Memory like a sieve? Try getting a good night's sleep, say scientists

The study found that sleeping well helps people remember tasks on their to-do lists.

US researchers found waking up feeling refreshed after a full night's sleep was a great aid to "prospective memory" — being able to remember to do something in the future.

The scientists, who focused on this future memory rather than "retrospective memory" — being able to recall the past — also discovered that remembering to call the bank or post a letter has less to do with how firmly it is embedded in our minds, and more to do with a "trigger" the next day, such as seeing a monthly statement or a stamp.

An unbroken night's sleep helps people take advantage of these triggers when we see them, making us remember things we have to do. The scientists said the findings, published in the journal Psychological Science, helped in the understanding of the role sleep plays in cognition as well as memory.

Dr Mark McDaniel, from Washington University in St Louis, said: "We found that sleep benefits prospective memory by strengthening the weak associations in the brain, and that hasn't been shown before." The study found that sleep specifically helped take advantage of what he called "weak" memory cues, rather than "strong" ones.

"Let's say that you intend to give a colleague a message tomorrow. Seeing the colleague the next day will be a strong cue for remembering to give the message," he said.

"But, during the time your brain encoded the intention, you're also vaguely thinking of a meeting the two of you will attend the next afternoon.

"The context of the conference room is weakly associated with your intention to give the message.

"Before sleeping, you remembered you had a message to deliver to your colleague and you would see him in the conference room tomorrow. Sleep enhances the likelihood that you will tell him in the conference room, but not in some other context — the elevator, for example."

The researchers believe that the prospective memory process happens during "slow wave" sleep — an early pattern in the sleep cycle — involving communication between two areas of the brain, the hippocampus and the cortical regions.

Junior researcher Michael Scullin said: "We think that during slow-wave sleep, the hippocampus is reactivating these recently learned memories, taking them up and placing them in long-term storage regions in the brain."

Professor Colin Espie, from the University of Glasgow Sleep Centre, said previous studies had highlighted how sleep affected performance: "Different parts of sleep are important for different purposes.

"So we should not be surprised that sleep helps us to remember things. People learn tasks better if they have a sleep."