An evolutionary approach to the study of higher nervous activity

Anatomical concept of reflex.

Mechanical concept of reflex.

Development of reflex theory.

This is the teaching of Rene Descartes (1596-1650). He represented nervous processes on the model of the circulatory system, using the principles of optics and mechanics that existed at that time. By reflex, Descartes understood the movement of “animal spirits” from the brain to the muscles, similar to the reflection of a light beam. Important in his theory is the development of the concept of the stimulus necessary to activate the mechanisms human body, i.e. he tried to explain the reflex from a materialistic point of view, but he attributed the ability to think and feel not to the brain, but to the soul (for him they existed separately).

Biological concept of reflex: This is the teaching of the Czech scientist Jiri Prochazka (1749-1820), he introduced the term “reflex” and the description of the reflex arc into science. "External impressions arising in sensory nerves, spread along them, are reflected in the motor muscles and are directed along them to the muscles. The reflex response always manifests itself in size according to the strength of the applied stimulus.” The structure of the reflex and its purpose were considered with biological point vision. The principle of reflex extended to mental activity.

In the 19th century, it was carefully studied anatomical structure nervous system. English doctor Charles Bell (1774-1842) experimentally discovered that when cutting the anterior roots spinal nerves a reflex response is observed: contraction of the back muscles. The French physiologist F. Magendie (1783-1855) came to the same conclusions. These scientists formulated the Bell-Magendie law: transition nervous excitement carried out by afferent nerves through spinal cord to efferent nerves. The English physician Marshall Hall coined the term “reflex arc.” M. Hall and I. Muller believed that the reflex mechanism is characteristic only of the spinal cord.

Charles Darwin in “The Origin of Species by Means of Natural Selection” (1859) formulated the principle of the evolution of living organisms: “the driving force for the development of organisms lies in adaptive relationships with the environment.” Consequently, the main reason for the evolution of behavior is adaptation to environmental conditions. Darwin clearly identified rational activity as one of the main components complex shapes animal behavior. Darwin's teaching was a prerequisite for the creation of the teaching of I.M. Sechenov.

Sechenov I.M. (1829-1905). His most important work is “Reflexes of the Brain” (1863). He identified two types of reflexes - congenital and acquired. Material Processes brain activity are primary, and mental ones are secondary. Consciousness is a reflection of reality; the progress of the psyche is associated with the improvement of the brain in the process of evolution in animals. All acts of conscious and unconscious life in their origin are reflexes, but did not identify psychic phenomena with reflexes. Behavioral reactions are carried out through the central nervous system, like reflex reactions. He introduced the evolutionary principle into physiology, but Sechenov's views were only theoretical. Among the main achievements of this scientist was the discovery of the process of inhibition, which exists in the nervous system along with excitation, without which it is impossible to imagine the implementation of integrative functions by the central nervous system. Gained international recognition for the discovery of central braking. He was the first to discover that inhibition is not a passive, but an active process.

In the center scientific interests famous Russian scientist V.M. Bekhterev (1857-1928) there was a human problem. His greatest contributions to science were his works on brain anatomy and neuropathology. He introduced the concept associative, i.e. actually a conditioned reflex as an acquired property of the nervous system, as well as the idea of ​​complex organic reflexes, i.e. instincts, the mechanism of which he also considered purely reflexive. Bekhterev believed that the source of knowledge about the behavior and functioning of the brain of humans and animals is objective observation and experiment, and not a subjective analysis of behavior. In 1926, the book “Fundamentals of Human Reflexology” was published, which reflected the complex theory created by Bekhterev, called “reflexology”.

In the article we will talk about the founder of the reflex theory. It is generally accepted that its creators are several people at once, but this is not at all true. The fact is that many scientists made a certain contribution, but today we will look at the specific contribution of Rene Descartes. We will also learn in detail about the provisions of his theory and get acquainted with the biography of the scientist himself.

A little about the topic

The name of Rene Descartes is associated with a very important and difficult period in the development of psychological science. The scientist’s statements served to create new concept which allowed me to look at the world differently psychological problems. The psyche began to be viewed as the inner world of a person, which is completely amenable to introspection, but at the same time is an absolutely independent substance, separate from the external world.

