If you believe that when you go to sleep your brain takes rest， you are wrong —— it actually strengthens the memories of events that took place during the day.
　　Researchers in the United States have carried out a study and found while you sleep，your brain remains busy in strengthening the memories of what you did during the day and it does it in quick spurts， as if your day was being replayed in fast-forward.
　　"The brain's medial prefrontal cortex replays daytime activities during sleep six to seven times faster than real time，" the WebMD reported，quoting lead researcher Dr David Euston was quoted as saying.
　　In fact， Dr Euston and his fellow researchers at the University of Arizona came to the conclusion after monitoring brain activity in rodents that had spent the day learning to scamper around a circular arena in a particular pattern.
　　The team found that while the rats slept，their medial prefrontal cortex had spurts of activity that matched brain activity while the rodents had been running around the arena earlier in the day.
　　They took that as a sign which the rats' brains were replaying the experience of learning the route around the arena. But during sleep，those brain patterns happened six to seven times faster than the time it had taken the rodents to scurry around the arena while awake.
　　"In short， the rats' brain activity kicked into overdrive during sleep to consolidate memories，" Dr Euston，who reported the findings in the latest edition of Science journal，was quoted as saying.