Electroencephalographic activity after prolonged sleep loss

Abstract

The P 4-O 2 EEG of four subjects was measured by visual inspection and by auto-spectral analysis before, during and after 205 h of total sleep deprivation. A marked reduction of alpha activity which overrode circadian variations and individual differences was observed. Alpha reduction was paralleled by deterioration of subjective ratings on feeling and effort, by deterioration of tracking performance, and by reports of hypnagogic illusions. These findings are not unlike those made during the sleep stage 1. After 120 h of sleep loss, there was a slight increase of alpha activity which was accompanied or “anticipated” by partial returns of oral temperature, subjective ratings, and 17-hydroxy-corticosteroids to pre-sleep deprivation levels. The increase of alpha activity and other changes are postulated to reflect shifts in basic coping mechanisms. After 2 nights of recovery sleep (12 h and 8 h), the return to the pre-deprivation levels was complete for all variables, except the absolute alpha activity of one subject. The follow-up study conducted 1 month or 2 months later showed that all subjects had a complete recovery. Alpha activity can be reasonably estimated by alpha index and, as such, it will be sufficient to indicate a gross sleep debt. In those who lack dominant alpha activity, the simple subjective ratings associated with standardized tasks may be used for detection of sleep debt. The poor indicators of sleep loss were 17-hydroxycorticosteroids, oral temperature, and time- off-target. Respiration rate, heart rate, and arterial pressure were useless in detecting even a gross sleep starvation.