Influence of Lifetime Mild Traumatic Brain Injury and Repetitive Head Impact Exposure on the Aging Brain

This dissertation aims to examine associations between remote mild traumatic brain injury (mTBI), and cortical thickness, subcortical volumes, and cognitive functioning via a systematic literature review and retrospective data analyses. Study 1 consisted of a systematic review of the literature investigating long-term brain impacts, assessed in vivo using neuroimaging methods, of exposure to mTBI and repetitive head impacts (RHIs) during adulthood. Findings from the systematic review showed that remote mTBI/RHI exposure was associated with neurological abnormalities revealed by neuroimaging across several modalities (i.e., diffusion tensor imaging, magnetoencephalography, magnetic resonance spectroscopy, positron emission tomography, spectral domain optical coherence tomography, and several magnetic resonance imaging techniques), though conclusions are limited due to methodological constraints in the studies examined. Given the gaps in the literature identified in Study 1 (i.e., a lack of research on long-term mTBI exposures in veteran samples), Study 2 consisted of analyses to examine associations between mTBI exposure and cortical thickness across the brains of Vietnam War Veterans. Data from this sample of service members was obtained from the Alzheimer’s Disease Neuroimaging Initiative - Department of Defense (ADNI-DOD). Participants included 47 male veterans with mTBI exposures (mean age = 69.43, SD = 5.02) and 82 controls (veterans without mTBIs; mean age = 68.51, SD = 4.69). Associations between mTBI, age, education, cognitive status, PTSD symptoms, and cortical thickness were examined. Three regions, i.e., the left caudal middle frontal and bilateral superior frontal cortices, showed greater cortical thickness for the mTBI group. These findings indicate potential regions for future analyses examining long-term mTBI sequelae. Finally, given the close association between TBI and Alzheimer’s disease pathology, study 3 examined the impact of mTBI on cortical thickness and subcortical volumes in AD-vulnerable regions, as well as memory functioning in this cohort. Narrowing ROIs to those implicated in AD revealed several regions that were associated with mTBI exposures (i.e., left lateral temporal cortex, right posterior cingulate cortex, right amygdala, and right inferior frontal cortex). These studies show that mTBI can have long-term but circumscribed effects on the brain.