For generations, medicine has treated the brain damage left by stroke as a permanent condition — neurons lost, function gone, the self quietly rearranged around absence. Now researchers at the University of Zurich and the University of Southern California have challenged that assumption in mice, transplanting human neural stem cells into stroke-damaged brains and watching them not only survive and become functional neurons, but awaken a broader cascade of biological repair. The finding does not yet promise a cure, but it reopens a question science had largely closed: whether the injured brain