Conditioned and unconditioned reflexes

Higher nervous activity is a system that allows the human and animal body to adapt to variable environmental conditions. Evolutionarily, vertebrates have developed a number of innate reflexes, but their existence is not enough for successful development.

In the process of individual development, new adaptive reactions are formed - these are conditioned reflexes. Outstanding domestic scientist I.P. Pavlov is the founder of the doctrine of unconditioned and conditioned reflexes. He formed the conditioned reflex theory, which states that the acquisition of a conditioned reflex is possible through the action of a physiologically indifferent irritation on the body. As a result, a more complex system of reflex activity is formed.

I.P. Pavlov - the founder of the doctrine of unconditioned and conditioned reflexes

An example of this is Pavlov's study of dogs that salivated in response to a sound stimulus. Pavlov also showed that innate reflexes are formed at the level of subcortical structures, and new connections are formed in the cerebral cortex throughout the life of an individual under the influence of constant irritations.

Classification and types

All reflexes, depending on their origin, can be divided into conditioned (acquired) and unconditioned (otherwise called innate) . Also, according to their biological role, they can be of the following varieties:

Approximate.
Food.
Sexual

There is a classification of reflexes according to localization, which perceives the action of the stimulus:

Proprioceptive. They are characterized by stimulation of the striated muscles of animals and humans. Thanks to this, motor activity occurs.
Interoceptive. They are produced by the impact of any changes on the internal organs (temperature, blood acidity, homeostasis).
Exteroceptive. In this case, irritation is perceived by the body's receptors.

Depending on the location of the centers, they can be cortical or cerebellar, diencephalic or mesencephalic, as well as bulbar, spinal or spinal. Autonomic and somatic reflexes are distinguished by efferent links. According to effector changes, they come in the following varieties:

Vomiting and coughing.
Blinking.
Swallowing.

They can also be classified into inhibitory and excitatory.

The types of reflexes can be different depending on their purpose and the influencing factor:

By type of origin: unconditional and conditional.
According to the type of receptors: proprioceptive (joints, tendons, muscles) and exteroceptive (olfactory, auditory, skin and visual), as well as interoceptive (from internal organs).
By effectors: motor and somatic, autonomic.
According to biological significance: indicative, sexual and protective, as well as digestive and defensive.
Depending on the degree of complexity of the neural arc organization, receptors can be divided into monosomatic (their arcs consist of an efferent and afferent neuron) and polysynaptic.
According to the effect on the activity of the human body: inhibitory and excitatory.
Anatomically, the reflex arc can be located in the brain or in the spinal cord.

Reflexes can also be conditionally divided into natural (formed by the presence of a stimulus similar to unconditioned) and artificial (appear under the influence of a stimulus that has nothing in common with the innate one).

Reflex of support, straightening and automatic walking

If a newborn baby is taken under the arms and raised so that his feet are in contact with the surface, he will begin to move his legs, as if walking on air. This is how the support and automatic walking reflex manifests itself. Remember that for now this is an unconditioned reflex of the newborn, and not a sign of readiness to go. You will need to be patient to wait for the joyful moment when your baby takes his first steps.

Conditioned reflexes

These are formed during the individual development of the organism due to the variability of worldview and environmental conditions. According to the theory of conditioned reflexes I.P. Pavlov, its acquisition is possible when a living organism is exposed to a physiologically unlimited stimulus. It is as a result of this that a system of reflex activity develops, which is more complex. This concept should not be confused with instinct.

The reflex arc includes three components:

Afferent.
Insert (intermediate).
Efferent.

Impulses are transmitted to the links, they are able to perceive irritations and form a response to them. For a conditioned reflex to begin to develop, certain conditions are necessary:

The presence of a signal that will precede the unconditional.
Stimulus. It must be inferior in strength to the influence of what is biologically significant.
There should be no distractions.
The cerebral cortex should function normally.

It is worth remembering that they cannot be formed instantly. This variety is formed under prolonged exposure to these conditions. The reaction during formation can be renewed or fade away until the reflex activity becomes stable. An example of conditioned reflexes is the following: dogs salivate when they smell meat and other tasty foods.

Higher nervous activity

Higher nervous activity (HNA), carried out by the cerebral cortex, ensures the most perfect adaptation of humans and animals to constantly changing environmental conditions and underlies higher mental functions of humans, such as thinking, memory, consciousness and learning.

