Behavioural and performance characteristics of sleep inertia following awakening from naps

grantor: University of TorontoThis study examined (a) time of night effects on sleep inertia upon awakening from naps and, (b) whether subjective ratings are in concordance with cognitive performance measures of sleep inertia. Thirteen healthy males (aged 20-35) completed two 34 hr protocols. Subjects were randomly assigned to a 90 min afternoon nap scheduled at either 1300h (protocol A) or 1600h (protocol B) followed by a series of four 60 min nap opportunities scheduled at 0000h, 0130h, 0300h, and 0430h (protocol A), and at 0300h, 0430h, 0600, and 0730h (protocol B). Cognitive performance and subjective ratings were derived from hourly test sessions (including immediately before and after the naps) of logical reasoning, serial reaction time, synthetic work (multi-task performance task), and self-reports of fatigue, sleepiness, drowsiness, and mood. Sleep inertia effects were determined by comparing pre- and post-nap measurements using repeated measures analysis of variance. Afternoon naps did not result in any significant sleep inertia effects as measured by performance tasks. Significant sleep inertia effects (pre- vs post-nap performance measures) occurred after naps scheduled at 0000h, 0130h, and 0300h in both protocols but not with naps at 0600h and 0730h in protocol B. After 15 min of wakefulness, deteriorated performance measured upon awakening always significantly recovered in protocol A but not after the 0430h and 0600h naps in protocol B. Therefore, differences between pre- and post-nap performances in protocol B became smaller resulting in apparent smaller sleep inertia effects. When only post-nap performances were compared between naps and protocols, no significant differences in sleep inertia effects were found. Sleep inertia effects were found for fatigue and sleepiness ratings after the 1300h and midnight naps in protocol A, and the 1600h nap in protocol B. Nocturnal subjective ratings did not show any significant improvements after 15 min spent awake. In conclusion, the severity of sleep inertia effects on cognitive performances does not vary with time of night but the duration of impairments was longer following 0430h and 0600h naps. Subjective ratings of fatigue, sleepiness, drowsiness, and mood do not reflect sleep inertia effects as measured with cognitive performance tasks.Ph.D