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\ Art. VI.?TBffi PHYSIOLOGY OF NIGHTMARE. BY

EDWIN VOOTON.

or incubus, the bane of so many lives, is the term used to denote the psychological state of the man when, having been overcome by sleep, visions of the horrible and loathsome rise before him?now pursuing their victim, now strangling him ; while he, the sufferer, feels himself helpless as a child, barely able to move a limb, without power?save to silently gasp the words his being is panting to utter, and which he knows would, if spoken, bring to his immediate aid the strong and friendly arm. It were needless to describe the diverse forms assumed by this malady?for such I must term it; enough, that throughout its various manifestations it presents to the mind of the sufferer one common trait?immediate danger. Of what, then, is this peculiar mental state the result ? Blood is supplied to the brain from two sources, the vertebral and internal carotid arteries; it is the storehouse from whence the cells of the encephalon draw the materials by which they are enabled to elaborate themselves for the subsequent discharge of their functions. To the majority of persons if the head be laid on a low pillow so as to result in an increase of the brain's blood supply, sleep will not supervene ; and on the other hand, it has been proved that if in the case of the restless the head be supported on a high pillow, sleep is the more readily obtained. From these facts we are led to conclude that the manifestation of energy on the part of the brain is in direct proportion to its blood supply. The left internal carotid artery of a rabbit was cut, the right being ligatured, as also the proximal extremity of the cut left; insensibility occurred in 4 min. 36 sees. Another rabbit was then taken of similar age, size, and apparent strength; both its internal carotids were cut, and insensibility ensued in 3 min. 45 sees. In the case of a third rabbit, in whom not only the internal carotid but the vertebral arteries were cut, insensibility ensued in 70 sees. The conclusions to which these experiments led were as follows: That the brain is constantly depending for manifestations of energy on its blood supply; that it has not the accumulative and retentive power of the muscle, which latter, after the severance of all arterial communication, is yet capable of acting

Nightmare,

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considerable time. Hence, we have a right to consider that abnormal localisation of this organ's arterial supply would produce a corresponding increase in the functional discharge of the part affected. It were, perhaps, needless for me to remind the reader of the perfect symmetry of the brain and its arteries ; the latter, indeed, appear designed for the purpose of distributing an equal and unceasing current of blood to all the parts supplied. Now, in the very general, and most healthy, posture for sleeping?on the side?there can be, evidently, no tendency to a localisation of blood; and here also we are met by the fact, that nightmare seldom, if ever, occurs when the sleeper is in this position; on the contrary, in the vast majority of cases, in all that have come under my notice, the person is affected only when lying on his back. In this latter position, it need hardly be pointed out, we have two physical results, the latter consequent on the former: first, an increase in the arterial supply of the back of the brain ; secondly, a decrease in that of its front. Let us now consider with what psychological phenomena these two positions correspond. In the former?when lying on the side?there is sometimes a performance of rational processes ; the sleeper will argue, take part in, and appreciate the merits of, a conversation. But in the latter position, when the wretched dreamer is on his back, the mental phenomena are horrible and diabolical, and it is to these the name of nightmare lias been given. We are thus led to conclude that the primary cause of the malady is the increase of the blood supply to the back of the brain, and a consequent manifestation of local energy ; and this opinion is backed by the fact that the respiratory movements of the sufferer are so vigorous as to cause a feeling of pain, pointing to the fact that the reflecting power of the medulla is increased. We have now to enquire as to the particular agencies concerned in the production of the two principal phases of nightmare, namely, inability to speak and to walk. Perhaps I had better include these, together with other similar phenomena, under the term, loss of control over muscular actions. It has been asserted that this loss of control is due to absence of the co-ordinating power. If, for the sake of argument, I grant this to be true, it would not clash with my theory as hitherto demonstrated. In every case where the actions of the voluntary muscles are co-ordinated, two parts, at least, of the encephalon are engaged, the cerebrum and the cerebellum ; and it has been demonstrated beyond all dispute that the power of will is lodged in the former, the latter merely fulfilling the mechanical function of co-ordination proper, i.e. the distribution of nerve force to muscles intended for combined action. This property, for

an

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tlien, of the cerebellum is simply secondary?it can only be put in action in obedience to a higher authority; the organ is totally incapable of manifesting this species of energy by itself; and consequently, an increase of its blood supply would produce no result in this direction. If, then, the theory of lack of co-ordination be still accepted, we have but one hypothesis remaining, that it is due to the feebleness of the will. Subject to a very considerable modification, I shall strive to demonstrate this as correct. The advocates of the theory of non-co-ordination use the latter word in a sense. They assume, physical purely that the sensations in experienced nightmare are due to the actual inaction of the muscles, and in this they are guilty of the grossest absurdity. What then, I ask, is dreaming ? Its very essence consists in imagination?not movement. Dreamers not suffering from the more horrible phenomena of nightmare, walk, 1-,-in, and speak without moving a muscle. Were the theory I am opposing true, it would logically follow that, if not in all, in at least the vast majority of cases, whenever the sleeper dreams ?f an performing action the latter must necessarily correspond t0 the idea. I need hardly say that common experience proves this to be utterly untrue. It is only in very rare cases that action ever follows the impression. In one, when any rational processes are being enacted, men will sometimes speak and laugh. In another, when the sexual passion is excited, the action " semper eadem " is probably reflex. But were these cases manifold, instead of few, it would give no man the right to assume that the lack of ability to perform an imaginary action rested in the powerlessness of the actual muscle. Such an assumption, again, would give us an equal right to suppose that, where a sleeper dreams of performing an action, he must be enabled at least in his " waking hours to carry his idea into effect. Ad reductio absurdum," should a sailor whose arms have been amputated above the elbow dream of rowing, his ability to cany out the latter feat cannot be questioned, ^et such di earns 111 similar cases to the one cited have often occurred. Bettei let us fall back on Bishop Berkeley's theory of the non-existence o matter. Further, instances are known of men in A\hom tie cerebella have been diseased, when all co-ordinating powei has been actually lost, having dreamt of performing various muscular actions. I come now to consider the hyjiothesis of the feebleness ot the will as the cause of the imaginary loss of musculai action m nightmare. In the rational processes I have before spoken where physical movement follows the idea, theie is an evident exercise of the will. In dreams far less horrible than those ofnightmare, when the sleeper, lying on his side,is engaged 1 PART I. VOL. Y. NEW SERIES.

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the motive power is put forth?he wishes But the phenomena of nightmare point an utter absence of will even sufficient to imagine a bold muscular action?the sleeper feels himself feeble, helpless, and terror struck. To what, then, can this lack of mental power be due ? We know that the will is seated in the cerebral hemisphere. We have seen that the manifestation of energy on the part of the brain is in proportion to its supply of blood. We have seen also that in nightmare there is an increased vascular supply to the back of the brain, and one considerably lessened. to its front, the amount of blood increasing from before backWe are therefore led to conclude that the will is wards. situated in the front part of the cerebral hemispheres, and that its lack of manifestation, owing to the paucity of material to be transformed into force, is the cause of the imaginary lack of muscular action in nightmare. Further, that the back of the brain is not the organ of will, reason, or exalted imagination, but is the seat of emotions which, when manifested by itself alone, without the controlling power, are ignoble and debased. in

to to

imaginary fights,

hit, and he does

so.

The Physiology of Nightmare.

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