http://www.smh.com.au/world/science/to-sleep-perchance-to-clear-your-brains-inbox-20100222-orqz.html
To sleep, perchance to clear your brain's inbox February 23, 2010 CURLING up for an afternoon nap can improve the brain's ability to learn by clearing out cluttered memory space, psychologists say. People who nodded off for an hour after lunch performed better in learning tests than those who stayed awake all afternoon, the scientists found. A study of students revealed that their brains were refreshed by napping only if they entered what is called stage 2 non-REM sleep, which takes place between deep sleep and the dream state known as REM, or rapid-eye-movement, sleep. The research follows a recent study by the same scientists that showed that staying up all night reduced students' ability to cram new facts by nearly 40 per cent, a consequence, they said, of brain regions in effect shutting down through sleep deprivation. ''Sleep not only rights the wrong of prolonged wakefulness but, at a neurocognitive level, it moves you beyond where you were before you took a nap,'' said Matthew Walker, of the University of California, Berkeley. Professor Walker's team divided 39 students into two groups. At midday all the volunteers took part in a learning test designed to exercise a region of the brain called the hippocampus, which is involved in storing memories. Two hours later one of the groups settled down for a nap while the other group stayed awake. Later that day, at 6pm, both groups took part in a second test. Those who napped for an hour not only performed better than the group that stayed awake, they scored better than they did in the first test. The findings suggest that sleep clears the brain's short-term memory and makes room for new facts to be remembered, Professor Walker said. Previous studies have established that fact-based memories are stored temporarily in the hippocampus before they are moved to the prefrontal cortex region of the brain. ''It's as though the email inbox in your hippocampus is full and, until you sleep and clear out those fact emails, you're not going to receive any more mail,'' Professor Walker said. Guardian News & Media
