Circadian variation in performance, subjective sleepiness, sleep, and oral temperature during an altered sleep-wake schedule

Abstract

The effect of an altered sleep-wake schedule on the interrelation of oral temperature, performance, and sleepiness was studied in 38 male Naval volunteers who maintained a 60 min treatment — 160 min testing schedule for 40 consecutive hrs. During the 60 min treatment portion of each epoch, 8 subjects napped, 10 subjects exercised, and 20 subjects rested in bed. Sleep measures (for the nap subjects), oral temperature, performance on several tests, and Standford Sleepiness Scale ratings were obtained at 10 equidistant intervals throughout the 40-hr period. Within-subject correlations showed that minimum oral temperature was significantly associated with maximum nap sleep time, errors on a vigilance task, and sleepiness ratings. In the nap subjects, errors and sleepiness ratings were highest following naps with high total sleep time, suggesting that sleep was detrimental to immediately subsequent performance and alertness. The distribution and interrelation of temperature, errors, and sleepiness, however, was similar in the three groups; this indicated that the synchronous circadian variation in these measures was responsible for the apparent detrimental effect of sleep in the nap subjects. When the diurnal effect was removed by holding time of day constant, the correlations among the variables fell to near-zero, indicating no causal relationship among the variables independent of the circadian rhythm.