Henry Molaison, 82, who lived for decades with profound amnesia and whose participation in research allowed doctors to better understand the brain, died Tuesday at a nursing home in New Haven, Conn.

Mr. Molaison, who was known as Henry M. or H.M. in scientific studies, participated in more than a half-century of research and hundreds of studies that shed light on learning and memory.

Mr. Molaison developed seizures after being hit by a bicyclist in his neighborhood when he was 9. He later suffered convulsions and could no longer work as a mechanic.

Eighteen years after the accident, Mr. Molaison underwent an experimental brain operation in Hartford to correct the seizures, but he developed profound amnesia and lost the ability to form new memories.

Leading surgeons studied Mr. Molaison, and the research helped scientists understand that the brain had at least two systems for creating memories.

After his death, scientists took detailed MRI scans of his brain and arranged to have his brain preserved for future study.

- AP