Circadian and homeostatic influences in the EEG during 30-hours of wakefulness

Abstract

Numerous studies have revealed the existence of circadian and homeostatic influences in the sleeping EEG. Over recent years, these influences have also been identified in the waking EEG. EEG activity within the lower frequency bands has been associated with increased sleepiness, increased reaction time and decreased performance, while EEG activity in the higher frequency bands has been associated with increased alertness/vigilance. The aims of this study were: (1) to further define the homeostatic and circadian influences in the waking EEG and to identify if these influences are present in subjective assessments; (2) to define the relationship between EEG frequencies and physiological parameters (core body temperature and melatonin) and (3) to define the relationship between EEG frequencies and subjective assessments.;Nine subjects underwent a modified constant routine protocol. EEG activity, the primary dependent variable, was monitored continuously and was subjected to a Fast Fourier Transform. Other dependent variables included core body temperature (CBT), salivary melatonin (MEL) and subjective ratings of sleepiness, alertness and mood. Data was subjected to linear regression, non-linear regression (24-hour cosine curve) and correlation analysis.;Homeostatic influences were documented in alpha and beta frequencies, as well as in subjective sleepiness, alertness and mood states. Circadian influences were found in delta, theta, alpha and beta frequencies, as well as in subjective sleepiness, alertness and mood states. Less than 24-hour cycles were revealed within delta and alpha frequencies. A significant inverse relationship was found between CBT and delta and theta, while a significant positive relationship was found between CBT and alpha and beta. MEL was not significantly related to any of the EEG frequencies. Delta, theta and beta frequencies were significantly correlated to subjective assessments in the expected directions. Alpha was not significantly related to any of the subjective assessments.;These results suggest that homeostatic and circadian influences are involved in the regulation of the waking EEG and of subjective sleepiness, alertness and mood states. They also suggest that EEG activity, particularly beta, may be a useful objective measurement of subjective vigilance/mood states.