Being well-rested helps the brain absorb new information. What if a good night's sleep also helps you remember what you've learned?

Sleeping on newly acquired knowledge boosts recall, according to a recent study published in Psychological Science, a journal of the Association for Psychological Science. 

The findings indicate that sleeping between study sessions may make it easier to recall what you've learned and also to relearn what you've forgotten.

What the Study Showed

Sleep researchers have long known that both repeated practice and sleep can help improve memory. What has been less clear is how repetition and sleep combine to influence memory. 

Lead study author Stephanie Mazza and colleagues at the University of Lyon in France hypothesized that sleeping between study sessions might sharpen the relearning process. This could reduce the effort needed to commit information to memory.

"Our results suggest that sleep between practice sessions leads to a twofold advantage, reducing the time spent relearning and ensuring a much better long-term retention than practice alone," Mazza tells Science Daily, noting that previous research had shown that sleeping after learning is a good strategy. “Now we show that sleeping between two learning sessions greatly improves such a strategy."

How They Did It

The researchers randomly assigned 40 French adults to either a "sleep" group or a "wake" group. They tested the participants by assigning them to learn material they almost certainly didn't know: words in the African language Swahili.

At the first session, all participants received 16 French-Swahili word pairs in random order. 

After briefly studying a word pair, participants typed the French version of a Swahili word. Participants continued until they had correctly translated each word pair.

Twelve hours after the initial session, the participants repeated the translation task.

The major difference between the wake and sleep groups appeared during the second translation sessions. The wake group worked through a morning session, then later the same day, an evening session.

The sleep group had an evening session first, went about their regular overnight sleep routine, and then resumed for a morning study session the following day.

Faster Learning, Less Effort

The two groups showed no difference in how many words they could recall during their first session. But after 12 hours, the groups split: those who slept between sessions learned the words more quickly and easily, an average of 10 of the 16 words compared to an average of 7.5 words for the nonsleepers.

People in the sleep group needed about three attempts to recall all 16 word pairs. The wake group needed about six attempts each.

Mazza says sleep appeared to transform memories that were “not explicitly accessible" when relearning began: "Such transformation allowed subjects to re-encode information faster and to save time during the relearning session."

Lasting Benefits

The sleep-bolstered memory boost seemed to last over time. The researchers retested the participants a week later and found the sleep group outperformed their peers again. This benefit was still noticeable six months later.

If you're seeking an easy, effective way to remember information over longer periods of time with less effort – and who isn't – try study sessions on multiple days, interspersed with overnight sleep.

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