A reflex is the body's response to an internal or external stimulus, carried out and controlled by the central nervous system. Our compatriots I.P. Pavlov and I.M. Sechenov.

What are unconditioned reflexes?

An unconditioned reflex is an innate stereotyped reaction of the body to the influence of the internal or environment, inherited from the offspring from the parents. It remains with a person throughout his life. Reflex arcs pass through the brain and the cerebral cortex does not take part in their formation. The significance of the unconditioned reflex is that it ensures the adaptation of the human body directly to those changes in the environment that often accompanied many generations of its ancestors.

What reflexes are unconditioned?

The unconditioned reflex is the main form of activity of the nervous system, an automatic response to a stimulus. And since various factors affect a person, then the reflexes are different: food, defensive, indicative, sexual ... Salivation, swallowing and sucking are food. Defensive are coughing, blinking, sneezing, withdrawal of limbs from hot objects. Orienting reactions can be called turns of the head, squinting of the eyes. Sexual instincts include reproduction, as well as caring for offspring. The value of the unconditioned reflex lies in the fact that it ensures the preservation of the integrity of the body, maintains the constancy of the internal environment. Thanks to him, reproduction occurs. Even in newborns, an elementary unconditioned reflex can be observed - this is sucking. By the way, it is the most important. The irritant in this case is the touch to the lips of an object (nipples, mother's breasts, toys or fingers). Another important unconditioned reflex is blinking, which occurs when a foreign body approaches the eye or touches the cornea. This reaction refers to the protective or defensive group. It is also observed in children, for example, when exposed to strong light. However, the signs of unconditioned reflexes are most pronounced in various animals.

What are conditioned reflexes?

Reflexes acquired by the body during life are called conditioned reflexes. They are formed on the basis of inherited ones, subject to the influence of an external stimulus (time, knock, light, and so on). A vivid example is the experiments carried out on dogs by Academician I.P. Pavlov. He studied the formation of this type of reflexes in animals and was the developer of a unique technique for obtaining them. So, to develop such reactions, it is necessary to have a regular stimulus - a signal. It starts the mechanism, and repeated repetition of the stimulus effect allows you to develop. In this case, a so-called temporary connection arises between the arcs of the unconditioned reflex and the centers of the analyzers. Now the basic instinct is awakening under the action of fundamentally new signals of an external nature. These stimuli of the surrounding world, to which the body was previously indifferent, begin to acquire exceptional, vital importance. Each living being can develop many different conditioned reflexes during his life, which form the basis of his experience. However, this applies only to this particular individual; this life experience will not be inherited.

An independent category of conditioned reflexes

In an independent category, it is customary to single out conditioned reflexes of a motor nature developed during life, that is, skills or automated actions. Their meaning lies in the development of new skills, as well as the development of new motor forms. For example, over the entire period of his life, a person masters many special motor skills that are associated with his profession. They are the basis of our behavior. Thinking, attention, consciousness are freed when performing operations that have reached automatism and have become a reality of everyday life. The most successful way of mastering the skills is the systematic implementation of the exercise, the timely correction of the noticed mistakes, as well as the knowledge of the ultimate goal of any task. In the event that the conditioned stimulus is not reinforced for some time by the unconditioned stimulus, its inhibition occurs. However, it does not completely disappear. If, after some time, the action is repeated, the reflex will quickly recover. Inhibition can also occur under the condition of the appearance of an irritant of even greater force.

Compare unconditioned and conditioned reflexes

As mentioned above, these reactions differ in the nature of their occurrence and have a different formation mechanism. In order to understand what the difference is, just compare unconditioned and conditioned reflexes. So, the first are present in a living being from birth, during the whole life they do not change and do not disappear. In addition, unconditioned reflexes are the same in all organisms of a particular species. Their meaning is to prepare the living being for constant conditions. The reflex arc of such a reaction passes through the brain stem or spinal cord. As an example, here are some (congenital): active salivation when a lemon enters the mouth; sucking movement of the newborn; coughing, sneezing, pulling hands away from a hot object. Now consider the characteristics of conditioned reactions. They are acquired throughout life, can change or disappear, and, no less important, they are individual (their own) for each organism. Their main function is the adaptation of a living being to changing conditions. Their temporary connection (centers of reflexes) is created in the cerebral cortex. An example of a conditioned reflex is the reaction of an animal to a nickname, or the reaction of a six-month-old child to a bottle of milk.

