Human sleep EEG analysis using the correlation dimension

Sleep electroencephalograms (EEG) were analyzed by non-linear analysis. Pol ysomnography (PSG) of nine healthy male subjects was analyzed and the corre lation dimension (D2) was calculated. The D2 characterizes the dynamics of the sleep EEG, estimates the degrees of freedom, and describes the complexi ty of the signal. The mean D2 decreased from the awake stage to stages 1, 2 ,3 and 4 and increased during rapid eye movement (REM) sleep. The D2 during each REM sleep stage were high and those during each slow wave sleep stage were low, respectively, for each sleep cycle. The mean D2 of the sleep EEG in the second half of the night was significantly higher than those in the first half of the night, Significant changes were also observed during sle ep stage 2, but were not seen during REM sleep and sleep stages 3 and 4. Th e D2 may be a useful method in the analysis of the entire sleep EEG.