Sleep helps the brain remember facts better: study

Sleep seems to helpthe human brainconsolidate memories such as the ability to recall recently learned facts, researchers say.

The benefits of sleep for non-declarative memories, such as the steps of learning to tap numeric sequences on a keyboard,are well established. The new experiment focused on declarative memory — such as recalling facts for a test —in which the brain's hippocampus is involved.

Dr. Jeffrey Ellenbogen of Harvard Medical School in Boston and his colleagues studied 48 healthy adults aged 18 to 39 who had no sleep problems.

The experiment was designed to test whether sleep helps build and maintainmemory and overcome interference, the tendency to forget something else when learning a new piece of information.

In the lab, participants tried to memorize20 pairs of words and were later tested on their recall.

Participants were divided into four groups:

• Sleep before testing.
• Wake before testing.
• Sleep before testing with interference.
• Wake before testing with interference.

Brain active during sleep

In this case, the interference or distraction was a second list of word pairs that participants were supposed to try to ignore during testing.

Those who slept between learning and testing were able to recall more of the original words compared with those who didn't get to sleep.

The beneficial effect was even starkerbetween the sleep-interference group, with an average recall of 76 per cent, and the the wake-interference group at 32 per cent, the team reports in Tuesday's onlineissue of the journal Current Biology.

"This is the first study to demonstrate that sleep protects declarative memories from associative interference in the subsequent day," the researchers wrote, adding that sleep"plays an active role in declarative-memory consolidation."

The results add to the evidence supportingthe role sleep plays in declarative memory, based on studies on animals and brain imaging, the researchers said.