Concussions aren’t the only type of head injuries that damage the brains of football players. Other hits — the ones football players sustain routinely while practicing or playing competitively — can also cause observable structural changes to the brain.
“Public perception is that the big hits are the only ones that matter. It’s what people talk about and what we often see being replayed on TV,” said senior author Brad Mahon in a released statement. Mahon is a professor of psychology at Carnegie Mellon University and scientific director of the Program for Translational Brain Mapping at the University of Rochester, in Rochester, N.Y.
“The big hits are definitely bad,” he added, “but with the focus on the big hits, the public is missing what’s likely causing the long-term damage in players’ brains. It’s not just the concussions. It’s everyday hits, too.”
How the study was done
For the study, Mahon and his colleagues had 38 University of Rochester Division III football players wear accelerometers — devices that measure acceleration forces — in their helmets for an entire season (2011, 2012 or 2013). The accelerometers detected all hits of 10 gs or more.
To put the force of 10 gs in perspective, Carnegie Mellon’s press release on the study notes the following: “Astronauts on the space shuttle experienced 3 gs during lift-off. Race car drivers feel the effects of 6 gs, and car crashes can produce brief forces of more than 100 gs.”
Each player also underwent magnetic resonance imaging (MRI) of their brain within two weeks before and after the season.
The accelerometers revealed that the players sustained a combined total of more than 19,000 hits of at least 10 g force while participating in the study. Most of those hits — 59 percent — occurred during practices, while 37 percent occurred during games and 4 percent during scrimmages or other team gatherings.
The median force of the hits was about 25 gs, which means, of course, that half of the hits exceeded that amount.
Only two of those hits — affecting two players — were concussions, but the MRIs revealed that two-thirds of the remaining players experienced a decrease in the structural integrity of their brain — specifically, a reduction in the integrity of the white matter (the fibers that carry messages between neurons) in their midbrain.
The more hits a player experienced, the greater the amount of damage.
The study also found that hits in which the head twisted were more damaging to the midbrain than linear, or head-on hits.
‘Canary in the coal mine’
Why did the researchers look for changes in the midbrain? Because, as Mahon told New York Times’ reporter Gretchen Reynolds, the midbrain is particularly susceptible to hits to the head and thus acts as a kind of “canary in the coal mine” — an advanced warning of the silent damage that sub-concussive hits (ones that don’t produce the dizziness, headaches, ringing in the ears and nausea of full-blown concussions) might be doing to the brain.
To help validate these findings, the researchers also looked at white matter in the midbrains of 29 University of Rochester athletes who had sustained concussions while playing various other contact sports. The players had undergone MRIs within 72 hours of their concussion.
In addition, the researchers studied MRI images of the midbrains of 58 other individuals, including a few students who had played non-contact sports at the University of Rochester. None in this “control” group had a history of concussion.
The players who had experienced a concussion — but not those in the control group — exhibited the same kind of changes in the white matter of their midbrains as the football players in the study.
They also had higher levels of tau, a protein, in their blood. Elevated blood levels of tau are associated with neurodegenerative brain diseases like chronic traumatic encephalopathy (CTE), which has been linked to the early deaths of many professional football players.
Mahon and his colleagues did not test the University of Rochester players to see if the brain changes that showed up on the MRIs had an effect on their cognitive skills. Nor did they scan the brains of the players a third time to see if their white matter returned to normal.
Mahon told the Times that he presumed some healing was likely to have taken place because the veteran players who participated in the study showed no signs of damage to their midbrains before the season, only afterward.
Still, the study’s findings are in line with other research that has shown the cumulative and long-term effects that sub-concussive hits can have on the brain.
“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 told reporter Justin Martin of the Rochester Democrat and Chronicle. “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,” he added.
FMI: You can read the study in full on the website for Science Advances, which is published by the American Association for the Advancement of Science. Funders for the study included the National Football League Foundation, the National Institutes of Health and the U.S. Army. Based on this research, Carnegie Mellon University has taken out a provisional patent for a device that assesses “asymptomatic brain injury caused by head injuries.”