The essence of Descartes' entire teaching is precisely to prove the complete opposition of the concepts of material and spiritual worlds. The scientist introduced the concept of reflex into use without naming it, and this gave impetus to the fact that people and animals began to be considered from the natural scientific and psychological side, taking into account their relationship.

About the author

Now let’s learn a little about the founder of the reflex theory. Descartes was born in 1596 in France. From his parents he received a small but still significant fortune, which allowed him not to worry about his food and devote himself entirely to science. At the Jesuit college he received a decent education in the humanities and mathematics. Later he excelled in studying psychology, philosophy and physics.

Due to poor health, the college director allowed the young man to skip morning services. Thanks to this, the scientist developed a habit that he retained for the rest of his life - staying in bed until almost noon. At the same time morning hours were the most productive for the thinker.

After training

After Rene Descartes completed his studies, he hurried to Paris, where he indulged in the amusements of his youth. However, all this superficial fuss very quickly tired young man, whose thoughts went very far from the present day. That is why very soon he began to lead a more secluded and quiet lifestyle in order to devote free time studying mathematics.

At the age of 21 he became a soldier and spent several years on the front lines in Hungary, Holland and Bavaria. He learned to handle weapons and matured, becoming a bit of an adventurer. The guy really liked to attend various balls and had fun gambling. He was incredibly lucky, largely due to the fact that he was an excellent mathematician. Soon Rene Descartes met his beloved woman, who bore him a beautiful daughter. By for unknown reasons at the age of 5, the baby died, and this greatly shocked Descartes. After that, he always said that the death of his daughter was the most tragic event in his life.

It must be said that the development of reflex theory was directly related to events in the life of the scientist himself. Almost everything he talked about, one way or another, found manifestation in his own life. He was always interested in how all theoretical knowledge could be applied in practice, so he did not lose heart and regularly conducted a wide variety of experiments.

It is known that the man was trying to find a way to prevent his hair from turning gray. He also experimented with a rocking chair. Later, the founder of the reflex theory talked about his dream, which became a real revelation for him. This happened during his military service. He was in a large Bavarian house, which was heated by a powerful stove. The man dozed off, he dreamed amazing dream. He supposedly saw the spirit of truth accusing him of laziness. The spirit said that the life task of a scientist is to prove the principles of mathematics and their usefulness in the study of nature. Thus, Descartes had a serious mission ahead of him.

Dedication to one thing

After this dream, the scientist served for some time and returned to Paris, but he was again tired of youth life, and he decided to retire to study mathematics. Rene sold his father's estate and bought a small house in Holland. By the way, in just 20 years, Descartes changed about 24 houses, and all because he strived for complete solitude. At the same time, he visited 13 cities, and carefully hid his residential address from his closest friends, with whom he regularly corresponded.

He really disliked unexpected guests and meaningless gatherings. When buying a new house, I always took into account two main points - that there should be a Catholic cathedral nearby, and that a university should be located nearby.

Descartes: reflex theory

The theory of reflexes became the most important discovery XVII century. The concept of a reflex first began to appear in Descartes's writings on physics. It was necessary in order to completely complete the picture of the mechanistic world created by the scientist. And all that was missing from it was the behavioral characteristics of living beings. In this case, it is necessary to take into account the general background of events against which Descartes’ discovery took place. At this time, the body and its functions began to be viewed from a new angle, which gradually led to a complete revolution in the study of the anatomical and physiological nature of man. The final blow to the basic medieval concepts of essence and form was dealt by the discovery of Harvey's blood circulation. That is why it is worth understanding the basic principles of Descartes’ reflex theory as total product of that time, which matured under the most suitable conditions. At the same time, due to the lack of knowledge about the activity of the central nervous system, the reflex theory still did not have such a basic basis. scientific basis, as a theory of blood circulation.

Many compare these two discoveries, and it must be said that Descartes’ contribution is much more significant, since it concerned not any function of the body, but the very process of interaction of living beings with each other.

Beautiful metaphor

The founder of the reflex theory made his discovery precisely thanks to the above-mentioned discovery of Harvey. The fact is that Descartes imagined the interaction of living beings in the form of the reaction of nervous “machines” to each other. He created an association of the nervous system that was similar to the circulatory system.

