Sleep

SLEEP is an active physiological function of the organism, inherited phylogenetically and developing ontogenetically; during sleep, processes of assimilation, construction, and restoration occur. Processes occurring during sleep exhibit their own rhythm and course. A number of special studies have established the following changes regarding the activity of individual organs and the processes taking place. Gas exchange and general metabolism are reduced and correspond to metabolism during muscular rest; only according to data from Benedict is a more significant deviation noted—a lowering of the basal metabolic rate by 13%. When examining alveolar air, some acidosis is revealed, which gives a decrease in the alkalinity of the blood. During sleep, according to the studies of a number of authors, fluid flows from the tissues into the blood, poor in protein and rich in sodium chloride and phosphates. The influx of anions and cations occurs in equivalent quantities. The deficit of anions in the blood serum is somewhat reduced by a corresponding decrease in the amount of proteins. The amount of HCO₃, K, and Ca remains at the same level as during wakefulness. Heart activity and blood circulation change. The main thing is the slowing and weakening of cardiac activity and a drop in blood pressure. The number of heartbeats decreases by 1/5, according to Benedict—by 1/7; the pulse slows down, according to Wichmann, by 19.9 per minute, which is caused by the lengthening of the diastolic phase. Blood pressure drops in accordance with the depth of sleep, according to C. Landis, from 110-74 to 94-68. The distribution of blood is uneven; a more significant blood supply to the abdominal cavity has been established. Whether anemia or hyperemia of the brain occurs has not been established. According to data from Ebbecke, capillaries dilate, due to which the blood supply in the brain increases, whereas the total amount of blood flowing through the brain decreases. A lowering of vascular tone was established by plethysmographic experiments by Mosso and Weber, which is expressed by hyperemia of the skin due to an increased influx of blood, which is related to the special sensitivity of even minor skin injuries when falling asleep. Respiration during sleep has a slowed, uniform character, due to which pulmonary ventilation is lowered by 1/5. The appearance at times of Cheyne-Stokes type respiration draws attention, which is a consequence of the lowered excitability of the respiratory center; in accordance with this are data indicating an increase in carbon dioxide tension in alveolar air. According to some data, the abdominal type of respiration is replaced by the thoracic type. In the activity of glands, a change is noted. There are observations that during sleep, hyperaciditas is revealed; processes of chemical action on food substances continue during sleep. The excretory capacity of the kidneys decreases by half, the concentration of urine increases, but its toxicity decreases. Some glands lower their secretion, in connection with which dryness of the mucous membranes of the eyes and oral cavity occurs, which explains the cessation of even severe runny noses during sleep. In contrast to these glands, the activity of sweat glands increases, which is especially sharply expressed in infants and tubercular patients. The most significant changes occur in the neuropsychic sphere. The main sign of sleep is a decrease in the excitability of the central nervous system. Consciousness changes up to its complete loss (see Dreaming), muscle tone decreases, which, according to data from Rozhansky, regarding the cervical musculature, is the first sign of sleep for dogs, and also, apparently, for humans in a number of cases. However, hypotonia does not spread evenly; the decrease in tone is most of all discovered in the muscles supporting the vertical position of the body, and is less expressed in the muscles of the limbs. Other muscles, on the contrary, are in a state of increased tone; these include: the circular muscle of the eye, as well as the muscles of the pupillary and vesico-rectal sphincters, and the masticatory musculature. The so-called sleep position of the eyeballs draws attention—their rotation upward and outward, which is not observed during other physiological processes. The aforementioned refers to normal sleep; in some cases, there occurs not only active contraction of individual muscle groups but also the possibility of performing complex coordinated movements, such as, for example, the sleep of cavalrymen during a march, skiers during a run, etc., sleep in a standing posture in horses, on one leg in some breeds of birds. In connection with the change in tone is the state of reflexes: both a decrease and an absence of tendon