Human consciousness and sleep/waking rhythms: a review and some neuropsychological considerations.

The relevance of sleep/waking rhythms to issues of human consciousness is reviewed from data in the literature and from personal studies. Consciousness is often considered to be markedly attenuated or absent in sleep. There is, however, much evidence for a rich subjective experience during sleep, much of which is not recalled later. This implies that William James' "stream of consciousness' persists continuously throughout sleep as well as wakefulness, but that problems of memory recall interfere with its being reported as such. Sleeping subjects show selective awareness of external stimuli, with significant stimuli generally leading to awakening and relatively nonsignificant stimuli, at least at times, being incorporated into the ongoing mental activity of REM or NREM sleep. Mentation throughout sleep is characterized by a high degree of autonomy and little willful control. Creative insight and problem solving of a very high order may occur in sleep and involve either dreaming or thought-like mentation. Parameters of waking consciousness show possibly sleep-related rhythmic fluctuations at both circadian (24 hr sleep/waking) and ultradian (90-120) min, NREM/REM sleep) rates. Moreover, waking consciousness is markedly influenced by the quality of temporal stability of preceding sleep. A substantial number of so-called "altered states of consciousness" is found to involve primarily or exclusively dysfunction of sleep/waking mechanisms. Cerebral lesions can produce selective impairment of aspects of sleep mentation. It is concluded that further analysis of subjective awareness in sleep or in partial sleep states is very relevant and indeed vital to a more comprehensive understanding of human consciousness.