A genomic atlas of the mouse brain, the Allen Brain Atlas, has been completed. It contains 85 million images and documents the activity of more than 21,000 genes across the entire mouse brain in such fine detail that it is possible pick out individual cells.

Already, the atlas has revealed that the mammalian brain contains “hidden” structures, defined by common patterns of gene activity and that at least 80 percent of the genes studied are active in the brain — more than had been predicted.