Sleep and Its Derangements

by William A. Hammond

The sense of touch is very differently affected, for so far from being diminished in its action, it is invariably unduly exalted. Though the eyes do not see, the ears hear, the tongue taste, or the nose smell, the somnambulist has one sense which is fully awake, and by which he is enabled to guide himself through the most devious passages in dangerous paths.

In this fact it appears to me we have a strong argument in favor of the theory of somnambulism which I have already referred to, and which appears to me to be supported by much additional evidence. I propose this view not without hesitation; but much study of the phenomena of somnambulism, and of analogous states of the nervous system, has certainly tended to convince me of its general correctness, and I am not without the hope that other students of neurology will find it reconcilable with their observations and experiments.

In my opinion, somnambulism is a condition of the organism in which through profound sleep the action of the encephalic ganglia is so materially lessened that the spinal cord becomes able to control and direct the body in its movements.

That the spinal cord even in the waking state constantly exercises this power, is a matter of common observation. I have already alluded to some of the facts which establish this proposition; but, for the purpose of giving as complete and connected a view as possible of all the points which bear upon the theory of somnambulism above enunciated, I shall not hesitate to recall them to the recollection of the reader, and to bring forward other circumstances which appear to be in relation with the question.

If an individual engaged in reading a book allows his mind to be diverted to some other subject than that of which he is reading, he continues to see the words, which make no impression upon his brain, and he turns over the leaf whenever he reaches the bottom of a page with as much regularity as though he comprehended every word he has read. He suddenly, perhaps, brings back his mind to the subject of his book, and then he finds that he has perused several pages without having received the slightest idea of their contents.

Again: when, for instance, we are walking in the street and thinking of some engrossing circumstance, we turn the right corners and find ourselves where we intended to go, without being able to recall any events connected with the act of getting there.

In such instances as these—and many others might be adduced—the brain has been occupied with a train of thought so deeply that it has taken no cognizance or superintendence of the actions of the body. The spinal cord has received the several sensorial impressions, and has furnished the nervous force necessary to the performance of the various physical acts concerned in turning over the leaves, avoiding obstacles, taking the right route, and stopping in front of the right door.

All cases of what are called “absence of mind” belong to the same category. Here the brain is completely preoccupied with a subject of absorbing interest, and does not take cognizance of the events which are transpiring around. An individual, for instance, is engaged in solving an abstruse mathematical problem. The whole power of the brain is taken up in this labor, and is not diverted by circumstances of minor importance. Whatever actions these circumstances may require, are performed through the force originating in the spinal cord.

The phenomena of reverie are similar in some respects to those of somnambulism. In this condition the mind pursues a train of reasoning often of the most fanciful character, but yet so abstract and intense, that though actions may be performed by the body, they have no relation with the current of thought, but are essentially automatic, and made in obedience to sensorial impressions which are not perceived by the brain. Thus a person in a state of reverie will answer questions, obey commands involving a good deal of muscular action, and perform other complex acts, without disturbing the connection of his ideas. When the state of mental occupation has disappeared, there is no recollection of the acts which may have been performed. Memory resides in the brain and can only take cognizance of those things which make an impression on the mind, or of those ideas which originate in the encephalon.

In the case of a person performing on a piano, and at the same time carrying on a conversation, we have a most striking illustration of the diverse though harmonious action of the brain and spinal cord. Here the mind is engaged with ideas, and the spinal cord directs the manipulations necessary to the proper rendering of the musical composition. A person who is not proficient in the use of this instrument, cannot at the same time play and converse with ease, because the spinal cord has not yet acquired a sufficient degree of automatism, and the mind cannot be divided in its action.