Can head impacts alter athletes’ brains even without a concussion?
Like boxing, many other sports, such as rugby, see similar amounts of subclinical head impacts. These are head impacts that are relatively strong, but not strong enough to require clinical intervention (i.e., not strong enough to cause a concussion). A recent 2018 study showed that female rugby players had on average 14 ‘large’ but non-concussive head impacts per game.
Image by Yousif Haddad
There is growing evidence suggesting that these repetitive subclinical head impacts may have longer-term effects on the brain. Researchers at Western University in 2020 examined how these impacts may change the brains of non-concussed female rugby players compared to non-contact athletes, such as rowers.
The researchers used Magnetic Resonance Imaging (MRI) to visualize the brain structure of the participants. Over a 5-year period they followed a group of nationally competitive women’s rugby athletes during both the in-season (70 participants – during competition) and the off-season (60 participants – no competition). None of the participating athletes had been diagnosed with a concussion within 6 months of the study. The researchers compared the women playing rugby to a group of similarly aged non-contact female varsity rowers and swimmers also during the in-season (31 participants) and off-season (23 participants).
The connections between brain regions are important for many cognitive functions, and previous research has shown that these connections can be altered after a concussion. The researchers in this study wanted to examine if these connections are also altered after multiple head impacts that do not result in a concussion.
To examine brain connections the authors used a specialized type of MRI, called diffusion MRI (dMRI). dMRI measures the movement of water in the brain, which is used to probe brain material known as white matter. This can be thought of as highways that connect cities, where the highways are the white matter, and the cities are the brain cells. At a small scale, white matter contains the projections from a brain cell that eventually connect to another brain cell, allowing for communication between them.
Concussions typically affect memory and emotions and are also thought to disrupt the flow of information between the left and right side of the brain. The authors found significant differences across dMRI measures within white matter regions when comparing concussion-free contact athletes to non-contact athletes. Two of the main regions showing changes were the cingulum, which helps connect regions of emotion and memory, and the corpus callosum, which connects the left and right sides of the brain. Although these athletes were not concussed, they still showed noticeable changes in brain regions that are thought to be affected by a concussion.
Overall, the dMRI results suggest that repetitive subclinical head impacts produce noticeable changes in the structure of brain’s white matter, but a crucial question remains: do white matter changes during competition that disappear when an athlete stops competing?
The brainstem, a structure important for breathing and heartbeat regulation, was found to change in contact athletes between the in-season and off-season. This change was not seen between the in-season and off-season in non-contact athletes. During a season of repetitive contact there are some detectable brain changes that are not seen once the athlete stops competing, suggesting that there may be some recovery in the brainstem in the off-season. Overall, differences were found in the white matter of the brain not only between contact and non-contact athletes, but also between in-season and off-season.
While many studies have examined brain changes in concussed contact-athletes, less is known about how the brain evolves over time in non-concussed contact athletes. The authors of this study addressed this gap by examining brain changes across time in non-concussed contact athletes. Using dMRI, the Western University researchers found changes in the connections between brain regions involved in emotion and memory in contact athletes when compared to non-contact athletes. These brain changes are likely a result of the subclinical impacts that accumulate throughout multiple years of contact sports, as these changes were not observed in non-contact sports.
Athletes who experience repetitive head impacts do have detectable brain changes, even if they are not concussed. But before you put away your rugby cleats or boxing gloves for good, there are other factors to consider such as genetics that may affect whether these changes will lead to cognitive problems in the future. Nonetheless, many people, from children to adults, participate in and enjoy contact sports, where repetitive head impacts are inevitable. Fully understanding the changes these impacts bring will be essential in designing new ways to keep all those participating in sports safe and in the game.