Understanding white matter structural connectivity differences between cognitively impaired and nonimpaired active professional fighters

Abstract

Long‐term traumatic brain injury due to repeated head impacts (RHI) has been shown to be a risk factor for neurodegenerative disorders, characterized by a loss in cognitive performance. Establishing the correlation between changes in the white matter (WM) structural connectivity measures and neuropsychological test scores might help to identify the neural correlates of the scores that are used in daily clinical setting to investigate deficits due to repeated head blows. Hence, in this study, we utilized high angular diffusion MRI (dMRI) of 69 cognitively impaired and 70 nonimpaired active professional fighters from the Professional Fighters Brain Health Study, and constructed structural connectomes to understand: (a) whether there is a difference in the topological WM organization between cognitively impaired and nonimpaired active professional fighters, and (b) whether graph‐theoretical measures exhibit correlations with neuropsychological scores in these groups. A dMRI derived structural connectome was constructed for every participant using brain regions defined in AAL atlas as nodes, and the product of fiber number and average fractional anisotropy of the tracts connecting the nodes as edges. Our study identified a topological WM reorganization due to RHI in fighters prone to cognitive decline that was correlated with neuropsychological scores. Furthermore, graph‐theoretical measures were correlated differentially with neuropsychological scores between groups. We also found differentiated WM connectivity involving regions of hippocampus, precuneus, and insula within our cohort of cognitively impaired fighters suggesting that there is a discernible WM topological reorganization in fighters prone to cognitive decline.

Rich-club in the brain’s macrostructure: Insights from graph theoretical analysis

“…In patients with traumatic brain injury (TBI), the strength of local connections is increased, but rich-club connectivity is decreased [107] . These results have been replicated in cognitively impaired and nonimpaired active professional fighters [108] . These findings suggest that peripheral subnetworks may compensate for biologically high-cost rich-club subnetworks after TBI.…”

Data_Sheet_1.docx

“…Our analysis first demonstrates sFC changes in a subset of fighters with impaired performances during visual-perception and finemotor tasks through the group comparison between nonimpaired and impaired fighters. Our definition for the impaired fighters' group is consistent with previous studies (19,20), where only fighters with standardized PSS and (or) PSY scores below 97.8% of the age and education matched general populations are classified as impaired fighters. In impaired fighters, our results show significant decreases in frontal-temporal, limbic-frontal, temporal-temporal, and temporal-limbic sFC connections, as compared to non-impaired fighters ( Table 3).…”

“…Previous studies have reported structural brain damage specifically in impaired fighters (19,20,39). We were also interested in functional brain changes in this same cohort.…”

“…These observed sFC abnormalities in impaired fighters are also in line with previously reported structural observations. With the same group definition of impaired and non-impaired fighters, diffusion-weighted MRI data have revealed widespread structural connectivity damages in regions of the hippocampus, frontal, and parietal cortices, cingulum, striatum, and occipital regions in impaired fighters' group (19,20). Furthermore, previous studies in TBI patients have shown that injuries to axons during one severe head trauma might disrupt the exquisite timing of neuronal communication within and between brain regions and might therefore account for the post-traumatic cognitive and executive dysfunctions (5,53,54).…”

“…The Professional Fighters Brain Health Study (PFBHS) launched at our center in 2011 (17) has focused on investigating brain changes related to repetitive head trauma and their associations with clinical and neuropsychological deficits in active professional fighters. Specifically, in PFBHS, structural MRI studies have revealed both cross-sectional and longitudinal brain volumes loss in fighters (18); and in a subset of fighters with neuropsychological impairments, abnormal white matter microstructural organization (19) and white matter topological reorganizations (20) have been observed with diffusion-weighted MRI studies.…”