Effects of scheduled afternoon naps and bedrest on daytime alertness

Abstract

A forced-rest postulate and recuperative theory of sleep function were tested. Eighteen normal, healthy young adult males were studied in a balanced design which comprised single treatment replicates of polygraphically recorded 2:40-4:00 p.m. 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 12:30 p.m. for 1.2 hr and then again 20 min following the conditions from 4:20 until 5:30 p.m. Measurements were obtained from: (a) short-term memory, visual four-choice reaction time, and auditory vigilance tasks; (b) 4-7 Hz EEG theta rhythm; (c) sublingual temperature; (d) the Stanford Sleepiness Scale; and (e) mood subscales (activation, euphoria, fatigue) on an adjective check list. During bedrest compared with napping, subjects averaged significantly more: (a) stage 1 (in aggregate: X = 27 min.); (b) intermittent wakefulness (X = 43 min.); (c) transitions into stage 1; and (d) awakenings, but (e) 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 (X= 8 min.), 4 (X = 17 min.) and REM (X = 16 min.). Following bedrest versus napping, there were statistically significant decrements on the neurobehavioral tasks, lower activation scale scores, but significantly increased levels of sublingual temperature at 4:30 p.m., EEG theta rhythm during 5:00-5:30 p.m. 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 hr or shortened sleep, the impairments incurred in the bedrest treatment increased negligibly as the tasks continued. These neurobehavioral decrements are attributed 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 napping was replaced by physical recumbency in conjunction with increased accumulations of transitional stage 1 and waking.