Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

Nervous System (general structural and developmental plan of the nervous system)
Central Nervous System
Higher Nervous Activity — Conditioned Reflexes

Conditioned Reflexes are adaptive reactions acquired individually during an Organism's lifetime or through special training, which arise through The formation of a temporary connection between a conditioned stimulus (signal) and an unconditioned reflex act.

All stimuli from the external and internal environment can be divided into unconditioned, indifferent, and conditioned. Some stimuli are unconditioned, meaning they act as biologically significant signals. Their presence triggers an unconditioned reflex without eliciting the "what-is-it?" reflex. The response to them is genetically programmed, and the resulting reflex acts are innate.

Indifferent stimuli are any stimuli that do not cause any noticeable Changes in the body. When first presented, they trigger the orienting unconditioned "what-is-it?" reflex and temporarily inhibit other activities. With repeated exposure, habituation occurs, meaning the manifestation of the unconditioned orienting reflex becomes inhibited.

The third group of stimuli consists of conditioned signals (stimuli) that elicit corresponding conditioned reflexes. These signals are perceived and learned over the course of individual development.

The rules for establishing conditioned reflexes are as follows:

1) healthy animals in an awake state are used for the experiment;

2) a combination of two stimuli is used: a conditioned stimulus paired with an unconditioned one;

3) the application of the conditioned stimulus must slightly precede that of the unconditioned stimulus;

4) the conditioned stimulus must be physiologically weaker than the unconditioned one;

5) during the ESTABLISHMENT OF THE conditioned reflex, Other types of activity responding to other stimuli must be excluded.

The complete establishment of a conditioned reflex is achieved when the biological subject systematically responds to the application of the conditioned stimulus without reinforcement by the unconditioned stimulus.

General characteristics of conditioned reflexes: 1) conditioned reflexes make behavior plastic and responsive to specific environmental conditions; 2) all conditioned reflexes are formed only with the participation of the Cerebral Cortex; 3) the vast majority of conditioned reflexes are formed only through the repeated pairing of conditioned and unconditioned stimuli, and are acquired and extinguished during the individual life of each specific organism; 4) a conditioned reflex arises only after a preceding unconditioned reflex.

Stages of conditioned reflex formation. The formation of a conditioned reflex involves two main stages: the initial stage—the generalization of the conditioned reflex—and The final stage—the concentration of the conditioned reflex.

In humans, unlike animals, conditioned reflexes are developed faster and in response to a small number of repetitive events. The functioning of the conditioned reflex mechanism is based on two nervous processes: Excitation and Inhibition. Furthermore, as the conditioned reflex becomes established, The Role of the inhibitory process increases.

Significance of the conditioned reflex. The acquisition of the capacity for learning by living organisms during individual development—without passing this experience on through heredity—has enabled better and faster adaptation to the surrounding world. The conditioned reflex mechanism underlies the formation of any acquired skill and the learning process itself. A series of conditioned reflexes forms a dynamic stereotype, which serves as the basis for human habits and professional skills. Conditioned reflexes dramatically expand the range of signaling stimuli that are significant for the organism, ensuring an incomparably higher level of adaptive behavior.

Inhibition of conditioned reflexes. It is impossible to explain behavior by recognizing only the existence of the excitatory process. If only excitatory processes were present, the result would be Muscle spasms rather than purposeful, coordinated activity. The functioning of conditioned reflex mechanisms is based on both excitation and inhibition. As a conditioned reflex becomes consolidated, the role of the inhibitory process increases. The inhibition of conditioned reflex activity manifests as external (unconditioned) inhibition and internal (conditioned) inhibition. External (unconditioned) inhibition is innate, genetically programmed inhibition. There are two types of external (unconditioned) inhibition: supramaximal (protective) inhibition and induction inhibition.

Supramaximal inhibition of a conditioned reflex develops either when a stimulus is excessively strong or when the Central Nervous system is functioning weakly. Supramaximal inhibition has a protective function.

Induction (external) inhibition is observed when a novel stimulus is introduced after a conditioned reflex has been established, or alongside a familiar conditioned stimulus. The impact of the new stimulus triggers a strong innate orienting reflex—the "what-is-it?" response—aimed at assessing the Biological Significance of the novel stimulus.

Internal, or conditioned, inhibition of conditioned reflexes is acquired in nature and requires special training to develop. The biological significance of internal inhibition is that under changing environmental conditions, the reaction to existing (even familiar) signals changes. In this case, the conditioned reflex is suppressed or dampened. There are Three types of internal inhibition in conditioned reflexes: differential inhibition, extinction inhibition, and delayed inhibition.

As a result of differential inhibition, a person learns to distinguish between stimuli that are similar in parameters and responds only to biologically significant ones.

Extinction inhibition occurs when, for a previously established conditioned reflex, the presentation of the conditioned stimulus ceases to be reinforced by the unconditioned stimulus.

Delayed inhibition occurs if the established conditioned reflex is postponed in time relative to the reinforcing unconditioned stimulus.

In these cases, the time of appearance of the conditioned reflex response will also begin to shift and be delayed in time. All types of internal inhibition of conditioned reflexes are intricately intertwined and interrelated.

Dynamic stereotypes. The highest manifestation of the analytical and synthetic Functions of the cerebral cortex is The Development of a dynamic stereotype. A dynamic stereotype is a system of conditioned reflex acts in which each subsequent reflex is triggered by the completion of the preceding one. It forms the foundation of human habits and professional skills.