Scheme of the unconditioned reflex

According to the research of academician I.P. Pavlov, the general scheme of unconditioned reflexes is as follows. Certain receptor nervous devices are affected by certain stimuli of the internal or external world of the organism. As a result, the resulting irritation transforms the entire process into the so-called phenomenon of nervous excitation. It is transmitted through nerve fibers (as through wires) to the central nervous system, and from there it goes to a specific working organ, already turning into a specific process at the cellular level of this part of the body. It turns out that these or those irritants are naturally connected with this or that activity in the same way as the cause with the effect.

Features of unconditioned reflexes

The characteristic of unconditioned reflexes presented below, as it were, systematizes the material presented above, it will help to finally understand the phenomenon we are considering. So, what are the features of inherited reactions?

Unconditional instinct and animal reflex

The exceptional constancy of the nervous connection underlying the unconditional instinct is explained by the fact that all animals are born with a nervous system. She is already able to respond properly to specific environmental stimuli. For example, a creature might flinch at a harsh sound; he will secrete digestive juice and saliva when food enters the mouth or stomach; it will blink with visual stimulation, and so on. Innate in animals and humans are not only individual unconditioned reflexes, but also much more complex forms of reactions. They are called instincts.

The unconditioned reflex, in fact, is not a completely monotonous, stereotyped, transfer reaction of an animal to an external stimulus. It is characterized, though elementary, primitive, but still by variability, variability, depending on external conditions (strength, peculiarities of the situation, position of the stimulus). In addition, it is also influenced by the internal states of the animal (reduced or increased activity, posture, and others). So, even I.M. Sechenov in his experiments with decapitated (spinal) frogs showed that when the toes of the hind legs of this amphibian are acted upon, the opposite motor reaction occurs. From this we can conclude that the unconditioned reflex still has adaptive variability, but within insignificant limits. As a result, we find that the balancing of the organism and the external environment achieved with the help of these reactions can be relatively perfect only in relation to slightly changing factors of the surrounding world. The unconditioned reflex is not able to ensure the adaptation of the animal to new or dramatically changing conditions.

As for the instincts, sometimes they are expressed in the form of simple actions. For example, a rider, thanks to his sense of smell, looks for the larvae of another insect under the bark. He pierces the bark and lays his egg in the found victim. This is the end of all its action, which ensures the continuation of the genus. There are also complex unconditioned reflexes. Instincts of this kind consist of a chain of actions, the totality of which ensures the continuation of the species. Examples include birds, ants, bees and other animals.

Species specificity

Unconditioned reflexes (species) are present in both humans and animals. It should be understood that such reactions in all representatives of the same species will be the same. An example is a turtle. All species of these amphibians retract their heads and limbs into their shells when threatened. And all the hedgehogs jump up and make a hissing sound. In addition, you should be aware that not all unconditioned reflexes occur at the same time. These reactions change according to age and season. For example, the breeding season or the motor and sucking actions that appear in an 18-week-old fetus. Thus, unconditioned reactions are a kind of development for conditioned reflexes in humans and animals. For example, in young children, as they grow older, there is a transition to the category of synthetic complexes. They increase the adaptability of the body to external environmental conditions.

Unconditional braking

In the process of life, each organism is regularly exposed - both from the outside and from the inside - to various stimuli. Each of them is able to cause a corresponding reaction - a reflex. If all of them could be realized, then the vital activity of such an organism would become chaotic. However, this does not happen. On the contrary, reactionary activity is characterized by consistency and orderliness. This is explained by the fact that inhibition of unconditioned reflexes occurs in the body. This means that the most important reflex at a particular moment of time delays the secondary ones. Usually, external inhibition can occur at the time of the start of another activity. The new exciter, being stronger, leads to the attenuation of the old one. And as a result, the previous activity will automatically stop. For example, a dog is eating and at that moment the doorbell rings. The animal immediately stops eating and runs to meet the visitor. There is an abrupt change in activity, and the dog's salivation stops at that moment. Certain innate reactions are also referred to as unconditional inhibition of reflexes. In them, certain pathogens cause a complete cessation of some actions. For example, the anxious clucking of a chicken causes the chickens to freeze and cling to the ground, and the onset of darkness forces the kenar to stop singing.

In addition, there is also a protective id that arises as a response to a very strong stimulus that requires actions from the body that exceed its capabilities. The level of such exposure is determined by the frequency of impulses of the nervous system. The stronger the neuron is excited, the higher the frequency of the flow of nerve impulses that it generates will be. However, if this flow exceeds certain limits, then a process will occur that will begin to prevent the passage of excitation through the neural circuit. The flow of impulses along the reflex arc of the spinal cord and brain is interrupted, as a result, inhibition occurs, which preserves the executive organs from complete exhaustion. What follows from this? Thanks to the inhibition of unconditioned reflexes, the body selects from all possible options the most adequate one, able to protect against excessive activity. This process also contributes to the manifestation of the so-called biological caution.

