Brain state and body position. A time-lapse video study of sleep.

Human sleep is characterized by episodes of immobility and by major body movements occurring in phase with the EEG sleep cycle. Using time-lapse videotape recording and electrophysiological monitoring, we studied the sleep of four normal subjects to determine the relationship of the movements to sleep cycle phase and the consistency of the power of the movement data to quantify sleep parameters. We were able to measure sleep latency and to predict the time of occurrence of non-rapid eye movement sleep episodes in our subjects from the video movement data alone. In addition, we discovered evidence of small body movement specific to rapid eye movement sleep.