Junior Seau sustained many concussions during his career and was suffering from a degenerative brain disease when he killed himself in May 2012. Otto Greule Jr./Getty Images hide caption

itoggle caption Otto Greule Jr./Getty Images

Researchers have only recently been able to use brain scans to detect Alzheimer's risk factors in living people. iStockphoto hide caption

itoggle caption iStockphoto

Kansas City Chiefs linebacker Jovan Belcher's body has been exhumed more than a year after he killed his girlfriend and himself so that his brain can be examined for signs of a degenerative condition linked to repeated concussions. Seth Perlman/AP hide caption

itoggle caption Seth Perlman/AP

Dartmouth defenders sandwich a New Hampshire wide receiver during a game in Durham, N.H., in 2009. Josh Gibney/AP hide caption

itoggle caption Josh Gibney/AP

Junior Seau sustained many concussions during his career and was suffering from a degenerative brain disease when he killed himself in May 2012. Otto Greule Jr./Getty Images hide caption

itoggle caption Otto Greule Jr./Getty Images

Robert Monges, a coach for James Lick High School, checks tight end Dominic Brewster for a concussion during a football game played in Morgan Hill, Calif., in 2006. Patrick Tehan/San Jose Mercury News/MCT/Landov hide caption

itoggle caption Patrick Tehan/San Jose Mercury News/MCT/Landov

Dr. Ann McKee, professor of neurology and pathology of Boston University School of Medicine and co-director of the Veterans Affairs Center for the Study of Traumatic Encephalopathy, inspects a brain in the Bedford Veteran Medical Center last year. Stan Grossfeld/Boston Globe via Getty Images hide caption

itoggle caption Stan Grossfeld/Boston Globe via Getty Images