An afternoon nap between classes may help improve school grades, according to a recent study.

Findings from researchers from the University of Geneva suggests that receiving rewards while learning can help cement new facts and skills in one's memory, particularly when combined with a daytime nap. It also revealed that memories associated with a reward are preferentially reinforced by sleep. Even a short nap after a period of learning is beneficial.

"Rewards may act as a kind of tag, sealing information in the brain during learning," lead researcher Dr. Kinga Igloi from the University of Geneva said in a statement. "During sleep, that information is favorably consolidated over information associated with a low reward and is transferred to areas of the brain associated with long-term memory."

For the study, researchers collected and analyzed data from 31 people. They were randomly assigned to either a sleep group or a 'wake' group and the sensitivity of both groups to reward was assessed as being equal. Participants' brains were scanned while they were trained to remember pairs of pictures. Eight series of pictures were shown and volunteers were told that remembering pairs in four of them would elicit a higher reward.

Following a 90-minute break of either sleep or rest, they were tested on their memory for the pairs and asked to rate how confident they were about giving a correct answer. Participants were also asked to take part in a surprise test of exactly the same nature three months later.

They found that both groups' performance was better for highly rewarded picture pairs, but the sleep group performed better overall. During the surprise test three months later participants who had slept after learning were selectively better for the highly rewarded pairs.

"We already knew that sleep helps strengthens memories, but we now also know that it helps us select and retain those that have a rewarding value," Igloi said. "It makes adaptive sense that the consolidation of memory should work to prioritize information that is critical to our success and survival."

The findings are detailed in the journal eLife.