The next time your boss catches you nodding off at your desk, simply wipe the drool from your mouth and say: Scientists have uncovered the first evidence that napping improves performance--at least on certain types of visual tasks. The finding may help explain what happens to the overworked brain and how sleep combats such problems.
Students, medical residents, and long-haul truck drivers have long known the value of a good nap. Although lab studies have shown that a good night's sleep improves performance on learning and memory, none had pinpointed the benefits of shorter snoozes.
To see whether napping could improve visual discrimination, a team led by Robert Stickgold, a neuroscientist at Harvard University in Cambridge, Massachusetts, had college students who were not sleep deprived stare at a video screen filled with horizontal bars. Periodically, three diagonal bars flashed in the lower left corner of the screen, and the students had to say whether these bars were stacked horizontally or vertically. The researchers graded students' performance by measuring how long the diagonal bars had to be shown in order for them to answer correctly 80% of the time. Students sat through 1250 frustrating trials during each session, so those who did not nap did worse and worse over the course of the day. But students who took a 1-hour nap returned to their original performance levels in the next test, the team reports in a paper published online 28 May in Nature Neuroscience.
Further results hint at the source of the visual fatigue, Stickgold says. When the researchers switched the diagonal bars to the lower right corner of the screen after the first three testing sessions, students performed as well as in their first test. To Stickgold, this suggests that fatigue occurs early in the brain's visual system, before signals from the left and right visual fields are combined. Stickgold says the findings suggest that the "burnout" sensation that comes with any sort of information overload may result from fatigue in specific brain regions. "Burnout is a signal that says you can't take in more information in this part of your brain until you've had a chance to sleep."
"This really connects the dots between the nature of a specific task and the impact of sleep on the ability to improve performance," says neuropsychologist David Dinges of the University of Pennsylvania in Philadelphia. But he cautions that the findings may not extend beyond visual discrimination performance.