Constant light suppresses sleep and circadian rhythms in pigeons without consequent sleep rebound in darkness.

Sleep patterns and circadian rhythms of body temperature, activity, body weight, and electroencephalographic (EEG) power spectra of pigeons were compared among three photic conditions: a 12:12-h light-dark cycle (LD), followed successively by constant bright (LL) and dim light (DD) periods. LL suppressed non-rapid-eye-movement and rapid eye movement sleep and circadian rhythms of the measured variables without producing increased drowsiness or other physiological or behavioral changes. Sleep patterns after LL-DD transitions also showed no evidence of prior sleep deprivation during LL. Sleep latency after LL-DD transitions was 93 min longer than after L-D transitions in LD. Total sleep and EEG slow wave activity during the first 24 h in DD did not differ from D in LD. Free-running circadian rhythms subsequently reappeared in DD after LL.