Researchers will also want to cross-reference this atlas with similar projects. After all, there’s more than one way to map a brain. You can classify its neurons by shape, location, or the genes they express. You can map the gene expression of old brains, young brains, and brains of different species. A recent project from the Allen Institute even classifies neurons according to their electrical activity. Brain atlases are like puzzle pieces that way: The more you have to work with, the easier it is to see the big picture—and how all the pieces fit.