Feature: Even mild hits to the head in contact sports show obvious changes in the brain

images of brain MRIs with coloured maps indicating changes in teh brain for contact athletes versus non-contact

Coloured maps represent average brain connectivity in a brain network known as the default mode network, overlaid on regular anatomic MRI of the subjects' brains. There is an increased strength of connections during the season in rugby players (top) compared with non-contact athletes (bottom)
By Crystal Mackay, MA'05

Suffering a concussion can cause serious and often lasting damage in the brain. For athletes, it could be one strong blow to the head during a tackle, or an aggressive head-first check into the boards, but what about all of those minor hits to the head in everyday practices?

New research published in the June 17, 2020, online issue of Neurology®, the medical journal of the American Academy of Neurology, shows that those mild impacts are causing subtle brain changes, even in the brains of otherwise, healthy symptom-free athletes.

“Even with no concussions, the repetitive impacts experienced by players clearly had effects on the brain,” said Ravi Menon, PhD, Professor at Western University’s Schulich School of Medicine & Dentistry and principal investigator on the study. “We were able to show quite strikingly a very obvious trend in athletes that play contact sports over multiple seasons.”

The study followed 101 female varsity athletes at Western – 70 who played rugby, and 31 who participated in either rowing or swimming. The idea was to compare the brains of the athletes who played contact sports, with age and sex matched controls who were also involved in the same level of intense exercise without the contact. It is the first study of its kind to use another group of athletes as the control rather than using baseline pre-season measures.

The athletes wore devices to record head impacts during practises and games to provide insight into the amount of impact they were experiencing in a regular season. They also used high-field Magnetic Resonance Imaging (MRI) brain scans to look for changes in the structure of the white matter in the brain and how the different brain regions communicate with each other.

They found while rowers did not experience any impacts, 70 per cent of the rugby players experienced an average of three impacts during two practices and one pre-season game. The research team also found changes to the microstructure of the white matter in the brain of the rugby players. In some of the rugby players, those changes increased over time, and while they also seemed to recover slightly in the off season, there was evidence to show that they worsened over multiple seasons. Those same changes were not evident in the brains of the swimmers or rowers.

“These white matter tracts connect all the areas of the brain. They are the highways along which information travels between different areas, and so when you damage them, you have difficulty moving information around,” Menon said. “What your brain does, is find ways to reroute the information along a different route, which is why behaviourally you won’t be able to find any difference.”

But Menon says what they don’t yet understand is what happens when all of those routes are exhausted. The data shows that there are also compensatory changes in the brain along the other routes, so the brain is working really hard to compensate for this damage.

“We suspect that if something else happens late in life, like a stroke or dementia, you’ve now used every available pathway, and there are only so many roads you can take, so we may not see the impact of this damage for another 50 years.”Menon says this is why further research is needed to longitudinally study the impact of these contact sports over time.

“It’s clear that even sub-clinical impacts have an effect on the brain, and this has immediate implications for concussion research. Though the long-term effects of sub-clinical impacts remains unclear, an effort to limit the number of impacts athletes experience in practice could be beneficial,” said study author and alumna Kathryn Manning, PhD’18, now a postdoctoral research fellow at the University of Calgary.

Menon says this is important information for athletes, parents and coaches to understand when designing practices.

“When you’re 20, you probably feel like you’re invincible, but the fact is your brain is demonstrably showing changes when you have these multiple impacts, even if you don’t get obviously hurt on the field.”