Snooze power: midday nap may awaken learning potential. (This Week).

Naps aren't just for the very young, old, and slothful. Daytime dozing may enhance a person's capacity to learn certain tasks.

That, at least, is the eye-opening implication of a new study in which college students were challenged to detect subtle changes in an image during four different test sessions on the same day.

Participants improved on the task throughout the first session, says psychologist Sara C. Mednick of Harvard University and her colleagues. The students' speed and accuracy then leveled off during the second session.

The scores of the participants who didn't nap declined throughout the final two sessions. In contrast, volunteers who took a 30-minute nap after completing the second practice session showed no ensuing performance dips. What's more, 1-hour nappers responded progressively faster and more accurately in the third and fourth sessions.

"Napping may protect brain circuits from overuse until those neurons can consolidate what's been learned about a procedure," says neuroscientist Robert Stickgold of Harvard Medical School, a coauthor of the new study.

A version of this phenomenon occurs among musicians, according to Stickgold. A nap or a night's sleep often leads to a breakthrough in learning a complex musical piece.

Slumber's alleged assist to learning (SN: 7/22/00, p. 55) has usually been attributed to brain activity during rapid-eye-movement (REM) sleep. In the new study, slated to appear in Nature Neuroscience, the performance-enhancing naps consisted mainly of a non-REM sleep stage known as slow-wave sleep.

In this work, Mednick's group trained 30 volunteers on a task requiring them to identify the vertical or horizontal orientation of three diagonal bars flashed in the lower left quarter of a computer screen against a background of horizontal bars. Hour-long sessions occurred at 9 a.m., noon, 4 p.m., and 7 p.m.

Ten participants didn't nap. Beginning at 2 p.m., the others took either a 30-minute or a 1-hour nap. Brain-wave measurements established that the nappers slept throughout most of their allotted times.

Additional trials indicated that naps refresh specific neural circuits involved in the perceptual task, Mednick and her colleagues say. Another 12 volunteers completed four sessions without napping but viewed the diagonal bars on the right side--instead of the left side--of the screen during the final session. Their performance improved substantially after this switch, a sign that a different, now fresher, neural circuit mediated the learning in the right portion of the visual field.

Fatigue or boredom can't explain performance declines among non-nappers, Mednick says. These individuals reported no surges of sleepiness on questionnaires administered after each training session. Moreover, even after they were offered $25 at the start of the third session if they could stay at their previous performance levels, 10 additional non-nappers still suffered declines. Finally, 10 volunteers who rested quietly for an hour without napping after the second session also did more poorly thereafter.

"This new linkage of naps to learning a repetitive task is exciting, but it's too soon to say that naps work like this for everybody," remarks psychologist Rosalind Cartwright of Rush-Presbyterian St. Luke's Medical Center in Chicago.

Still, comments psychologist Mark Blagrove of the University of Wales, Mednick's group has raised the profile of slow-wave sleep as a possible means by which naps might foster learning.