripen” in the process of postnatal life (L.A. Orbeli). Behavior is usually regarded as innate if it is not possible to detect the influence of training or other factors on it in ontogeny.

Classifications of conditioned reflexes may be different:

1. According to the receptive field of the conditioned stimulus: intero-, extero- and proprioceptive.

2. According to the efferent link that implements the response: somatic and vegetative.

3. According to the biological significance of the response: food, defensive, parental conditional.

4. By coincidence in time of the signal and reinforcement: coinciding, lagging and trailing.

5. Difficulty: reflexes first order, second, third, etc.

General signs of conditioned reflexes:

1. Conditioned reflexes are adaptive in nature.

2. Conditioned reflexes require higher parts of the brain for their participation.

3. They are acquired and canceled in the individual life of each individual.

4. The conditioned reflex has a signal character, i.e. precedes, prevents the subsequent occurrence of an unconditioned reflex.

The development of the theory of automatic regulation has led to the concept of information and control activity of the brain. 6 levels of its organization were identified, based on the levels of reflex reactions:

- elementary reflexes,

- coordination reflexes,

- integrative reflexes,

- the most complex unconditioned reflexes,

- elementary unconditioned reflexes

- complex forms of higher nervous (mental) activity.

Conditioned reflexes are developed on the basis of unconditioned ones. The conditioned reflex is called so because for its formation certain conditions are needed and, above all, a conditioned stimulus or signal. It can be any irritant from the external environment or a certain change in the internal state of the organism. For example, an electric bell, gurgling water, clanking dishes, etc. Conditioned reflexes for a while are developed in a person subject to the regime of work, eating at the same time, a constant time for going to bed, etc. (but they are easier to produce if they coincide with biorhythms - daily, etc.).

For the formation of a conditioned reflex, it is necessary to combine in time some change in the external environment or the internal state of the organism, perceived by the cerebral cortex, with the implementation of some kind of unconditioned reflex. In this case, such a change in the external or internal environment becomes a conditioned stimulus. For the formation of a conditioned reflex, a repeated coincidence of the conditioned signal and the unconditioned stimulus is necessary. Those. for the formation of conditioned reflexes, it is necessary to create a temporary connection, a closure between the neurons included in the arc of the unconditioned reflex. A prerequisite for the formation of a conditioned reflex is that the onset of the action of an indifferent (indifferent, future conditioned) stimulus must precede the onset of the unconditioned stimulus more (it is easier to develop a conditioned reflex to a call in a hungry dog ​​than in a well-fed one).

Additional mandatory conditions for the development of a conditioned reflex are the absence of strong extraneous stimuli, the absence of painful phenomena.

The closure of temporary connections between the foci of excitation of the conditioned and unconditioned stimulus occurs not only horizontally (cortex-cortex), but also with the participation of subcortical structures: cortex-thalamus-hippocampus-reticular formation-cortex-subcortex-cortex (zone of unconditioned reflexes). Ukhtomsky's dominant principle plays an important role in the mechanisms of formation of conditioned reflexes. The dominant focus - dominating, prevailing - attracts to itself the excitation that enters other nerve centers, and due to this it intensifies. For example, a hungry puppy, when its paw is irritated by an electric current, does not withdraw its paw, but rather more quickly locates milk, while a well-fed puppy withdraws it.

It is believed that during the formation of a conditioned reflex, the focus of persistent excitation that has arisen in the zone of the unconditioned reflex "attracts" to itself the excitation that has arisen in the zone of the conditioned stimulus. With repeated combinations of these excitations, a temporary connection arises, leading to the formation of a conditioned reflex. The formation of a temporary connection is associated with the mechanisms of storage of traces of excitation.

Rules for developing a conditioned reflex:

1) for the experiment, healthy animals are taken in a state of wakefulness;

2) use two stimuli - a signal and reinforcement;

3) the signal must precede the reinforcement by a few seconds;

4) the signal stimulus must be less in strength than the unconditioned one, because a temporary connection between the central ends of the analyzers is formed only when the impulse is directed from the weakly excited center of the center of the signal stimulus to the strongly excited center of reinforcement (according to the principle of dominance).

Stages of development of a conditioned reflex:

1) generalization of the conditioned reflex;

2) the stage of specialization or differentiation;

3) the stage of automatism.

Every biology textbook says that the founder of the reflex theory is Ivan Pavlov. This is true, but even before the famous Russian physiologist, many researchers studied the nervous system. Of these, the most huge contribution was introduced by Pavlov's teacher Ivan Sechenov.

