DYNAMICS OF THE HUMAN EEG DURING PROLONGED WAKEFULNESS - EVIDENCE FORFREQUENCY-SPECIFIC CIRCADIAN AND HOMEOSTATIC INFLUENCES

The electroencephalogram (EEG) of nine healthy individuals was recorde d at half-hourly intervals during similar to 40 h of sustained wakeful ness in a constant routine protocol. EEG power density in the 0.75-9.0 Hz range exhibited a global increasing trend, and a local trough in t he evening, centered similar to 6 h prior to the temperature minimum. The former could be attributed to a wake-dependent influence, and the latter to a circadian influence. Power density in the 9.25-12.0 Hz ban d showed a circadian modulation, the trough coinciding with the minimu m of the endogenous rhythm of body temperature, whereas a wake-depende nt influence was not evident. Power density in the 12.25-25.0 Hz range exhibited a wake-dependent increase, whereas a circadian modulation w as absent. It is concluded that the circadian pacemaker and the wake-d ependent (i.e. homeostatic) process affect the waking EEG in a frequen cy-specific manner. (C) 1997 Elsevier Science Ireland Ltd.