The heart was the brain, from which various “tubes” branched off, that is, blood vessels. They transmit nerve impulses, which provide a person with information from the outside world. At the same time, by the movement of blood in the vessels, that is, by the transmission of a nerve impulse to the nervous system, one can judge a living creature and many of its features.

Descartes called impulses “animal spirits” - a very ancient and mystical term that actually meant nothing more than tiny particles, which move quickly in the human body.

Basic provisions

The study of reflexes led the scientist to the fact that he was able to form some basic principles. Firstly, it should be noted that a reflex, according to Descartes, is an act of the nervous system. At the same time, it must be clearly understood that the scientist did not use the term “reflex” itself, but he outlined it incredibly clearly, and the followers only had to come up with a suitable word, which is what they did. Secondly, the man still considered the activity of animals to be machine-like, while human activity was presented in the form huge amount acts of the nervous system, that is, a complete set of certain reflexes. To explain his thoughts more clearly, Rene compared nervous process with thermal and light phenomena, and yet such comparisons have been encountered since ancient times.

Reflex theory and physiology turned out to be very connected, because knowledge about the soul and its properties, as it later became clear, was largely based on new discoveries in physics, especially in the field of optics. The studies of Ibn al-Haytham and R. Bacon showed how much the sphere of sensations depends not only on the soul, but also on the laws of physics. Based on this, we can conclude that the founder of the reflex theory created his discovery on the basis of modern knowledge of physics and mechanics. The isolated understanding of the soul disappeared, but a clear understanding of its inseparability from physiology appeared.

Descartes considered the first cause of a motor act to be a certain nerve impulse, the cause of which lay outside himself. Thus, the body receives a signal from the outside world, which is transmitted along nerve fibers to the brain. At the same time, the scientist did not deny the disposition of organs and even recognized it as a basic necessity.

Despite the fact that a fixed system of nerves and muscles was recognized, it was still subject to change. Descartes believed that with each new impulse the nerve “threads” do not acquire their old uniform, but stretch and change their configuration.

And what after?

The followers of Descartes, studying examples of conditioned reflexes, no longer doubted that explaining the activity of the soul, that is, the nervous system, in terms of some invisible forces, is as pointless as explaining the work mechanical forces the action of superpowers.

Rene formed a methodological rule, which is that what a person experiences applies only to himself and directly to his body. This means that everyone can feel and see the whole picture of the world in their own way, and in many ways it is based on physiology, that is, on how impulses are transmitted and interpreted by the nervous system.

Conditioned reflexes, examples of which are still remembered in schools, are nothing more than an individual and acquired over time basic set of the person himself, that is, it is not applicable to other people and their model of the world. And conditioned reflexes are pure physiology, which at the same time has a decisive influence on the nervous system.

Behavior modeling

Having come to his conclusions, the scientist realized that human behavior can be controlled and modeled. Almost all body systems lend themselves to creating reflexes. Descartes emphasized that only speech and intelligence can not be modeled. Thus, the researcher tried to explain the process of learning, which is why he is considered one of the predecessors of associationism.

Descartes believed that the importance of this knowledge lies in the fact that it enables a person to control his passions. After all, if you can teach this to animals that have a brain but no mind, then even more so can people, who can program themselves and change their attitudes, succumb to this.

Sechenov

Below we will consider the principles of the reflex theory of Sechenov and Pavlov. The views of I. Sechenov were formed by the middle of the last century. He studied the functioning of the brain and came to the conclusion that nervous activity is provoked not by the soul, but by factors external environment. The scientist was able to show that the psyche is not something original and given, but only a property of the brain that can be consciously changed.

Ivan Pavlov

The views of I. Pavlov were formed under the influence of I. Sechenov. Man for a long time studied the functioning of the brain, and later became the discoverer of conditioned reflexes. Brain activity was considered as a result of the functionality of the cortex. Thanks to a series of experiments on people and animals, he was able to show that the basis of any mental processes- these are reflexes. The scientist’s research later made it possible to create a classification of people by character, but initially it was a classification by the type of activity of the nervous system. I. Pavlov identified an unbalanced type, a balanced type with active nervous processes, a balanced type with low activity of nervous processes, and a weak type, in which excitatory and inhibitory processes were equally weak. Based on this knowledge, each person can now determine his strengths and weaknesses, learn to manage your reactions and thus decisively change your whole life.

