Alteration of Default Mode Network in High School Football Athletes Due to Repetitive Subconcussive Mild Traumatic Brain Injury: A Resting-State Functional Magnetic Resonance Imaging Study

Abstract

Long-term neurological damage as a result of head trauma while playing sports is a major concern for football athletes today. Repetitive concussions have been linked to many neurological disorders. Recently, it has been reported that repetitive subconcussive events can be a significant source of accrued damage. Since football athletes can experience hundreds of subconcussive hits during a single season, it is of utmost importance to understand their effect on brain health in the short and long term. In this study, resting-state functional magnetic resonance imaging (rs-fMRI) was used to study changes in the default mode network (DMN) after repetitive subconcussive mild traumatic brain injury. Twenty-two high school American football athletes, clinically asymptomatic, were scanned using the rs-fMRI for a single season. Baseline scans were acquired before the start of the season, and follow-up scans were obtained during and after the season to track the potential changes in the DMN as a result of experienced trauma. Ten noncollision-sport athletes were scanned over two sessions as controls. Overall, football athletes had significantly different functional connectivity measures than controls for most of the year. The presence of this deviation of football athletes from their healthy peers even before the start of the season suggests a neurological change that has accumulated over the years of playing the sport. Football athletes also demonstrate short-term changes relative to their own baseline at the start of the season. Football athletes exhibited hyperconnectivity in the DMN compared to controls for most of the sessions, which indicates that, despite the absence of symptoms typically associated with concussion, the repetitive trauma accrued produced long-term brain changes compared to their healthy peers.

Preliminary findings of altered functional connectivity of the default mode network linked to functional outcomes one year after pediatric traumatic brain injury

“…Recent studies suggest that subconcussive hits may relate to within-DMN connectivity, and so it is possible that this may have contributed to our findings. 48,49 …”

Collegiate women's soccer players suffer greater cumulative head impacts than their high school counterparts

“…Whether these changes result in long-term deficits likely depends on a variety of, as yet unknown, factors but it has been established that up to 72% of a typical high school football team exhibits changes that persist well into the off season when examined using functional MRI . In addition, resting state functional MRI imaging has demonstrated significant differences between collision sport athletes at their pre-season evaluation and non contact sport controls (Abbas et al, 2015a(Abbas et al, , 2015bBailes et al, 2013;Johnson et al, 2014;Johnson et al, 2012;McKee et al, 2009;Talavage et al, 2014). Taken together, these data indicate that elucidating which physical insults eventually lead to traumatic brain injury requires a characterization of the overall distribution of head impacts experienced by athletes during competition.…”

“…More importantly, studies looking at all levels of soccer play have shown that participation in soccer is associated with neurological deficits, even in the absence of a head injury diagnosis (Matser et al, 1999;O'Kane et al, 2014;Witol and Webbe, 2003). It has also been shown that subconcussive hits (defined as head impacts inducing no readily observable symptoms) in contact sports have the ability to cause neurophysiological changes that accumulate from one season to the next (Abbas et al, 2015a(Abbas et al, , 2015bBailes et al, 2013;Breedlove et al, 2014). Whether these changes result in long-term deficits likely depends on a variety of, as yet unknown, factors but it has been established that up to 72% of a typical high school football team exhibits changes that persist well into the off season when examined using functional MRI .…”

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“…3 In addition, recent work has demonstrated that between 70% and 95% of high school football athletes exhibited substantial neurophysiological changes without easily identifiable symptoms. [4][5][6][7][8][9][10] These changes depend primarily on the number and rate of head impacts as well as their magnitude and location. The effects persist well into the offseason and may not resolve by the beginning of the subsequent season.…”