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

Boston: R. Badger, 1909



Motor Reactions and the Nature of Sleep 1

BEFORE we conclude the account of the experiments it may be of interest to make a brief statement of a statistical inquiry in regard to our mode of going to sleep. It is usually supposed that the course and mode of our activities are due to voluntary decisions, that they are irregular, changeable with mood and caprice as our whimsical will is. We are free agents and anything we decide to do we can do in any old way; we do it just as we please and it does not matter to us what the course and arrangement be, provided the will wills it so. As a matter of fact we are far more creatures of habit and instinct than of reason and will. This holds especially true of our fundamental reactions, such as the induction of sleep. If we ask the ordinary person on which side he goes to sleep or on which side he falls asleep most comfortably, the question puzzles him at first. At the first blush it seems to him he can go to sleep on either side; it does not matter. When the question is repeated to him and made clear and he begins to think about it, he soon finds out that he has a definite way of going to sleep. Should he try to go to sleep in a somewhat different manner, he would find it very difficult to fall asleep. We have definite ways of reactions which are due either to habit or to the structural arrangement and mode of function of our organism.

            Manaceine in studying motor reactions in sleep has found that right-handed people react in their sleep with the left hand, while left-handed react with their right hand. I have similarly experimented on human subjects and could not confirm Manaceine’s results. In my experiments on infants I found that in early infancy the reactions in sleep differ but little from that of waking state. The reactions are undifferentiated, but I found that later on in the course of the child’s development, the motor reactions mostly conform to Pflüger’s laws of reflex action.1 To quote from my notes:

            Boy two weeks old; sound asleep. I tickled his left nostril: bilateral reaction, both hands are thrown up a once. When the tickling is more intense or more persistent and prolonged, motor reactions in both legs are induced; The same holds true in the case of the tickling of the tickling of the right nostril, the reactions are bilateral and become more diffused bilaterally if the stimulus is more prolonged or more intense.

            The baby reacted in the same way in the in the same way in the waking state; so that there was no difference in the reactions of the two states.

            When the baby is fast asleep, I tickle the right temple, the response is a slight reaction with the left hand. This is really accidental. On other similar occasions the reaction is of the right hand and sometimes the reaction is of both hands and also of both legs, according to the intensity or to the cumulative effect of the stimulation.

            I invariably found that a slight stimulation given the first time produced a reaction, while a second and third stimulation of the same intensity often produces no result.

            Boy six weeks old. Tickling of the left ear excites at first movements in the head, in the trunk and then in both hands; when the stimulation is continued, the whole body becomes involved in the reaction, then the left hand is raised. The same holds true in the case of the right ear,—the movements are first in the head, then spread to the trunk, then to the lower extremities, then only to the side specially stimulated. In other words the reaction is at first diffused and then only becomes more special,—the hand is raised corresponding to the side stimulated. This mode of reaction holds true both in waking and sleeping states.

            Boy twelve weeks old. I observed an interesting phenomenon which may be described as that of associated movements. The infant has both hands in his mouth. When one hand is taken away from the mouth the other goes off simultaneously, as if an invisible power has pulled it away at the same time.

            Boy thirteen weeks old. When he was asleep, I tickled his left temple, he reacted with the left hand. Tickled his right temple, reacted with the left hand again. When the stimulus became more intense and prolonged, he moved his head, left hand and also the right hand.

            I tickled the left foot when the boy was asleep, both hands reacted, the left hand having the start; I tickled the right foot, both hands reacted, the left hand having the start again.

            Tickled the left temple; moved right hand; tickled right temple moved right hand again. The reaction is indeterminate,—sometimes it is bilateral and sometimes crossed. There actions do not conform to Pflüger’s laws. On the whole bilateral reactions predominate.

            When the child was asleep, I passed a pencil over the whole length of the left side of his face,—he reacted with the left hand first and then started with both. I passed the pencil over the right side of the face, he threw up both hands, the right having the lead.

            Now and then one can begin to observe the manifestation of Pflüger’s laws. When the child was asleep, I tickled his right foot; he drew away the foot. When the stimulation is slight, the right foot alone reacted; when the stimuli became summated he also reacted with the right hand. The same holds true, when the left foot is tickled,—on slight stimulations the left foot is drawn away; on continuous stimulation the left hand also reacts.

            Reactions of four months’ old babies and older conformed more and more to Pflüger’s laws.

            Experiments on older children give results of like character. Boy of seven years; when asleep, I tickled right side of his face, the right hand reacted; I tickled left side of face, the left hand reacted. When stimulations became summated or more intense the whole trunk reacted.

            In experimenting on adults in the waking state results are somewhat uncertain. When touching with moistened object the right side of the face, for instance, a telling the subject to wipe it immediately, sometimes right and sometimes the left hand reacts. One can often observe that when the subject reacts to sudden irritation Pflüger’s laws hold good; and sometimes one can observe reactions with the left hand alone, the right hand being used for more differentiated movements.

            Experiments on adults, when asleep, almost entirely conform to Pflüger’s laws of reflex reaction, especially is this the case, if the person has his hands free or sleeps his back. In cases of hypnoidal states and hypnosis, reactions are somewhat modified. If the subject happens to react with one hand, he keeps on reacting with it. Thus when the subject is touched with a wet or irritating object and is told to react, if it be the right side, he reacts with the right hand. If now the left side is similarly stimulated the right hand keeps on reacting crossing to the left side. This takes place, even if there is a long series of stimulations,—the subject reacts with the hand he first starts react with. This may be largely due to subconscious suggestion. I observed similar reactions in very suggestible subjects even in the waking state.

