A recent study looked at the donated brains of former football players including professional, semi-professional, collegiate, and high school athletes. Researchers found a change in the brains of former NFL players, known as chronic traumatic encephalopathy or CTE. CTE is a progressive degenerative disease of the brain. Researchers found that of the 202 brains studied, nearly 88 percent of them had CTE. The results were more pronounced among former NFL players.