The Science Behind the Power Nap

When you think about the sheer amount of “stuff” that we do every single day, it is astounding that we only sleep once in a typical 24 hour cycle. We make three meals a day (and maybe even more if we are being honest to our occasional midnight snacking), we walk the dog, we go to class or our job, we write our dissertation, drive the kids to school, and the list goes on.

According to the CDC, one third of people admit that they get less than seven hours of sleep at night, which is the typical amount of hours that adults should be sleeping.

This becomes even more shocking given the statistic that 85% of mammals are polyphasic, or they sleep more than once a day. As astounding as it is, humans accomplish much more than animals but still sleep for less hours.

The National Commission on Sleep Disorders (1993) estimates that sleep deprivation costs $150 billion a year in reduced productivity and higher stress. Further, the National Sleep Foundation also reports the results of a Gallup poll (2000) where 51% of a random sample of adults admit that sleep deprivation negatively affects their job performance. They report that they are fatigued and drowsy, and they are unable to think clearly under these conditions. They are prone to bad judgement and are more likely to employ faulty reasoning.

Recently, much research has been done to research the benefits of the “power nap”, or a short sleep taken during the workday to increase one’s mental alertness. A study was done to prove that there is a correlation between an ultra-short episode of sleep (or a power nap) and declarative memory performance. Various studies had demonstrated that a night of sleep had a beneficial effect on the retention of previously acquired declarative material and the experimenters were researching whether this effect extended to daytime naps as well.

In the first experiment, scientists researched recall capabilities of thirty words after a sixty minute retention period of either daytime napping or an everyday waking activity. They tested this on twenty six university students between the ages of twenty and twenty nine. They had to memorize thirty adjectives in two minutes. After the two minutes, they had to repeat as many of the adjectives as they could with no time limit. They were also told that the order of the words was irrelevant for scoring. Each of the subjects underwent both the napping condition and the waking condition with a week in between the conditions so as to prevent carry-over effects. In the napping condition, electrodes were placed on the subject to test for the sleep and they were in a sound attenuated sleep chamber to enable napping. After fifty minutes the subject was awoken through the experimenter calling their name on the intercom. They took off the electrodes in the next ten minutes, which at this point the subject was fully awake. They then tested for recall of the previously memorized words. In the wake condition, the subject played simple computer games that were strictly nonverbal so as to not interfere with the words that the subject had memorized.

On average, the students remembered two more words when they had napped as opposed to when they were awake. Memory performance was significantly enhanced after napping as opposed to waking activity. Interestingly, enhancement of the recall of the words was not correlated with time spent in slow wave sleep or the total amount of sleep time within the napping condition. In other words, if you just lie down and “pretend” to nap, it is more likely that you will remember the information better than if you went about doing your daily activities.

A similar second experiment was done that was designed to clarify the role of total sleep time in memory retention. There were eighteen university students between the ages of twenty one and twenty nine. None of them had taken place in the first experiment. Each student went through three phases of waking activity, short napping of no more than six minutes, and long napping. There was a week in between each test to prevent carry-over effects.  In comparing word recall after all three conditions of waking, short napping, and long napping, it was found that there was superior recall for both napping conditions in contrast to waking. On average, there were eight words recalled when short napping, nine words recalled when long napping, and six words recalled when participating in the waking activity. Even a nap as short as six minutes significantly boosted memory recall. Even though one to two words extra might not seem so impressive, it is statistically significant because there were only thirty words that needed to be memorized.

These results demonstrate that even an ultra short period of sleep is sufficient to enhance memory processing, retention, and recall. The researchers suggest that the mere onset of sleep may initiate the active processes of consolidation which, once it is triggered, remain effective once the person has woken up. Perhaps this a neurobiological, most likely hippocampus related, process, which once triggered with sleep onset does not need any additional maintenance such as actually sleeping.

