Non-Concussive Head Hits Influence the Brain’s Microstructure

Conversations about injuries in high-impact sports, such as football, hockey, and rugby, typically center around concussions, brain injuries that can affect memory, cognition, and balance. But not every collision yields a concussion, and even repeated, seemingly harmless impacts can alter the microstructure of white matter, myelinated neurons located deep in the brain, researchers reported in Neurology in July.

The study followed 104 female collegiate athletes in rugby, swimming, and rowing. Athletes wore headband sensors to measure the force of collisions during practices and games. None of the hits experienced by any athlete caused a concussion. Still, MRI and other imaging techniques showed differences in the white matter of rugby players who suffered low-impact collisions compared with the white matter of swimmers and rowers who didn’t suffer head hits. The differences were most noticeable in the corpus callosum, a nerve bundle that facilitates communication between the brain hemispheres, says study coauthor Ravi Menon, a neuroscientist at Robarts Research Institute in Canada.

Specifically, imaging during and after the athletes’ competitive seasons showed altered axon placement and increased functional connectivity among white matter neurons in the brains of the rugby players. Such neural rewiring, previous research suggests, could be a way for the brain to compensate for an injury.

Following athletes in the off-season is novel, says Pashtun Shahim, a physician at the National Institutes of Health Clinical Center who was not involved with the work. But, he cautions, “whether these changes in functional connectivity or white matter integrity are transient or persist over a long time is unclear.” Blood biomarkers that can be tracked noninvasively over longer periods of time, Shahim suggests, would be a more practical way to identify potential axon disruption in college athletes.