Response of the sleep-wake rhythm to an 8-hour advance of the light-dark cycle in the rat.

We have studied the effects of an 8-h advance of the environmental light-dark (LD) cycle on the sleep-wake rhythm in the rat. Electroencephalograms and electromyograms were recorded simultaneously on chart paper through a two-channel telemetry system for 3 days before phase shift (baseline) and 8 days during and after phase shift. Phase advance of the LD cycle led to an increase in both non-rapid eye movement (NREM) and REM sleep. The amount of NREM sleep in the light period correlated positively with that in the preceding dark period for 4 days after phase advance. The duration of REM sleep in the light period correlated negatively with that in the preceding dark period. The results suggest that homeostatic control of the amount of NREM sleep between the preceding dark period and the following light period is disturbed by phase advance of the LD cycle.