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Boris Sidis, Ph.D., M.D.

Boston: R. Badger, 1909



Theories of Sleep

FROM the very earliest times man wondered about sleep and attempted some explanation of it. It was supposed that in sleep the soul wanders away from the body and leaves it in a lifeless condition. Many of the savage tribes are on that account afraid to waken people lest the soul may be frightened away and not return at all to the body. That is why even at present we often hear the saying that sleep is the companion of death. On the other hand death is often described as sleep. On the same basis dreams were explained by the primitive mind,—the soul in sleep leaves the body and wanders away; on its wanderings the soul meets with all kinds of adventures and it is such experience that gives rise to dreams. In sleep the wandering soul, not encumbered by the gross body, can visit great distances in a short time and can even communicate with heavenly powers,—with angels and gods.

                        The impassive soul reluctant flies,
                        Like a vain dream, to these infernal skies.

            Modern spiritualists adopt this ancient belief in full or express it as “the release of human personality from the subliminal.”

            The scientific theories of sleep are numerous, but they can be reduced to a few main types. This reduction will help the reader to become oriented in the vast literature that has gathered about the subject. The theories of sleep may be classified as follows:

            1) The Physiological theories, which may be subdivided into:

                        a)  Mechanical


                        b)  Chemical

            2) Pathological

            3) Histological

            4) Psychological

            5) Biological

            The mechanical theories are of the circulatory variety and are usually much favored by physicians,—they attempt to explain sleep by changes in the blood circulation of the cerebrum. As far back as the eighteenth century the theory of sleep greatly in vogue among the physiologists was—congestion of the brain favored by the position of the head. This view was entertained by Haller, J. Müller, Hartley and others. Cappie has somewhat enlarged on it, inasmuch as he ascribes sleep to the venous congestion of the brain. This congestion of blood was supposed to bring about pressure on the brain with the result of depression of all the cerebral functions. The great psychologist Hartley summarises the physiological theories of his time thus: “It appears then that during sleep the blood is accumulated in the veins and particularly in the venal sinuses which surround the brain and spinal marrow. . . . And it is agreeable to this that in most dissections after lethargies, apoplexies, etc., the venal sinuses of the brain and consequently those of the spinal marrow which communicate freely with them are particularly full. . . . It follows therefore that the brain and spinal marrow will be particularly compressed during sleep, since the blood then takes up more space, is particularly accumulated within the cavities of the skull and vertebrae, and the hardness of these bones will not suffer them to yield or make more room. . . . In short this compression will result in sleep.” These generalizations were favored by observations on the famous case of the Parisian beggar whose injured skull gave the opportunity to observe the rise and fall of the exposed cerebrum in the waking or sleeping state. Recently Mosso claimed the same causation of sleep and on similar observations. As to the circulatory changes proper, two opposing views have been taken. Some, such as Durham, Cl. Bernard, Kussmaul Howell, Lehman, de Fleury ascribe sleep to cerebral anemia. Others again, such as Brown, Czerny, Broadman maintain that sleep is due to cerebral hyperemia. Claperede in reviewing the circulatory theories of sleep quotes Richet’s apt criticism: “Sleep and waking states bring about all kinds of changes in cerebral circulation depending but little on the position of the head. Birds whose hemispheres have been removed still present the same changes of sleep and waking. Biologically regarded, sleep is a far more general phenomenon than that of the presence of a brain irrigated by a blood circulation. Finally the activity of a tissue is not entirely dependent on the amount of blood circulating in it.” There are however still more cogent objections to such theories of sleep, objections which clearly show the incongruence of the circulatory theories. We shall point them out further in our present study.

            We may turn now to the chemical theories which are far more favored by the conservative physiologist, inasmuch as they fall in with what the physiologist regards as more scientific. With the experiments of Pettenkofer and Voit on the respiratory quotient new life was injected into sleep theories. Those two investigators have found the respiratory quotient CO2/O is diminished during sleep. The tissues absorb relatively more oxygen during the day than during the night. This fact of the using up and impoverishment of blood of intermolecular oxygen started new life in the theories of sleep. Pflüger, Sommer and others attempted to work out a scientific theory of sleep based on research of the biochemistry of the cell and the intermolecular activity of the oxygen molecule or atom. Pflüger’s authority lent vitality to this view so that even Heubel whose theory of sleep is really psychological in character tries to shelter it under Pflüger’s physiological wings.*

            With the chemical theories we pass by degrees into the pathological theories of sleep. Already in the early part of the nineteenth century Marshall Hall proposed the view that sleep was a kind of epilepsy. This view however met with little favor, because of lack of facts to support it. With the advance of chemistry and of its application to physiological research, and especially with the rise of the modern views of the role of autointoxication and toxins in diseases, the pathological theories of sleep were resuscitated under the new guise of autointoxication. Obersteiner and Preyer launched the theory that sleep was an autointoxication of the system by toxic matters accumulating in the blood, due to the activity of the various tissues. Lactic acid was supposed to be the particular substance in question. Others such as Dubois ascribed the same state to the accumulation of carbonic acid. These were followed by a host of writers such as Binz, Errero, Bouchard, Breisacker and others. The toxic and autotoxic theories of sleep enjoy quite a wide popularity, because they fall in with the scientific notions of the age. Those theories would make of sleep a pathological state, but the facts are against such a view.

