Concussion History Predicts Reduced Cortical Thickness in Special Operations Forces Personnel

Abstract

Special Operations Forces (SOF) personnel are at high risk for repetitive blast and head impact exposure. Non-invasive neuroimaging techniques, such as magnetic resonance imaging (MRI), have identified concussion-related structural differences even when observable behavioral and cognitive deficits are absent. The relationship between injury history, neuroimaging, and standard clinical tests has not previously been defined in the SOF population. PURPOSE: To compare cortical morphology, symptom scores, and neurocognition in SOF personnel with and without concussion history. METHODS: SOF personnel completed an assessment battery including 3T high-resolution MRI and the Immediate Postconcussion Assessment and Cognitive Test (ImPACT). We examined symptom reporting and the ImPACT composite scores for verbal and visual memory, visual-motor processing speed, reaction time, and impulse control. The SOF personnel were categorized by self-reported concussion history (no history vs. 1+ concussions). We used FreeSurfer (v6) to reconstruct and segment the cerebral cortex. Cortical thickness was regressed on concussion history controlling for estimated total intracranial volume. The symptom reporting and ImPACT composite scores were regressed on concussion history. RESULTS: We imaged 166 SOF personnel (160 males; 65 self-reported concussion history) using MRI. Of these, 155 completed the ImPACT during a healthy baseline testing session. Two brain regions had reduced cortical thickness associated with concussion history, controlling for the total intracranial volume: left pericalcarine (t164=2.00, p=0.04); and left parahippocampal (t164=2.81, p=0.006). One region had larger cortical thickness in those with a concussion history: right transverse temporal (t164=2.35, p=0.02). Concussion history did not predict symptom or ImPACT composite score differences (p>0.05). CONCLUSIONS: Concussion history predicted cortical thickness in brain regions associated with vision and memory, which are cognitive functions affected following concussive injury. The ImPACT composites were not sensitive to concussion history. Supported by the United States Army Special Operations Command (USASOC)