Researchers at Stanford University have discovered what causes Alzheimer’s—potentially leading to a cure. The scientists noticed that disease sets in when a particular type of cell in the brain, called microglia, stops working. Microglia clean your brain, they keep out viruses and prevent A-beta, a gummy protein on your brain, from building up. When microglia don’t work then too much A-beta forms—the symptomatic cause of Alzheimer’s. Next question: How to keep microglia going.