A midday nap can keep us mentally sharp, and may even make us smarter. It seems to wipe clean the 'memory tape' and allows us to cope better with new challenges, a new study among students has discovered. Even staying awake throughout the day, as most of us do, can mean we are not so efficient if we need to carry out a new task in the early evening, researchers at the University of California at Berkeley have discovered. They tested the benefits of the midday nap on a group of 39 students, who either had a 90-minute nap in the middle of the day or stayed awake all day. But when both groups were asked to perform a new round of learning exercises at 6pm, the 'nap group' dramatically outperformed the 'no-nap' group. The researchers believe that a nap helps to clear the brain's short-term memory store and makes room for new information, says lead researcher Matthew Walker. (Source: Annual meeting of the American Association of the Advancement of Science, San Diego, California. February 21, 2010).