New research suggests that sleeping makes memories easier to access.

Researchers at the University of Exeter and the Basque Centre for Cognition, Brain and Language found that after sleep people are more likely to recall facts that they could not remember while still awake.

"Sleep almost doubles our chances of remembering previously unrecalled material. The post-sleep boost in memory accessibility may indicate that some memories are sharpened overnight," researcher Nicolas Dumay of the University of Exeter said in a statement. "This supports the notion that, while asleep, we actively rehearse information flagged as important. More research is needed into the functional significance of this rehearsal and whether, for instance, it allows memories to be accessible in a wider range of contexts, hence making them more useful."

In two situations where subjects forgot information over the course of 12 hours of wakefulness, a night's sleep was shown to promote access to memory traces that had initially been too weak to be retrieved.

For the study, researchers tracked memories for novel, made-up words learnt either prior to a night's sleep, or an equivalent period of wakefulness. Study participants were asked to recall words immediately after exposure, and then again after the period of sleep or wakefulness.

They found that compared to daytime wakefulness, sleep helped rescue unrecalled memories more than it prevented memory loss.

Dumay, an experimental psychologist, said he believes the memory boost comes from the hippocampus, an inner structure of the temporal lobe, "unzipping recently encoded episodes and replaying them to regions of the brain originally involved in their capture," leading people to effectively re-experience the major events of the day.

The findings are detailed in the journal Cortex.