. >> reporter: robert stern, a cte expert at the boston university school of medicine is a bit more skeptical. he says small's brain scan doesn't just measure tow, it measures another protein, which is present in alzheimer's disease. >> we don't know if what's lighting up is the tau protein. >> reporter: are they suffering from alzheimer's? >> i agree we need to do alzheimer's study to pin down our hypothesis is correct. >> reporter: remember, researchers found tau in his brain, but he is a cogatively normal 65-year-old. whether it necessarily means an early death or other factors like genetics also play a role. still, clark says he's willing to keep up the brain scans until he dies to help figure it out. >> be able to find out what our conditions are now, address possible interventions earlier, so we don't have to wait until we're dead and autopsy our brains. >> i could tell you that players are much more concerned about head injuries than they were even just a few years ago. in fact, i want to take a moment to introduce you to lamar campbell. he took and gave out a lot of hard hits and he's