Matt Birk knows concussions. The Ravens center has had three confirmed in his life, the most recent of which left him in a fog on the sideline of a home game in Minnesota trying to remember how exactly to leave the field.

Birk is not as knowledgeable, however, about the practice thuds and collisions that never register on the concussion meter but jostle the brain nevertheless. Those are the ones that concern him now, the ones that might come back to haunt him 20 years down the road when he suddenly forgets where he left the car keys - or the car.

"What worries me," Birk, 33, said last week, "is the repeated trauma every day, the many collisions of playing offensive line. What's the cumulative effect of those?

"You always want to know, or try to predict, the future. And 20 years from now, the possibility of me being affected mentally in some way by all this is a scary deal."

That is one of the reasons Birk, Sean Morey of the Arizona Cardinals and Lofa Tatupu of the Seattle Seahawks agreed to donate their brains, time and - in Birk's case - money to brain research. They are the first three active players to volunteer their brains upon death. What's more, the NFL has recognized the need for more research into the effects of repetitive blows to the head.

Recent studies on brain trauma suggest that repetitive blows to the head might cause a form of dementia known as chronic traumatic encephalopathy (CTE), a progressive, degenerative brain disease. Two different groups at different universities are working along parallel tracks in an attempt to identify risk factors and possible treatment and cure for the disease.

Since Dr. Bennet Omalu, a forensic neurologist, discovered CTE in the brain of Hall of Fame center Mike Webster in 2003, these two groups have found tau, a toxin protein that kills brain cells and impairs function, in the brains of at least 10 deceased professional or college football players.

It was also found in the brains of former NFL players Terry Long, Justin Strzelczyk, Andre Waters, Tom McHale and John Grimsley, all of whom died prematurely.

"When you're talking about CTE, there are long-term consequences to repetitive blows to the head, whether they are concussions or sub-concussive blows, in some people," said Dr. Robert Stern, co-director of the Center for the Study of Traumatic Encephalopathy at Boston University School of Medicine. "Pretty much every brain that's been looked at of a football player who died prematurely ... was shown to have CTE."

It is an alarming incidence of pathology that has gotten the attention of the NFL. Although the NFL's concussion committee has suggested there is no evidence that repetitive blows to the head have long-term consequence, the committee is reconsidering its position.

The league hired Dr. Peter Davies, professor of pathology and neuroscience at Albert Einstein College of Medicine, as a consultant on brain trauma. Davies, an expert in the Alzheimer's field, has worked with Omalu and Dr. Julian Bailes at the Rockefeller Neuroscience Institute at West Virginia University. It is Davies' influence, after reviewing slides with Omalu and Bailes, that prompted the concussion committee to rethink the effect of repeat trauma to the brain.

"I think the committee was skeptical at first," said Dr. Andrew Tucker, the Ravens' team physician and a member of the committee. "Now I think the collective mindset is there is something here, but we're probably not sure about the cause and effect. That's really where the debate is.

"The committee is saying, yes, there's something there, but the question is, is it all due to trauma, or part trauma and other factors that haven't been identified yet?"

Omalu and Bailes originally worked with the Boston University team of researchers, only to break off and form the Brain Injury Group, affiliated with the Rockefeller Neuroscience Institute.

Bailes, chairman of the department of neurosurgery at West Virginia, said after looking at a "very large number" of brains, his group has moved the bar forward on cause, but has not reached a conclusion.

"We think the predominant common exposure here is multiple concussive and sub-concussive blows to the head," he said. "That means you weren't necessarily knocked out and maybe didn't recognize that you had trauma.

"[But] I do believe there could be other contributing or mitigating factors, as others have suggested. I have a feeling that genetic predisposition may play a role."

Genetics may help explain why a deceased 18-year-old athlete also was found to have CTE, when the majority of cases involve older players and athletes.

At Boston University, the Center for the Study of Traumatic Encephalopathy works hand-in-hand with the Sports Legacy Institute, which studies brain injury under co-founders Dr. Robert Cantu, one of the leading authorities on concussion, and Chris Nowinski.

Nowinski's 2006 book " Head Games" raised a public red flag on brain injuries. He said he suffered six concussions in five years while playing football at Harvard - with Birk - and wrestling professionally in the WWE, where he was sometimes known as Chris Harvard.

It was Nowinski's Harvard connection to Birk that got Birk's commitment to the brain bank. In his 12th NFL season, Birk doesn't expect that research results will arrive in time to necessarily help him.

"If we can make it better for future generations, that would be great," he said.

Birk hopes that research eventually will produce a test that can diagnose CTE in living athletes and find a cure. There is no way to find CTE in the brain now except by autopsy.

Nowinski began his personal crusade on concussions after he developed a sleep disorder in the wake of his most recent concussion in June 2003, suffered when he hit the ground in a match against the Dudley Boyz.

"I finished the match, but basically I had severe post-concussion symptoms for five weeks because I never got the proper advice to rest," he said.

Nowinski is hopeful that the push for more research will ultimately help not only professional athletes, but young athletes as well.

"I think we are going to be able to get an idea of how many people have this," he said. "With the clinical work, we'll find out what the risk factors are and be able to diagnose CTE in living people. And then be able to treat it and maybe even cure it. With the work BU is doing, we will have more leverage to adjust how children play the game, too."

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