A region on the brain stem (orange) could serve as the “canary in the coal mine” to identify brain damage caused by repetitive head trauma from sports.

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Just one season of playing football—even without a concussion—can cause brain damage

The familiar thudding soundtrack of football means nothing more to many fans than a well-executed game. But for neuroscience researchers, those sounds can signal something much darker: brain damage. Now, a new study shows playing just one season of college football can harm a player’s brain, even if they don’t receive a concussion.

Doctors and players should take note of the findings, says Stephen Casper, a medical historian at Clarkson University in Potsdam, New York, who studies concussions but was not involved with the work. “It just adds to the mountains of evidence that people should be given very clear and transparent warnings about playing football.”

Only clinicians can diagnose a concussion. They typically check for slurred speech and impaired coordination, and they conduct a physical examination for symptoms such as dilated or uneven pupils. Injuries that fall short of concussions are often overlooked, but if they happen frequently, they could be just as damaging to the brain.

In the new study, researchers at the University of Rochester (U of R) in New York followed 38 of the school’s football players. The athletes wore helmets outfitted with accelerometers to track the number and force of hits during practices and games. Before and after each season, the scientists took MRI scans of the players’ brains. The researchers looked specifically at the midbrain, a region on the brain stem that governs primitive, thoughtless functions such as hearing and temperature regulation. When a player’s head is hit from any angle, the brain ripples like the surface of a pond after a rock is thrown, explains study author Adnan Hirad, a medical student at U of R. Although the forces can affect many regions of the brain, the midbrain’s central location makes it likely to sustain damage.

The results were striking. Although only two of the 38 players received a concussion, more than two-thirds of them showed changes to the integrity of the white matter of their midbrains. Rotational hits—when a player’s helmet is struck by a glancing blow—were particularly bad for the midbrain’s white matter, the team reports today in Science Advances.

The researchers also found the same MRI signature of injury in the midbrain in a separate cohort with diagnosed concussions. In this second cohort, the changes in the midbrain were correlated with increased levels of tau protein in those individuals’ bloodstreams. The protein, which indicates brain cell damage, is linked to chronic traumatic encephalopathy, a condition that can cause memory loss, depression, and emotional instability, and can eventually lead to dementia.

The midbrain is like the “canary in the coal mine for the whole brain,” says study author Bradford Mahon, a neuroscientist at Carnegie Mellon University in Pittsburgh, Pennsylvania. Mahon and Hirad hope the region will prove useful to doctors and researchers in the future, and show a more nuanced picture of how football’s repetitive hits can harm players’ brains, even when they are not concussed.

The scientists plan to use their research to develop algorithms that could glean data from helmet accelerometers and signal when a player has sustained dangerous levels of damage. As a first step, the team has created the Open Brain Project, where players can upload their helmet data.

Still, although Casper applauds the study, he says the real question is whether college students should play football at all, given the risks. “I fear the answer is no.”

*Correction, 9 August, 5:35 p.m.: This story has been updated to reflect that higher levels of tau protein were found in a separate cohort of people who had experienced concussions.