Correlations between sleep and wake in internally synchronized and desynchronized circadian rhythms in humans under prolonged isolation.

The authors report the results of their experiments performed on the sleep-wake and rectal temperature rhythms of human subjects, who were held in prolonged social isolation for periods of 15-43 days in a specially constructed facility. Of 13 experiments performed with 11 subjects, the sleep-wake and rectal temperature rhythms free ran with circadian periods, remaining internally synchronized for the entire duration of the experiments in 9 subjects. The relationship between sleep and wake that is highlighted in this article is a trend that clearly and significantly expresses itself in four long-term experiments performed on a male subject and a female subject in separate experiments. There was clear-cut positive correlation between episodes of sleep and preceding episodes of wake. In all four experiments, the circabidian sleep-wake cycle and circadian rectal temperature rhythms, were in a state of internal desynchronization. The authors therefore attribute the differences reported in the literature and this article in the quality of correlation between sleep and wake to the phenomenon of internal desynchronization. However, they do not find significant correlation between sleep and wake episodes in 8 of their 9 subjects; in 1 35-year-female, there is a strong negative correlation between sleep and (preceding or following) wake episodes. It is of much physiological significance that the phenomenon of internal desynchronization should so radically alter the "quality of correlation" between sleep and wake and may be of interest for models of sleep regulation.