By the way, everyone modern theories about attracting the Universe to fulfill desires, the power of positive thinking, etc. are based, as you already guessed, on reflexes.

It is almost impossible to unequivocally answer the question of who is the founder of the reflex theory. Descartes undoubtedly laid its foundations, but further development occurred thanks to a number of outstanding scientists.

The rapid development of physiology and biology, discoveries in psychophysics and psychophysiology also stimulated the development of an anatomical and morphological model of the reflex, which filled the rather speculative concepts of Descartes and Hartley with real content.

In the works of the psychophysiologist and physician I. Prochazka, the “general sensory” was discovered - the area of ​​​​the brain where the nerves originate, the irritation of which causes a transition from sensation to the body’s motor response to an external impulse, i.e. from sensory (sensory, centripetal) nerves to motor (motor, centrifugal). More low levels The innervations of behavior that he wrote about are related to the work not of the brain, but of the spinal cord, which is involved in the organization of elementary forms of behavior, a kind of automatisms, which, however, do not act purely mechanically, but according to the biological needs of the body.

The study of the reflex system was continued in the works of the English anatomist and physiologist C. Bell and the French scientist F. Magendie, who identified fibers running from the roots through the spinal cord to the fibers that activate the muscular apparatus. Thus, the model of the reflex was defined as a kind of automaton, consisting of three blocks: centripetal, central and centrifugal. This anatomical and morphological model of the central nervous system was called the Bell-Magendie law. This law describes the distribution pattern nerve fibers in the roots of the spinal cord: sensory fibers enter the spinal cord as part of the dorsal roots, and motor fibers enter as part of the anterior ones.

Research by I.M. Sechenov systematized previous concepts, transforming reflex system in accordance with experimental physiological data. In the structure of the analyzer, he identified three parts - centripetal, i.e. sensing receptor central part, processing information, and centrifugal, transmitting signals to the muscle. An important point For modern understanding The reflex has an image put forward by Sechenov - a signal that not only “triggers” the reflex, but also regulates its course. In other words, it is not the external stimulus, but its reflection in the sense organ that is the signal that triggers the reflex act. In this case, the signal (i.e., the image of an object or situation), which allows one to distinguish the properties of objects in the external environment, directs and corrects the course of the reflex, optimizing its course.

In the central part, several information processing centers are distinguished, the main of which are: the center of inhibition (volitional regulation), information storage (memory), warning (thinking) and signal amplification (emotions).

Having put forward the principle of “coordinating movement with feeling,” Sechenov fundamentally revised the role of muscle efforts in the reflex act. His idea that the muscular sense contains a system of signals about the spatiotemporal parameters of the external world has been proven by a significant number of works by modern psychologists and physiologists. Thus, a muscle is not only an organ of movement, but also an organ of cognition, since objective actions are external analogues of certain mental operations (analysis, synthesis, classification, etc.), helping the formation of internal, actually mental operations.

Sechenov’s thoughts about feedback (i.e., signals from muscles to sensory organs) for self-regulation of behavior were developed by N.A. Bernstein, who studied the mechanisms of movement construction.

Bernstein showed that automatic execution muscle commands sent by nerve centers cannot form the basis of a complex movement, since it is continuously adjusted during execution. This occurs due to the fact that there is a cyclic connection between the muscle and the center. From the centers, signals are sent to the periphery in advance (Bernstein called them sensory corrections), which reflect the final result, according to the changing situation.

That is, the body, while working, solves a motor problem. Moreover, there are five different levels building movement. Each level has its own, in its language, “afferent syntheses.” This means that in the nerve centers there is, as it were, encoded information that carries information in advance about the external world, in the space of which one or another class of movements is to be performed - “advanced reflection”. Thanks to this, the body is able to anticipate and predict the conditions in which it will have to act in the future, and not just store information about the past and respond to stimuli that affect its nervous system at the moment.

