Correlation dimension of the human sleep electroencephalogram

Sleep electroencephalogram (EEG) was analyzed by nonlinear analysis. Polyso mnography of a healthy male subject was analyzed and the correlation dimens ion was calculated. The mean correlation dimensions decreased from stage 'a wake' to stages 1, 2 and 3, and increased during rapid eye movement (REM) s leep. These results were also seen at every sleep cycle. During each sleep cycle the correlation dimensions decreased for slow wave sleep, then increa sed for REM sleep. The mean correlation dimension of the sleep EEG in the s econd half of the night was significantly higher than those in the first ha lf of the night. A significant change was seen both during REM sleep as wel l as in sleep stage 2. Nonlinear analysis may be a useful method in the ana lysis of the entire sleep electroencephalogram.