What happens to cerebrospinal fluid during sleep?

Our study used brain imaging to look at what’s happening in cerebrospinal fluid in the brain during sleep, and that’s a liquid that envelops the brain, it cushions it and it’s important for things like waste clearance from the brain. We ended up having people come into the lab at midnight or so and getting brain scans while they were sleeping. What we saw was when people would fall asleep, we would actually see these large waves of fluid that seemed to kind of wash through the brain. We also went on to image different aspects of brain function and we realized that a specific pattern of electrical activity that happens in the brain during sleep is followed by a wave of blood oxygenation and then the wave of fluids so it seems that all of these things are coupled together.