So whenever we are feeling extra tired during the day, how many minutes should we power nap? Dr. Sara Mednick, an assistant professor of psychology at the University of California, Riverside breaks down the different types of naps and which one you should utilize for maximum productivity. The ten to twenty minute nap is perfect for a quick energy boost and improved alertness. This nap is filled with NREM sleep, or non rapid eye movement, which makes it easier for you to go about your day and not feel groggy when you wake up. There is the thirty minute nap which increases concentration, alertness, creativity, and mood. Research conducted by NASA illustrates the power of the thirty minute nap. Their research concluded that pilots and astronauts that take a nap around forty minutes, called the “NASA nap”, in flight (while the co-pilot takes the controls) improved performance by 34% and were 100% more alert.

There is also the sixty minute nap, which is best if you want to improve your memory for faces, names, and facts. The sixty minute nap includes the deepest type of sleep, which is the slow-wave sleep. The downside of this nap is that you might feel groggy after waking up because you were in such a deep sleep, so it might take you some time to recover from it.

Lastly, there is the ninety minute nap which is where you undergo a full sleep cycle, which includes both the lighter and deeper stages of sleep and REM sleep which is where our dreams occur. This sleep cycle improves emotional and procedural memory and creativity. Sleeping for ninety minutes prevents sleep inertia,which one can get after a thirty or sixty minute nap, because you are not interrupting the ninety minute sleep cycle.

Mednick also lists the four different types of power naps. There is the planned nap, which involves taking a nap before you get tired. This is especially beneficial if you know that you have a long night ahead of you. The second type of power nap is the emergency nap, which is when you are so tired that you cannot engage in your current activity. There is also the habitual nap, which is a nap that you take at the same time everyday, and the appetitive nap, when you are addicted to napping and nap only out of pure enjoyment.  

There is also an incredible biological benefit to power napping. The National Heart, Lung, and Blood Institute report that the most common health conditions that are linked to poor sleep are heart failure, heart disease, obesity, diabetes, hypertension, stroke, depression, and ADHD. Taking advantage of a power nap can go a long way toward helping you avoid these health problems. In a study done in Greece, researchers discovered that adult males who took an afternoon nap at least three times a week were 37% less likely to die from a heart-related disease compared to men who never took an afternoon nap.

So how do we accomplish these productive power naps? For one, you need to trick your brain into thinking it is night time. Shut the lights, close the curtains, put on an eye mask, and get rid of as much natural light as possible. By the same token, this is also why you should not look at your phone before you go to sleep. The artificial light of your phone makes your brain think that it is still day time, which makes it harder for you to fall asleep. Trick your brain into thinking that it is time to go to sleep by laying down, getting a blanket, and getting comfortable.

Try to not power nap after 4:00 in the afternoon, as it might interrupt your sleeping schedule that night. Also, the later in the afternoon that you go to sleep, the more deeply you will fall asleep, making it harder to wake up from it. In addition, to maximize performance after you wake up, drink a cup of coffee or green tea right before you fall asleep. It takes caffeine twenty minutes to kick in and you will get an extra boost of energy for when you wake up.

Power naps improve creative problem solving, verbal memory, perceptual learning, statistical learning, and object learning. It improves performance in math, symbol recognition, logical reasoning, and our reaction times. Napping is also incredibly beneficial for our physical well-being. “You snooze, you lose” never applies to the case of the power nap.

References:

LahlO, Pietrowsky P, Wispel C, Willigens B (2008) An ultra short episode of sleep is sufficient to promote declarative memory performance. Journal of Sleep Research 17: 3-10.

Baxter,Vern, and Steve Kroll-Smith. “Normalizing the Workplace Nap: Blurring the Boundaries between Public and Private Space and Time.” Current Sociology, vol. 53, no. 1, Jan. 2005, pp. 33–55, doi:10.1177/0011392105048287.

MacDowell,Camden. "Want to Remember Paris? Take a Nap!."

Mednick, Sara, Ken Nakayama, and Robert Stickgold. "Sleep-dependent learning: a nap is as good as a night." Nature neuroscience 6.7 (2003): 697-698.

https://www.lunella.com/blog/the-science-behind-napping-power-nap-benefits-considerations-and-tips

 

By Elisheva Hoffman
Just Five Minutes a Day
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