Researchers say getting a good night's sleep is probably the best tool for memory and learning. But short periods of sleep may help our brains work better, says a recent study on napping. And taking a nap  may also help old adults fight off age-related memory loss.

    CDC, an American scientific organization, found that 50 to 70 million Americans have chronic（长期的）sleep disorders. So, someone who naps as a way of paying off a sleep debt may not experience the same improvements from napping as a well-rested person would. Also, that only children, the very old, sick or  lazy people nap is not an uncommon opinion.

    Researchers recently looked at information provided by nearly 3,000 Chinese adults, aged 65 years or older, to learn if napping after a mid-day meal had any effect on the mental performance of the subjects.

    First, they asked the people if they napped and for how long. Then, based on their answers, researchers put them into four groups: non-nappers (0 min), short nappers (≦30 min), moderate nappers (30-90 min), and extended nappers (≧90 min).  Nearly 60% of the people said they did take a nap after lunch and that   their naps lasted anywhere from 30 to 90 minutes. Most of the subjects said they napped for about an hour.

    The study found that people who took an hour-long nap did much better on mental tests than those      who did not nap. The hour-long nappers also did better on the tests than those who napped for shorter and longer periods. In this study, it seemed that the most effective nap lasted for about an hour, but not much longer.

    Yet Doctor Michael Twery notes that an hour long nap may be too long for young, healthy adults. 30 minutes is enough to remove the pressure to sleep and will help us feel more awake.