Can We Replace the Brain Cells Lost to Parkinson’s Disease? Scientists are testing whether lab-grown dopamine neurons can do something drugs cannot: replace part of the circuitry damaged by Parkinson’s disease. New trials — and Japan’s first conditional approval — bring that possibility closer, while exposing difficult questions about safety and benefit. Scientists are exploring whether stem cell-derived dopamine neurons could replace cells lost to Parkinson’s disease. Early clinical trials suggest that transplanted cells can survive in the human brain, opening a possible new chapter in regenerative medicine. A person reaches for a coffee cup. The destination is obvious and the muscles are still capable of lifting it. But the movement starts late, proceeds in small, hesitant steps, or stalls midway. Buttoning a shirt takes concentration. Walking across a room can feel like planning a route. Parkinson’s disease can create a painful gap between wanting to move and being able to move ...