Brains Sweep Themselves Clean Of Toxins During Sleep --- While the brain sleeps, it clears out harmful toxins, a process that may reduce the risk of Alzheimer's, researchers say. -- The process is important because what's getting washed away during sleep are waste proteins that are toxic to brain cells, Nedergaard says. This could explain why we don't think clearly after a sleepless night and why a prolonged lack of sleep can actually kill an animal or a person, she says. -- So why doesn't the brain do this sort of housekeeping all the time? Nedergaard thinks it's because cleaning takes a lot of energy. "It's probably not possible for the brain to both clean itself and at the same time [be] aware of the surroundings and talk and move and so on," she says. -- That's probably not a coincidence, Nedergaard says. "Isn't it interesting that Alzheimer's and all other diseases associated with dementia, they are linked to sleep disorders," she says. - More, Jon Hamilton - NPR