A nap during the day won’t give you relief from a sleepless night, according to a study from Michigan State University’s Sleep and Learning Lab1.

We are interested in understanding cognitive deficits associated with sleep deprivation. In this study, we wanted to know if a short nap during the deprivation period would mitigate these deficits. We found that short naps of 30 or 60 minutes did not show any measurable effects,

said Kimberly Fenn, director of the Sleep and Learning Lab. The research is one of the first to measure the effectiveness of shorter naps — which are often all people have time to fit into their busy schedules.

While short naps didn’t show measurable effects on relieving the effects of sleep deprivation, we found that the amount of slow-wave sleep that participants obtained during the nap was related to reduced impairments associated with sleep deprivation,

Fenn adds.

Slow-wave Sleep

Slow-wave sleep (SWS), is the deepest and most restorative stage of sleep. It is marked by high amplitude, low frequency brain waves, and is the sleep stage when your body is most relaxed; your muscles are at ease, and your heart rate and respiration are at their slowest.

SWS is the most important stage of sleep. When someone goes without sleep for a period of time, even just during the day, they build up a need for sleep; in particular, they build up a need for SWS. When individuals go to sleep each night, they will soon enter into SWS and spend a substantial amount of time in this stage,

Fenn says.

The research team, which included colleague Erik Altmann, professor of psychology, and Michelle Stepan, a recent alumna currently working at the University of Pittsburgh, recruited 275 college-aged participants for the study.

Attention And Placekeeping

The participants completed cognitive tasks when arriving at the lab in the evening and were then randomly assigned to three groups. The first group was sent home to sleep; the second stayed at the lab overnight and had the opportunity to take either a 30 or a 60 minute nap; and the third did not nap at all in the deprivation condition.

The next morning, participants reconvened in the lab to repeat the cognitive tasks, which measured attention and placekeeping (ability to complete a series of steps in a specific order without skipping or repeating them after being interrupted).

The group that stayed overnight and took short naps still suffered from the effects of sleep deprivation and made significantly more errors on the tasks than their counterparts who went home and obtained a full night of sleep. However, every 10-minute increase in SWS reduced errors after interruptions by about 4%,

Fenn says.

These numbers may seem small but when considering the types of errors that are likely to occur in sleep-deprived workers — like those of surgeons, police officers, or truck drivers — a 4% decrease in errors could potentially save lives

The findings highlight the importance of prioritizing sleep and that naps — even if they include SWS — cannot replace a full night of sleep.


  1. Michelle E Stepan, Erik M Altmann, Kimberly M Fenn. Slow-wave sleep during a brief nap is related to reduced cognitive deficits during sleep deprivation. Sleep, 2021;, zsab152 ↩︎


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