The perception of wakefulness within sleep

We studied the relationship between electroencephalographic (EEG)-defined awakenings and subjects' awareness of them at the time of their occurrence in 40 men (mean age, 55.3 years). The subjects used a push-button device to signal wakefulness during an evening's sleep in the laboratory; continuous EEG and electro-oculograms were also made. Results were as follows (after eliminating data for 12 nonresponders): 52% of the responses occurred during EEG-defined wakefulness (stage 0), 12% in a sleep stage that was followed immediately by stage 0, and 36% in a sleep stage not followed by stage 0. However, analysis of the last finding indicated that 73% of these responses were associated with at least 4-6 sec of preceding alpha activity. Thus, signals in the absence of EEG criteria were actually less than 10% of the total recorded. Signals of wakefulness were closely associated with the onset of EEG-defined wakefulness (and 84% of the signals occurred within 4 sec to 1 min of the EEG period). We conclude that self-signaled arousals deserve consideration in clinical analyses in which reports of arousals are a part of the reported sleep disturbance.