Sleeping between study sessions could make it easier to remember what was studied and relearn forgotten information, even 6 months later, according to a new study from Psychological Science.
While analyses have revealed both repeated practice and sleep can help enhance memory, the study team said there is little research looking into how repetition and sleep affect memory when used in tandem.
“Our results suggest that interleaving 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,” Stephanie Mazza, psychological scientist at the University of Lyon in France, said in a news release. “Previous research suggested that sleeping after learning is definitely a good strategy, but now we show that sleeping between two learning sessions greatly improves such a strategy.”
Looks Like It’s Time to Take a Nap
In the study, 40 adults were arbitrarily allotted to either a “sleep” group or a “wake” group. In the initial session, all volunteers were offered 16 French-Swahili word couples in arbitrary order. After investigating a pair for 7 seconds, the Swahili word was shown on a computer screen and volunteers were asked to type the French translation. The proper word pair was then revealed for 4 seconds. Any words that were not accurately translated were shown again, until each word couple had been properly translated.
Twelve hours after the primary session, the volunteers did the recall task again, doing the whole list of words until all 16 words were correctly translated. The “wake” group had their first session in the morning and second session later in the day. The “sleep” group concluded the first session in the evening, slept, and performed the second session in the morning.
In the first session, the groups exhibited no difference in performance. After 12 hours, however, volunteers who had slept between sessions recalled 10 of the 16 words, on average, while those who hadn’t slept recalled only around 7.5 words. And when it came to relearning, those who had slept required only around 3 trials to recall all 16 words, while those who had remained awake needed around 6 trials.
Ultimately, both groups learned all 16 word pairs, but sleeping between sessions appeared to permit volunteers to do so faster and with less effort.
“Memories that were not explicitly accessible at the beginning of relearning appeared to have been transformed by sleep in some way,” Mazza said. “Such transformation allowed subjects to re-encode information faster and to save time during the relearning session.”
The memory improvement that volunteers received from sleeping between sessions appeared to last over time. Follow-up tests revealed volunteers in the sleep group outperformed their peers on the recall test one week later. The sleep group recalled around 15 word pairs, as opposed to the wake group, who could recall around 11 word pairs. This benefit was still apparent 6 months later.
The advantages of sleep could not be attributed to volunteers’ sleep quality or sleepiness, or to their short-term or long-term memory capacity, the researchers said, as the two groups exhibited no variances on these actions.
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