The organism encounters the world already having a supply of projects for possible movements. The creation of these projects reveals the activity of the body, the ability to be creative, to create something new, to build, as Bernstein wrote, a model of the “required result.” This is how the reflex model was finally formulated, while the most important reason there was no activity direct action stimulus to the organs of its perception, but the preparation of a model of a possible future action.

In addition to the structure of the reflex act, scientists were also interested in the ways of its transformation, changes under the influence of training and education. Great value for psychological implications of this problem there were works by I.P. Pavlova and V.M. Bekhterev.

Having studied the patterns of dynamics of nervous processes (inhibition, irradiation, concentration, etc.), which determine external manifestations behavior, scientists have identified two levels reflex behavior- unconditioned (simple) and conditioned (or combination) reflexes. Having a biological basis, conditioned reflex is formed on the basis of an innate, unconditional (certain need, for example, for food, protection from harmful influences, etc.), and the body constantly learns to distinguish and differentiate signals. If the signal leads to success, i.e. is reinforced, a connection is formed between it and the body’s response, which becomes stronger with repetition. This is how a conditioned reflex arises and is reinforced.

The orienting reflex discovered by Pavlov, or, as he called it, the “What is it?” reflex was also of great importance. It lies in the fact that the body continually asks this question to the world around it, trying to find out the meaning of the situation in which it finds itself, and in the best possible way“calculate” what is of greatest value to him. Orienting reflex not only helps adaptation in an unfamiliar environment, but is also the biological basis of any cognitive motivation, stimulating interest in unfamiliar, new stimuli.

Exploring biological mechanisms reflex activity, Bekhterev proved that the flexibility and plasticity of the nervous system makes it possible to change reflexes of any degree of complexity in the desired direction. That is, in the behavior of living beings, inherited reflexes play a minimal role, while the leading one belongs to acquired, conditioned ones.

So, Sechenov was the first to formulate the reflex theory. Its main provisions are as follows:

A reflex is a unique universal form of interaction between an organism and the environment, based on evolutionary biology. Sechenov identified two types of reflexes:

Constant, innate, which are carried out by the lower parts of the nervous system ("pure" reflexes).

Changeable, acquired in individual life, which he considered both physiological and mental phenomena.

The activity of nerve centers is represented as a continuous dynamics of the processes of excitation and inhibition.

Brain centers can delay or enhance spinal cord reflexes.

Sechenov introduces the concept " physiological state nerve center", which is directly related to biological needs. The state of the center represents the nervous substrate of the need.

The concept of “reflex association” is introduced, which underlies the learning of humans and animals.

However, Sechenov did not have enough experimental confirmation of his “brilliant guesses.” Pavlov experimentally confirmed and supplemented Sechenov’s ideas. He supported Sechenov's ideas with the scientific concept of a conditioned reflex and introduced it into the strict framework of laboratory experiment. We can highlight the following most important achievements of Pavlovian theory:

Created laboratory method objective study of the adaptive activity of humans and animals (conditioned reflex method).

The adaptive-evolutionary meaning of conditioned reflexes for the animal world is emphasized.

An attempt was made to localize the process of temporary connection closure in the cortex cerebral hemispheres.

I noted the presence of b.p. in the cortex. braking process.

The doctrine of analyzers is clearly formulated (3 blocks in the structure of any sensory system).

Formulated the idea of ​​the cortex as a mosaic of processes of excitation and inhibition.

At the end of his life he put forward the principle of systemic functioning of the brain.

So, the basic principles of the Pavlov-Sechenov reflex theory are as follows:

The principle of determinism (causality). This principle means that any reflex reaction is causally determined, that is, there is no action without a reason. Every activity of the body, every act of nervous activity is caused by a certain influence from external or internal environment.

The principle of structure. According to this principle, each reflex reaction is carried out using certain brain structures. There are no processes in the brain that do not have material basis. Each physiological act of nervous activity is associated with some structure.

