The effects of repetitive, non-concussive head acceleration events on brain morphology

Repetitive exposure to non-concussive head acceleration events (ncHAEs) often lack overt acute symptoms but are associated with a neuroinflammatory response. Whether the accumulation of ncHAEs over time leads to neurodegeneration remains unknown. The current study assessed whether exposure to ncHAEs altered brain morphology by evaluating regional brain volumes in military snipers and age- and sex-matched controls. We hypothesize that military snipers will display brain atrophy in the regions previously documented to experience high strain during firing, such as the corpus callosum, hippocampus, thalamus, and motor cortex. A total of 18 snipers from the Canadian Armed Forces (36±6 years; 177 cm; 86±9 kg; 100% righthanded) and 9 controls (37±8 years; 177±9 cm; 87±11 kg; 100% righthanded; data collection is ongoing) completed anatomical magnetic resonance imaging (MRI) scans. Brain morphology metrics were derived from the T1-weighted MRI scans, and analyzed using FreeSurfer software, with subcortical segmentation and cortical parcellation corresponding to the FreeSurfer automatic subcortical segmentation Atlas and Destrieux Atlas, respectively. Structural data was analyzed using a mixed model ANOVA. Total corpus callosum volume was non-significantly greater in snipers (P=0.0788). Anterior and posterior volumes were similar (P≥0.4954), but the central corpus callosum volume was greater in snipers (P=0.0419). Total, left and right hippocampal volumes were similar between groups (P≥0.5397); however, within the sniper group, the right hippocampus volume was greater than the left (P=0.0154). Total, left and right thalamus volumes were similar between groups (P≥0.5488), and in both groups the left thalamus volume was greater than the right (P≤0.0370). Total motor cortex volume was lower in snipers (P=0.0050). The right motor cortex volume was lower in snipers (P=0.0091) compared to controls but mean differences in the left were not significant (P=0.0793). In both groups the left motor cortex volume was greater than the right (P≤0.0008). Of the structures that experience heightened strain during rifle firing, subcortical structures were not smaller, but the sole cortical structure was. These preliminary findings highlight that the cortex of the brain may be particularly vulnerable to strain during repetitive ncHAEs. Funding: This work was supported with funding provided by the Natural Sciences and Engineering Research Council of Canada #ALLRP 558260-20. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.