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 processes, both of which change daytime energy and sleepiness levels. Methods: Under the unmasking conditions of a 40-hour constant routine protocol (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 any of the measures. The time course of subjective sleepiness was characterized by a circadian modulation and an overall increase during extended wakefulness in both SAD patients and control subjects. A prominent circadian rhythm of subjective sleepiness was not different in SAD patients and control subjects; however the progressive buildup of sleepiness, as quantified by nonlinear regression analysis, was significantly reduced in SAD patients, mainly because they were sleepier than control subjects during the fir-st 12 hours 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. In contrast to control subjects,who showed a progressive increase in the course of the 40-hour episode of extended wakefulness, EEG theta-alpha activity 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 than state) deficiency in the homeostatic buildup of sleep pressure during extended wakefulness as indexed by subjective sleepiness and EEG theta-alpha activity. (C) 2000 Society of Biological Psychiatry.