Background of the reflex theory

The term "reflex" means a stereotyped reaction of a living organism to an external stimulus. Surprisingly, but this concept has mathematical roots. The term was introduced into science by the physicist Rene Descartes, who lived in the 17th century. He tried to explain with the help of mathematics the laws by which the world of living organisms exists.

Rene Descartes is not the founder of the reflex theory in its modern form. But he discovered much of what later became part of it. Descartes was helped by William Harvey, an English physician who was the first to describe the circulatory system in the human body. However, he also presented it in the form mechanical system. Later this method will be used by Descartes. If Harvey transferred his principle to the internal structure of the organism, then his French colleague applied this construction to the interaction of the organism with the outside world. He described his theory using the term "reflex", taken from the Latin language.

The importance of Descartes' discoveries

The physicist believed that the human brain is the center responsible for communication with the outside world. In addition, he suggested that nerve fibers come from it. When external factors affect the ends of these threads, a signal is sent to the brain. It was Descartes who became the founder of the principle of materialistic determinism in the reflex theory. This principle lies in the fact that any nervous process occurring in the brain is caused by the action of a stimulus.

Much later, the Russian physiologist Ivan Sechenov (the founder of the reflex theory) rightly called Descartes one of those scientists on whom he relied in his research. At the same time, the French had many delusions. For example, he believed that animals, unlike humans, act mechanically. The experiments of another Russian scientist - Ivan Pavlov - showed that this is not so. The nervous system of animals has the same structure as that of humans.

Ivan Sechenov

Another person who made an important contribution to the development of the reflex theory is Ivan Sechenov (1829-1905). He was an educator and creator of Russian physiology. The scientist was the first in world science to suggest that the higher parts of the brain work only on reflexes. Before him, neurologists and physiologists did not raise the question that, perhaps, all mental processes of the human body are physiological in nature.

During research in France, Sechenov proved that the brain affects motor activity. He discovered the phenomenon of central inhibition. His research made a splash in the then physiology.

Formation of the reflex theory

In 1863, Ivan Sechenov published the book "Reflexes of the Brain", which removes the question of who is the founder of the reflex theory. In this work, many ideas were formulated that formed the basis of the modern doctrine of the higher nervous system. In particular, Sechenov explained to the public what the reflex principle of regulation is. It lies in the fact that any conscious and unconscious activity of living organisms is reduced to a reaction within the nervous system.

Sechenov not only discovered new facts, but also did a great job of summarizing already known information about physiological processes inside the body. He proved that the influence of the external environment is necessary both for the usual pulling of the hand, and for the appearance of a thought or feeling.

Criticism of Sechenov's ideas in Russia

Society (especially Russian) did not immediately accept the theory of a brilliant physiologist. After the book "Reflexes of the Brain" was published, some of the scientist's articles were no longer published in Sovremennik. Sechenov boldly attacked the theological ideas of the Church. He was a materialist and tried to prove everything in terms of physiological processes.

Despite the ambiguous assessment in Russia, the foundations of the theory of reflex activity were warmly received by the scientific community of the Old World. Sechenov's books began to be published in Europe in gigantic editions. The scientist even moved his main research activities to Western laboratories for some time. He worked productively with a French physician

Receptor theory

In the history of science, one can find many examples of how scientists went down the wrong path, offering ideas that did not correspond to reality. The receptor theory of sensations, which contradicts the views of Sechenov and Pavlov, can be called such a case. What is their difference? The receptor and reflex theory of sensations explain the nature of the body's reaction to external stimuli in different ways.

Both Sechenov and Pavlov believed that the reflex is an active process. This point of view was established in modern science and today it is considered definitively proven. The activity of the reflex lies in the fact that living organisms react more sharply to some stimuli than to others. Nature separates the necessary from the unnecessary. The receptor theory, on the contrary, states that the sense organs react passively to the environment.

Ivan Pavlov

Ivan Pavlov is the founder of the reflex theory along with Ivan Sechenov. He studied the nervous system all his life and developed the ideas of his predecessor. This phenomenon attracted the scientist with its complexity. The principles of the reflex theory have been proven empirically by a physiologist. Even people far from biology and medicine have heard the phrase "Pavlov's dog." Of course, we are not talking about one animal. This refers to the hundreds of dogs that Pavlov used for his experiments.

The impetus for the discovery and final formation of the entire reflex theory was a simple observation. Pavlov had been studying the digestive system for ten years and had many dogs in his laboratory, whom he loved very much. One day, a scientist wondered why an animal would salivate even before it was given food. Further observations showed a surprising connection. Saliva began to flow when the dog heard the clink of dishes or the voice of the person who brought her food. Such a signal triggered a mechanism that causes the production of gastric juice.

