Theories And Phenomena Of Sleep
( Originally Published 1914 )
THE problem that confronts the victim of insomnia is to determine why he does not sleep soundly, adequately or refreshingly. To do this he should know the significance of sleep and something of its theories.
There has been a vast amount of study and experimentation by physicians and psychologists to discover the so-called cause of sleep. As to its virtue there can be no discussion. "To sleep," wrote Amiel, "is to strain and purify our emotions, to deposit the mud of life, to calm the fever of the soul, to return into the bosom of maternal nature, thence to reissue, healed and strong. Sleep is a sort of innocence and purification. Blessed be he who gave it to the poor sons of man as the sure and faithful companion of life, our daily healer and consoler."
The human being asleep, is in a state of total unconsciousness. All cognizance of personality and action and, for the most part, man's sense and ideas cease to exist. It is not possible to decide to what extent this abnegation of the conscious life, these intimations of oblivion, are merely a seeming and a forgetting. The chance recall of dreams warns us of the possible existence of mental phenomena during the sleeping state which, under ordinary circumstances of life, do not connect themselves with the conscious memory.
Theories of Sleep.—The nature and cause of sleep are still a mystery. Many theories as to the underlying causes of sleep, that is, of the physical and chemical changes that occur in the brain and other parts of the body during sleep, have been propounded.
The first theory. The most generally accepted one is that sleep is accompanied by a diminution in volume and velocity of the blood in the brain, and that this is the physical basis of sleep. This theory makes sleep akin to the unconsciousness which attends what is popularly called fainting. Those who attempt to explain sleep in this fashion claim that insomnia is the expression of the opposite state, namely an excess of blood in the brain, an exaggerated blood pressure and increased velocity.
The second theory. A more recent theory is that the physical basis of sleep is a certain physical alteration in particular prolongations of the cells or units of which the brain is largely constructed. Each nerve cell has a number of processes which jut out from its side like the feet of a centipede. These are called "dendrites." These processes come in contact with those of other cells and in this way form a continuous link. When they are thus continuous, the current (of whatever nature it is), that is necessary to consciousness flows through harmoniously. When the contact is broken the current ceases to flow and the result is sleep. Consciousness is unquestionably due to a certain state of the nerve cells and any departure from complete consciousness must be due to some change in this condition. It is probable that this state and its alterations are of a chemical nature.
The third theory. The chemical theory,, of sleep is one which has a wide acceptance amongst those who have studied the subject. It is based upon the hypothesis that during the waking hours there is developed, and to some measure accumulated within the system, by-products of the system's activities, and that these, soporific in their effect, produce a sensation of tranquillity, drowsiness and sleep. When sleep occurs, the tissues concerned in producing poisonous products cease their activity. The substances which were produced and which acted as soporific are thrown off during the night and when they are all eliminated the cells are ready to start in fresh. Then the cycle is repeated.
These theories testify to man's ingenuity. There is no doubt whatsoever that cellular activity, whether it be muscle cells, gland cells or brain cells, is accompanied by formation of products which, if retained in the system, are poisonous, but it is difficult to see the justification for contending that this is the cause of sleep.
The fourth theory. The interpretation of sleep as one of the essential phenomena of life has recently been elaborated into a theory which is called the biological theory. Claparede contends that sleep is a phenomenon of nature in the shape of a reaction of defence to protect the organisation against fatigue. Sleep is an instinct, and we sleep not because we are exhausted, but because we cannot help it. Like every instinct it is a manifestation of evolutionary development. It did not exist at all times and it is not in any way an essential phenomenon of life. If sleep has developed, it is probably due to the fact that those animals whose activity was broken by periods of repose or immobility have been favoured in the struggle for existence, for they have been enabled, owing to an accumulation of energy during these periods, to manifest, in consequence, a more intense activity. As to these periods of immobility, they are themselves derived from the function of cessation of defence which plays such a great role in the animal kingdom.
Unquestionably the position taken by Claparede will be acceptable to scientists. It harmonises with what the physiologist and psychologist know about sleep and its physical basis.
Sleep is a resting state of consciousness which is facilitated, and, if one likes to affirm it, caused, by cessation or interruption of all those stimuli that come from without, and which reach the human organisation principally, through the special senses.
