Researchers have discovered significant changes in the brain function of high school football players over one season, despite the absence of diagnosed concussions. Their study, published in Scientific reportsfound that their brain connectivity had changed in such a way that their individual ‘brain fingerprints’ were less distinguishable.
A growing body of research has shed light on the potential health risks associated with American football, particularly the effects of repeated head impacts. While the dangers of concussions have long been recognized, less attention has been paid to the cumulative effects of smaller, sub-concussions that players often experience.
Previous studies have suggested that these smaller consequences, which are often overlooked because they do not cause immediate symptoms, can still lead to significant neurological changes over time. This concern is especially acute for high school players, who are thought to be more vulnerable because of their developing brains.
“Our group has a history of interest in investigating and protecting the brain health of contact athletes,” explains study author Bradley Fitzgerald, a doctoral candidate in electrical and computer engineering at Purdue University and a member of the Purdue Neurotrauma Group. “One of our ‘big picture’ goals is to better understand any negative consequences of repeated exposure to sports-related head acceleration events, especially in cases where the athletes may not have outwardly observable symptoms of brain injury. With this goal in mind, we are interested in investigating as many dimensions of brain health and function in contact athletes as possible.”
To conduct the study, the researchers recruited 72 male high school athletes and divided them into two groups based on their sports participation. Fifty-eight of these athletes were active participants in American football, either at the varsity or junior-varsity level, and were identified as the main focus of the study due to their exposure to repetitive head impacts. The remaining 14 athletes, who participated in sports generally free of such effects, served as a control group.
The researchers used resting-state functional MRI (rs-fMRI), a technique that can observe brain activity when a person is not engaged in a specific task, to measure the brain’s functional connectivity. They paid particular attention to the changes over time and in relation to the number and severity of head impacts, which were monitored using head-mounted sensors that recorded the maximum linear acceleration of impacts exceeding 20 g, a measure that indicates significant strength.
The football players underwent four MRI scans during their football season. These include a pre-season scan before the start of contact training, two scans at different points during the season and a post-season scan after the end of contact activities. The control group athletes underwent two MRI scans during their sporting season, allowing comparison without the variable of repeated head impacts.
The researchers found that functional connectivity in football players changed significantly during the season, with the most pronounced changes observed between the preseason and the second half of the season. Specifically, players’ brain connectivity patterns were less similar to their own preseason baseline, indicating that the repetitive head impacts associated with football matches could disrupt normal communication pathways in the brain.
These changes were most pronounced in specific parts of the brain related to movement and attention. Furthermore, a closer look at the data revealed a correlation between the magnitude of these connectivity changes and the number and severity of head impacts recorded, underscoring the potential link between repeated head impacts and changes in brain function.
But the study also found evidence of a partial recovery of these connectivity patterns after the season ended and no football-related activities had been undertaken. This suggests that although repeated head impacts may alter the functional organization of the brain, there is potential for the brain to recover its original connectivity patterns with adequate rest after exposure to such shocks.
“The core finding of our study was that functional connectivity patterns in the brains of youth football athletes changed over the course of the playing season,” Fitzgerald told PsyPost. “These changes were most pronounced late in the playing season (after several months of contact activities). At this time point at the end of the season, the functional connectivity patterns of some individuals had arguably changed so much that the connectivity profiles appeared as if they belonged to a different individual. The functional connectivity profiles appeared to return to their original pre-season patterns when the players were given time (approximately a month or more) to rest without contact activities.
“At the very least, this finding represents evidence that the brain changes and adapts as players engage in contact sports. In the worst case, these changes could be a result of brain injury, raising concerns about the long-term health of the athletes. It’s important to note that our research alone does not prove that these changes are necessarily bad for brain health, but we believe the research raises a number of warning signs that point to the need for more in-depth research into how brain health affects youth athletes can best be protected. ”
The researchers came across two big surprises in their study. The first surprise came from the discovery that changes in brain functional connectivity correlated with cumulative head acceleration metrics, especially when lower intensity acceleration events were included in the analysis. This finding was unexpected because the accuracy of head acceleration measurements was a concern.
The researchers had expected that the imprecise nature of these devices could obscure any correlations between the number of head impacts and changes in brain connectivity. But just counting these events provided valuable insights into how repeated head impacts, regardless of their individual severity, could collectively affect brain function.
“It was encouraging to find that ‘counts’ of detected events are of great value even without exceptional precision in main acceleration measurements,” Fitzgerald said.
The second surprise came from the observation that changes in brain connectivity during the second half of the football season were not as closely linked to the accumulated number of head acceleration events as they were earlier in the season.
“However, this is likely due to the fact that early season measures are strongly influenced by playing time (i.e. there is, in percentage terms, a larger difference between the accumulated main effects for starters than for reserves – of whom some barely had any impact – then later. points in the season),” Fitzgerald explained.
Going forward, the researchers emphasize the need for further research to investigate the long-term effects of these changes in brain connectivity. Questions remain about how these changes over time might affect cognitive and neurological health and whether extended periods without head impact exposure could lead to a full recovery of brain function. Future research could also investigate the effectiveness of different strategies to minimize head impact during play, possibly involving changes in sporting practices or protective equipment.
“Our long-term goals are to understand how the accumulation of repetitive head acceleration events contributes to changes in measures of brain health,” Fitzgerald said. “Knowledge of key quantifications of such events (e.g. total numbers; individual or aggregate impact intensities) provides us with technical design criteria that allow us to make recommendations on the frequency and nature of such exposures (i.e. reduced contact in practice , as per the efforts of the late Buddy Teevens at Dartmouth), or to quantify characteristics that should be included in protective equipment (for example, how much energy absorption is required for a helmet to be effective).”
The study, “Longitudinal changes in resting-state fMRI brain self-similarity of asymptomatic high school American football athletes,” was authored by Bradley Fitzgerald, Sumra Bari, Nicole Vike, Taylor A. Lee, Roy J. Lycke, Joshua D. Auger, Larry J. Leverenz, Eric Nauman, Joaquín Goñi, and Thomas M. Talavage.