reflexes were noted. In some cases, the Babinski reflex was observed in sleepers. During sleep, according to Piéron, 'sleep reflexes' arise, expressed in the movement of the body and random movements. This also includes inarticulate sounds, sometimes talking. The cessation of various kinds of hyperkinesis during sleep draws attention, which is apparently in connection with the weakening of incoming stimuli and the decrease in the excitability of the central nervous system. But in some cases, the appearance of hyperkinesis occurs (jactatio nocturna, etc.). In the vegetative sphere, a number of changes occur, as was indicated above. The change in tone occurs suddenly, reflex-like. The cited data regarding the nervous system show that its individual parts are involved in the process of sleep non-simultaneously and not with equal intensity. The depth of sleep, determined by the application of various stimuli, as well as (which is a particularly precise method) by the examination of alveolar air, is different at different hours. In general, in the sleep curve, an increase in depth is noted in the first hour and a half with a subsequent slow fall. The character of the depth of sleep is subject to significant individual fluctuations, and various states of the organism exert their influence on it. The same applies to the duration of sleep: in the first year of life, a child sleeps up to 18 hours, then the duration of sleep decreases with age, and in adults, it equals 6-8 hours, and in the very elderly, it falls to 3-4 hours per day. To explain the origin of sleep, a number of theories were proposed, many of which have lost their significance due to their speculative nature. At the present time, proceeding from the generally accepted position that sleep is an active physiological function of the organism, the goal of which is assimilation, restoration, and creation of tissues, one should admit the existence of a special apparatus that includes and regulates sleep mechanisms. Thus, the concept of a sleep center arises. Pathological-anatomical studies in epidemic encephalitis, where sleep disturbance is a cardinal symptom, reveal a change allowing, according to Economo, the localization of the sleep center in the posterior wall of the III ventricle and the adjacent gray matter of the interpeduncular region of the Sylvian aqueduct, which coincides with the hypnogenic zone established by Mauthner in 1890. The indicated data were confirmed by a number of studies. Less substantiated are the assumptions about localization in other parts of the brain. Tremner localizes the sleep center in the thalamus, proceeding from the central position of this organ, which possesses the ability to quickly, reflex-like, cause general inhibition in the underlying sections and in the cerebral cortex, due to the presence of extensive anatomical connections. Pötzl localized the sleep center in the nucleus of Darkschewitsch, Grinstein—in the tuber cinereum. Experimental studies to a significant degree also confirm the existence of Economo's hypnogenic zone. Upon poisoning dogs with Veronal (Oppenheim) and Medinal (Hoff and Kauders), changes were discovered around the Sylvian aqueduct. Especially indicative are the experiments of Demole, who induced sleep by introducing CaCl₂ into the infundibular region. According to Economo, there are 2 centers in the hypnogenic zone: in the anterior section, the wakefulness center, and in the posterior—the sleep center, with the action of the center regulating sleep consisting of the inhibition of the wakefulness center. Economo's point of view about two centers did not meet with support, since the presence of two antagonistically acting centers must presuppose, as Nickmanson points out, the existence of a 3rd center uniting their activity. The most correct is the assumption that in Economo's hypnogenic zone there is a center causing both sleep and wakefulness; its periodically occurring inhibition causes sleep (Sklyar). Sharply differing from Economo's theory is the theory of Academician Pavlov. According to Pavlov, sleep—internal inhibition—is one and the same process in its physico-chemical basis. The main condition leading to the appearance and development of both this inhibition and sleep is a more or less prolonged and repeatedly repeated isolated conditioned stimulus, i.e., stimulation of a cortical cell. Internal inhibition is observed in the form of extinction, differentiation, conditioned delayed, and trace inhibition, with the difference that internal inhibition is a narrowly localized, confined within certain limits due to the process of excitation counteracting it—sleep of a separate group of cells, and ordinary sleep is internal inhibition that has spread over the entire cortex and descended to the midbrain.