The principle of analysis and synthesis of stimuli. The nervous system constantly analyzes (distinguishes) with the help of receptors all external and internal stimuli acting on the body, and on the basis of this analysis forms a holistic response - synthesis. In the brain, these processes of analysis and synthesis occur continuously and constantly. As a result, the body extracts the information it needs from the environment, processes it, records it in memory and forms response actions in accordance with circumstances and needs.

Another important concept in the physiology of VND is the concept of nervism - this is a concept that recognizes the leading role of the nervous system in regulating the functions of all organs and tissues of the body. A great contribution to the development of the concept of nervism was made by I.M. Sechenov and especially Botkin S.P. (1832-1889). Botkin considered various diseases as a consequence of disturbances in normal nervous regulation(clinical nervism).

Introduction

Human interaction with reality is carried out through the nervous system.

The human nervous system consists of three sections: the central, peripheral and autonomic nervous systems. The nervous system functions as a single and integral system.

The complex, self-regulating activity of the human nervous system is carried out thanks to reflex nature this activity.

This work will reveal the concept of “reflex”, its role and significance in the body.

Reflex theory and its basic principles

The provisions of the reflex theory developed by I.M. Sechenov. I. P. Pavlov and developed by N. E. Vvedensky. A. A. Ukhtomsky. V. M. Bekhterev, P. K. Anokhin and other physiologists are the scientific and theoretical basis of Soviet physiology and psychology. These provisions find their creative development in the research of Soviet physiologists and psychologists.

The reflex theory, which recognizes the reflex nature of the activity of the nervous system, is based on three main principles:

1) the principle of materialistic determinism;

2) the principle of structure;

3) the principle of analysis and synthesis.

The principle of materialistic determinism means that each nervous process in the brain is determined (caused) by the action of certain stimuli.

The principle of structure is that the differences in the functions of different parts of the nervous system depend on the characteristics of their structure, and changes in the structure of parts of the nervous system during development are determined by changes in functions. Thus, in animals that do not have a brain, the higher nervous activity is much more primitive compared to the higher nervous activity of animals that have a brain. In a person during historical development the brain has reached especially complex structure and perfection that is associated with it labor activity and social living conditions that require constant verbal communication.

Principle of analysis and synthesis is expressed as follows. When centripetal impulses enter the central nervous system, excitation occurs in some neurons, and inhibition occurs in others, i.e., physiological analysis occurs. The result is the distinction between specific objects and phenomena of reality and processes occurring inside the body.

At the same time, during the formation of a conditioned reflex, a temporary nervous connection (closure) is established between two foci of excitation, which physiologically expresses synthesis. The conditioned reflex is the unity of analysis and synthesis.

Reflex - concept, its role and significance in the body

Reflexes (from the Latin slot reflexus - reflected) are called responses body to stimulate receptors. Nerve impulses arise in the receptors, which enter the central nervous system via sensory (centripetal) neurons. There the information received is processed interneurons, after which motor (centrifugal) neurons are excited and nerve impulses activate the executive organs - muscles or glands. Intercalary neurons are those whose bodies and processes do not extend beyond the central nervous system. The path along which nerve impulses travel from the receptor to the executive organ is called a reflex arc.

Reflex actions are holistic actions aimed at satisfying a specific need for food, water, safety, etc. They contribute to the survival of an individual or species as a whole. They are classified into food, water-producing, defensive, sexual, orientation, nest-building, etc. There are reflexes that establish a certain order (hierarchy) in a herd or flock, and territorial ones, which determine the territory captured by a particular individual or flock.

There are positive reflexes, when a stimulus causes a certain activity, and negative, inhibitory reflexes, when the activity stops. The latter, for example, includes the passive defensive reflex in animals, when they freeze when a predator appears or an unfamiliar sound.

Reflexes play an exceptional role in maintaining the constancy of the body’s internal environment and its homeostasis. So, for example, when increasing blood pressure a reflex slowdown of cardiac activity occurs and the lumen of the arteries expands, so the pressure decreases. When it drops strongly, opposite reflexes arise, strengthening and speeding up the contractions of the heart and narrowing the lumen of the arteries, as a result of which the pressure increases. It continuously fluctuates around a certain constant value, which is called the physiological constant. This value is determined genetically.

