Littell's Living Age/Volume 125/Issue 1614/Dreams
From The Lancet.
The intrinsic study of dreams throws little light upon their physiology. It is only by a comparative examination of them, studying them in common with the other phenomena of sleep, that they can be in any measure understood. The characteristic of the state of sleep is the absence of all outward sign of consciousness and will, which are seemingly withdrawn from all connection with the organs of sense, or with those of motion, by which their existence could be manifested. But the functions of the muscles and of the lower portions of the nervous system which immediately control the muscles are by no means dormant, as the sudden cramp and painful start sufficiently show. The spinal cord is awake and capable of function even in insubordinate excess, unrestrained by any higher centre. The action of the lower centres is restrained by the inhibitory influence which the higher centres exercise over them, and during sleep this is withdrawn. The muscular spasm, which rudely wakes the sleeper to consciousness of pain, may never occur while the brain is active and alert; and, as far as can be understood, it is only in the withdrawal of a higher central influence that the difference between the states of the spinal cord in the waking and sleeping condition consists. Thus the same tendency of unrestrained excessive action obtains during sleep in both higher and lower centres. A very similar relation may be traced in the involuntary intellectual action which constitutes a dream. The will has absolutely no control over the train of ideas. They may arise in apparent spontaneity, or more rarely as a consequence of some waking thought or state, and may run their course entirely uncontrolled and uncontrollable, uninfluenced not only by the will, but by the accumulated experience of the waking hours, so that the absurd inconsistencies and impossible relations of the fancied action excite no sense of doubt or wonder. They pass away as mysteriously as they commenced, and their track may be so separated from the lines of waking thought that, like a distant second image in diplopic vision, the existence of which may be unknown till an accident reveals its place and character, their occurrence may be unsuspected until some chance association reproduces them.
Thus the same tendency to unrestrained excess of action obtains during sleep in both higher and lower regions of nervous phenomena, in both brain and cord. And in some other details a further analogy may be traced. The physical sensation which excites a reflex movement is effective in proportion to its unaccustomed character. A sudden change of sensation may provoke the movement which a constant pain fails to elicit. Something of the same relation may be traced in dreams. Feelings and ideas which are dominant by day may be entirely absent in sleep — nay, be even "conspicuous by their absence." "Sleep, deaths twin brother, knows not death;" and, although the statement of the Laureate has less accuracy than some of his aphorisms, it is sufficiently exact to illustrate the independence of the reproduced ideas on those from which they have arisen. Unfelt, in short respite, the burden of sorrow may vanish, while some chance perhaps unremembered association of the day before originates a train of ideas in happy contrast to the reality which returning consciousness reveals.
The influence of the physical organs on the mind in sleep is familiar to all students of mental physiology. Sensations unnoticed during the day may be sufficient to set up a train of ideas of definite character and vivid distinctness, and such sensations are especially effective when sudden and contrasted with those previously influencing the sensorium. As Dr. Maudsley has pointed out, the character of the delusion may be so determined by the organ diseased as to be sometimes the earliest indication of a subsequent malady, which may thus seem to be foretold during the dream, which had apparently no physical origin.
Such an effect of an organic derangement of the brain is no doubt the explanation of this peculiar delusion of motion through the air, which has lately furnished a daily contemporary with a subject for abundant correspondence. There is probably no one to whom the feeling of such passive locomotion is not common enough. No delusions are more vivid than those which, in the waking state, accompany the phenomena of vertigo and its allied sensations. A subjective sense of movement, too sudden, too intense to allow at once the consciousness to realize the contrary evidence of other senses, produces a conviction, sometimes invincible, of change of place in the individual or surrounding objects. It is, then, a matter of small surprise that when the other senses are in entire abeyance, as they are, for the most part, during sleep, a "swimming in the head" produces the distinct impression of "levitation;" but beyond this the phenomenon has no significance, and is only interesting as a train of ideas which can have no counterpart in any preceding physical experience, and as an instance of the novel associations which may be provoked by the action of a sensory centre uncontrolled by remembered experience or correcting sensations of other organs.