Myelin is the insulating layer that wraps nerve fibers, allowing brain cells to communicate quickly. In adults, new myelin is made by oligodendrocytes that arise from precursor cells (OPCs). Using genetic tools and live imaging in mice, this study publishes in Science, led by Yevgeniya A. Mironova from Kavli NDI member, Dwight Bergles’ lab, shows that OPCs attempt to mature into myelin-producing cells on a regular, internal schedule across the brain and spinal cord.