What she discovered was that during non-REM sleep, large, slow waves of cerebrospinal fluid were washing over the brain. The EEG readings helped show why. During non-REM sleep, neurons start to synchronize, turning on and off at the same time. Because the neurons had all momentarily stopped firing, they didn’t need as much oxygen. That meant less blood would flow to the brain. But Lewis’s team also observed that cerebrospinal fluid would then rush in, filling in the space left behind.

Just a few days ago I told someone, we didn't know yet how our sleep clean toxins from the brains. And now we know. Fuck yeah, for science!

And in case you don't remember why all this is important:

The study also could have clinical applications for treating Alzheimer’s. Recent attempts at developing medications have targeted beta-amyloid. But drugs that looked promising at first all failed once they got into clinical trials. Instead of trying to act on one particular molecule, new interventions might instead focus on increasing the amount of cerebrospinal fluid that washes over the brain.