In a study of 48 individuals between the ages of 18 and 30, researchers tested how well each of four groups of 12 remembered word pairings. All of the study participants had regular sleep habits and were not taking any medications.

Two groups were taught the pairings at 9 a.m. and tested at 9 p.m. after staying awake all day. The other two groups were taught the word pairings at 9 p.m. and tested at 9 a.m. after a normal night of sleep.

In both the morning and evening sessions, one group was tested on the word pairings without any interference, while the other group was given a second list of word pairings to learn just before the test. On both lists, the first word of each pairing was the same, but the second word differed on the second list, creating interference.

The individuals who slept after learning the word pairings were able to remember their lists better. Of those who were tested without interference, the participants who slept after learning the words recalled 12 percent more pairs than those who stayed awake.

Of those who were tested following interference, those who slept recalled 44 percent more pairs than the group who stayed awake.

"This is the first study to show that sleep protects memories from interference," said study author Jeffrey Ellenbogen, MD, of Harvard Medical School. "These results provide important insights into how the sleeping brain interacts with memories: It appears to strengthen them. Perhaps, then, sleep disorders might worsen memory problems seen in dementia."

The study will be presented at the 59th Annual Meeting of the American Academy of Neurology taking place in Boston April 28 through May 5.