            Manaceine’s results are not confirmed by me, and still there is some truth in Manaceine’s statement. Now have suspected for some time that if the condition of limitation of voluntary movements is one of the import factors in the induction of sleep, we should expect that would not be a matter of indifference on which side we rest. We should expect that, if the right side is the more active, that the limitation of the voluntary movements would be more marked on that side. In carrying on my experiments on children and adults when in their sleeping states, I had occasion to observe that there was a definite course in the motor reactions, in the process of falling asleep. There is method in sleep. Some people go to sleep only on their back and find it difficult to fall asleep otherwise, while others who go to sleep on their side and who form the greater majority always go to sleep on the same side; there are very few who can fall asleep indifferently on either side. Moreover, my observations have shown me that by far the majority of right-handed people go to sleep on the right side, while left-handed people go to sleep on their left side. I further verified this interesting fact by statistical inquiry among my, patients as well as among Harvard students. Some of the right-handed people who-go to sleep on the right side may after some time turn to their left to change position, while others keep on sleeping on the same side through the whole night. The majority change position, the right-handed to the left and the left-handed to the right. More than seventy-five percent of right-handed people have given records to the effect that they sleep on the right side or rather fall asleep on that side. Of the left-handed persons, I find only one out of ten who falls asleep on the right side. One case is specially interesting to quote: “Up to my seventh year I slept on my right side and I was right-handed. At about the age of seven I met with an accident, I was run over by a team and my right side was injured so that I could not use the limbs of the right side. I used my left hand only, I began to sleep on my left side. This I did up to my fifteenth year. I then began to practice with my right hand too and am now ambidextrous. I sleep now on either side. I use both hands.”

            Some claim that the reason why they sleep on the right side is because of the dreams produced by the pressure of the heart when sleeping on the left; but it is interesting to observe that others sleeping on their left write in their accounts that they cannot sleep an their right side, because of the bad dreams, restlessness and nightmares produced. Some claim that it is simply a matter of habit, but the very fact that habit should give such a large percentage of right-handed, sleeping on the right side, and of left-handed, sleeping on their left side, points to a fundamental condition of our functioning activities and mode of rest. This condition we have found in the variability of our consciousness, by the ceaseless variations of the incoming sensory impressions from sense organs, muscles, joints and various other organic activities. The kinaesthetic sensations coming from the motor activities of our muscles and joints are very important in this respect. To bring about a state of rest and sleep, we must have the condition of monotony and limitation of voluntary movements, hence we can well see the reason why right-handed people whose right side is more active limit that side, while left-handed people prefer to limit the left side most active in them. We can also partly account for Manaceine’s results, namely that in sleep, right-handed people react with their left hand which remains free as they sleep on the right side, while left-handed people react in sleep with their right hand, because they sleep on their left side. Manaceian's explanation is pointless in referring these reactions to the activities of the right and left hemispheres. According to Manaceine the left hemisphere of right-handed people is fatigued and hence in sleep the right hemisphere and the left hand have the ascendency. This explanation is fanciful and does not agree with facts. For when the experiments are carried out rigorously, the reactions are found to conform, with the exception of very young infants, to Pflüger’s laws.

            Thus the experiments and observations made on lower animals, infants, children and adults all point in one direction, they point to the fundamental conditions of sleep, to monotony and limitation of voluntary movements. Taking as my motto the dictum “hypotheses non fingo” I strictly followed the logic of facts. Sleep is not so much due to merely cutting off sensory impressions, be they intense or faint, as to the monotony of sensory impressions which in fact may even be intense and numerous. It is the invariability of sensory impressions that reduces the organism to the passive state which we experience as sleep.



1. The following are Pflüger’s laws of reflex action.
                 (I) Law of unilateral reflexes.
                 If peripheral stimulations cause contraction in only half of the body, the contraction always occurs on the same side as the stimulus, and in general those muscles contract whose nerves arise from that segment of the cord, to which the irritated sensory nerve belongs.
                 (II) Law of reflex symmetry.
                If the effects of stimulating a sensory nerve upon one side extend to the other side, only such motor fibres are called into activity which correspond with those which are already excited on the stimulated side.
                (III) Law of unequal contraction on the two sides.
                If the contraction is unequal on the two sides, the stronger reflex is always on the side of stimulation.
                (IV) Law of reflex irradiation.
                (1) When stimulation of a cerebral nerve causes reflex contraction, the motor nerve concerned is invariably either in the same level as the sensory nerve, or it is further downward toward the medulla oblongata. (2) When stimulation of a spinal nerve causes reflex contraction beyond its own segment, irradiation always takes place toward the medulla oblongata.
                (V) The law of three locations of reflex contractions.
                Upon stimulation of a sensory nerve, reflexes can occur in only three parts of the body. These are:
                (a) at the level of the stimulated nerve.
                (b) in parts innervated from the medulla oblongata.
                (c) in the whole body.


1. The Table of Contents lists the title of this chapter as "Motor Reactions of Infants, Children and Adults and Subwaking and Sleeping States."

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