Constrained Topology Of Cortical Microstructural Profile Covariance Is Associated With Head Impact Exposure In Amateur MMA Athletes

PURPOSE: Gradients of cortical architecture represent a fundamental organizational principle of the brain and can be characterized by patterns of myelin-sensitive contrast across different cortical depths ("microstructural profile covariance"; MPC). We tested whether MPC topology is sensitive to the effects of sport-related head impacts. METHODS: Impact data was collected using instrumented mouthguards in 7 amateur Mixed Martial Arts (MMA) athletes (1 female; 21-32 years old) over 30 weeks. Magnetic resonance imaging was performed between 20 and 23 weeks (n = 5) and again between 28 and 30 weeks (n = 6) using T1w (1 mm isotropic; TR/TE = 1950/4 ms) and T2w (.48 mm x .48 mm x 1 mm; TR/TE = 3200/449 ms) sequences at 3 T. Preprocessing was performed using a containerized version of the HCP Lifespan Pipelines (v4.7.0). Maps of the scaled T1w/T2w ratio were re-sampled at 17 equidistant surfaces between the pial and white matter surfaces and parcellated according to the ‘Schaefer 1000’ atlas. Diffusion embedding was employed to derive individual MPC gradients of spatial similarity among the surfaces, which were then aligned with a group average MPC gradient using Procrustes analysis. The topology of individual, aligned MPC gradient trajectories in Euclidean space were characterized using complementary manifold metrics (convex hull volume and surface area) and recurrent quantification analysis (determinism, recurrence rate). Head impact exposure was quantified by the sum of peak linear acceleration (PLA) and peak rotational acceleration (PRA) for all impacts exceeding 10 g. Inference was performed by regressing each topological measure onto each exposure metric (fixed effects) with random intercepts for each participant. RESULTS: 1758 impacts [Mean(SD); PLA = 14.4(5.0)g; PRA = 1138(699)rad/s2] were recorded over 133 practice sessions and 2 competitions. No participants reported a diagnosed concussion during the study period. Greater total PLA and PRA were independently associated with reduced convex hull volume and surface area (F(1,9) > 10.46, p < .01) and greater recurrence rate and determinism (F(1,9) > 6.27, p < .03). CONCLUSIONS: Our findings suggest that head impacts sustained by MMA athletes reduce the diversity and complexity of cortical microstructural organization in a dose-dependent manner. Supported by: Instrumented mouthguards were provided through 5R24NS098518 (PI: Camarillo)