The majority of University of Rochester football players wearing force-measuring devices in their helmets "experienced a decrease in the structural integrity of their brains" after one season, even if they did not suffer a concussion, according to a new study.

The research by current and former UR scientists adds to mounting evidence that repetitive hits to the head of the sort common in football and other high-impact sports have a far greater cumulative effect than previously thought.

The study, led by UR doctoral student Adnan Hirad along with former UR and current Carnegie Mellon psychologist Brad Mahon, involved placing accelerometers, which measure force of impact, inside 38 UR football players' helmets during the 2011, 2012 and 2013 seasons for every practice and game.

The output of those devices was paired with pre- and post-season brain scans to determine the relationship between hits to the head and structural changes to the brain.

They looked in particular for an effect in the midbrain, the uppermost part of the brain stem. It is relatively rigid compared to the rest of the brain, making it more susceptible to strong impacts, and it mostly controls eye movement, a function often affected in traumatic brain injuries.

The accelerometers recorded a combined 20,000 hits to the head for the 38 players. Only two of them resulted in concussions, but the researchers found that the more hits a player sustained, the more the white matter in their midbrains was damaged.

The most damaging hits were not straight-on collisions but rather those involving some rotation.

While other studies have pointed to the cumulative damage that sub-concussive hits can have, Hirad and Mahon said their study is one of the first to observe the effect in near-real time and locate it in a specific part of the brain.

"Just because you don’t have symptoms doesn’t mean you don’t actually have injuries that you need to recover from," Hirad said. "And, we don’t know if recovery from symptoms means objective recovery of the brain tissue."

The ultimate goal, they said, would be to devise a real-time monitoring system so that a player could be assessed and potentially removed from competition based on the impact to his or her brain, rather than just observing for symptoms.

The study appears in the journal Science Advances. It is the latest in a stream of research on football and concussions from UR, which in 2015 joined the national Concussion Assessment Research and Education Consortium.

The current study received funding from the National Football League Foundation as well as the U.S. Army, the National Institutes for Health and Mahon's Open Brain Project. Jeffrey Bazarian, a prominent expert on head injury at UR, was also a co-author.

Mahon and Sarah Heilbronner, another co-author, are among the plaintiffs against UR in a federal lawsuit related to brain and cognitive sciences professor Florian Jaeger.

UR football head coach Chad Martinovich declined to comment on the study. Mahon said he hopes football players, coaches and parents are developing a keener understanding of how all hits to the head, not just concussions, exact a cost.

"It’s close to being settled science that repetitive head hits are their own source of permanent damage to the brain, independent of concussions," Mahon said. "In the mainstream discourse, I don’t think we’re anything close to that being the settled understanding. … That’s potentially a very dangerous attitude."

JMURPHY7@Gannett.com

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