The famous Soviet physiologist P.K. Anokhin showed that the actions of animals and humans are determined by their needs. For example, the lack of water in the body is first replenished from internal reserves. Reflexes arise that delay the loss of water in the kidneys, the absorption of water from the intestines increases, etc. If this does not lead to the desired result, in the centers of the brain that regulate the flow of water, excitement arises and a feeling of thirst appears. This arousal causes goal-directed behavior, the search for water. Thanks to direct connections, nerve impulses, coming from the brain to the executive organs, are provided necessary actions(the animal finds and drinks water), and thanks to feedback connections, nerve impulses going in the opposite direction - from peripheral organs: oral cavity and the stomach - to the brain, informing the latter about the results of the action. Thus, during drinking, the center of water saturation is excited, and when thirst is satisfied, the corresponding center is inhibited. This is how the controlling function of the central nervous system is carried out.

A great achievement in physiology was the discovery of conditioned reflexes by I. P. Pavlov.

Unconditioned reflexes are innate, inherited reactions by the body to environmental influences. Unconditioned reflexes are characterized by constancy and do not depend on learning and special conditions for their occurrence. For example, the body responds to painful stimulation with a defensive reaction. There is a wide variety of unconditioned reflexes: defensive, food, orientation, sexual, etc.

The reactions underlying unconditioned reflexes in animals have been developed over thousands of years in the course of adaptation various types animals to environment, in the process of struggle for existence. Gradually in conditions long evolution unconditional reflex reactions necessary to satisfy biological needs and preserve the vital functions of the organism were consolidated and passed on by inheritance, and those unconditional reflex reactions that lost their value for the life of the organism lost their expediency; on the contrary, they disappeared without being restored.

Under the influence of constant changes in the environment, stronger and more advanced forms of animal response were required, ensuring the organism’s adaptation to changed living conditions. In the process of individual development, highly organized animals develop special kind reflexes, which I. P. Pavlov called conditioned.

Conditioned reflexes acquired by an organism during life provide an appropriate response of a living organism to changes in the environment and, on this basis, balance the organism with the environment. Unlike unconditioned reflexes, which are usually carried out by the lower parts of the central nervous system (dorsal, medulla oblongata, subcortical nodes), conditioned reflexes in highly organized animals and in humans are carried out mainly by the higher department of the central nervous system (cerebral cortex).

Observing the phenomenon of “psychic secretion” in a dog helped I.P. Pavlov discover a conditioned reflex. The animal, seeing food from a distance, began to salivate intensively even before the food was served. This fact has been interpreted in different ways. The essence of “psychic secretion” was explained by I. P. Pavlov. He found that, firstly, in order for a dog to start salivating at the sight of meat, it had to have seen and eaten it at least once before. And, secondly, any irritant (for example, the type of food, a bell, the blinking of a light bulb, etc.) can cause salivation, provided that the time of action of this irritant coincides with the time of feeding. If, for example, feeding was constantly preceded by the knocking of a cup containing food, then there always came a moment when the dog began to salivate just by knocking. Reactions that are caused by stimuli that were previously indifferent. I.P. Pavlov called them conditioned reflexes. The conditioned reflex, noted I.P. Pavlov, is a physiological phenomenon, since it is associated with the activity of the central nervous system, and at the same time, psychological, since it is a reflection in the brain of specific properties of stimuli from the outside world.

Conditioned reflexes in animals in the experiments of I. P. Pavlov were most often developed on the basis of food unconditioned reflex, when the unconditioned stimulus was food, and the function of the conditioned stimulus was performed by one of the stimuli that were indifferent (indifferent) to food (light, sound, etc.).

There are natural conditioned stimuli, which serve as one of the signs of unconditioned stimuli (the smell of food, the squeak of a chicken for a hen, causing a parental conditioned reflex in her, the squeak of a mouse for a cat, etc.), and artificial conditioned stimuli, which are completely unrelated to unconditioned reflex stimuli (for example, a light bulb, the light of which caused a dog to develop a salivary reflex, the ringing of a gong, to which moose gather for feeding, etc.). However, any conditioned reflex has a signal value, and if the conditioned stimulus loses it, then the conditioned reflex gradually fades away.