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A Boston University study released Thursday provided scientific evidence that repeated hits to the head, even those that do not produce concussion or concussion-like symptoms, can lead to the degenerative brain disease chronic traumatic encephalopathy (CTE). 

The study, which was published in the scientific journal Brain, calls into question the NFL's current method of dealing with head injuries, which focuses primarily on concussion symptoms. It also highlights the danger young athletes face while playing contact sports. 

"We've had an inkling that subconcussive hits — the ones that don't [show] neurological signs and symptoms — may be associated with CTE," Dr. Lee Goldstein, an associate professor of psychiatry at the Boston University School of Medicine and the lead investigator on the study, told NPR. "We now have solid scientific evidence to say that is so."

The study used two methods to test the hypothesis that subconcussive hits are deleterious to brain function, as well. The first method was a postmortem examination of four teenage brains who played contact sports, while the other was observation of mice who showed abnormalities in brain function after suffering brain trauma that did not produce concussion symptoms—namely, nausea, dizziness or disorientation. 

Chris Nowinski, the head of the Concussion Legacy Foundation, summarized the real-life application of this research perfectly in this harrowing statement to NPR. 

"We see the hard hits all the time, where a guy pops up and smiles and [signals] a first down, and [we think], 'OK, that hit was fine.' But what this study says is: No, that hit probably wasn't fine, and that poor guy can't feel the damage that's happening in his brain right now."

Dr. Ann McKee, the director of BU's CTE Center and a foremost authority on brain injury, said the symptom-oriented treatment practices currently in place in the NFL do not address the rot of the problem, which is the hits themselves. 

"There must be a reduction in the number of head impacts," McKee said in a statement. "The continued focus on concussion and symptomatic recovery does not address the fundamental danger these activities pose to human health."