Sleep Restrictions and Sleep Deprivation Introduction Global Trends of Increased Work, Domestic and Social Demands, and Associated Nocturnal Sleep Reduction and Daytime Sleepiness Have

GLOBAL TRENDS OF INCREASED WORK, DOMESTIC AND SOCIAL DEMANDS, AND ASSOCIATED NOCTURNAL SLEEP REDUCTION AND DAYTIME SLEEPINESS HAVE stimulated research interest into countermeasures of this daytime sleepiness. One countermeasure that has received attention in recent years is brief napping. Naps as brief as 19.8,1 10.8,2 10.2,3 10,4,5 and 9.1 minutes6 have been shown to improve alertness and performance following restricted nocturnal sleep. Similar benefits have also been observed after normal nocturnal sleep from brief naps of mean durations of 20,7,8 15,9 and 7.310 minutes. In addition, brief workplace naps during a night shift have also been shown to be beneficial.11,12 Brief naps have been shown to be at least as restorative as longer naps.4,10 Comparing a 15-minute nap opportunity (mean sleep duration 7.3 minutes) with a 45-minute nap opportunity (mean sleep duration 30.1 minutes) after a night of normal sleep, Takahashi et al10 observed significantly improved alertness 30 minutes after the 15-minute nap opportunity and comparable improvements for the 2 nap conditions 3 hours after napping. Under conditions of mildly restricted nocturnal sleep, Tietzel and Lack4 found that an afternoon nap of precisely 10 minutes’ sleep was at least as recuperative as a 30-minute nap in terms of improved alertness and performance for an hour following the napping. However, it is important to recognize the limitations of these studies. In terms of the Takahashi et al study,10 dependent measures were administered only twice. In the Tietzel and Lack4 study, postnap testing was limited to 1 hour. Hence, the longer nap may have ultimately shown greater benefits had greater time been allowed for postnap testing. In fact, after a night of total sleep loss, longer naps (i.e., 1 to 2 hours) have been shown to be more alerting than brief naps for at least 3 hours after napping.13,14 Although longer naps may be recuperative, especially following total sleep deprivation, any benefit of longer naps must be weighed against their practical disadvantages of greater length of time consumed by the nap and greater sleep inertia after the nap and their possible detrimental impact on subsequent nocturnal sleep. Sleep inertia refers to a period of disorientation, confusion, and sleepiness that an individual may experience immediately upon awakening from sleep.15,16 Since sleep inertia appears to be directly related to duration of slow-wave sleep during a sleep episode, it follows that sleep inertia will be greater following longer naps that typically contain more slow-wave activity than shorter naps.17-19 Even naps with as much as 30 minutes of sleep show the negative effects of sleep inertia.4 Considering that there have been no studies comparing more than 2 nap lengths, there is clearly a need to measure the effects of several different length naps over an extended postnap period. Therefore, the present investigation examined the 3-hour time course of effects following 5-, 10-, 20-, and 30-minute naps after a night of mildly restricted sleep. A practical aim of this study was to provide information that would allow a more informed decision regarding the most effective nap duration for improving alertness and cognitive performance in the afternoon. In addition to this practical consideration, a careful examination A Brief Afternoon Nap Following Nocturnal Sleep Restriction: Which Nap Duration is Most Recuperative?