Return-to-play protocols could be improved by a better understanding of the physiologic effects of mild traumatic brain injury (mTBI). Autonomic dysregulation is thought to underlie many of the multi-dimensional symptoms following mTBI and may derive from altered connectivity in the brain central autonomic network (CAN). Understanding the relationship between injury and CAN connectivity could lead to a useful biomarker for mTBI. Toward this end, the present study aimed to establish a formal relationship between non-symptomatic head-to-ball impacts (“headers”) and CAN connectivity in collegiate soccer athletes.
Eleven male NCAA Division I soccer players were monitored by athletic training staff throughout 1 season for the number of headers. Ten male NCAA Division I athletes (3 cross-country and 7 golfers) served as controls. All participants underwent resting-state fMRI pre- and post-season. Twenty ROIs were selected based on regions previously implicated in control and modulation of autonomic function. Graph theoretical analyses were used to probe changes in network architecture and connectivity. Specific contrasts focused on pre- and post-season changes that were explained by individual differences in exposure to headers (p < 0.05 uncorrected).
Within the 20 node network, increases in headers were associated with reduced degree centrality of the left and right insular cortex and right putamen (p< 0.02), increased degree and betweenness centrality in the left anterior and right posterior Para hippocampal gyri (p< 0.03), and increased betweenness centrality in the anterior cingulate cortex (p = 0.006). Headers were also associated with reduced functional connectivity within the subnetwork including the anterior cingulate cortex (p = 0.0073), right hippocampus, left putamen, and left insular cortex (p< 0.04).
Highly skilled soccer players who sustained the greatest number of head impacts also experienced the greatest altered connectivity among regions associated with autonomic function. Future work to establish autonomic function as an injury biomarker should consider the importance of cumulative impact magnitudes.