Splitting up sleep may help teenagers learn

Teenagers who split their sleep into an overnight chunk and an afternoon snooze learned complex information better than those who got all their sleep at night, according to a two-week study.

Experts say the research, published in January 2022 in the journal Sleep, is a testament to the cognitive boost napping can provide — but they warn it’s not a sign that young adults should upend their sleep schedules.

It’s well-known among scientists that sleep helps sort and solidify memories. But this study targets a specific piece of the memory puzzle: schemas, or the frameworks we use to make sense of new information. From a research perspective, “not much has been done about schemas and sleep, and much less about napping and schemas,” said lead author Hosein Aghayan Golkashani, a sleep and cognition researcher at the National University of Singapore.

To get a sense of how schemas work, imagine you’re learning what a cat is, suggested Jessica March, who studies sleep and cognition at Royal Holloway, University of London. Your schema for the concept “cat” will be a collection of traits that you gather from the felines you come across: furry, friendly, whiskered.

“Then you meet a cat and it hisses at you,” said March, who was not involved with this research. Realizing, perhaps sadly, that the “friendly” trait isn’t universal, you will tweak your schema accordingly.

“Schema updating is arguably one of the most important types of memory consolidation that humans do in order to be flexible creatures,” said Tony Cunningham, who studies sleep and memory at Harvard Medical School and was not part of this research.

The authors of this study explored how napping affects that updating process. In an empty school dormitory, they randomly assigned 53 people aged 15 to 19 years old to two groups. Both spent the same total amount of time in bed per day, but it was divided up differently: One group was allowed eight hours at night, while the other got 6 ½ hours plus a 90-minute afternoon nap.

The experiment lasted two weeks. At the start, participants learned a type of schema: They saw photos of strangers and learned how those strangers had scored relative to one another on a hypothetical test. Later, the strangers’ score rankings shifted when new photos were added or the photos were rearranged. Participants were quizzed on the rankings after each change and at the experiment’s end.

The napping group consistently performed better, suggesting they updated their schemas more effectively. By the final quiz, nappers correctly answered 82% of questions on average, outstripping non-nappers by 10 percentage points.

There are a couple of potential explanations, Golkashani said. For one thing, “you get drowsy during the day,” he said. “The nap clears this sleep pressure and optimizes learning.”

What the brain is doing during the nap might also play a role, Golkashani said. To explain this, he pointed to another part of the experiment. The team tested all participants, nap and no-nap alike, on a list of photos they didn’t have a chance to acquaint themselves with at the start; in other words, they had no schema. Across the board, having a schema led to better results than not having one — but just how much better depended on sleepers’ brain waves. Participants who had a higher density of spiky electrical signals known as “fast spindles,” which have been linked to memory benefits in the past, saw more of a boost from having a schema.

Golkashani emphasized that correlation doesn’t necessarily mean the spindles were responsible. And while the team didn’t find significant differences in spindle density between the nap and no-nap groups, he says he thinks timing might be crucial: Having the chance to get some shut-eye and generate spindles in the middle of the learning process, rather than just at night, may have helped nappers learn better.

He noted this research only applies to adolescents. But that’s an important group, said Temitayo Oyegbile-Chidi, a clinician and researcher in sleep medicine at the University of California, Davis. Adolescents’ sleep cycle patterns are unique in that they are delayed, she said, meaning teens tend to go to sleep later and sleep in longer. Plus, they’re often not getting the sleep they need. 

So, should high schoolers chop up their sleep into shorter nights and daytime naps? Not so fast, said Oyegbile-Chidi, who was not involved in the study. “There are so many other things you need sleep for,” she said. She noted that it’s critical for a range of processes — like hormone secretion, among many others — so changing your sleep schedule could affect things besides cognition.

Unraveling exactly what made napping effective in the study, Cunningham said, could be a useful next step.

“This is a great study for speaking to the power of napping,” he said. “You want to make sure you know why it’s happening the way it is.”