Unconditioned and conditioned reflexes

The above case interested Pavlov, and he began a series of experiments. What conclusions did the founder of the reflex theory come to then? As far back as the 17th century, Descartes spoke about the body's reactions to external stimuli. The Russian physiologist took this concept as a basis. In addition, Sechenov's reflex theory helped him. Pavlov was his direct student.

Watching dogs, the scientist came to the idea of ​​unconditioned and conditioned reflexes. The first group included congenital features of the organism, transmitted by inheritance. For example, swallowing, sucking, etc. Pavlov called conditioned reflexes those that a living being receives after birth thanks to personal experience and characteristics of the environment.

These qualities are not inherited - they are strictly individual. At the same time, the body may lose such a reflex if, for example, environmental conditions have changed, and it is no longer needed. The most famous example is Pavlov's experiment with one of the laboratory dogs. The animal was taught that food is brought after the light bulb turns on in the room. Next, the physiologist monitored the appearance of new reflexes. And indeed, soon the dog began to salivate by itself when he saw the light bulb turned on. However, she was not given any food.

Three Principles of Theory

The generally accepted principles of the reflex boil down to three rules. What are they? The first of them is the principle of materialistic determinism, formulated by Descartes. According to him, each nervous process is caused by the action of an external stimulus. The reflex theory of mental processes is based on this rule.

The second is the principle of structure. This rule states that the structure of the parts of the nervous system directly depends on the quantity and quality of their functions. In practice, it looks like this. If an organism does not have a brain, then it is characterized by primitiveness.

The last principle is the principle of analysis and synthesis. It lies in the fact that inhibition occurs in some neurons, while excitation occurs in others. This process is a physiological analysis. As a result, a living organism can distinguish between surrounding objects and phenomena.

The content of the article

CONDITIONED REFLEX. The term, which was first used by the Russian physiologist I.P. Pavlov to describe the acquired reflex, i.e. not being (unlike an unconditioned reflex) innate, and therefore characteristic of an individual, and not all representatives of a given species. When lemon juice gets on the tongue, saliva is released - this is an unconditioned reflex. However, saliva can also be released at the sight of a lemon or at the sound of the word "lemon" - this is a conditioned reflex. The difference is that the sight of a lemon, or the sound of the word, does not always cause salivation, and in addition may not have an effect on certain people. Such stimuli become capable of eliciting a response only after they have been presented more or less simultaneously with the stimulation of the taste buds by lemon juice. The sight of a lemon or the sound of the word "lemon" in this case turn out to be conditioned (signal) stimuli that replace the unconditioned stimulus - lemon juice.

Pavlov's method.

The experiment carried out by Pavlov required a soundproof room where it was possible to control the conditions of the external environment, a specially equipped place for the animal and a device for automatic feeding. As needed, stimuli of different nature (ringing, flashes of light, etc.) could be presented. Through a simple surgical operation, Pavlov brought the salivary duct out of the dog so that saliva could be collected and measured. In a typical experiment, a moderately hungry dog ​​was left several times in a soundproof room to get used to the environment and not experience emotional stress. During this period, salivation was carefully measured, which was usually negligible. Then a stimulus was presented - a bell was turned on, which could cause a slight increase in salivation (as a result of the orienting reflex discovered by Pavlov), but after several repetitions the dog usually lost interest in it. Next, the process of developing a conditioned reflex began. The bell sounded, and after a few seconds food was falling into the dog's bowl. While the dog was eating, the amount of saliva released was measured, and when the salivation stopped, the bell rang again and food appeared. After several such combinations of the bell and food, the following experiment was carried out, in which the bell was not accompanied by the appearance of food. The signal, previously neutral, now caused pronounced salivation - a conditioned reflex was triggered. In such a situation, food is the unconditioned stimulus, the bell is the conditioned stimulus or signal, and the combined appearance of food and the bell is called a reinforcer. The very formation of conditioned reflexes is designated by the term "conditioning".

Pavlov's discoveries.

