Stage 1 is characterized by things like headache and concentration problems. By the time a person reaches Stage 4, the disease is full-blown and things like explosivity, aggression, paranoia and impulsivity become pronounced.
There is no simple answer for football fans about the spate of recent deaths. But what is simple: Repetitive head trauma is not good.
"It is wrong to focus on the suicides," said Nowinski. "The takeaway shold be that brain trauma can unlock the door to a whole lot of terrible things and we have a lot of work ahead of us to both learn how to treat (CTE) and to prevent it in the next generation."