Phase changes in HNA during sleep onset
Studies conducted in the laboratory of I.P. Pavlov (specifically, the work of I.P. Razenkov) made it possible to study in detail the process of transition from wakefulness to sleep using the method of classical conditioned reflexes. It has been established that falling asleep is accompanied by the gradual development of inhibition in the cerebral cortex.
The main sign of this state is the disruption of the law of strength of stimuli. Normally, a strong signal causes a strong reaction, and a weak signal causes a weak one. However, three successive stages are distinguished during sleep onset:
- Equalizing phase: the nervous system produces conditioned reflex responses of absolutely identical magnitude to signals of completely different intensities.
- Paradoxical phase: an inversion of reactions occurs. Responses to weak conditioned stimuli become more pronounced than to strong ones.
- Narcotic phase: deep inhibition sets in, during which any responses to conditioned signals cease completely.
Features of HNA in children
The cerebral cortex of a newborn is functionally immature. Although conditioned reflexes can be formed from the first days of life, this requires significantly more time and repetitions (pairings) than in adults.
The school of I.P. Pavlov identified key typological features of nervous processes in childhood:
- Dominance of excitation: activation processes prevail over inhibition (especially at an early age).
- Weakness of inhibitory processes: internal inhibition is extremely unstable, which manifests as rapid exhaustion of attention and easy distractibility in the child.
- Irradiation of excitation: due to the poor concentration of nervous processes, the reaction to a stimulus is often generalized in nature (e.g., involvement of facial expressions and associated movements when performing a simple task).
Maturation of sensory systems and sleep rhythms
The development of analyzers in a child occurs heterochronously:
- Tactile, gustatory, and olfactory sensitivity are well-developed at birth. The smell of mother's milk plays a crucial role in bonding, while touch and taste are critical for the rooting and sucking reflexes.
- The auditory analyzer functions even intrauterinely (from the end of the 2nd trimester), causing unconditioned reactions to sound (startle, changes in breathing).
- The visual analyzer matures slowly: fixation of gaze appears by 2–3 weeks, binocular vision by 3–6 months, and adult visual acuity is reached only by 5–7 years.
Sleep patterns deserve special attention. An infant sleeps 16–20 hours a day in a polyphasic manner, in short cycles of 50–60 minutes. The circadian rhythm is initially absent and forms by 3–6 months due to the maturation of the suprachiasmatic nuclei of the hypothalamus and the alternation of light-dark cycles. Up to 50% of the time is occupied by rapid eye movement sleep (REM sleep), which is vital for the maturation of the central nervous system (in adults, this proportion is only 20–25%).
Contribution of the Russian physiological school
The doctrine of HNA rests on a powerful foundation laid by prominent Russian scientists:
- I.M. Sechenov — founder of the first Russian physiological school and pioneer of the doctrine of brain reflexes. His ideas provided a materialistic explanation for goal-directed behavior.
- I.P. Pavlov — creator of the science of higher nervous activity, who investigated conditioned reflexes.
- I.I. Mechnikov — founder of immunology and pathophysiology, discoverer of the phagocytic theory of immunity.
- V.V. Pashutin — founder of pathophysiology as an independent scientific discipline.
- P.K. Anokhin — founder of the theory of functional systems.
Impact on psychiatry
I.P. Pavlov's work on types of HNA had a profound impact on the formation of scientific psychiatry in the late 19th and early 20th centuries, bringing it closer to physiology. Concurrently, E. Kraepelin's nosological approach developed, identifying schizophrenia and manic-depressive psychosis as independent entities. In Russia, S.S. Korsakoff described alcoholic polyneuritic psychosis and introduced a system of non-restraint for patients, while S. Freud opened the era of psychological research by studying the role of the subconscious.
The abbreviation EPN will help remember the order of cortical inhibition phases during sleep onset: Equalizing, Paradoxical, Narcotic.
Class and exam questions
What is the essence of the paradoxical phase during sleep onset?
In this phase, the organism gives a stronger conditioned reflex response to weak stimuli than to strong ones, which violates the law of strength.
Why are young children easily distracted?
This is due to the weakness and instability of internal inhibition processes, as well as the predominance of excitation in the cerebral cortex.
What is the role of REM sleep in newborns?
In infants, the REM sleep phase (REM sleep) occupies up to half of all rest time. It is believed to be critically important for the full maturation of the central nervous system.
What else to study on this topic
- Mechanisms of conditioned reflex formation in newborns
- P.K. Anokhin's Theory of Functional Systems
- E. Kraepelin's nosological approach to the classification of mental disorders
- S.S. Korsakoff's reforms and the Moscow Psychiatric School
- I.I. Mechnikov's phagocytic theory of immunity
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