Daytime nap boosts memory

Giving children rewards and allowing them a short nap after a period of learning can significantly boost their ability to remember new facts and skills for a long period, new research suggests.

Memories associated with a reward are reinforced by sleep, the findings showed. "Rewards may act as a kind of tag, sealing information in the brain during learning," said lead researcher Kinga Igloi from University of Geneva in Switzerland.

"During sleep, that information is favourably consolidated over information associated with a low reward and is transferred to areas of the brain associated with long-term memory," Igloi said.

For the research, thirty-one healthy volunteers 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. Both groups' performance was better for highly rewarded picture pairs, but the sleep group performed better overall. Strikingly, during the surprise test three months later participants who had slept after learning were selectively better for the highly rewarded pairs.

The MRI scans revealed that the sleep group showed increased connectivity between the hippocampus, the medial prefrontal cortex and the striatum, areas of the brain implicated in memory consolidation and reward processing. (The study will be published in a forthcoming issue of the journal eLife)