Mapping default mode connectivity alterations following a single season of subconcussive impact exposure in youth football

Abstract

Repetitive head impact (RHI) exposure in collision sports may contribute to adverse neurological outcomes in former players. In contrast to a concussion, or mild traumatic brain injury, "subconcussive" RHIs represent a more frequent and asymptomatic form of exposure. The neural network-level signatures characterizing subconcussive RHIs in youth collision-sport cohorts such as American Football are not known. Here, we used resting-state functional MRI to examine default mode network (DMN) functional connectivity (FC) following a single football season in youth players (n = 50, ages 8-14) without concussion. Football players demonstrated reduced FC across widespread DMN regions compared with non-collision sport controls at postseason but not preseason. In a subsample from the original cohort (n = 17), players revealed a negative change in FC between preseason and postseason and a positive and compensatory change in FC during the offseason across the majority of DMN regions. Lastly, significant FC changes, including between preseason and postseason and between in-and off-season, were specific to players at the upper end of the head impact frequency distribution. These findings represent initial evidence of network-level FC abnormalities following repetitive, non-concussive RHIs in youth football. Furthermore, the number of subconcussive RHIs proved to be a key factor influencing DMN FC.

Subconcussive changes in youth football players: objective evidence using brain vital signs and instrumented accelerometers

“…Regarding the possibility of transient abnormalities, in the study of default mode network functional connectivity by DeSimone and colleagues, they reported positive, though non-significant, changes from post-season to pre-season of the following year. 32 These results demonstrate that brain neurophysiology is dynamic and subject to both maladaptive and adaptive changes. It is yet to be determined whether changes in brain vital signs observed in this study persist in the absence of RHI or if they resolve naturally over time.…”

“…Negative changes in default mode network functional connectivity have recently been reported after one season in players aged 8–13 years, and these were significantly associated with players’ HIE. 32 Collectively, pre-existing research suggests that while structural subconcussive changes in brain health can be observed using advanced neuroimaging, deficits in clinical and/or functional measures are either less common or more difficult to detect. In support of this observation, neuroimaging studies of non-concussed high school and collegiate football players have demonstrated white matter and neurophysiological changes in the absence of cognitive and neuromotor impairment.…”

“…However, this is consistent with attrition rates in other youth football studies. 32 Second, the clinical utility of head impact accelerometers has been questioned, given that high variability and error rates have been demonstrated between devices. 36 The consistent relationship between impacts and sessions in this study was noteworthy, as exposure to sessions provided a comparable metric.…”

Visuo‐vestibular and cognitive connections of the vestibular neuromatrix are conserved across age and injury populations

“…Young athletes may also have greater (or lesser) overall exposure to head impacts. Repetitive head impacts during collision sports, even in the absence of clinical SRC, have been demonstrated to result in changes to brain function and structure 37,78,79 . Head impact and injury‐related changes to brain functional connectivity are highly complex and it is probable that there were differing, or at least unique, external biomechanical forces that elicited symptoms in patients with SRC versus those who developed PCVD 32,80 .…”

“…For instance, internal jugular vein compression via an externally worn “neck collar” was effective in mitigating longitdunal alterations in graph theory metrics in a large cohort of young female soccer players (regions defined based on network “communities” rather than a priori selected ROIs [global vs. indvidual connectivity]) 37 . Likewise, more consistent and specific investigation into ROI changes could suppot decision‐making related to thresholds of head impact exposure that elicit maladapative change (e.g, frequency and magnitude) and/or support the targeted development of more traditional protective technologies (e.g., helmets and headgear) aiming to preserve brain function and structure in youth athletes 79,87–89 …”