Concerned that a midday snooze might ruin a good night's sleep? Fret not; ongoing research from NewYork-Presbyterian Hospital/Weill Cornell Medical Center indicates that napping has little effect on sleep onset -- and that a nap today may be beneficial for mental processing tomorrow.

People over age 60 sleep two hours less per night than their younger counterparts. Patricia Murphy and Scott Campbell, associate director and director, respectively, of the Human Chronobiology Laboratory at NewYork-Presbyterian/Weill Cornell, have evidence that a midday nap may improve daytime performance and mood in the elderly and others.

Their research subjects are all normal sleepers. "By learning more about how normal people sleep, we may gain a better understanding of what is happening in the bodies and minds of those with sleep disorders," says Murphy.

Study participants spend several sessions in the sleep lab, attached to scalp electrodes and a wrist activity monitor that record their sleep and wakefulness states. They are then asked to perform arithmetic, decision-making and reaction time tests after napping and on the following day.

The subjects showed improved cognitive performance immediately after a nap and into the next day, when compared with days that didn't include (and weren't preceded by a day with) a nap. Napping did not seem to affect nighttime sleep.