Summary: Short naps of up to 60 minutes do not fully reverse the cognitive effects of a night without sleep, according to a new study. Still, the amount of slow-wave sleep achieved during a nap was linked to smaller deficits on some tasks.
Source: Michigan State University
A daytime nap cannot fully replace a sleepless night, reports new research from Michigan State University’s Sleep and Learning Lab.
“Our goal was to understand which cognitive deficits result from sleep deprivation and whether brief naps can reduce those deficits,” said Kimberly Fenn, associate professor at Michigan State University, director of the Sleep and Learning Lab and lead author of the study. “We found that short naps of 30 or 60 minutes produced no measurable group-level improvement compared with staying awake.”
Published in the journal Sleep, the study is among the first to evaluate the practical effectiveness of short naps—sessions many people use because of busy schedules. The research focused on two broad cognitive processes: vigilant attention and placekeeping, the ability to complete sequential steps in order without skipping or repeating them, even after interruptions.
Although brief naps did not eliminate the effects of sleep loss overall, Fenn and her team found an important nuance: when naps contained a greater amount of slow-wave sleep (SWS)—the deepest, most restorative sleep stage—participants showed fewer performance deficits.
Slow-wave sleep is characterized by high-amplitude, low-frequency brain waves and coincides with the body’s most restful state: relaxed muscles, slower heart rate and reduced breathing. “SWS is the most critical stage for recovery,” Fenn explained. “When people go without sleep they accumulate a homeostatic need for sleep, and particularly for SWS. When they do sleep, they enter SWS and spend substantial time there, which helps restore function.”
Fenn’s team, which included MSU professor Erik Altmann and Michelle Stepan, a recent MSU alumna now at the University of Pittsburgh, recruited approximately 275 college-aged volunteers for the experiment. Participants completed initial cognitive testing in the evening at MSU’s Sleep and Learning Lab and were then randomly assigned to one of three conditions: go home and sleep normally, remain in the lab overnight with the opportunity to nap for either 30 or 60 minutes, or remain in the lab overnight without napping.
Participants who stayed overnight returned the next morning to repeat the cognitive tasks. Overall, those who took short naps still showed the effects of sleep deprivation and made significantly more errors than participants who had slept at home. Nevertheless, the researchers observed a clear relationship between the amount of SWS obtained during a nap and performance: roughly every 10 additional minutes of slow-wave sleep correlated with an approximately 4% reduction in errors following interruptions.
Though a 4% improvement may appear modest, the authors note it can be meaningful in high-stakes environments where sleep-deprived operators face critical decisions—fields such as medicine, law enforcement or commercial driving. Any decrease in errors under sleep-deprived conditions can have important real-world consequences.
“Participants who achieved more slow-wave sleep during their brief nap tended to make fewer errors on both the vigilance and sequence-maintenance tasks,” Fenn said. “Still, even those with relatively more SWS did not perform as well as participants who had a full night’s sleep.”
The study’s main takeaway is clear: short naps, while potentially helpful when they include deeper sleep stages, are not a substitute for a full night of restorative sleep. Fenn emphasizes the importance of prioritizing nightly sleep for cognitive health and reliable performance.
About this sleep research news
Author: Caroline Brooks
Source: Michigan State University
Contact: Caroline Brooks – Michigan State University
Image: The image is in the public domain
Original Research: Closed access. “Slow-wave sleep during a brief nap is related to reduced cognitive deficits during sleep deprivation” by Kimberly Fenn et al. Published in Sleep (DOI: 10.1093/sleep/zsab152)
Abstract
Slow-wave sleep during a brief nap is related to reduced cognitive deficits during sleep deprivation
Brief naps may help reduce some impairments caused by sleep deprivation, but evidence on very short naps is limited. This study examined the effect of a 30- or 60-minute nap opportunity during an overnight period of sleep deprivation on vigilant attention and placekeeping.
In the evening, participants (N ≈ 280 in the study sample reported in the abstract) completed a sequential task (UNRAVEL) and a vigilance test (Psychomotor Vigilance Task, PVT) and were randomly assigned to either sleep at home or remain awake overnight. Participants assigned to the deprivation condition were further randomized to receive no nap opportunity, a 30-minute opportunity, or a 60-minute opportunity. Those who napped were monitored with polysomnography to measure sleep stages.
The following morning, all participants repeated the UNRAVEL and PVT tests. Sleep deprivation impaired performance on both tasks, and the short nap opportunities tested did not produce group-level reductions in impairment. However, within the napping group, greater time spent in slow-wave sleep was associated with smaller performance deficits on both measures. The authors interpret these findings in terms of SWS’s role in reducing sleep pressure and supporting memory consolidation.