Reflex- the response of the body is not an external or internal irritation, carried out and controlled by the central nervous system. The development of ideas about human behavior, which has always been a mystery, was achieved in the works of Russian scientists I. P. Pavlov and I. M. Sechenov.

Reflexes unconditioned and conditional.

Unconditioned reflexes- these are innate reflexes that are inherited by offspring from parents and persist throughout a person's life. Arcs of unconditioned reflexes pass through the spinal cord or brain stem. The cerebral cortex does not participate in their formation. Unconditioned reflexes provide only those changes in the environment that many generations of a given species often encountered.

To include:

Food (salivation, sucking, swallowing);
Defensive (coughing, sneezing, blinking, pulling the hand away from a hot object);
Approximate ( skew eyes, turns);
Sexual (reflexes associated with reproduction and care of offspring).
The significance of unconditioned reflexes lies in the fact that thanks to them the integrity of the body is preserved, the maintenance of constancy and reproduction occurs. Already in a newborn child, the simplest unconditioned reflexes are observed.
The most important of these is the sucking reflex. The irritant of the sucking reflex is the touch of an object on the child's lips (mother's breasts, nipples, toys, fingers). The sucking reflex is an unconditioned food reflex. In addition, the newborn already has some protective unconditioned reflexes: blinking, which occurs if a foreign body approaches the eye or touches the cornea, constriction of the pupil when strong light is applied to the eyes.

Particularly pronounced unconditioned reflexes in various animals. Not only individual reflexes can be innate, but also more complex forms of behavior, which are called instincts.

Conditioned reflexes- these are reflexes that are easily acquired by the body during life and are formed on the basis of an unconditioned reflex under the action of a conditioned stimulus (light, knock, time, etc.). IP Pavlov studied the formation of conditioned reflexes in dogs and developed a method for obtaining them. To develop a conditioned reflex, a stimulus is needed - a signal that triggers a conditioned reflex, repeated repetition of the action of the stimulus allows you to develop a conditioned reflex. During the formation of conditioned reflexes, a temporary connection arises between the centers and centers of the unconditioned reflex. Now this unconditioned reflex is not carried out under the influence of completely new external signals. These irritations from the outside world, to which we were indifferent, can now become of vital importance. During life, many conditioned reflexes are developed, which form the basis of our life experience. But this life experience makes sense only for this individual and is not inherited by its descendants.

into a separate category conditioned reflexes allocate motor conditioned reflexes developed during our life, i.e. skills or automated actions. The meaning of these conditioned reflexes is the development of new motor skills, the development of new forms of movements. During his life, a person masters many special motor skills associated with his profession. Skills are the basis of our behavior. Consciousness, thinking, attention are freed from performing those operations that have become automated and become habits of everyday life. The most successful way to master skills is through systematic exercises, correcting mistakes noticed in time, knowing the ultimate goal of each exercise.

If the conditioned stimulus is not reinforced for some time by the unconditioned stimulus, then the conditioned stimulus is inhibited. But it doesn't disappear completely. When the experiment is repeated, the reflex is very quickly restored. Inhibition is also observed under the influence of another stimulus of greater force.

The term "reflex" was introduced by the French scientist R. Descartes in the 17th century. But to explain mental activity, it was used by the founder of Russian materialistic physiology, I. M. Sechenov. Developing the teachings of I. M. Sechenov. IP Pavlov experimentally investigated the features of the functioning of reflexes and used the conditioned reflex as a method for studying higher nervous activity.

All reflexes were divided by him into two groups:

• unconditional;
• conditional.

Unconditioned reflexes

Unconditioned reflexes- innate reactions of the body to vital stimuli (food, danger, etc.).

They do not require any conditions for their production (for example, salivation at the sight of food). Unconditioned reflexes are a natural reserve of ready-made, stereotyped reactions of the body. They arose as a result of a long evolutionary development of this species of animals. Unconditioned reflexes are the same in all individuals of the same species. They are carried out with the help of the spinal and lower parts of the brain. Complex complexes of unconditioned reflexes manifest themselves in the form of instincts.

