Sleep Study Reveals Influence of 90-Minute Power Naps on Decision-Making

Treat yourself (and your brain).

There’s a mountain of research that shows the frightening downsides of not getting enough sleep, which range from the development of mental health issues to loneliness. Fortunately for those of us who have issues sleeping or simply don’t have time to do enough of, some research suggests napping can at least improve some of the symptoms of being tired. According to a study published in the Journal of Sleep Research, a well-timed nap could prevent the decision-making mind from getting led astray by subconscious influences.

Led by Liz Coulthard, Ph.D., a senior lecturer who studies cognitive neuroscience, and research associate Netasha Shaikh, Ph.D., both at the University of Bristol’s Medical School in the United Kingdom, this trial investigated the effects of a 90-minute nap (quite a long one) on the ability of people to sort through the subconscious factors that influence their decisions.

In the study, 16 volunteers took 90-minute naps — enough to equate to a full sleep cycle — before completing a series of tricky association tests meant to test the brain’s decision-making in deliberately confounding circumstances. In real life, subconscious factors like hunger can lead to impulsive decision making; in this test, the researchers used words to subconsciously complicate the decision-making process.

This trial was designed to make it difficult for participants to make the right decision so the team could observe how sleep affected that process. 

Journal of Sleep Research 

Participants were told to simply identify a word that flashed on the screen as a negative or positive word. Of course, it wasn’t as simple as that. Right before they saw the main word, a different positive or negative word flashed for 33 milliseconds — so briefly that it would be impossible to consciously register what that word was but long enough for the subconscious to pick up on it. This was the “unconscious prime.”

As you might expect, earlier studies have shown that seeing an unconscious prime that’s congruent with the main word (for example, “peace” followed by “happy,” both positive words) makes it easier to categorize the main word. But in non-congruent word pairs it’s much trickier to identify the second word, regardless of how sleep deprived you might be.

Nevertheless, the 16 volunteers who performed the test immediately after a 90-minute nap placed words into their correct categories faster — indicating that the task was easier than it had been before they retreated to their beds in the lab. The average time for participants to identify the words in congruent pairs dropped from over 670 milliseconds before napping to just over 610 milliseconds after napping. It’s a small difference, but the researchers think it can be chalked up to what’s going on beneath the surface.

This study showed that 90 minute naps improved decision making by improving our ability to disentangle unconscious processing from conscious processing 

The Journal of Sleep Research 

This difference, the researchers write, indicate that sleep increases processing in “fast subcortical pathways” — circuits within the brain that are constantly processing information without your knowledge, though the study didn’t include any brain imaging to confirm this. In a sense, napping appeared to help the participants ignore the conflicting information that could potentially taint their decision.

These are early findings on a small group of individuals, so it might not be time to invest in a “nap-nook” just yet. But their findings go a long way toward understanding the myriad influences that lead us to make decisions the way we do. Sleep, even in short, 90-minute segments, seems to be a way to wade through the unconscious noise and focus on the task at hand.

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