“Father of Russian physiology” - I.M. Sechenov wrote the book “Reflexes of the Brain,” where he put forward a theory about the reflex principle that underlies the activity of the internal nervous system. These ideas were continued and developed by I.P. Pavlov, who experimentally proved that conditioned reflexes underlie GNI.

While studying the digestive system, you learned about the experience of I.P. Pavlov, with the help of which he studied the mechanism of salivation. After conducting experiments, Pavlov discovered that some of the reflexes are innate - permanent, and the other - acquired.

With numerous coincidences of the conditioned (signal) and the unconditioned stimulus reinforced by it, a conditioned reflex is formed. That is, a conditioned reflex always arises on the basis of an unconditioned reflex with repeated coincidence of the above stimuli.

Now let’s look in more detail at the differences between conditioned reflexes and unconditioned ones:

Acquired - congenital

Conditioned reflexes are acquired: they are absent in a newborn and can arise and fade throughout life. Unconditioned reflexes are innate, genetically determined and inherited.

Individual - group

Conditioned reflexes are individual, determined by previous experience: a child who sees a lemon for the first time in his life does not salivate, but after eating it, even the thought of a lemon can cause profuse salivation. Unconditioned reflexes are characteristic of all individuals of the species without exception.

Nonspecific - specific

Conditioned reflexes arise in response to a nonspecific stimulus, for example, light, if the dog has a conditioned reflex to light. Unconditioned reflexes arise in response to a specific stimulus: sound is perceived by the receptors of the inner ear, light - by the rods and cones of the retina.

Changeable - constant

Conditioned reflexes are acquired as an adaptation to specific environmental conditions; when the environment changes, they also change and can be lost and reappear. Unconditioned reflexes are constant, given from birth and do not fade throughout life.

With bark - without bark

Conditioned reflexes always arise and are carried out with the participation of the cerebral cortex; unconditioned reflexes can do without its participation. The main thing is to remember and realize that any conditioned reflex is carried out on the basis of an unconditioned reflex.

The mechanism of conditioned reflex formation

The study of conditioned reflexes is closely connected with Pavlov and his students. Now we will conduct an experiment on a dog.

Let's assume that we need to develop a salivation reflex in an animal in response to turning on the light. We will use food as an unconditional stimulus, and turning on a light bulb as a conditioned stimulus.

A few seconds before we give food to the dog, we need to turn on the light bulb. If we repeat this manipulation several times, the dog will develop a conditioned reflex to turn on the light bulb, and in the future, salivation will begin at the moment the light turns on.

This effect is due to the fact that in the dog’s brain a temporary connection arises between the visual center (in the occipital lobe of the CBP) and the food center. As our manipulation is repeated, this temporary connection becomes stronger - a closure occurs and a conditioned reflex is formed.

Inhibition of reflexes

Inhibition processes are obligatory concomitants of excitation processes in the nervous system. Sechenov was the first to discover and describe the process of inhibition, proving that irritation of the nerve centers of the diencephalon inhibits the reflex activity of the spinal cord.

Pavlov developed the teachings of Sechenov and also studied the processes of inhibition. He came to the conclusion that in the nervous system the processes of excitation and inhibition are interconnected and occur continuously. Moreover, thanks to inhibition, the conditioned reflex is of the most accurate and perfect adaptive nature in relation to the environment.

Pavlov described two types of cortical inhibition:

Unconditional (external)
Conditional (internal)

Unconditional (external) inhibition is associated with the emergence in the cerebral cortex of a new (external) focus of excitation caused by the action of some external stimulus (sharp sound, loud noise). The action of this stimulus causes a weakening or complete disappearance of the current conditioned reflex.

This is an innate inhibition; it does not require development, which is why Pavlov called it unconditional (external).

Conditioned (internal) inhibition occurs in the same area of the cortex where the center of the conditioned reflex is located. Conditioned inhibition develops gradually. Remember how we developed a conditioned reflex in a dog to turn on a light bulb. If we stop giving food and continue to turn on the light bulb, then gradually the dog’s salivation will fade away - this is conditioned inhibition.

In order for the conditioned reflex to be maintained, it is necessary to reinforce it as often as possible: in our case, light (the conditioned stimulus) is reinforced with food (the unconditioned stimulus). If you stop turning on the light bulb before giving the dog food, the conditioned reflex will gradually weaken and disappear. This process is called extinction - the disappearance of a conditioned reflex, but if desired, it can be created again.

