Effects of scheduled afternoon naps and bedrest on daytime alertness

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Abstract
A forced-rest postulate and recuperative theory of sleep function were tested. Normal, healthy young adult males (18) were studied in a balanced design which comprised single treatment replicates of polygraphically-recorded 1440-1600 h napping and bedrest. Under both conditions subjects were required to lie quietly in bed with eyes closed. During bedrest, stage 1 sleep episodes were allowed to intervene, but for no longer than 1.5 min simultaneously. Dependent variables of waking function were initially assessed at 1230 h for 1.2 h and then again 20 min following the conditions from 1620-1730 h. Measurements were obtained from short-term memory, visual 4-choice reaction time, and auditory vigilance tasks; 4-7 Hz EEG theta rhythm; sublingual temperature; the Stanford Sleepiness Scale; and mood subscales (activation, euphoria, fatigue) on an adjective check list. During bedrest compared with napping, subjects averaged significantly more stage 1 (in aggregate: .hivin.X [mean] = 27 min), intermittent wakefulness (.hivin.X = 43 min), transitions into stage 1, and awakenings, but 52 min less total time spent asleep continuously. The cumulative aggregation of distributed (stage 1) sleep episodes which intervened in the bedrest condition significantly exceeded the individual accumulations of stages 3 (.hivin.X = 8 min), 4 (.hivin.X = 17 min) and REM [rapid eye movement] (.hivin.X = 16 min). Following bedrest vs. napping, there were statistically significant decrements on the neurobehavioral tasks, lower activation scale scores, but significantly increased levels of sublingual temperature at 1630 h, EEG theta rhythm during 1700-1730 h vigilance testing, reported fatigue, and intensified Stanford Sleepiness Scale ratings. Unlike the direct effects on choice reaction time and auditory vigilance tests of wakefulness extended beyond 16 h or shortened sleep, the impairments incurred in the bedrest treatment increased negligibly as the tasks continued. These neurobehavioral decrements are atttributed to disruptions of the diurnal rhythm potentiated by an acute sleep cycle phase shift. The adverse consequences on alert behaviors which resulted from the bedrest condition are explained from an ethological perspective as a generalized response to repeated delays of the consummatory phase in an adapted repertoire of afternoon sleep behavior. The hypothesis of physical rest/sleep equivalence received no substantiation from the present study. Similar effects were not produced when the consolidated sleep cycle during afternoon mapping was replaced by physical recumbency in conjunction with increased accumulations of transitional stage 1 and waking.