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Now that the football season is underway, players at all levels are starting to get sidelined by gridiron injuries.
Scrapes and sprains normally heal as expected - but, when a football player takes a hard hit to the helmet, some doctors think concussions can lead to a more mysterious and long-lasting condition called chronic traumatic encephalopathy or CTE.
Now, three current NFL players are planning to donate their brains to help find out just what kind of damage football-related head injuries can have.
Former Minnesota Vikings' Pro Bowl Center Matt Birk suffered from a mild concussion in the 2004 season and he is one of the NFL players involved in the study at Boston University.
Tom Crann talked with Matt Birk, now with the Baltimore Ravens, and Dr. Bob Stern from the Boston University School of Medicine. He is the Co-Director of the Center for the Study of Traumatic Encephalopathy.