An understanding of how gene expression varies across different cell types and brain regions may provide insights into brain function and evolution. Zeng et al. profiled the expression of 995 genes at cellular resolution in the visual and temporal cortices of the human brain, revealing distinct expression patterns in different cell types and populations. These patterns were highly conserved across individuals. The authors also compared the expression of most of the genes in mouse and human brains, revealing a large degree of conservation across species, but also identifying a small number of genes that exhibit species-specific expression patterns.