Rice. Fig. 14. Location of some functional areas in the human cerebral cortex: 1 - area of ​​speech education (Broca's center), 2 - area of ​​the motor analyzer, 3 - area of ​​analysis of oral verbal signals (Wernicke's center), 4 - area of ​​the auditory analyzer, 5 - analysis of written verbal signals, 6 - area of ​​the visual analyzer

Conditioned reflexes

But the behavior of higher animals is characterized not only by innate, i.e., unconditioned reactions, but also by such reactions that are acquired by a given organism in the process of individual life activity, i.e., conditioned reflexes. The biological meaning of the conditioned reflex lies in the fact that numerous external stimuli surrounding the animal in natural conditions and in themselves not of vital importance, preceding food or danger in the experience of the animal, the satisfaction of other biological needs, begin to act as signals, according to which the animal orients its behavior (Fig. 15).

So, the mechanism of hereditary adaptation is an unconditioned reflex, and the mechanism of individual changeable adaptation is conditional. a reflex produced by a combination of vital phenomena with accompanying signals.

Rice. 15. Scheme of the formation of a conditioned reflex

• a - salivation is caused by an unconditioned stimulus - food;
• b - excitation from a food stimulus is associated with the previous indifferent stimulus (light bulb);
• c - the light of the light bulb became a signal of the possible appearance of food: a conditioned reflex developed on it

A conditioned reflex is developed on the basis of any of the unconditioned reactions. Reflexes to unusual signals that do not occur in a natural setting are called artificial conditioned. In laboratory conditions, you can develop many conditioned reflexes to any artificial stimulus.

With the concept of a conditioned reflex, I. P. Pavlov associated signaling principle of higher nervous activity, the principle of synthesis of external influences and internal states.

The discovery by Pavlov of the main mechanism of higher nervous activity - the conditioned reflex - became one of the revolutionary achievements of natural science, a historical turning point in understanding the connection between the physiological and the mental.

With the knowledge of the dynamics of education and changes in conditioned reflexes, the discovery of complex mechanisms of the activity of the human brain, the identification of patterns of higher nervous activity began.

In the course of evolutionary and social development, a person has developed a natural system of protection from adverse environmental factors, i.e. from dangers. It is based on the nervous system. Thanks to it, the connection of the organism with the external environment (light, sound, smell, mechanical influences) and various information about the processes inside and outside the body is carried out. The body's response to irritation, carried out and controlled by the central nervous system, is called a reflex, and all the activity of the nervous system is called a reflex. In a variety of reflex activities, there are innate unconditioned reflexes that are inherited and persist throughout the life of the organism.

Unconditioned human reflexes are diverse. For example, pulling back a hand in response to a skin burn, closing the eyes when there is a danger of damaging them, profuse release of tears under the influence of substances that irritate the eyes, etc. These and many other reflexes are called defensive.

A special place among the unconditioned reflexes in ensuring security is occupied by the orienting reflex. It appears in response to a new stimulus: a person is alert, listens, turns his head, squints his eyes, thinks. The orienting reflex provides the perception of an unfamiliar stimulus.

Unconditioned reflexes are a hereditary "program" of behavior. They provide normal interaction only with a stable environment. However, man lives in an exceptionally changeable, mobile, diverse environment. Unconditioned reflexes as permanent connections are not enough to ensure flexible response in a changing environment. It is necessary to supplement them with temporary flexible connections. Such connections are called conditioned reflexes.

Conditioned reflexes are formed on the basis of individual experience. Since the acquisition of individual experience is learning, the formation of conditioned reflexes is one of the types of learning.

The conditioned reflexes formed in the learning process allow the body to adapt more flexibly to specific environmental conditions and underlie the development of habits in a person, the whole way of life.

The adaptive value of conditioned reflexes is enormous. Thanks to them, a person can take the necessary actions in advance to protect himself, focusing on the signs of a possible danger, without seeing the danger itself. Conditioned stimuli are signaling in nature. They warn of danger.

All direct sensations, perceptions and corresponding human reactions are carried out on the basis of unconditioned and conditioned reflexes. However, in the specific conditions of the social environment, a person is guided and reacts not only to direct stimuli. For a person, the signal of any stimulus is the word denoting it, and its semantic content. Words spoken, audible and visible are signals, symbols of specific objects and environmental phenomena. The word man denotes everything that he perceives with the help of the senses.

Words, like other environmental factors (physical, chemical and biological), in relation to human health can be indifferent, can have a beneficial effect, or can be harmful - up to and including death (suicide).

