Researchers say 96% of former NFL players who donated their brains to science after death tested positive for a brain disease linked to concussions. CNN’s Sanjay Gupta explains.
Researchers: 96% of ex-NFL players had brain disease

American rock band The Doors mirror their looks for a photoshoot, 1967. They are vocalist Jim Morrison, keyboardist Ray Manzarek, drummer John Densmore, and guitarist Robby Krieger. (Photo by Mark and Colleen Hayward/Getty Images)