Researchers have discovered significant changes in the brain function of high school football players over a single season, despite the absence of diagnosed concussions. Their study, published in Scientific Reports, found that their brain connectivity was altered to a point where their individual ‘brain fingerprints’ became less distinguishable.
A growing body of research has been shedding light on the potential health risks associated with American football, particularly the impacts of repeated head collisions. While the dangers of concussions have long been acknowledged, less attention has been given to the cumulative effects of smaller, sub-concussive hits that players frequently experience.
Previous studies have suggested these lesser impacts, often overlooked since they don’t cause immediate symptoms, could still lead to significant neurological changes over time. This concern is especially acute for high school players, who are thought to be more vulnerable due to their developing brains.
“Our group has a history of interest in exploring and protecting the brain health of contact sports athletes,” explained study author Bradley Fitzgerald, a PhD candidate in electrical and computer engineering at Purdue University and member of the Purdue Neurotrauma Group. “One of our ‘big picture’ goals is to better understand any negative consequences of repetitive exposure to sports-related head acceleration events, especially in cases where the athletes may not have outwardly observable symptoms of a brain injury. With this goal in mind, we’re interested in exploring as many dimensions of brain health and function in contact sports athletes as possible.”
To conduct the study, the researchers recruited 72 male high school athletes, dividing 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 designated as the study’s main focus due to their exposure to repetitive head impacts. The remaining 14 athletes, who participated in sports typically free from such impacts, served as the control group.
The researchers used resting state functional MRI (rs-fMRI), a technique that allows for the observation of brain activity when a person is not engaged in any 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 peak linear acceleration of impacts exceeding 20g, a measure indicating a significant force.
The football players underwent four MRI scans throughout their football season. These included a pre-season scan before the start of contact practices, 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 sports seasons, allowing for comparison without the variable of repetitive 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, the connectivity patterns of players’ brains became less similar to their own preseason baseline, indicating that the repeated head impacts associated with football play could disrupt the normal communication pathways within the brain.
These changes were most pronounced in specific areas of the brain associated with movement and attention. Moreover, a closer look at the data revealed a correlation between the extent of these connectivity changes and the number and severity of head impacts recorded, underscoring the potential link between repetitive head impacts and alterations in brain function.
But the study also found evidence of partial recovery in these connectivity patterns after the season ended and no football-related activities were undertaken. This suggests that while repetitive head impacts can alter the brain’s functional organization, there is potential for the brain to recover its original connectivity patterns with sufficient rest from exposure to such impacts.
“The core finding of our study was that the functional connectivity patterns in the brains of youth football athletes changed over the course of the play season,” Fitzgerald told PsyPost. “These changes were most pronounced late in the play season (after multiple months of contact activities). At this late-season time point, some individuals’ functional connectivity patterns had arguably changed so much that the connectivity profiles appeared as if from a different person. The functional connectivity profiles appeared to change back towards their original pre-season patterns when the players were given time (about a month or longer) to rest without contact activities.”
“At a minimum, this finding represents evidence of the brain changing and adapting while the players engage in contact sports. In a worst-case scenario, these changes may reflect injury to the brain, raising concerns for the long-term health of the athletes. It is important to note that our study alone does not prove that these changes are necessarily bad for brain health, but we believe the study raises some warning flags that signal a need for deeper investigation on how to best protect the brain health of youth athletes.”
The researchers encountered two main surprises in their study. The first surprise came from the discovery that self-similarity changes in brain functional connectivity correlated with cumulative head acceleration metrics primarily when lower-intensity acceleration events were included in the analysis. This finding was unexpected because the accuracy of head acceleration measurements has been a point of concern.
The researchers had anticipated that the inexact nature of these devices might obscure any potential correlations between the number of head impacts and changes in brain connectivity. But the mere count of these events provided valuable insights into how repetitive head impacts, regardless of their individual severity, could collectively influence brain function.
“It was encouraging to find that ‘counts’ of detected events are of high value even without exceptional precision in head acceleration measurements,” Fitzgerald said.
The second surprise arose from the observation that changes in brain connectivity during the latter 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 likely arises from early season measures being greatly affected by playing time (i.e., there is, percentage-wise, a greater difference between accumulated head impacts for starters than reserves — some of whom have barely had any impacts — than at later points in the season),” Fitzgerald explained.
Moving forward, the researchers emphasize the need for further studies to explore the long-term effects of these brain connectivity changes. Questions remain on how these alterations might affect cognitive and neurological health over time and whether longer periods without exposure to head impacts could lead to a complete recovery of brain function. Future research could also explore the effectiveness of different strategies to minimize head impacts during play, potentially involving changes in sports practices or protective gear.
“Our long-term goals are to understand how accumulation of repetitive head acceleration events contributes to alterations in measures of brain health,” Fitzgerald said. “Knowledge of the key quantifications of such events (e.g., aggregate counts; individual or aggregated impact intensities) provides us with engineering design criteria allowing us either to make recommendations about 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 features that should be incorporated into protective equipment (e.g., how much energy absorption is necessary 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.