Unconditioned reflexes are constant innate reactions of the body to certain influences of the external world, carried out through the nervous system and not requiring special conditions for their occurrence.

All unconditioned reflexes, according to the degree of complexity and severity of the body's reactions, are divided into simple and complex; depending on the type of reaction - to food, sexual, defensive, tentative-research, etc.; depending on the attitude of the animal to the stimulus - into biologically positive and biologically negative. Unconditioned reflexes arise mainly under the influence of contact stimulation: food unconditioned reflex - when food enters and acts on the tongue; defensive - with irritation of pain receptors. However, the occurrence of unconditioned reflexes is also possible under the influence of such stimuli as the sound, sight and smell of an object. So, the unconditioned sexual reflex arises under the influence of a specific sexual stimulus (sight, smell and other stimuli emanating from a female or male). An orienting-exploratory unconditioned reflex always occurs in response to a sudden little-known stimulus and usually manifests itself in turning the head and moving the animal towards the stimulus. Its biological meaning lies in the examination of a given stimulus and the entire external environment.

Complex unconditioned reflexes include those that are cyclic in nature and are accompanied by various emotional reactions (see). Often carry to such reflexes (see).

Unconditioned reflexes serve as the basis for the formation of conditioned reflexes. Violation or perversion of unconditioned reflexes is usually associated with organic lesions of the brain; the study of unconditioned reflexes is carried out to diagnose a number of diseases of the central nervous system (see Pathological reflexes).

Unconditioned reflexes (specific, innate reflexes) are innate reactions of the body to certain influences of the external or internal environment, carried out through the central nervous system and not requiring special conditions for their occurrence. The term was introduced by I. P. Pavlov and means that a reflex certainly occurs if adequate stimulation is applied to a certain receptor surface. The biological role of unconditioned reflexes is that they adapt an animal of a given species in the form of appropriate acts of behavior to constant, familiar environmental factors.

The development of the doctrine of unconditioned reflexes is associated with the studies of I. M. Sechenov, Pfluger (E. Pfluger), Goltz (F. Goltz), Sherrington (C. S. Sherrington), Magnus (V. Magnus), N. E. Vvedensky, A. A. Ukhtomsky, who laid the foundations for the next stage in the development of the reflex theory, when, finally, it was possible to fill the concept of the reflex arc with physiological content, which had previously existed as an anatomical and physiological scheme (see Reflexes). The undoubted condition that determined the success of these searches was the full realization that the nervous system acts as a whole, and therefore acts as a very complex formation.

The brilliant predictions of I. M. Sechenov about the reflex basis of the mental activity of the brain served as the starting point for research, which, developing the doctrine of higher nervous activity, discovered two forms of neuro-reflex activity: unconditioned and conditioned reflexes. Pavlov wrote: “... it is necessary to recognize the existence of two types of reflex. One reflex is ready, with which the animal is born, a purely conductive reflex, and the other reflex is constantly, continuously formed during individual life, of exactly the same regularity, but based on another property of our nervous system - on closure. One reflex can be called innate, the other - acquired, and also, respectively: one - species, the other - individual. Inborn, specific, permanent, stereotyped we called unconditional, the other, since it depends on many conditions, constantly fluctuates depending on many conditions, we called conditional ... ".

The most difficult dynamics of interaction of conditioned reflexes (see) and unconditioned is a basis of nervous activity of the person and animals. The biological significance of unconditioned reflexes, as well as conditioned reflex activity, lies in the adaptation of the organism to various kinds of changes in the external and internal environment. Such important acts as self-regulation of functions are based on the adaptive activity of unconditioned reflexes. The exact adaptation of unconditioned reflexes to the qualitative and quantitative characteristics of the stimulus, especially carefully studied in Pavlov's laboratories on examples of the work of the digestive glands, made it possible to interpret the problem of the biological expediency of unconditioned reflexes materialistically, bearing in mind the exact correspondence of the function to the nature of the stimulus.

The differences between unconditioned and conditioned reflexes are not absolute, but relative. A variety of experiments, in particular with the destruction of various parts of the brain, allowed Pavlov to create a general idea of ​​​​the anatomical basis of conditioned and unconditioned reflexes: “Higher nervous activity,” Pavlov wrote, “is composed of the activity of the cerebral hemispheres and the nearest subcortical nodes, representing the combined activity of these two major divisions of the central nervous system. These subcortical nodes are ... the centers of the most important unconditioned reflexes, or instincts: food, defensive, sexual, etc. ... ". Pavlov's stated views must now be recognized only as a scheme. His own doctrine of analyzers (see) allows us to consider that the morphological substrate of unconditioned reflexes actually covers various parts of the brain, including the cerebral hemispheres, meaning the afferent representation of the analyzer from which this unconditioned reflex is evoked. In the mechanism of unconditioned reflexes, an important role belongs to the reverse afferentation about the results and success of the completed action (P.K. Anokhin).

