The function of FOXP1 is to turn on and off the expression of other genes. In this study, the authors sought to understand which genes FOXP1 regulates in the brain. Both human brain cells and mice with FoxP1 mutations were used, and the authors found that FoxP1 regulates other genes that are known to be implicated in autism. Furthermore, Foxp1 mutations in mice increase the activity of a subset of neurons in a region of the brain called the striatum. FoxP1 also regulates the expression of autism genes in these striatal neurons. Taken together, this study showed an important role for FoxP1 in regulating other known autism genes in the striatum, a brain region important for behaviors associated with autism.