Pavlov managed to show how a conditioned reflex arises in response to various signals and different types and reinforcement conditions. In addition, he found that in the case when the conditioned signal is repeatedly presented without reinforcement, the reflex is attenuated. In this case, the reaction weakens, often becomes irregular, and eventually the conditioned signal ceases to act. Pavlov also showed the presence of behavioral reactions associated with conditioned reflex reactions. For example, after the conditioned reflex reaction of salivation to the sound of a bell of a certain pitch was developed, it was also possible to evoke it with a bell with a different pitch; in another experiment, salivation was induced by scratching not only a certain place on the paw, but also neighboring areas. In each case, the degree of response to the new stimulus depended on how similar it was to the original stimulus. A call slightly different in pitch, or scratching a place close to the original, resulted in almost the same salivation as the original signals; a call that was very different in height or scratching at a distant site caused the release of a smaller amount of saliva. As it turned out, this effect, called generalization, can be neutralized by reinforcing only the original signal, stopping the reinforcement of the rest. In this case, the animal develops the ability to distinguish: the reaction is fully manifested only to the initial conditioned signal, and to all others it is insignificant or completely absent. Using this technique, Pavlov was able to determine what are the minimum changes in the stimulus that the dog is able to distinguish.

Based on his experiments, Pavlov developed several theories of the work of the cerebral cortex, in particular the theory of excitation and inhibition - cortical states characterized by increased and decreased activity. He suggested that inhibition, spilling over the cortex, is the cause of such a phenomenon as the attenuation of the conditioned reflex. Pavlov believed that sleep is a state in which inhibition completely captures the cerebral cortex. Later work in the field of neurology and psychophysiology showed that the work of the cortex is much more complicated than he thought.

Modern ideas.

Pavlov applied the term "conditioned reflex" to any individually acquired types of behavior. The concept of a signal stimulus, however, does not explain all types of learning. The term "conditioned reflex" is now used in a narrower sense, in relation to situations similar to Pavlov's original experiments, for example, to the work of the autonomic nervous system, which controls the activity of glands and smooth muscles. It is also recognized that conditioned reflexes are widely represented in emotional behavior. The conditioned human reflexes that arise on the basis of the blinking reflex, salivation, sweating, constriction and expansion of the pupils, contraction and relaxation of the smooth muscles of the walls of blood vessels are well studied. Nevertheless, there is a significant area of ​​acquired behavior that is formed on the basis of other mechanisms. So, it turned out that, unlike a conditioned reflex, in which the appearance of a reaction to a conditioned signal is always preceded by its reinforcement, the animal can form a reaction that was reinforced in the past. after its manifestations (this mechanism is called operant conditioning).

an acquired reaction of the body to a specific stimulus, resulting from a combination of the impact of this stimulus with positive reinforcement from the actual need.

REFLEX CONDITIONAL

acquired reflex) - a reflex formed when any initially indifferent stimulus approaches in time with the subsequent action of the stimulus that causes an unconditioned reflex. The concept was introduced by IP Pavlov to denote a dynamic connection between a conditioned stimulus and the subject's reaction, originally based on an unconditioned stimulus. It is based on the development of new - temporary - connections. With repeated actions of irritation, if it is not reinforced (does not serve to satisfy vital needs), the reaction to it weakens and disappears. This extinction is based on the process of cortical inhibition.

During experimental studies the rules for the development of conditioned reflexes were determined: the joint presentation of stimuli - initially indifferent and unconditional - with a certain delay in the second; in the absence of reinforcement of the conditioned stimulus by the unconditioned temporal connection is gradually inhibited. As a result of the formation of a reflex, a conditioned stimulus that previously did not cause a corresponding reaction begins to cause it, becoming a signal stimulus (conditioned - detected under certain conditions).

There are two types of conditioned reflexes:

1) conditional classical reflexes - obtained in the specified way;

2) conditional instrumental (operant) reflexes - during their development, unconditional reinforcement is given only upon the occurrence of a certain motor reaction (-> operant conditioning).

The mechanism of the formation of conditioned reflexes was initially understood as breaking a path between the centers of conditioned and unconditioned reflexes. Nowadays, the idea of ​​their mechanism as a complex functional system with feedback is accepted - organized according to the principle of a ring, and not an arc.

In animals, conditioned reflexes form a signal system, where signal stimuli are agents in their habitat; In humans, along with the first signal system, generated by environmental influences, there is a second signal system, where the word “signal of signals” acts as conditional stimuli.

CONDITIONED REFLEX

English conditional reflex) - a temporary connection developed by combining conditioned and unconditioned stimuli. U. r. It is carried out by the higher parts of the brain and is based on temporary connections formed between certain nervous structures in the individual experience of an animal and a person. Unconditioned reflexes are, in principle, the same in all representatives of the same species, and U. r. individual and infinitely varied. The term "U. R" was introduced by I. P. Pavlov (V. M. Bekhterev and other reflexologists called the same "combinative reflex." - Ed.). On the basis of experimental studies, Pavlov formulated the rules for developing U. R. and patterns of their manifestation.

