Most neuroscience research still runs on mice, even though much of what applies to mice does not hold up in humans. Marmosets have emerged as a bridge between species. However, comparing the brains of mice and marmosets runs into a chicken-and-egg problem. Scientists need to know which part of one brain matches the respective region of the other, but almost every brain map draws those areas differently.

For a new study published in Communications Biology, Cold Spring Harbor Laboratory Professor Partha Mitra and colleagues built the first cross-species map to systematically link mouse and marmoset brain regions.

“It’s the kind of problem that nobody wants to address, because it’s hard,” Mitra says. Comparing genomes across species is relatively straightforward. DNA aligns letter by letter. But brain circuits vary even within one species. Compounding the problem, research teams have built different brain atlases that divide the same mouse brain differently.