Sleepy brains take learning seriously.

For much of the time that we snooze, our brains generate an electrical output known as slow-wave activity. This sleep-specific pattern arises from neural processes involved in learning rather than in recharging fatigued brain cells as scientists have often assumed, a new study suggests.

Guilio Tononi of the University of Wisconsin in Madison and his coworkers instructed 11 adult volunteers to practice a hand-eye coordination task shortly before spending a night in a sleep laboratory. In the task, each participant used a handheld device to move a cursor toward a target on a computer screen while the scientists slightly altered the cursor's trajectory, as if it were fighting a current.

After falling asleep, participants displayed slow-wave activity that was largely confined to two areas toward the back of the right brain, Brain scan studies had implicated these areas in skilled actions that depend on spatial perception.

In line with earlier investigations (SN: 6/1/02, p. 341), volunteers performed the task better after a night's sleep. Those who had exhibited the greatest amount of slow-wave activity in the two right-brain areas while asleep showed the most improvement on the task the next day.

Tononi's group reports its findings on June 6 in the online version of Nature.--B.B.