Pavlov's doctrine of the first and second signal systems

Animals have only the first signaling system. Pavlov considered it as a set of nervous structures with the help of which the perception of the surrounding world occurs through the senses. The signals in the first signaling system are smell, color, sound - they cause unconditioned reflexes and serve as the basis for the formation of conditioned reflexes.

Pavlov also proved that animals do not have a second signaling system. His experiment consisted of placing a monkey on a raft in the middle of a lake. The monkey could use a pole to climb onto two other rafts. On one of them there was a bailer and a tank of water, on the other raft a fire started. The monkey put out the fire by performing complex actions: each time he climbed onto a raft with a water tank and scooped water from there, instead of scooping water from a lake, which was much closer. Consequently, animals are not capable of generalization and abstract thinking.

In the process of work and communication, a person developed a second signaling system, closely related to the emergence of speech. Here, the specific irritant is the words into which a person puts meaning, some concept.

Words have a generalizing meaning, which served as the basis for the possibility of generalization, abstraction and operating with concepts. Language puts the results of human activity into words, so you can imagine a monkey even if you don't see it. Thanks to oral and especially written speech, it becomes possible to transfer experience to future generations. For any book, including this textbook, it is also worth saying special thanks to the second signaling system.

Temperament types

Pavlov identified four types of temperament, depending on the strength, balance and mobility of nervous processes in the cerebral cortex. Choleric is an easily excitable type, sanguine is balanced. Phlegmatic - processes of excitation and inhibition of weak strength, persistent and diligent in work. And finally, a melancholic person - the processes of excitation and inhibition are unbalanced and weak - are very vulnerable and weak-willed, prone to deep experiences.

Emotions, thinking and memory

Emotions are a person’s subjective reactions to external and internal stimuli. Emotions can be positive and negative; they reflect subjective experiences about the objective surrounding reality.

Thinking is a set of mental processes aimed at understanding the surrounding reality and thanks to which a person understands the essence of phenomena and things - as a result of thinking, concepts are formed. A distinction is made between elementary thinking, which is inherent in all animals (the first signaling system), and abstract thinking, which is characteristic only of humans (the second signaling system).

Memory is the ability of the nervous system (brain), which consists in the possibility of consolidating, storing and further reproducing received information. Based on the storage time of information, memory is divided into short-term and long-term.

Any information we receive first goes into short-term memory, only with repeated reproduction does this information move into long-term memory. The following types of memory are distinguished: visual, auditory, motor, tactile, mixed.

Dream

Sleep is a state of depression of consciousness, during which all types of sensitivity are reduced. Normally, the duration of sleep in an adult is 7-8 hours; in newborns, the duration of sleep reaches 18-20 hours a day. During sleep, information received during the day is transferred to long-term memory. Without sleep for more than 1-2 weeks, death is possible.

There are two phases of sleep: slow and fast, which alternate several times in one night. The slow-wave sleep phase consists of physiological rest of all body systems: heart rate, blood pressure, and body temperature decrease. Hormones begin to be released more actively, the action of which is associated with tissue restoration.

The REM sleep phase is the phase in which we dream. In this interval, the eyeballs actively move, breathing may become more frequent, and the hands make movements. This phase occurs approximately every 60-80 minutes (after the slow-wave sleep phase). Thus, in one night we see many dreams, most of which we forget. By the way, various “smart” alarm clocks catch exactly the moment of the REM sleep phase, in which it is easiest to wake a person, and upon awakening, the dream is usually remembered.

A dream is a unique representation of received information in the form of visual images. Let me note an interesting fact: we have already seen all the people we see in our dreams in reality. It could have been the face of a random passerby we met several years ago: such information is hidden deep in the subconscious.

Many of us, including me, have experienced a state of altered consciousness - a lucid dream. This is surprising, but sometimes during sleep a person can realize that he is dreaming, his dream is unreal, and it can be changed as soon as he pleases. After such moments, you experience extreme euphoria, dreams with your own scenario are remembered for a long time.

Diseases

Somnambulism (obsolete - sleepwalking) is a painful condition in which people perform any actions while in a state of sleep. Most often, sleepwalking occurs during a period of incomplete awakening after a deep sleep phase. An attack of sleepwalking can last up to several hours; sleepwalking most often occurs in children.

