Seau's family donated his brain to the National Institutes of Health's National Institute of Neurological Disorders and Stroke, which found definitive signs of chronic traumatic encephalopathy (CTE) — the degenerative brain disease associated with concussions and repeated blows to the head that. CTE can only be diagnosed post-mortem. According to a Department of Veterans Affairs and Boston University study, 90 of 94 former NFL players' brains tested positive for CTE. Seau was not alone. Bears cornerback Dave Duerson and the Eagles safety Andre Waters also committed suicide with gunshots to the chest in order to preserve their brains for study, both of which had CTE.