For humans, sleep is an absolute requirement for survival, almost on par with food and water. When we don’t get it, we not only feel terrible, but our cognitive abilities go downhill, and in extreme cases sleeplessness can lead to seizures and contribute to death. And while we share with many other animals this intense commitment to spending much of our lives unconscious, we don’t really know why we do it. A paper published in Science last monthsuggests that the answer may lie in part with a recently discovered plumbing system that drains waste from the brain. Scientists essentially found that the brain likes to wait till sleep comes before taking out the garbage.
The study follows up on the discovery last year by the same team, based at University of Rochester, that the brain’s waste is removed by a network of channels that run alongside blood vessels. The channels work like the lymphatic system that operates in the rest of the body, collecting and draining what isn’t needed, but they are made of brain cells called glia, instead of the membrane cells that form lymphatic vessels. The channels were effectively invisible to biologists until the development of methods to watch a living brain under the microscope—mouse brains, in these experiments. The discovery of these channels suggested that diseases like Alzheimer’s, in which waste products build up in the brain, might be linked to problems with drainage.