Inhibition, like excitation, is a fundamental function of the cerebral cortex, each of which possesses the property of irradiation, concentration, and induction. The basis for the development of inhibition, and following it the onset of sleep, is provided by the exhaustion of the cortical cell, which ceases further work and thereby protects it from dangerous destruction; during the period of inhibitory sleep, the cell restores its normal composition. With monotonous stimuli, drowsiness occurs more quickly, but at the same time, activity rich in diverse impressions also leads to sleep, since many points are created in the cerebral cortex that are in a state close to inhibitory. According to Pavlov, sleep is a moving process; in some cases, it may be limited only to the cerebral cortex, without spreading to the underlying apparatuses that control statotonus, which was observed during experiments in some dogs that were in a state of sleep but at the same time retained their body position. A whole range of phenomena of both normal and pathological sleep can be interpreted using Pavlov's theory. This includes the drowsiness of a person who has just slept, occurring under the influence of monotonous stimuli, then the possibility of a mother sleeping in deep sleep waking up at the slightest sign of the child's distress, which testifies to the existence of sentry points during sleep, i.e., the presence of less inhibited areas of the cortex. This includes purely cortical sleep, when body position is maintained—sleep while walking, attacks of sleep during narcolepsy, etc. Among the theories that arose on the basis of Pavlov's theories is the theory of Rozhansky, who believes that sleep is a function of the predominant importance of the eye in the life of an animal and the peculiarities of its structure. This function was formed as an adaptation of the animal to the conditions of life and, having strengthened, acquired the authority of an instinct, which can be observed in animals possessing different specialization of eyes for daylight and night light. An owl sleeps during the day because its eye does not see during the day; dogs and cats, whose eyes possess amphoteric properties, sleep at any time. Krasnogorsky put forward a theory according to which the process of inhibition, which causes sleep, originates from peripheral analyzers, since the cerebral cortex works only with an insignificant part of itself; the "concentration field" constantly moves, allowing a significant part of the cortex to be in a state of rest, while the peripheral analyzers are in a state of constant irritation, accompanied by inhibition, after which the cortex secondarily falls into an inhibitory state due to the absence of irritation. The following objections were made against Pavlov's theory: firstly, the presence of sleep in animals deprived of the cerebral cortex; secondly, the lack of clarity regarding the essence of the inhibitory process, which, according to Pavlov, is some kind of physico-chemical process, which coincides, as Sklyar believes, with the views of authors who view sleep as a result of intoxication. Likewise, Pavlov's theory does not explain sleep disorders in epidemic encephalitis. Brailovsky combines the theories of Economo and Pavlov, believing that the irradiation of inhibition that has occurred throughout the cortex will entail sleep when the inhibition reaches the hypnogenic centers of Economo, and, on the other hand, the dysfunction of this zone will cause sleep. In a number of other theories, the concepts of cause are confused with the conditions and symptoms of sleep. This includes chemical theories explaining the onset of sleep by autointoxication of the organism due to fatigue. Preyer, by analogy with experiments on muscle fatigue, believed that the gradual accumulation of lactic acid entails sleep. Dubois attributed a similar role to carbonic acid, based on the appearance of acidosis during sleep, which, according to available studies, is a consequence of the reduced excitability of the respiratory center. Weygandt speaks of kenotoxins that are complex in their chemical structure. Legendre and Pieron isolated hypnotoxin, which they obtained in the blood, cerebrospinal fluid, or brain of dogs subjected to prolonged artificial insomnia. Hypnotoxin, when introduced into dogs that had recently woken up, had a hypnotic effect on them. Zondek suggested the importance of bromine metabolism, based on its uneven distribution in parts of the brain and the change in its content during periods of physiological changes in sleep. A number of authors attributed the importance of a causal moment to the disruption in the activity of the endocrine glands. Salmon sees the cause of sleep in the special action of the increte of the posterior lobe of the pituitary gland on the central vegetative apparatus. Mingazzini explained sleep by the action of hormones that increase the tone of the parasympathetic system, and wakefulness by the action of hormones that tone the sympathetic nervous system. The blockade of external stimuli as a cause of sleep was especially supported by Strümpell, according to whom the exclusion of prolonged stimuli leads to sleep, proof of which is Strümpell's patient, who had contact with the outside world only through the ear and eye. When closing the eye and plugging the ear, the patient immediately plunged into sleep. However, according to Kreidl's data, the character of sleep in deaf and blind people does not differ from the sleep curves of normal people. Thus, the theories of fatigue, blockade of sensory organs, and autointoxication are not explanatory theories, and the moments cited in them are conditions under which sleep arises. A number of objections were raised against the theory of fatigue; it was pointed out that people who are not very busy sleep a lot, that severe overwork and affects often entail insomnia, and that long sleep causes lethargy instead of the expected vigor; the same arguments are put forward against the chemical theory of sleep, because if sleep were autointoxication, the development of the sleep state would occur slowly and, once it had occurred, could not be interrupted under the influence of emotional experiences. The large number of existing theories of sleep testifies to the fact that the question of sleep is not fully resolved at the present time. The available facts allow...

