Beneath the surface of every thought and memory, the brain quietly labors to clean itself — a process whose failure may lie at the heart of Alzheimer's and other diseases of the aging mind. Researchers at the University of Rochester, working with colleagues at Brown and Copenhagen, have used AI-trained neural networks to measure, for the first time, the true speed of this hidden fluid system — finding that waste moves fifty times faster near the brain's surface than in its depths. The discovery does not yet offer a cure, but it offers something medicine has long needed: a way to see what was p