Revving up recall while fast asleep.

Scientists have discovered a way to give memory a modest lift while people slumber. Application of a gentle electrical current to the scalp, which nudges sleepers into a particular phase of sleep, boosts recall the next day for recently learned facts, say neuroscientist Jan Born of the University of Lubeck in Germany and his colleagues.

Born's team explored a particular sleep phase called slow-wave sleep, which some researchers suspect enhances learning (SN: 6/26/04, p. 414). A group of 13 volunteers first memorized as many of 46 word pairs as they could during an evening session. As each participant slept that night, the researchers delivered the current through scalp electrodes for 30 minutes just before slow-wave sleep started.

The procedure increased the period of individuals' slow-wave sleep. The same course was followed during a second night, after volunteers had studied another set of word pairs, but this time the scientists used electrodes that delivered no current.

Participants remembered an average of 37 word pairs when tested before going to sleep. The next day, those who received brain stimulation recalled an average of 41 word pairs, versus 39 pairs for those who received sham stimulation.

Born's group reports its findings online Nov. 5 in Nature.--B.B.