            By the middle of the nineteenth century, when physiological experiments on nerve-conduction were at their height, Purkinje proposed the theory that sleep might be due to the interruption of neural conductivity between the cortical matter and the rest of the cerebrum. This view was further developed by Mautner, Warlomont, Oppenheimer and others. As a further modification of the same theory, but based on more fundamental physiological processes may be mentioned Verworn’s theory which refers sleep and waking-states to processes of assimilation and dissimilation going on in the organism. At the same time with Verworn, Van Gieson and Sidis worked out their theory of sleep, basing it on similar processes, namely on anabolism and catabolism and developing the interrelation of waking and sleeping states with the symptom complexes of nervous and mental diseases. The theory of Van Gieson and Sidis is based on the variability of different levels of neuron energy. We may dismiss this latter theory in a few words as we shall discuss it in our study. We can only say here that the theory is essentially based on the concept of neuron energy.

            This brings us close to the famous theories of retractility of neuron-elements which have been of late utilized by many writers for various purposes. The development of the histology of the nervous system and especially of neuropathology have brought new life to the solution of the problem of sleep. The biological investigations of the cell by Kölliker, Remak, Nageli, Hoffmeister, Virchow, Max Schultze, Hertwig, Fol, Van Beneden, Strassburger, Heidenhein, Boveri and many others opened up new horizons for theories of cellular activities. Naturally the sleep theories came in for their share. It was not however until the researches of Golgi and Ramon Y Cajal had laid the foundation for their famous doctrine of independence and contiguity of neural elements that the theories of sleep could seize on some tangible anatomical facts and work them for their benefit. Ramon Y Cajal was the first to advance the view that the neuroglia-cells by their expansions and contractions bring about dissociations and associations of the neural elements with the consequent loss or reappearance of normal waking-states. A somewhat different, but closely analogous theory was launched into the scientific world by Mathias-Duval. Instead of the retractility of neuroglia cells proposed by Cajal, Duval advanced the view that the neurons and their protoplasmic processes are endowed with contractility or retractility and that the functioning and loss of functioning of neural elements are due to contractions and expansions of the protoplasmic processes of the neurons. Demoor, Pupin, Berger and others have enlarged on this hypothesis. At first even Verworn accepted this hypothesis, although he discountenanced it afterwards. Sidis assumed provisionally the same hypothesis for abnormal dissociative manifestations, but refused to accept it as an explanation for the phenomena of sleep which do not warrant the assumption of such hypotheses.

            The psychological theories of sleep date from antiquity. The popular explanation is very simple,—it is a description of the phenomena, a description which the popular mind often takes for an explanation of the phenomena in question. Sleep is an abeyance of mental life, sleep is a rest of consciousness. Modern physiologists and psychologists who maintain the psychological theory of sleep have not much improved on that statement. The only modern substitute is that of inhibition. Brown-Sequard, Wundt, Siemens, Forel, Oscar Vogt, all in different scientific phraseology refer sleep to inhibition of cerebral activity, especially of the frontal lobes where mental activity is supposed to “reside,” according to some authors. Manaceine in her work on sleep echoes this view and comes to the conclusion that “sleep is the resting state of consciousness.” Surely it is an elaboration of the obvious, if one has to write a whole volume in order to arrive at such an important conclusion.    The only one who really made some advance in the psychological theory of sleep was Heubel, Privatdocent at Kiev University, Russia. I can say his is an excellent piece of work based on a series of well performed experiments. Unfortunately, when I started my experiments, I was not acquainted with the work of that investigator. I have gone over in my experimental research a good deal of the same work and may say that Heubel’s experiments have been fully confirmed by me. Although Heubel’s theory is incomplete, there is a good deal of truth in it and his work well deserves the attention of the student of sleep. His view may be briefly summarized in the following statement: Mental activity depends on the incoming peripheral, sensory stimulations; where such peripheral sensory stimulations are absent, mental activity is in abeyance and sleep results. In other words, brain activity depends on sensory activity which in its turn depends on peripheral stimulations. Psychologically stated, consciousness is a function of sensations which in their turn are a function of external stimuli or impressions. In accordance with this view a series of experiments have been carefully carried out by Huebel. As my own experiments were carried out on somewhat similar lines I shall refer again to Huebel’s work, when I give an account of my experiments, in order to test a somewhat similar theory arrived at from totally different considerations, viewing the subject of sleep not only from a physiological and psychological, but also from a biological standpoint.

            An altogether different departure from the usual theories of sleep was recently taken by Claperède. He points out that biologically regarded, sleep has its significance not as a passive state, but as an active instinct, like all the other instincts of animal life. To put it in his own words: “Le sommeil n’est pas un état purement négatif, passif, il n’est pas la consequence d’un simple arrêt de fonctionnement: il est un fonction positive, un acte de ordre rèflexe, un instinct, qui a pour but cet arrêt de fonctionnement; ce n’est pas parce que nous sommes intoxiqués, ou épuises, que nous dormons, mais nous dormons pour ne pas l'être.” This biological view of Claperède forms one of the most valuable contributions to the theory of sleep. It throws altogether new light on the subject of sleep, and many obscure until now unexplained facts can be understood in the new light of the biological standpoint taken by Claperède. Claperède’s physiological theory of inhibition is not as clear, but with some modification I think it could well harmonize with my views and my work on sleep. While accepting the views of Claperède, my standpoint taken in this study is based on investigations published in previous works of mine mainly dealing with the subject of dissociative states in general.



* We may possibly refer to Loeb’s work on heliotropism and sleep of butterflies as an example of a purely bio-chemical view of sleep. See Dec. Public Univ., Chicago, V. I.


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