When cramming for an exam, students might be tempted to skip sleep and maximize the limited amount of time they have to prepare. But research suggests this is not the smartest strategy.

In a study published in the journal Psychological Science, researchers found that getting some sleep in between study sessions helped people recall the material they had been studying.

“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," says study co-author Stephanie Mazza, a psychological scientist of the University of Lyon in France. "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."

In the study, scientists showed 40 French adults 16 pairs of Swahili-French word pairs and asked them to study each pair for a few seconds. They then showed them the Swahili words alone and asked them to type their French translations. Afterward the scientists told the participants what the correct translations were. They repeated this process until the people learned to translate all of the words correctly.

The researchers repeated the word recall task 12 hours later.

Half of the people completed the first recall task in the morning and the second task in the evening of the same day. The other half performed the first task in the evening and completed the second task the following morning after getting a good night's sleep.

When the scientists compared the results of the first recall task between the groups, they did not find significant differences. But after 12 hours, the group that slept between the two sessions recalled 10 of the 16 word pairs, whereas those who did not sleep recalled only between 7 and 8 word pairs. The people who slept between study sessions also learned to translate the word pairs faster than those who did not.

The effects of sleep on memory seemed to be long lasting. When the scientists repeated the word recall task a week later, the sleep group was still able to recall 15 word pairs, compared with the other group, which was able to recall only 11 pairs. This difference still held 6 months later.

The findings suggest that interspersing learning sessions with sleep could be an efficient way to retain information for longer with less study, according to the researchers.

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