The effects of lowered EEG vigilance under the continuous dark environment on the amount and the duration of slow wave sleep (Stage 3+4 : SWS) were examined on 7 male subjects (19-26y). Two of 7 subjects gave up the experiment, so that the data of those 2 subjects were omitted from present analysis.
They lived alone for 72 h under the sound-proofed environment with no time cues and constant darkness, and their polygraphic recordings were monitored. Referential central (C3
) and occipital (O1
) EEGs were frequency-analyzed every 15 min for a duration of 61 s, when the C3
EEG was showing stage W (EEG waking). Peak analysis of power spectra in alpha band (8-13Hz) showed that the peak alpha frequency (frequency of the maximal peaks in alpha band) in the waking periods decreased from the first day of experiment to the end (mean 1.85Hz, SD 0.71Hz, range 1.0-3.0Hz). This decline of peak frequency was stepwise in each subject. The results of principal component analysis confirmed this tendency and the factor loading patterns well demonstrated the stepwise shift points of alpha peak. Then we divided the experiment periods in accordance with the peak shift points so as to equalize the level of EEG vigilance and gathered the sleep stage data in each of these periods.
The results of this study showed that the level of EEG vigilance in the waking periods did not affect the amount of SWS, but the duration of SWS. The occurrence of fragmented SWS increased in parallel with the lowering EEG vigilance.
We conclude that the appearance of SWS depends not simply on the quantity of waking period but the quality of the period.