 You have the water pipes and the sewage pipes. And so water comes in clean, and then you wash your hands, and then the dirty water goes out. But Kipnis says scientists haven't known what powers this system until now. Two independent mouse studies found that a distinct pattern of brain waves that appear during sleep turns neurons into tiny pumps that push fluid out of the brain. The fluid contains waste products from brain cells, including a substance called amyloid, which is thought to be a key driver of Alzheimer's.