When a person goes into deep sleep, waterlike fluid circulates around the brain, washing away metabolic waste that is linked to diseases such as Alzheimer’s. This process, known as the glymphatic system, was first described in 2012 by Maiken Nedergaard, a pioneering neuroscientist and co-director of the University of Rochester Center for Translational Neuromedicine.

But questions remain about the system’s mechanics—notably, how quickly the fluid circulates around the brain. Studying the circulation within a living brain is difficult to do without causing irreparable harm to a subject.