Stress is a physiological neurohormonal reaction to external and internal influences aimed at eliminating the consequences of the action of “damaging” factors, leading to a violation of the integrative activity of the brain and other body systems, and as a result, to a decrease in certain functional capabilities of a person. It follows from this definition that stress has both positive and negative manifestations. The activity of anti-stress systems is aimed at solving the negative consequences of stress, it is carried out in the cycle of “sleep-wakefulness” and determines the stress resistance of the individual. The mechanisms of the implementation of the anti-stress system can be conditionally divided into neurophysiological, humoral and psychological, which have their own characteristics, both during wakefulness and sleep. An important role in the activity of anti-stress mechanisms is assigned to sleep, as a multifunctional, self-regulating and multi-stage process of preparing the brain for subsequent wakefulness, having certain external and internal manifestations, actively participating in adaptation in acute and chronic stress of various modalities. The adaptive (anti-stress) sleep system (ACC) is a set of cerebral mechanisms that provide a single process of alternating appearance, course and end of sleep stages, leading to the restoration of a person’s functional capabilities. Its capabilities allow during sleep to optimize the body’s adaptation to the environment and partly determine stress resistance in general. A feature of this system is that it actively works during the entire time of sleep, namely, even in the absence of a stressor. The main properties of ACC are based on biological (gender, age, constitution, etc.) factors and are determined by the participation of various neurophysiological, biochemical and psychological mechanisms in the implementation of the adaptive function of sleep. Dwelling on the neurophysiological aspects of stress reactivity, it is necessary to note the important role in the development of sleep of both systems that form separate stages of sleep and integrative processes that ensure the work of the entire ASC mutually coordinated in sleep time. Changes in the ACC activity are an obligatory component of stress, which is expressed in changes in the functioning of various neurophysiological systems and are characterized by both direction and severity.
The stress response begins while awake and continues throughout the night’s sleep, and in chronic stress during several sleep-wake cycles. It is important to note that the sleep response has both general and particular neurophysiological patterns. The strength and direction of stress during wakefulness is determined by a combination of both the stressor (its strength, modality and duration) and the individual characteristics of a person (biological and psychological factors). The non-specific manifestation of stress is characterized by an increase in the activity of the ascending activating systems and manifests itself in an increase in the representation of wakefulness during sleep and in a violation of stability in maintaining functional sleep states. A variety of specific sleep changes depend on the type of exposure and the initial stress tolerance of the individual. At the same time, different somogenic systems are involved in stress reactions in different ways. All the above changes in sleep can be detected not only at the intrastressor stage , but also at the post-stress stage (a few days after the end of stress), which may cause the development of insomnia (nighttime sleep disorders) in the future. I would like to pay special attention to the principle of correspondence between sleep and subsequent wakefulness, which has an independent meaning. This principle is based on different functions and mechanisms of sleep and wakefulness. Lack of realization of the target function of sleep can lead to a decrease in the functional capabilities of a person during wakefulness. During the waking period, on the contrary, a person is able to actively influence the existing functional states, changing the program of behavior in accordance with the inner feeling of his capabilities. Wakefulness, in which a person does not take into account the characteristics of previous sleep, can be absolutely maladaptive . Thus , if the functional meaning of “sleep” does not correspond to the possibilities of subsequent “wakefulness”, an adaptive dissonance (AD) of the “sleep-wakefulness” cycle occurs, which can cause maladaptive reactions during wakefulness. The close interaction of the anti-stress mechanisms of wakefulness and sleep determines the adaptive capabilities of the organism. Prevention at the stressful and post-stress stage should take into account not only the features of ASC, but also all manifestations of wakefulness as factors capable of supporting and even aggravating chronic stress.