Shortly before he died in July, the former N.F.L. quarterback Ken Stabler was rushed away by doctors, desperate to save him, in a Mississippi hospital. His longtime partner followed the scrum to the elevator, holding his hand. She told him that she loved him. Stabler said that he loved her, too.

“I turned my head to wipe the tears away,” his partner, Kim Bush, said recently. “And when I looked back, he looked me dead in the eye and said, ‘I’m tired.’ ”

They were the last words anyone in Stabler’s family heard him speak.

“I knew that was it,” Bush said. “I knew that he had gone the distance. Because Kenny Stabler was never tired.”

The day after Stabler died on July 8, a victim of colon cancer at 69, his brain was removed during an autopsy and ferried to scientists in Massachusetts. It weighed 1,318 grams, or just under three pounds. Over several months, it was dissected for clues, as Stabler had wished, to help those left behind understand why his mind seemed to slip so precipitously in his final years.