Two members of the San Francisco 49ers' famed "Million Dollar Backfield" who died this year are having their brains examined by researchers studying head injuries in sports.

A spokeswoman at Boston University's school of medicine confirmed Thursday that the brains of Joe "The Jet" Perry and John Henry Johnson have been donated by their families to be examined. Researches at the university are studying head injuries, including the neurodegenerative disease chronic traumatic encephalopathy, or CTE.

Perry died at age 84 in April. Henry died last week at 81. They were part of a backfield with running back Hugh McElhenny and quarterback Y.A. Tittle. The group remains the only backfield to have all four of its members enshrined in the Pro Football Hall of Fame.