From VOA Learning English, this is the Health Report.

Why do we need sleep? Do our brains turn off for the night? Scientists recently discovered that our brains may be just as busy at night as they are during the day. While we sleep, our brains are doing much more than getting ready for the next day. Researchers at the University of Rochester found that the brain may be busy cleaning out harmful waste materials. The researchers studied mice that had colored dye injected into their brains. They observed the brains of the mice as they slept and when they were awake. The researchers say they saw that the brains of sleeping mice were hard at work.

Dr. Maiken Nedergaard led the study. He says our brains perform two very different jobs. He says, when we are awake, our brain is hard at work processing information about our surroundings. But at night, our brain works to remove all the waste that builds up during waking hours. The researchers say the waste material includes poisons, or toxins, responsible for brain disorders such as Alzheimer’s disease. They also found that during sleep, the brain’s cells shrink. This shrinking permits waste to be removed more effectively. The brain’s cleaning system could only be studied with new imaging technologies. And test animals must be alive in order to see the brain process as it happen.

Dr. Nedergaard says the next step is to look for the process in human brains. She says the results show just how important sleep is to health and fighting disease. The research may also lead to treatments that prevent or help fight neurological disorders.