All parents know the infant milestones: turning over, learning to crawl, standing, and taking that first unassisted step. Achieving each accomplishment presumably requires the formation of new connections among subsets of the billions of nerve cells in the infant's brain. But how, when and where those connections form has been a mystery. Now researchers have begun to find answers. In a newly published study, researchers describe the entire network of brain cells that are connected to specific motor neurons controlling whisker muscles in newborn mice.