Fluctuation of waking electroencephalogram and subjective alertness during a 25-hour sleep-deprivation episode in young and middle-aged subjects.

STUDY OBJECTIVES To evaluate the effects of a 25-hour sleep-deprivation episode on quantitative waking electroencephalogram (EEG) and subjective alertness in young and middle-aged subjects. DESIGN A 25-hour constant-routine protocol followed by a daytime recuperative sleep episode. SETTING Chronobiology laboratory. PARTICIPANTS Twenty-five normal subjects separated into 2 groups: young (aged 20-39 years) and middle-aged (aged 40-60 years). INTERVENTIONS None. MEASUREMENTS AND RESULTS Waking EEGs were recorded every 2 hours and subjective measures of alertness every 30 minutes during the 25-hour sleep-deprivation episode. Overall, results indicated no age-related differences over a 25-hour constant routine in the temporal evolution of subjective alertness and of spectral power in the theta/alpha (4-12 Hz) frequencies of the waking EEG. The middle-aged compared to the young subjects showed a reduced rebound of slow-wave activity in the recovery-sleep episode. While the waking EEG and subjective alertness levels showed strong correlations in both groups, there was no relationship between theta rise during wakefulness and slow-wave activity rebound in the recovery-sleep episode. CONCLUSIONS These results suggest a dissociation in the middle-aged population between the sensitivity of their alertness level on the one hand and the sensitivity of their sleep on the other to the number of hours of wakefulness. Hence, alertness of young and middle-aged subjects would show the same deterioration with an accumulation of wakefulness (possibly reflecting a similar sleep need), yet the middle-aged subjects would be less able to increase their recuperative sleep intensity following enhanced time awake (reduction in sleep ability).