Phenomena of Sleep.—The velocity of the circulation, and of the respiration is diminished during sleep. The pulse of sleeping individuals is slow and full as compared to that of the waking state. Breathing is more deliberate, sometimes laboured. Digestion and absorption may take their course with unabated vigour, but the blood supply of the brain and the organs under voluntary control is diminished. The temperature of the body is lowered during sleep. And all the secretions, except that of the skin, are lessened. The urine, saliva, the secretions from the mucous membranes are all less abundant in sleep than in waking. Perspiration, however, is frequently increased instead of diminished, not only as a result of relaxation of the vessels in sleep, but particularly from the custom, which is almost universal, of covering the body with layers of clothing that prevent radiation of bodily heat.
Most of the so-called reflexes are diminished or abolished. The fact that not all the reflexes are abolished is shown by the existence of respiration and heart pulsation. There are other reflexes which are neither diminished or arrested during sleep, for instance, those guarding the chief elemental portals of the body. No general statement can be made as to which are abolished, because a considerable difference obtains, in this respect, between the various species, and even between individuals of the same species.
That there are different degrees of sleep goes without saying. We constantly hear persons speak of deep, light sleep, and broken sleep. Besides there is every gradation between complete wakefulness and profound sleep. Sleep may vary in intensity or depth from a semi-conscious state in which complete ideas and sensations may subsequently be recalled either in whole or in part, to an absolute dreamless state. This temporary abeyance of consciousness, whether complete or partial, is without doubt associated with cessation of the acquired functions of the brain. It is perhaps safe to say that the progression from light to deep sleep marks a gradual diminution of the functions of the brain.
One cannot say that there is absolute cessation of the functions of the brain during sleep, although there seems to be. It has frequently been alleged that mathematical problems have been solved during sleep, that poetry and music have been composed, but in reality what has happened is that the whole body, having been rested during sleep (the whole body with which we think), takes up the problem with which it had previously been concerned and finishes it satisfactorily.
Increasing depth of sleep is marked by the same progressive diminution of many or of all the functions of the body. The closer the functions are associated with consciousness and especially with the will of the individual, the more completely are the functions suppressed. Depth of sleep is therefore not only proportioned to the abeyance of consciousness but also the depression of all bodily functions. The state of sleeplessness or insomnia may therefore be indicated as an approach to the normal waking, physical and mental condition. The main distressing feature of insomnia is the persistent continuance of mental activity in some form.
Whatever may be our explanation of sleep, it is certain that we cannot do without it. Patients oftentimes tell us that they have not slept a wink all night, but we may be sure that such a state of wakefulness cannot be maintained for more than a night or two.
Tales of extraordinary capacity for going without sleep excite a ready interest, and the public reads with avidity the records of great and famous personages regarding a matter in which all participate, and about which every-one has something peculiar to relate.
It is said that John Wesley found that five hours' sleep sufficed him, but he was often seen asleep whilst riding on his horse. It may have been with him as with many others ; little naps in the day are overlooked in the calculation of the sleep obtained at night. A momentary sleep often suffices to produce the rest that is needed.
It is generally believed that one-third of our existence should be spent in sleep, but this is no more true than that the preservation of health requires us to partake of food three times a day or to drink three pints of water in twenty-four hours.
Insomnia is a relative term. The amount of sleep that suffices for one individual would be in another productive of misery and a disorder of nutrition which might lead to disease. Sleep is measured by its depth as well as by its duration, and it is as difficult to express in minutes or in hours the requisite quantity, of sleep for the normal human being, as it is to state the proper degree of depth of sleep. Experience teaches that the deeper the sleep, in other words, the more profound the cessation of mental and bodily functions, the less protracted need that sleep be in order that the individual may receive physical and mental restoration and refreshment.
Sleep may indeed be indulged in to excess. Too much sleep produces lassitude and debases and stupefies the mind. Carried to extreme• it is as much an act of intemperance as excessive drinking and eating.
As to the time when sleep should be taken, night is of course preferable since it is the time when the sleeper is least likely to be disturbed by stimuli coming from without, such as light and noise. There is no evidence, however, to show that, were light and noise controllable, sleep obtained during the day would be less beneficial than sleep obtained at night.