EEG and subjective sleepiness during extended wakefulness in seasonal affective disorder: Circadian and homeostatic influences

Background: Seasonal affective disorder (SAD) may reflect a disturbance of circadian phase relationships or a disturbance of sleep-wake dependent proc esses, both of which change daytime energy and sleepiness levels. Methods: Under the unmasking conditions of a 40-hour constant routine proto col (CR), self-rated sleepiness and waking electroencephalogram (EEG) power density were assessed in women with SAD (n = 8) and in age-matched healthy control subjects (n = 9). Results: There was no significant effect of season or light treatment in an y of the measures. The time course of subjective sleepiness was characteriz ed by a circadian modulation and an overall increase during extended wakefu lness in both SAD patients and control subjects. A prominent circadian rhyt hm of subjective sleepiness was not different in SAD patients and control s ubjects; however the progressive buildup of sleepiness, as quantified by no nlinear regression analysis, was significantly reduced in SAD patients, mai nly because they were sleepier than control subjects during the fir-st 12 h ours of the CR. The time course of waking EEG theta-alpha activity showed a more rapid increase during the first 10 hours of the CR in SAD patients. I n contrast to control subjects,who showed a progressive increase in the cou rse of the 40-hour episode of extended wakefulness, EEG theta-alpha activit y in SAD patients did riot further increase over the remainder of the CR, Conclusions: The data suggest that SAD patients may have a trait (rather th an state) deficiency in the homeostatic buildup of sleep pressure during ex tended wakefulness as indexed by subjective sleepiness and EEG theta-alpha activity. (C) 2000 Society of Biological Psychiatry.