After decades of DBS studies, fundamental questions remain. “If someone tells you they know the mechanism of action, they’re being a bit ambitious,” says Michael Okun, a neuroscientist at the University of Florida in Gainesville, FL. Some studies suggest that DBS can either excite or inhibit individual neurons, depending on whether electricity hits a particular cell’s body or its branches (5). Across a population of neurons, these effects can activate or suppress a brain area and influence activity in connected regions. There are also signs that DBS induces supporting brain cells to release neurochemicals (6) or alters the brain’s vasculature (7). How these various effects lead to improved health remains unclear—and likely differs across disorders.