Age- and gender-associated differences in the sleepy brain's electroencephalogram.

Background. With the eyes closed, an increase in sleepiness is associated with a decrease of spectral electroencephalographic (EEG) power in the high-frequency rage (i.e. alpha activity) and an increase of the power in the low-frequency range (i.e. theta activity). It has been suggested that the changes in the high- and low-frequency ranges might determine the two (earlier and later) drowsiness stages that precede sleep onset, respectively.Objective. We tested whether such spectral EEG signatures of sleepiness vary with age or gender.Approach. The EEG signal was recorded at 2 h intervals in 48 volunteers (15-67 years, 27 females) deprived of sleep between Friday evening and Sunday evening. The EEG signatures of sleepiness were calculated by expressing each EEG spectrum as a deviation from the initial (Friday evening) EEG spectrum.Main results. An age- and gender-specific variation was found in the signatures. Only the pattern of age-associated variation changed with an increase in the sleepiness level. A two-stage response to the increase of sleepiness was confirmed, but only in younger study participants. Subjective sleepiness was associated with neither age nor gender.Significance. In sleep-deprivation research, accounting for age- and gender-specific variations in the spectral EEG measures of drowsiness might be recommended. The results did not reveal any disturbance of the motivational function of subjective sleepiness in older study participants.