Differences between morning-types and evening-types in the dynamics of EEG slow wave activity during night sleep.

During baseline nights in a sleep laboratory electrophysiological sleep records were made for 8 morning-type subjects (M-types) and 8 evening-type subjects (E-types). As compared with the E-types, the M-types were relatively advanced with respect to the times of maximum and minimum rectal temperature and sleep times. Also, the M-types showed a larger initial temperature drop after sleep onset. Comparisons of the outcomes of visual sleep scoring revealed for the M-types a shorter sleep latency and a longer sleep duration. In addition, the M-types reported a higher subjective sleep quality than the E-types. For the M-types sleep stages 3 + 4 and EEG delta (0.5-3.5 Hz) energy declined monotonically across the first 4 NREM/REM cycles. For the E-types, however, no decrement was observed over the first 2 cycles. Analysis of the wave forms of delta energy, employing a pattern recognition technique independent of visual sleep scoring, substantiated this finding. These results are discussed in relation to the differences in circadian characteristics between M-types and E-types.