Lt. Gen. Mark Milley speaks to reporters April 2 regarding the second shooting in five years on the Fort Hood Army post in Texas. Drew Anthony Smith/Getty Images hide caption

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

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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

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

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Hospital intensive care units save lives, but people there often suffer from delirium. Cal EMA / Flickr hide caption

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The cause of strokes in younger people remains largely a mystery. hide caption

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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

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Sgt. Victor Medina suffered brain damage in 2009 when a roadside bomb exploded in Iraq. Blake Gordon/Aurora Photos hide caption

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