Story highlights Of 35 football players studied, all but one had evidence of brain disease

Repeated head injury can lead to chronic traumatic encephalopathy

But "No brain disease could ever explain a single act," researcher says

When a professional football player meets his end with dramatic and terrifying suicidal flourish, lately the focus in the aftermath is on what was happening in his brain before he died.

Not about his mental state per se, but something happening in the deepest recesses of his brain: A complicated-sounding disease called chronic traumatic encephalopathy or CTE.

"Every time something like (a suicide) happens, I do worry about status of an individual's brain because brain trauma can change people," said Chris Nowinski, co-director of the Center for the Study of Traumatic Encephalopathy, or CSTE, at the Boston University School of Medicine.

"No brain disease could ever explain a single act. However, we should be mindful and respectful of what brain trauma can do," said Nowinski.

study published Monday in the journal Brain, the most comprehensive look at CTE published thus far, adds fuel to the discussion, especially as it relates to professional football players.

Of the 35 players, 34 of them at the professional level, who had brain tissue sampled posthumously for the study, all but one showed evidence of disease.

CTE begins when repeated blows to the brain are not allowed to heal. With each successive blow, damage builds and a dense, abnormal protein called tau accumulates.

In its later stages, CTE can lead to things like rage, aggression, paranoia, and suicidal thoughts.

So in the rare case when a player takes his own life -- think Dave Duerson Shane Dronett and Ray Easterling -- the mind races to give the act meaning, despite the fact that these deaths defy simple explanation.

"It's a sad statement that we immediately jump to a premature conclusion that CTE is the underlying cause of such a complex and dreadful situation," said Dr. Robert Stern, co-founder of the CSTE. "Suicide and homicide are such incredibly multifactorial behaviors that CTE is one of countless potential variables that could go into it."

David Hovda, a professor of neurosurgery at UCLA, stresses that thousands of people have suffered head injuries on the football field, and thousands have suffered head injuries in the war theater -- and yet many likely do not have this specific disease, or exhibit aggressive behavior.

"There are a lot of reasons people commit suicide and commit murder," said David Hovda, director of the UCLA Brain Injury Research Center, adding that what CTE actually means behaviorally is still up for question. "I'm not sure we can tag CTE onto this."

Of the 85 people whose brain tissue was examined -- including the 34 professional football players, military members, and others exposed to repeated head trauma -- 17 had no evidence of CTE.

The reality is that not everyone exposed to repetitive brain trauma will get CTE.

Nowinski adds the caveat that those 17 people had less intense -- and less prolonged -- head trauma.

"The good news is it's clear that a couple of concussions doesn't always lead to CTE and we hope it's rare," said Nowinski. "However, when you get to the people in the database who took more than 10 years of repetitive brain trauma, nearly all of them have CTE."

What the new study begins to do is characterize the disease that raises so many questions each time a player dies.

According to the study, CTE begins at a very deep and focused point in the brain, spreading "slowly over decades to involve widespread regions" of the brain and spinal cord.

"Early on, it only involves very discrete small lesions around the brain and as it progresses, more and more brain tissue gets destroyed," said Stern. "It is only in the more severe stages that we see full-blown dementia."

And it is the more severe stages that the symptoms become profound, and crippling.

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."