EEG slow wave activity, REM sleep, and rectal temperature during night and day sleep in morning-type and evening-type subjects.

During 3 baseline nights (2 for adaptation) and during 3 days of a sleep-wake reversal, electrophysiological characteristics of sleep and rectal temperature were recorded in 8 morning-type (M-type) and 8 evening-type (E-type) subjects, living in a quiet sleep laboratory. Outcomes of visual sleep scoring revealed the following general tendencies for day-sleep as compared to night-sleep: shorter sleep latencies, shorter REM (rapid eye movement sleep) latencies, advance of the time of maximum REM duration, increased duration of slow wave sleep, more intermittent wakefulness, and decreased subjective sleep quality. Furthermore, for the M-types consistently shorter sleep latencies and--for day-sleep--longer REM latencies were observed than those for the E-types. With regard to the parabolic time course of REM duration, M-types appeared to be relatively phase advanced, in particular for their day-sleep. In addition, subjective sleep quality was consistently higher for the M-types, with the exception of the first day-sleep. The temporal distributions of EEG delta (0.5-3.5 Hz) energy over the first four NREM/REM cycles of day-sleep all deviated from a monotonically decreasing trend. Compared to night-sleep the M-types showed a relative increase of delta energy for Cycle 2, whereas for the E-types a relative increase for Cycles 3 and 4 was observed. An analysis of delta energy, employing a pattern-recognition technique independently from visual sleep scoring, revealed an overall faster rate of accumulation for the M-types. Following sleep onset, rectal temperature showed a decrement, which was larger for the M-types. Moreover, rectal temperature and delta energy were negatively related, as indicated by a negative mean intra-individual correlation. These results are discussed in relation to the characteristic sleep-wake behavior of M-types and E-types.