The main condition for the formation of U. river. - the presence of reinforcement: the coincidence or closeness in time (single, but much more often multiple) of an indifferent stimulus with an unconditioned stimulus, with some advance of the first. As a result, an indifferent stimulus begins to evoke a response that it has never evoked before. For example, if you combine a bell signal or a flash of an electric lamp with feeding an animal, then a food reaction begins (salivation, turning the head, running towards the feeder, etc.), which without the combination would never have caused. Characteristic U. r. - their temporary nature. If the main condition for the development of U. r. ceases to be observed and the conditioned stimulus is not reinforced by the unconditioned one, then the temporal connection is inhibited, and the U. r. disappears.

This inhibition, according to Pavlov, refers to "internal (conditional) inhibition." The main reason for the development of internal inhibition is the non-reinforcement of conditioned stimuli or their individual components. There are several types of such inhibition: 1) fading, which is produced with a single or multiple non-reinforcement of the conditioned stimulus; 2) differentiation - with non-reinforcement of one of the indifferent stimuli and continued reinforcement of others; 3) conditional (in the narrow sense), arising when the previously generated and continued to be reinforced conditioned signal ceases to receive reinforcement in combination with c.-l. new agent (which is called "conditional brake"). If the reinforcement moves away in time from the action of the signal stimulus, then delayed inhibition develops, which occupies the period between the onset of the action of the conditioned signal and the delayed reinforcement.

Manifestation of unconditional inhibition are external and transboundary inhibition. External inhibition - suppression of conditioned reflex activity under the action of a (side) extra stimulus that causes an orienting reaction, or during an emergency switching n. With. to a more significant event (see Tower of Silence). Transboundary inhibition occurs in the nerve cells of the cortex when exposed to very strong stimuli. Its main function is to prevent the destruction of cells under the influence of excitations that are extraordinary in strength. Therefore, translimiting inhibition is also called protective (see also Parabiosis).

It has been established that the same stimulus under different conditions ( different time days, lighting, different experimental chambers, etc.), different U. r. For example, if a sound with a height of 1000 Hz in one chamber is reinforced with food, and in another - with irritation of the animal's paw by current, then in the 1st chamber this sound becomes a signal of food U. p., and in the 2nd - a defensive reflex. This phenomenon has received the name of switching U. river, or conditioned reflex switching.

At present, it is customary to distinguish between classical and instrumental U. p. Classic W. p. they are also called "U. R. 1st type", instrumental - "U. R. 2nd type", or "operant".

In the classical urns, which were first studied and described in the Pavlovian school, the response repeats and reproduces the unconditioned reaction evoked by unconditional reinforcement. During the development of instrumental U. rivers, which were discovered and investigated by Amer. behaviorists (e.g., B. F. Skinner), an animal or a person learns in response to certain stimuli to perform appropriate actions that either provide positive reinforcement (food, an individual of a different sex, a cognitive or communicative effect), or relieve them from the action of painful traumatic agents (avoidance reaction). For example, in response to a certain cue, or to the environment in which learning is being studied, the animal presses a lever to get food (or to get out of a cage whose floor is passed through electricity). In these cases, a conditioned motor reaction is, as it were, a means, an instrument for receiving reinforcement (hence the name - instrumental U. r.). See also Reflex. (D. A. Farber)

Addendum: At researchers U. r. and some psychologists are tempted to reduce the wealth of spiritual life to U. r. Such a temptation is caused by the illusion of all-understanding. On this occasion, A. A. Ukhtomsky wrote: “Workers on conditioned reflexes experienced this inner conviction that they understand to the subtlety those forces that govern the current inner world of a person and the motives of his behavior. Not understanding well their immediate experiments on dogs, they bravely reworked their conclusions into inner world person. And this made them ignorant par excellence" (Honored Interlocutor. - Rybinsk, 1997, pp. 230-231). Outside of science, there were also decisions of the Pavlovian session of the USSR Academy of Sciences and the USSR Academy of Medical Sciences in 1950, according to which the psyche was identified with higher nervous activity, and psychology - with the doctrine of U. R. There was no fault in this of I. P. Pavlov. (V. P. Zinchenko.)

REFLEX CONDITIONAL

conditioned reflex) - an acquired reflex, in which functional connections between the excitation of receptors and the characteristic response of effector organs are established in the learning process. In Pavlov's classic experiments, dogs were trained to associate the sound of a bell with the time of feeding, so that in response to the ringing of the bell, they began to salivate whether or not food was given to them.