Temporal EEG dynamics of non-REM sleep episodes in humans

The process of the human non-rapid eye movement (non-REM) sleep period has not been clarified. Time-based analysis on sleep EEG may provide an explanation. We focused on chronological aspects of initiation and termination of non-REM episodes, using spectral analysis of sleep EEG. The subjects were healthy male volunteers (n = 32, mean age +/- S.D.: 25.5 +/- 3.5 years). The rise latencies from non-REM sleep onset to the maximal power value and the decay latencies from the maximal power value to non-REM sleep offset were determined in the initial and final 21-min windows of individual non-REM episodes in each EEG band ranges. Low (12.1-13.7 Hz) and high (14.1-16.0 Hz) sigma ranges were analyzed separately. The rise and decay latencies were shorter in higher frequency ranges (> 14 Hz) and longer in lower frequency ranges (< 14 Hz). There were significant differences in the rise and decay latencies between low and high sigma ranges, indicating that the whole frequency ranges were clearly separated at the middle of the sigma range (14 Hz). The rise and decay latencies were significantly different in lower frequency ranges. The clock time of the night significantly affected only the rise latencies of the delta (0.78-3.9 Hz), alpha (8.2-11.7 Hz) and low sigma (12.1-13.7 Hz) ranges. In conclusion, initiation and termination of non-REM sleep was represented by higher frequency ranges, whereas further evolution and devolution of non-REM sleep was represented by lower frequency ranges, and only the evolution process was affected by the clock time of the night. (C) 2000 Published by Elsevier Science B.V. All rights reserved.