Michael Mosley traces the history of brain science, from the earliest attempts to locate thought and feeling somewhere inside the skull to the modern merger of brain anatomy with psychology. He moves through the centuries when the organ was barely studied at all, past the point where scientists began mapping specific functions to specific regions, and into today's research linking physical brain structure to mood, memory, and personality. Mosley frames each stage as a shift in what counts as evidence, arguing that everyone, in effect, runs their own informal experiment on the brain simply by living and reacting to the world from infancy onward. The film stays close to that throughline rather than cataloguing every discovery, using the history to explain why understanding the brain took so much longer than understanding the rest of the body.