The brain's motor cortex plans, controls and executes voluntary muscle movements. Whether you're playing catch, writing your name or chewing food, it all points back to this region and its connections to other parts of the brain. Yet despite extensive study, scientists still haven't created a detailed map of how the mouse motor cortex is internally organized. Most brain atlases have divided it into two general regions—primary and secondary—based on differences in connectivity, but this doesn't provide a detailed or consistent picture.