Scientists in the Center for Human Brain Variation at the Broad Institute have charted previously hidden architecture and patterns of cellular makeup in a key part of the brain called the striatum, which is involved in decision-making and movement and is affected in psychiatric disorders, addiction and neurodegeneration. The findings reveal six new zones within the striatum based on gene expression patterns. They also demonstrate how the zones' boundaries blur with age and highlight ways that advancing age and genetic variation affect gene expression in the brain.