In the early years of the development of the doctrine of conditioned reflexes, individual students of Pavlov, who studied salivary unconditioned reflexes, asserted their extreme stability and immutability. Subsequent studies have shown the one-sidedness of such views. In the laboratory of Pavlov himself, a number of experimental conditions were found under which unconditioned reflexes changed even during one experiment. Subsequently, facts were presented that testify that it is more correct to speak of the variability of unconditioned reflexes than of their immutability. Important points in this regard are: the interaction of reflexes with each other (both unconditioned reflexes among themselves, and unconditioned reflexes with conditioned ones), hormonal and humoral factors of the body, the tone of the nervous system and its functional state. Of particular importance are these questions in connection with the problem of instincts (see), which a number of representatives of the so-called ethology (the science of behavior) tries to present as unchanged, independent of the external environment. Sometimes it is difficult to determine the specific factors of variability of unconditioned reflexes, especially if it concerns the internal environment of the body (hormonal, humoral or interoceptive factors), and then some scientists fall into error when talking about spontaneous variability of unconditioned reflexes. Such adeterministic constructions and idealistic conclusions lead away from the materialistic understanding of the reflex.

IP Pavlov repeatedly emphasized the importance of systematizing and classifying unconditioned reflexes, which serve as the foundation for the rest of the body's nervous activity. The existing stereotyped division of reflexes into food, self-preserving, sexual ones is too general and inaccurate, he pointed out. A detailed systematization and a thorough description of all individual reflexes are needed. Speaking of systematization along with classification, Pavlov had in mind the need for a broad study of individual reflexes or their groups. The task should be recognized as very important and very difficult, especially since Pavlov did not single out even such complex reflexes as instincts from a number of unconditioned reflex phenomena. From this point of view, it is especially important to study the already known and to find new and complex forms of reflex activity. Here we must pay tribute to this logical direction, which in a number of cases receives facts of undoubted interest. However, the ideological basis of this trend, which fundamentally denies the reflex nature of instincts, remains completely unacceptable.

The unconditioned reflex "in its purest form" can manifest itself one or several times after the birth of the animal, and then, in a fairly short time, "acquires" conditioned and other unconditioned reflexes. All this makes it very difficult to classify unconditioned reflexes. So far, no single principle of their classification has been found. So, for example, A. D. Slonim based his classification on the principle of balancing the body with the external environment and maintaining the constancy of the composition of its internal environment. In addition, he singled out groups of reflexes that do not ensure the preservation of an individual, but are important for the preservation of the species. The classification of unconditioned reflexes and instincts proposed by N. A. Rozhansky is extensive. It is based on biological and ecological characteristics and dual (positive and negative) manifestation of the reflex. Unfortunately, Rozhansky's classification sins with a subjective assessment of the essence of the reflex, which is also reflected in the naming of some reflexes.

The systematization and classification of unconditioned reflexes should provide for their ecological specialization. With the ecological adequacy of stimuli and the biological fitness of the effector, a very subtle differentiation of unconditioned reflexes is manifested. The speed, strength, and the very possibility of the formation of a conditioned reflex depend not so much on the physical or chemical characteristics of the stimulus, but on the ecological adequacy of the stimulus and the unconditioned reflex.

Of great interest is the problem of the emergence and development of unconditioned reflexes. I. P. Pavlov, A. A. Ukhtomsky, K. M. Bykov, P. K. Anokhin and others believed that unconditioned reflexes arise as conditioned ones, and subsequently become fixed in evolution and turn into innate ones.

Pavlov pointed out that new emerging reflexes, while maintaining the same conditions of life in a number of successive generations, apparently continuously turn into permanent ones. This is probably one of the active mechanisms of the development of the animal organism. Without recognizing this position, it is impossible to imagine the evolution of nervous activity. Nature cannot allow such extravagance, - said Pavlov, - that each new generation should start everything from the very beginning. Transitional forms of reflexes, which occupied an intermediate position between conditioned and unconditioned, were found with a high biological adequacy of stimuli (V. I. Klimova, V. V. Orlov, A. I. Oparin and others). These conditioned reflexes did not fade away. See also Higher nervous activity.