Sleep stages, auditory arousal threshold, and body temperature as predictors of behavior upon awakening

Attempts to demonstrate sleep stage effects on waking behavior have been equivocal at best. The present study provided a more sensitive approach to this problem by assessing performance and subjective alertness at repeated awakenings across baseline sleep and across recovery sleep following 40 and 64 hours of sleep deprivation. These behaviors were then compared to changes in EEG sleep, body temperature, and auditory threshold within these nights. Comparison of means between baseline and recovery sleep indicated that the behavioral variables were generally more sensitive than sleep stages to different amounts of prior wakefulness. Multiple regression analyses revealed no consistent covariation between behavior and any sleep stage which was independent of the correlations among the sleep stages themselves. Thus, distinct functions for specific sleep stages were not apparent from the comparison of means or the regression analyses. However, significant positive covariations were obtained between body temperature and performance, and auditory threshold and sleepiness. Significant negative covariations were obtained between body temperature and sleepiness, and auditory threshold and performance. From these results it was concluded that the most reliable predictors of behavior upon awakening were: the amount of wakefulness prior to sleep, the total amount of accrued sleep, circadian time as indexed by body temperature, and depth of sleep.