The effect of a reversed cycle of sleep and wakefulness on diurnal EEG patterns in rhesus monkeys

Abstract

The modification of established daytime EEG patterns in four rhesus monkeys was effected by a reversal of the sleep-waking cycle. The lighting regimen was automatically controlled on a 12 h light, 12 h dark period and was phase shifted through 180° for a three month period. A progressive and significant reduction in wakefulness with a concomitant increase in sleep, along with the emergence of cyclic REM episodes occurred during reversal. A decrease in the latency to onset of sleep and the REM state was also observed. Behavioural observations suggested that motility was predominant during the lighted period. The EEG patterns returned to baseline conditions when the normal lighting regimen was reimposed.