Maintenance of alertness and performance by a brief nap after lunch under prior sleep deficit

We examined the effects of a 15-min nap after lunch on subsequent alertness, performance, and autonomic function following a short sleep the preceding night. Subjects were 12 healthy students who had slept for only 4 hours the night before being tested. They experienced both nap and no-nap conditions in a counterbalanced order, at least a week apart. The nap condition included a 15-min nap opportunity (12:30-12:45) in bed with polygraphic monitoring. We measured the P300 event-related potential, subjective sleepiness (Visual Analog Scale), and electrocardiogram (ECG) at 10:00, 13:15, and 16:15, and task performance (logical reasoning and digit span) at 10:00, 11:30, 13:15, 14:45, 16:15, and 17:45. Mean home sleep measured by actigraphy was 3.5 hours under both conditions. At 13:15, the P300 latency after the nap was significantly shorter than after no nap, but its amplitude was not affected by napping. Subjective sleepiness at 13:15 and 14:45 was significantly lower, and accuracy of logical reasoning at 13:15 was significantly higher after the nap than after no nap. No other performance measures or the ECG R-R interval variability parameters differed significantly between the nap and no-nap conditions. Mean total sleep time during the nap was 10.2 min, and no stage 3 and 4 sleep was observed. The above results suggest that under prior sleep deficit, a 15-min nap during post-lunch rest maintains subsequent alertness and performance, particularly in the mid-afternoon.