I don’t know about you, but I can’t get through my day without a nice little afternoon nap. It usually leaves me refreshed, recharged, and ready to attack the rest of my day. But there are those off-occasions when I wake up from a nap feeling like I just got hit by a bus. Why does this overwhelming feeling of grogginess happen? I will explore this question through this blog (and potentially* a couple others).
The feeling of grogginess experienced after waking up from a nap is known as “sleep inertia”. Sleep inertia occurs when you wake up from “REM” (rapid eye movement) sleep, the deepest level of sleeping. When you wake up during REM, you still have high levels of melatonin, causing sleepiness. The longer you sleep, the higher level of melatonin is observed during REM stage.
Does this mean I should avoid long naps? Well, not necessarily. With the intentions of finding the ideal amount of sleep for astronauts, David Dinges, a professor at the University of Pennsylvania School of Medicine, led an experiment in which 91 volunteers spent 10 days living on one of 18 different sleep schedules, all in a laboratory setting (NASA). The experiments measured subjects’ cognitive functions as well as body temperature and hormone levels. The results were interesting, as they found that longer naps actually benefited certain cognitive functions, but not others. Dinge says “To our amazement, working memory performance benefited from the naps, [but] vigilance and basic alertness did not benefit very much”. Dinge found that the total amount of sleep during 24 hours remained the most important factor.
But, since these subjects took longer naps, wouldn’t that mean they were in REM and should have actually felt groggy? Again, not necessarily. REM, as well as the other stages of sleep, occurs in a cycle. This cycle is best interpreted through a visual:
As you can see from the graph, REM occurs roughly around the one hour mark, then returns to the lighter levels of sleep. I believe the subjects in Dinge’s study slept through a cycle of REM and awoke in a lighter stage of sleep. That would explain the improved cognitive functions since REM has been shown to boost memory processing, creativity, as well as emotional and procedural memory (Pinola).
Now one could argue that Dinge’s study was flawed. Ninety-one subjects is by no means a large sample size, especially if he was testing eighteen different sleep cycles. The study also doesn’t disclose whether or not there was a control of any third variables or rule out reverse-causation (maybe smarter people sleep better). With that in mind though, we should seriously consider the effect of the sleep cycle on naps. It’s not a matter of how long you nap, but rather where in the sleep cycle you wake up in that has the impact on grogginess. I look forward to further looking into the perfect nap in my next blog.
Works Cited:
NASA. “NASA Naps – NASA Science.” NASA Science. NASA, 3 June 2005. Web. 8 Nov. 2014. <http://science.nasa.gov/science-news/science-at-nasa/2005/03jun_naps/>.
Pinola, Melanie. “How Long to Nap for the Biggest Brain Benefits.” Lifehacker. KINJA, 4 Sept. 2013. Web. 8 Nov. 2014. <http://lifehacker.com/how-long-to-nap-for-the-biggest-brain-benefits-1251546669>.
Valley Sleep Center. “12 Facts About Sleep Inertia.” 12 Facts About Sleep Inertia. 3 Nov. 2014. Web. 8 Nov. 2014. <http://valleysleepcenter.com/blog/12-facts-about-sleep-inertia/>.