To understand the function of FOXP1 in specific brain regions, in this paper, the authors again used a mouse model where Foxp1 is removed from the neocortex, the outermost layer of the brain, and the hippocampus, a brain region important for memory. The authors find that these mutant mice do not call out to their mothers as much, the usual organization of cells in the neocortex is changed, and the neocortex is overall smaller. Since the function of Foxp1 is to regulate how much other genes are expressed, the authors examined how loss of Foxp1 affects overall gene expression in the neocortex or hippocampus. They found that genes regulated by Foxp1 are relevant for the birth of neurons or for how neurons get to their destination in the brain. Indeed, when an altered version of Foxp1 is introduced to these mice, the neurons of these mice are not always able to reach their appropriate final location. The volume of the cortex and hippocampus was also reduced in these mice lacking Foxp1.