The brains of college football players are subtly different from the brains of other students, especially if the players have experienced a concussion in the past, according to an important new brain-scan study that, while restrained in its conclusions, adds to concerns that sports-related hits to the head could have lingering effects on the brain, even among the young and healthy.
Almost all of us have heard by now that concussions are more injurious than was once believed. It's been widely reported that the autopsied brains of some professional football and hockey players who experienced repeated hits to the head showed signs of severe and progressive brain damage. Meanwhile, recent studies with living animals suggest that the brain may respond to even mild concussive blows with inflammatory and other reactions that, while designed to spur healing, could also contribute to tissue damage.
But many fundamental questions about the long-term impacts of blows to the head during sports remain unanswered, including which portions of the brain are most affected, whether any brain changes also affect the ability to think, and if playing a contact sport might alter the structure and function of the brains of athletes, even ones who have never experienced a confirmed concussion.
So, for a study published last week in JAMA, researchers at the Laureate Institute for Brain Research and the University of Tulsa, both in Tulsa, Okla., and other institutions, started delving into those issues by turning to the university's Division I football team. Tulsa is, of course, in the heart of football country. But the researchers say they met no resistance from the school, team or players.
"Everyone around here loves football, including me," said David Polanski, the head athletic trainer for the university's sports teams and one of the study's co-authors.
"But we also know that you can't reduce the risks" of participating, he added, "unless you know what they are."
With his help, the scientists identified 25 players who had experienced at least one medically confirmed concussion while playing football. Most of the injuries had occurred in college play, but a few during high school. Some players had experienced as many as five concussions, but most only one or two.
The researchers also gathered another 25 players who never had a concussion diagnosis.
They asked all of the athletes how many years they had been playing football.
Finally, they rounded up 25 healthy, college-aged young men who'd never played football to act as a control group.
Then they scanned all of their volunteers' brains with a sophisticated M.R.I machine that could pick up slight differences in the size or shape of various parts of the brain.
And there were differences, as it turned out. As a group, the football players had less volume in the hippocampus, a part of the brain involved in memory and emotional processing, than did the nonplayers. Among the players who had no history of concussions, hippocampal volume was as much as 16 percent smaller than the control group's. And the difference in size was even more striking among the players who had experienced a confirmed concussion, whose hippocampal volume was about 25 percent smaller than in young men who'd never played.
"That was a greater differential than we'd anticipated," said Patrick Bellgowan, a faculty member at both the Laureate Institute and the University of Tulsa and the study's senior author.
The results are particularly baffling for the players with no history of concussion. Interestingly, those athletes in each group who had played the most seasons of football tended to have the least hippocampal volume, suggesting that, at least potentially, cumulative playing time and repeated tackles might affect the brain, even without a formal concussion.
Of course, the findings, although provocative, do not in fact show that playing a contact sport shrinks hippocampal volume. "This is a single snapshot" of the players' brains, Dr. Bellgowan said, and reveals nothing about changes over time. Indeed, the results could indicate that, in some indeterminate fashion, having a smaller hippocampus predisposes someone to enjoy or excel at football — meaning that the anomalous brain structure predated the playing
And encouragingly, the findings did not show that these brain changes are linked to impaired thinking or memory skills. The scientists found little correlation between smaller hippocampal volume and thinking skills when they compared players' scores on cognitive and coordination tests. Some athletes performed well, others less so, but the size of their hippocampus played little role, although, surprisingly, the more years a subject had played football, the slower his reaction time tended to be.
Over all, the study's results underscore the importance of additional research, Dr. Bellgowan said. He and his colleagues hope to re-scan the brains of current players, as well as of alumni who no longer play, to get a better sense of any brain changes over time. They also want to scan players in high school or younger.
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