At least one in four NFL players has CTE when they die, according to a new study that examined the brains of former pro players. CTE is a brain disease thought to be caused by years of sustained head trauma and can only be diagnosed after an autopsy of the brain. Amna Nawaz spoke with Dr. Chris Nowinski of the Concussion and CTE Foundation, and a co-author of this study.

The world is mourning the passing of the queen of country, Dolly Parton. Her enormous legacy spans not only music, but the world of movies and entertainment, health care, philanthropy and education. Amna Nawaz takes a look at Parton's extraordinary life.