The Relationship of Prior Concussion and Contact Sport Exposure With Cortical Macro and Microstructure.

Changes in cortical gray matter are a key feature of neurodegenerative diseases that have been linked with concussion and repetitive head impacts (RHIs). Prior evidence implicates prior concussion and RHI in reduced cortical thickness or volume in temporal and frontal regions, with results largely restricted to older retired contact sport athletes. Fewer studies have investigated similar associations in younger athletes or applied approaches to capture more subtle differences in gray matter earlier in the lifespan. The current study assessed the association of concussion and RHI with cortical macrostructure (cortical thickness, cortical surface area), and cortical microstructure (cortical mean diffusivity), the latter of which has been suggested to be an earlier marker of gray matter abnormalities in neurodegenerative diseases. A total of 207 otherwise healthy collegiate-aged athletes completed semistructured interviews for concussion and sport participation history, as well as a magnetic resonance imaging session including anatomical and diffusion imaging (N = 205 with available diffusion data). Cortical surface area and cortical thickness were estimated using FreeSurfer; cortical mean diffusivity was calculated with correction for partial volume. Bayesian multilevel modeling was conducted on regions of interest derived from Desikan-Killiany Atlas parcellations to determine the association of the number of prior concussions and RHI (included in the same models) with each metric, controlling for sex, age, and intracranial volume (area only). There was strong evidence for a positive association between the number of prior concussions and cortical mean diffusivity throughout most of the cortex. In addition, there was strong evidence for a positive association of the number of prior concussions with cortical surface area across several regions. For cortical thickness, there was strong evidence of inverse associations between the number of prior concussions and anterior and medial temporal cortical regions only. In contrast, only weak to no evidence of associations between years of contact sport exposure, a proxy for RHI, and any cortical surface metric was observed. These results demonstrate that cortical diffusivity may represent a more sensitive metric of subtle, early structural changes associated with repetitive neurotrauma, and highlight the importance of efforts to reduce concussion risk in sport.