Sleep Research Finds That Sleeping Between Study Sessions Can Help Retention

If saving things for the last minute and cramming the night before is your study method of choice, it’s time to reassess. A new small-scaled study—published in Psychological Science, a journal of the Association for Psychological Science—has found that sleeping between study sessions makes it easier to recall what you studies and relearn what you’ve forgotten.

Researchers at the University of Lyon randomly assigned 40 French adult subjects to two groups: a sleep group and a wake group. In the first session, participants studied 16 French-Swahili word pairings in random for 7 seconds and were then quizzed on Swahili-to-French translations. The correct word pair was shown for 4 seconds and mistaken pairings were presented until subjects got it right. All the participants went through the same recall task 12 hours later with one difference: one group was able to sleep and the other was not.

During the first session, there was no difference in recall between the two groups. But after 12 hours, there was a distinction between the subjects who were able to sleep and the subjects who did not. Those who were able to get some sleep in recalled an estimated 10 of 16 words while those who didn’t get to sleep only recalled an average of 7.5 words.

"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," said Stephanie Mazza, a psychologist at the University of Lyon, in a statement.

There was also a difference in relearning, as those who slept needed fewer trials to recall all 16 words than those who did not. Specifically, those who slept needed, on average, three trials to recall the words as opposed to those who did not sleep, who needed roughly six trials. In a follow-up test one week later, participants in the sleep group had better recall than their counterparts in the wake group.

"Memories that were not explicitly accessible at the beginning of relearning appeared to have been transformed by sleep in some way," said Mazza. "Such transformation allowed subjects to re-encode information faster and to save time during the relearning session."

Previous research have shown that sleep and repetition independently improve memory. This study marks the first of its kind to look at how both sleep and repeated practice impact memory when together. While the findings are preliminary, Mazza and his team hypothesize that sleep makes the learning process more efficient by reducing the amount of effort it takes to turn new information into a memory.

"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,” said Mazza.