This condition has been known since ancient times, but its causes still remain a mystery. There is also no information whether sudden awakening harms a sleepwalker in a state of sleepwalking or not. Most often, sleepwalkers perform stereotypical actions: getting up, cleaning, walking, after which they go to bed and the next morning they do not remember anything about what happened.

Sometimes the actions of sleepwalkers pose a danger to themselves and others. There are cases when sleepwalkers traveled hundreds (!) kilometers from their home, and after waking up they found themselves in another part of the country completely disoriented.

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Braking and its varieties

Braking has its own definition. The unconditional occurs under the influence of a fairly strong stimulus. Conditioned ones cease to act under the influence of a new stimulus.

Braking may be temporary. It occurs when the body is affected by several factors simultaneously. Conditioned inhibition should be developed. It can be divided into the following categories:

Delayed.
Conditional.
Differentiation.
Fading.

In the life of a living organism, inhibition is a necessary process. If it were not there, then quite a lot of reactions would arise, from which there was no benefit.

The difference between instincts and unconditioned reflexes

Instinct, like reflex, is a biologically significant form of animal behavior. Only the second is a simple short response to a stimulus, and instinct is a more complex activity that has a specific biological goal.

The unconditioned reflex is always triggered. But instinct is only in a state of biological readiness of the body to trigger this or that behavior. For example, mating behavior in birds is triggered only during a certain period of the year when chick survival may be maximum.

What is not typical for unconditioned reflexes?

In short, they cannot change during life. They do not differ between different animals of the same species. They cannot disappear or stop appearing in response to a stimulus.

Meaning in life

To survive and preserve one’s own species, reflexive unconditional activity is necessary. A good example of this is childbirth. The baby faces many unforeseen dangers in the new world. Conditioned reflexes will help you adapt to the environment. Thanks to them, the individual quickly adapts.

Animals can be located in a safer place and escape. And they do not allow a person to make a mistake when choosing food (spoiled, poisonous, etc.). When you see appetizing dishes, gastric juice is formed and produced in order to better digest food.

Creators of the science of reflexes

The term and the very concept of a biological reflex were introduced into science by the French philosopher, physicist and mathematician Rene Descartes (1596-1650). He described the external manifestations quite accurately, but his understanding of the physiology of these processes was far from the truth. Therefore, he is usually not included in the list of scientists who created the doctrine of reflexes.

The creator of this theory is considered to be the Russian scientist Ivan Sechenov (1829-1905). His ideas were developed and supported by real experiments by Vladimir Bekhterev (1857-1927) and Ivan Pavlov (1849-1936). Despite the fact that Bekhterev is mentioned less often in this context than Pavlov, his contribution is also enormous. It was he who created reflexology (a branch of psychology in which all higher nervous activity is considered as a set of reflexes).

Pavlov is known for his practical experiments, as well as for dividing conditioned and unconditioned reflexes. He conducted a huge number of experiments on animals, studying their reactions to various stimuli. At the same time, the most famous was, of course, the experiment with a bell that caused the dog to secrete saliva and gastric juice. Having conducted experiments on different animals, Pavlov became convinced that conditioned reflexes are always formed if the stimulus for the animal is sufficiently unambiguous.

Reflex acts

Almost all reflex acts are aimed at ensuring the vital functions of the body, so they are always reliable in their manifestation and cannot be corrected.

These include:

Breath.
Swallowing.
Vomiting.

In order to stop a reflex act, you simply need to remove the stimulus that causes it. This can be practiced when training animals. If you want natural needs not to distract from training, then you need to walk the dog before this, this will eliminate the irritant that can provoke a reflex act.

Spinal motor automatisms

Many unconditioned reflexes belong to this group. Examples include the following:

Moro reflex. When a reaction is caused, for example, by hitting the table near the baby's head, the latter's arms are spread to the sides. Appears up to 4-5 months.
Automatic gait reflex. When supported and slightly tilted forward, the baby makes stepping movements. After 1.5 months it begins to fade.
Galant reflex. If you run your finger along the paravertebral line from the shoulder to the buttocks, the body bends towards the stimulus.

Unconditioned reflexes are assessed on a scale: satisfactory, increased, decreased, absent.