Pavel Osten’s team used their qBrain brain-mapping platform to visualize and count inhibitory neurons in the mouse brain. Brainwide distribution of 3 major inhibitory cell types, expressing neuropeptides called SST, PV and VIP, is shown in this color-coded composite. These images revealed an unexpected cortical organizing principle: sensory-motor areas are dominated by output-modulating PV+ interneurons, while association areas are dominated by input-modulating SST+ interneurons. Other views revealed that despite their smaller size, female brains had more interneurons than male brains in most subcortical areas.