Sleep, its subjective perception, and daytime performance in insomniacs with a pattern of alpha sleep

Intrusion of alpha activity, an electroencephalographic (EEG) pattern typical for wakefulness, into sleep stages has repeatedly been described and investigated in various populations. Some studies suggested that it is a less deep and restorative sleep, but others did not support this interpretation. The present study was carried out to collect ample data on neurophysiology and subjective experience of sleep and on daytime cognitive performance to clarify this point. A sample of 128 primary insomniacs was investigated with polysomnography (PSG) that was submitted to a computerized, automatic analysis of alpha activity during sleep. It yielded two groups of 64 Ss each with a normal, that is, nonalpha sleep EEG and with alpha-sleep, respectively. Contrasting the two groups for PSG showed that alpha sleep Ss had significantly more stage 4 and a (nonsignificant) tendency for more awakenings. Subjectively, they largely underestimated intermittent wake time and consequently overestimated sleep duration by 50 min. The performance test battery showed a difference in one test only, that is, a better short-term memory function by alpha sleep Ss. In conclusion, there was no result supporting the assumption that alpha sleep is less restorative, but a significant lack of perception of intermittent awakenings during night sleep by alpha sleep Ss was found. The authors propose an explanation and point to the implications this misperception might have for the clinician.