Mapping the brain, one neuron at a time Spatial transcriptomics can link molecularly described cell types to their anatomical positions and functional roles. Moffitt et al. used a combination of single-cell RNA-sequencing and MERFISH (multiplexed error-robust fluorescence in situ hybridization) to map the identity and location of specific cell types within the mouse preoptic hypothalamus and surrounding areas of the brain (see the Perspective by Tasic and Nicovich). They related these cell types to specific behaviors via gene activity. The approach provides an unbiased description of cell types of the preoptic area, which are important for sleep, thermoregulation, thirst, and social behavior. Science , this issue p. eaau5324 ; see also p. 749