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.
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