Playing and supporting rugby is a cherished part of many New Zealanders’ lives, with this passion often starting in childhood. However, mounting evidence suggests that participation in contact sports like rugby may be associated with increased risk for long-term cognitive deficits, white matter deterioration, and neurodegenerative diseases. Our study aims to address the distinct lack of research into changes in structural brain connectivity that occur alongside subconcussive and concussive head impacts within an adolescent rugby cohort.

We used a 3T MRI scanner to obtain multi-shell diffusion weighted scans, T1 Bravo scans, and T2 FLAIR scans from a group of adolescent rugby players (n=35), rugby players diagnosed with mild traumatic brain injury (mTBI) (n=10), and a matched control group who engage in non-contact sport (n=21). We employed Anatomically Constrained Tractography within an MRtrix pipeline to create structural connectivity networks for each subject. The instrumented mouthguard from HitIQTM was used to record the head impacts experienced by the athletes during contact training and games. A structural connectivity analysis pipeline was developed in R to standardise and streamline the analysis of adjacency matrices for both the present and future studies, and also to correlate structural connectivity metrics with head impact data.

Findings from our study revealed a decrease in total network connectivity within the rugby player group from the early to mid-season and significant changes in node strength were noted in the right and left cerebellum. The changes in strength of the right and left cerebellum strongly correlated with the cumulative angular acceleration subjects experienced because of head impacts. In addition, the rugby group had significantly increased measures of structural connectivity in comparison to non-contact sport controls regardless of the mTBI incidence. Spatially, most notable differences were detected in the bilateral hippocampus and amygdala, which are subcortical areas within in the temporal lobe. These results imply that repeated head impacts in sports like rugby can lead to observable changes in brain connectivity, potentially affecting areas such as the temporal lobe. These findings underscore the need for further research into the effects of repeated head impacts in young athletes.