Sleep deprivation causes people to perform poorly on cognitive tests but some believe short naps are all they need to remain sharp. Research shows it’s not actually true. Scientists at the Michigan State University sleep lab found people who used short naps to make up for lack of sleep performed much worse in cognitive testing than those who got plenty of sleep in the first place.
"We are interested in understanding cognitive deficits associated with sleep deprivation," said Kimberly Fenn, director of MSU's Sleep and Learning Lab. "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."
The study results were published in the journal Sleep. Researchers focused on the effectiveness of shorter naps because it’s believed most people are too busy for longer rest periods.
"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 said.
Slow-wave sleep (SWS) is the deepest stage of sleep. It is considered the most restorative because the body is most relaxed, muscles are at ease and heart rate and respiration are at their lowest levels. It is characterized by high amplitude, low frequency brain waves.
"SWS is the most important stage of sleep," Fenn said. "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."
Researchers had a group of 275 college-aged study participants complete some cognitive tasks that required them to complete a series of steps in a specific order without repeating or skipping any, even while being interrupted.
The group was then randomly separated them into three smaller groups. One group went home to sleep while the other two groups stayed at the lab overnight. One of those groups was totally deprived of sleep while the other took a 30 or 60 minute nap. The study participants assembled again the next morning to repeat the same cognitive tasks.
"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," Fenn said. "However, every 10-minute increase in SWS reduced errors after interruptions by about 4%.”
While the error reduction may seem small with the 10 extra minutes of quality sleep, Fenn believes it’s enough to make a potentially life-saving difference in traditionally sleep deprived professions such as truck driver, surgeon or police officer.
"Individuals who obtained more SWS tended to show reduced errors on both tasks," Fenn said. "However, they still showed worse performance than the participants who slept."