When Molaison died in 2008, his brain was painstakingly preserved. Now it’s available online for scientists (or others who request permission) to explore, right down to the level of its cellular architecture.
At the time of Molaison’s surgery, the conventional wisdom was that memory traces were distributed throughout the brain. But his case showed that certain parts of the brain were essential for certain memory functions. The surgeon, William Beecher Scoville, had removed large parts of the medial temporal lobes, including the hippocampus. If this structure gets taken offline, we now know, a person can’t form new memories of people, places, things, and events. Molaison, for example, would greet researchers who’d worked with him for decades as if he’d never seen them before.