SLEEPING

...us to establish that Economo's theory should be considered the most correct, with the reservation that the division of the hypnogenic zone into two centers—sleep and wakefulness—proposed by the author is unacceptable, since the assumption of one wakefulness center, in which inhibition periodically occurs, sufficiently explains the phasic nature of sleep. Pavlov's theory explains a whole range of phenomena concerning cortical sleep; other theories, such as the theory of fatigue, the chemical theory, and the theory of the blockade of peripheral stimuli, explain only individual moments that contribute to and accompany normal sleep. Sleep disorders are extremely diverse; they can be expressed both in insomnia and increased drowsiness, but in addition, disturbances are observed in individual elements of the sleep mechanism, which causes the complex symptomatology of sleep disorders. Of the proposed classifications, the most complete is the classification of sleep disorders proposed by Epstein: 1) accidental sleep disorders, 2) secondary sleep disorders, 3) constitutionally neuropathic, 4) reactive, 5) symptomatic, 6) essential, 7) sleep disorders in connection with psychoses. Accidental disorders include those caused by various kinds of accidental stimuli. Secondary disorders are observed in diseases of the cardiovascular system, in gastrointestinal, renal, and other diseases of internal organs and are expressed both in drowsiness and in insomnia, in the disturbance of waking and falling asleep, in the presence of distressing dreams, etc. This also includes sleep disorders during autointoxications, metabolic diseases, and during intoxications and infections. In the latter, insomnia is most often present at first, giving way to increased drowsiness towards the end of the disease and during the recovery period. Sleep disorders arising on a neuropathic basis have a sharply pronounced pathological character, expressed in the splitting of complex elements of sleep, which causes the most diverse pathological combinations. Of these, the disorder of waking is particularly sharply expressed, expressed in the fact that the patient, having woken up, is unable to move, i.e., in the presence of mental awakening, somatic sleep continues; such a state is accompanied by distressing sensations of anxiety and fear. Likewise, a lack of sequence and simultaneity is also observed when falling asleep. Symptomatic sleep disorders include its disturbances in various organic lesions of the central nervous system (epidemic encephalitis, basal meningitis, tumors, etc.), in which the hypnogenic zone suffers. Sleep disturbances in psychoses are extremely diverse (see Psychoses). Essential disorders include narcolepsy (see), characterized by short-term attacks of drowsiness and cataplexy seizures, and pathological hypersomnia, described by Kleine (see Drowsiness). The therapy of sleep disorders is determined by causal moments and an analysis of the existing disorder.

Pavlov I., Twenty Years of Experience, Leningrad, 1932; Sklyar N., On the Origin of Sleep, Journal of Neuropathology and Psychiatry named after Korsakov, 1928, No. 5-6; Epstein A., Sleep and Its Disorders, Moscow-Leningrad, 1928; Economo C., Die Pathologie des Schlafes (Handbuch der normalen und pathologischen Physiologie, edited by A. Bethe, G. Bergmann and others, Vol. XVII, Berlin, 1926; Russian edition - Leningrad, 1927); Ebbecke U., Physiologie des Schlafes (ibid.); Lhermitte J., Le sommeil, Paris, 1931; Winterstein H., Schlaf und Traum, Berlin-Vienna, 1932. See also the bibliography for the article Dreams.