Nocturnal electrographic features of frequently changing-irregular sleep-wakefulness rhythms.

Polygraphic characteristics of nocturnal sleep associated with frequently changing-irregular rest-activity schedules were investigated in healthy young adults. Two groups each of 12 male university students were classified according to a priori criteria as either: (a) controls who slept regularly for 7--8 hr at night or (b) whose retiring and arising times combined varied chronically +/- 1.5 hr. Sleep was recorded during three consecutive 8-hr nocturnal periods at fixed clock times. Polygraphic indices generally reflected greater discontinuity and fragmentation associated with the nocturnal sleep in the young adults whose 24-hr rest-activity cycle tended to be frequently changing-irregular. The significantly: (a) larger absolute quantities of (i) transitional stage 1 sleep, (ii) intermittent wakefulness and (b) increases stage shifts provided some indication that the intrasleep cycle becomes disturbed when rest-activity schedules follow no predictable pattern in the everyday environment. Despite, or because of, the enforced hour (11:30 p.m +/- 30 min) for retiring, it is possible that the capacity to fall asleep had become phase-delayed among subjects with irregular rest-activity schedules who experienced more initial wakefulness (on average) before sleep onset stage 1. Finally, the recorded sleep perturbations associated with frequently changing-irregular schedules were extremely variable across nights and among individuals. This was especially pronounced on a nightly basis as reflected by significantly larger variability (SDs): (a) in the latency to sleep onset, for (b) total time asleep, (c) intermittent wakefulness, and (d) the ultradian (90-min) REM cycle. Variability (the SD) between individuals was also more substantial for these same polygraphic measures at statistically significant levels.