HUMAN BRAIN POTENTIALS DURING THE ONSET OF SLEEP

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Abstract
Brain potentials were recorded from subjects while they were going to sleep. Alterations in the pattern were related to the state of consciousness of the subject by means of signals given spontaneously by the subjects. Subjects who have a well-developed [alpha] (10-per-sec.) rhythm when awake often showed repeated depressions or loss of [alpha] waves while going to sleep. Just after such a depression the subject typically signaled that he had "floated" or "drifted off" for a moment. Slow [DELTA] waves, 0.2 to 0.3 sec. in duration, usually appeared during the depression of a waves. Subjects who have few or no [alpha] waves showed a corresponding but less clearly marked depression of their "quick" (15- to 20-per-sec.) waves, and the same appearance of "delta" waves. 9 of the 10 subjects gave signals which correlated clearly with alterations in their brain-potential records. The "floating" state of consciousness always involves a loss of awareness for immediate external stimuli. Some subjects, but not all, also describe visual fantasies, kinesthetic sensations, interruptions of logical thought, etc. "Real sleep" was regularly acknowledged when slow waves (recorded from the vertex) had reached 150 [mu]v and persisted for half a minute. The appearance of "spindles" of 14-per-sec. waves is a sure sign of real sleep. Dreams may occur in the low-voltage, B stage and also in the 14-per-sec, C stage. Alterations in the [alpha] and [DELTA] waves are not always simultaneous in different parts of the brain. We cannot define exactly the moment of going to sleep or the moment of awakening. In the clinical study of brain potentials the drowsy state must be strictly avoided because of the similarity of the patterns of very early sleep to those described for many abnormal conditions.

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