. National surveys in the past five years have shown a 7% increase in the number of workers sleeping six hours or less and a 9% decrease in those sleeping seven hours or more. 1 Decreased nocturnal sleep can lead to sleepiness, errors, and accidents during the daytime. 2 Even after a normal sleep at night, the mid-afternoon period (around 14:00) is characterized by decreased alertness, poor performance, and frequent errors in the workplace; or what has been recognized as the "post-lunch dip." 3-5 Thus, it is important to seek practical solutions to diminished daytime function resulting from less sleep.Recent research has documented that naps of less than 30 minutes are a promising strategy for counteracting the effects of a short sleep period of 4-5 hours the preceding night. [6][7][8][9] This research evaluated the roles of repeated (polyphasic) naps or a single nap taken in the morning or mid-afternoon. Such patterns of napping, however, seem unfeasible in most work settings, because of the obvious conflict with work schedules. In a previous study, we hypothesized that a post-lunch rest is an appropriate time to take a nap in the workplace, and therefore investigated the effects of a 15-minute nap taken at 12:30. 10 The results showed greater alertness and performance after the 15-min ute nap than after no nap or a 45-minute nap. These findings are in agreement with the latest evidence showing improved alertness after a 20-minute nap scheduled at 12:20 in a study in which the effects of meals and time cues were controlled. 11 However, since the subjects in both studies had a normal sleep the night before testing, the effects of a post-lunch nap following a short sleep remain to be determined.The purpose of the present study was to examine whether a 15-minute nap taken during post-lunch rest improves subsequent alertness and performance under prior sleep deficit. The effects of the nap were assessed by the P300 event-related potential (ERP) and neurobehavioral tasks. We also investigated the autonomic effects of the nap by measuring the electrocardiographic (ECG) R-R interval variability.
METHODS
SubjectsTwelve healthy students served as subjects for this experiment (7 males and 5 females, mean age 22.1±1.6 SD years). None of them reported sleep complaints or any history of medical disorders. Their habitual sleep duration was Abstract: 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...