Henry Molaison lived for decades with profound amnesia, but in death he will be remembered for his groundbreaking contributions to understanding the brain.

Molaison, who was known as Henry M. or H.M. in scientific studies, died Tuesday at a nursing home at the age of 82, said Suzanne Corkin, a neuroscientist at the Massachusetts Institute of Technology who worked closely with him.

Molaison participated in more than a half century of research and hundreds of studies that shed light on learning and memory.

"It was absolutely groundbreaking," Corkin said Friday. "Before him people didn't know memory could be localized to a specific part of the brain."

Molaison, who grew up in the Hartford area, developed seizures after being hit by a bicycle rider in his neighborhood when he was 9. He later suffered convulsions and could no longer work as a mechanic.

Eighteen years after the accident, 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.

Molaison could recall life in the 1940s and events like hiking along the Mohawk trail, but virtually nothing after that.

Leading surgeons began to study Molaison, and the research helped scientists understand there were at least two systems in the brain for creating new memories.

"He was a very gracious man, very patient, always willing to try these tasks I would give him," Brenda Milner, a McGill University psychologist who worked with him, told The New York Times. "And yet every time I walked in the room, it was like we'd never met."

Among her research with Molaison was a study in which he was able to gradually master a tricky drawing task, even though he never remembered doing it from one time to the next.

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

"He will help educate people forever and forever," Corkin said.

Molaison, who graduated from East Hartford High School when he was 21, lived with his parents and other relatives before entering a nursing home in 1980, Corkin said.

"The people in his nursing home adored him," Corkin said. "We're all very sad to have lost him." Oddly, while every experience seemed new to Molaison, he thought he knew Corkin from high school.

Molaison took part in the research because he wanted to help others, she said.

"He was very altruistic," she said. "He did it willingly and with all the right motivations."