Alpha attenuation soon after closing the eyes as an objective indicator of sleepiness

Attenuation of alpha rhythm in occipital derivation serves as a reliable electroencephalographic (EEG) marker of sleep onset. If such attenuation not only coincides with but also anticipates sleep onset, objective evaluation of sleepiness of permanently waking individuals might be facilitated by probing alpha attenuation immediately after closing eyes. We tested whether alpha-based EEG indexes reflect self-scored sleepiness and objectively measured waking ability. A total of 15 young adults self-scored their sleepiness before and after recording of their resting EEG with a 2-h interval in the course of 43-61-h wakefulness. For each EEG record, power spectra were calculated on 2-min intervals of the eyes open section and on five following 1-min intervals of the eyes closed section. Aking ability was assessed as latency to sleep onset marked by zero-crossing decline of such EEG indexes as alpha-theta power difference in occipital derivation and scores on the second principal component of the EEG spectrum in frontal and occipital derivations. Alpha attenuation during the first minute with eyes closed was found to be significantly related to the levels of subjective sleepiness and waking ability. The relationship between alpha attenuation and subjective sleepiness was confirmed by analysing 1-min eyes closed EEG recordings obtained with a 3-h interval in the course of 24-h sustained wakefulness of 130 adolescents and adults. We concluded that such 1-min eyes closed EEG recordings might be used for simple and quick measurements of sleepiness and waking ability in experimental and field studies of permanently waking individuals.