Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Medical Biophysics

Supervisor

Menon, Ravi S.

Abstract

Concussion is a prevalent injury associated with contact sports, however the underlying brain changes associated with concussion remain poorly understood. Therefore it is critical to (a) understand the complex sequelae that underlie concussion, (b) when or if the brain recovers, and (c) if there are brain changes associated with contact sports in general. Advanced imaging techniques may be sensitive to changes that persist beyond relatively prompt symptom recovery and clearance to return to play.

Resting state functional MRI (RS-fMRI) and diffusion tensor imaging (DTI) data was acquired on the 3T at Robarts Research Institute from healthy and concussed athletes from three separate cohorts. Healthy male hockey players were compared to longitudinal data acquired from concussed peers participating in Bantam-level hockey at 24-72 hours and 3 months after the injury. There were alterations in diffusion measures along multiple tracts with the largest significant decreases located along the superior longitudinal fasciculus at both times post-concussion. DTI tractography was used to relate diffusion changes with acute changes in functional connectivity. At 3 months post-concussion, network and regional connectivity analysis revealed compensatory functional hyperconnectivity patterns based on correlations with clinical symptoms and diffusion data.

Longitudinal imaging data was acquired from concussed female rugby players post-concussion (at 24-72 hours, 3 and 6 months after injury) and compared to non-concussed teammates throughout the in- and off-season. Using a data-driven linked independent component analysis we observed acute disruptions in diffusion metrics inferiorly along the brainstem that recovered by 3 months post-concussion. However, we also observed long-lasting signatures that reflect co-varying alterations in brain microstructure and functional connectivity that related to the number of self-reported concussions. Based on these findings it appears that concussion initiates both acute and persistent changes to central white matter structures with subtle changes in functional connectivity.

Given these findings, we acquired data from varsity-level female swimmers and rowers that were also scanned during the in- and off-season in order to directly compare with healthy rugby players and rule out the effects of high-level competitive exercise. We used accelerometers to quantify head rotational accelerations in a subset of the rowers and rugby players to confirm the number and magnitude of subclinical impacts. We quantified DTI alterations along major white matter tracts in contact compared to non-contact athletes that were in the opposite direction of our concussion findings. Diffusion changes within the genu and splenium of the corpus callosum were related to a history of concussion. Fluctuations in brainstem diffusion parameters between the in- and off-season as well as functional hyperconnectivity patterns within the default mode and medial visual networks were observed in contact athletes only.

Together, these studies suggest that concussions result in an acute set of symptoms and microstructural brain changes. Despite quick resolution of symptoms, evidence of persistent axonal disruption exists at 3 and 6 months post-concussion and well-beyond symptomatic recovery. While functional hyperconnectivity may be one mechanism that allows the brain to function despite these disruptions, concussion may also compromise neuroprotective microstructural changes that protect the young, healthy brain throughout years of contact play. It remains to be seen if the brain changes associated with contact play and concussions are directly related to later risks of neurodegenerative processes.

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