Sleep on it – and dream about it – to remember it

25 April 2010
Posted by Chris Smith.

Have you ever found that the advice to "sleep on it" turns out to be true, whether it's solving a problem or trying to learn something? We've known for some time that sleep helps us to remember things, by helping the brain to file away and strengthen memories. Now new research from Erin Wamsley at Harvard Medical School, published in the journal Current Biology, provides more evidence that the best way to remember something is, indeed, to sleep on it - and, more importantly, to dream about it.

Wamsley and her team asked 99 volunteers to memorise the layout of a complicated computer-based maze. Then they were tested to see if they could get to a specific place in the maze after being dropped at a random starting point.  Five hours later, the volunteers were tested again. But in the intervening time, some of them had been to sleep while some of them had stayed awake.

The scientists found that people who had an hour and a half shut-eye in between tests managed to get through the maze and average of around 3 minutes faster than the first time, while the people who'd stayed awake only managed to navigate it a mere 26 seconds faster.

As well as seeing whether the volunteers had had a cheeky nap, Wamsley also asked the nappers whether they dreamed about the maze. She found that people who had dreamed about doing the task during their nap improved in the second test far more than people who didn't. So it suggests that dreaming is a powerful form of mental 'rehearsal' for a task.

In Wamsley's experiments, her volunteers also had some pretty wacky dreams. For example, when the volunteers described their dreams, they didn't talk about specific things in the maze, such as certain points or router. But some of them did mention similar but related situations, such as different mazes, or being stuck in a cave.

And , intriguingly, they found that people who found the maze task most difficult were more likely to dream about it. So maybe their brains were more likely to be processing the information about the task - or worrying about the upcoming re-test - while they napped.

It's important to point out that the researchers don't think that the actual dreams themselves improve our memory - they're more like a side effect of the underlying brain 'filing' process that goes on while we sleep. But based on this research, you might draw the conclusion that it's best to study right before you go to sleep. Or, alternatively, this is a brilliant way to justify having a nap after a hard revision session.

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