In the living human brain, blood and cells must speak the same language — a constant, calibrated exchange of oxygen and energy that sustains thought, movement, and perception. Researchers at USC have now built a tool, called CCSI, that listens to that conversation for the first time, using high-powered MRI to measure how precisely blood flow aligns with the density of cells across the brain's layered architecture. Published in Nature Communications, the work reveals that this alignment is not uniform but varies meaningfully across regions, and that where it is strongest, the brain's cellular p