Assessing the Impact of Post-Traumatic Stress Symptoms on the Resting-State Default Mode Network in a Military Chronic Mild Traumatic Brain Injury Sample

The relationship between post-traumatic stress disorder (PTSD) and chronic symptoms of mild traumatic brain injury (mTBI) is difficult to discern and poorly understood. An accurate differential diagnosis, assessment, and treatment of mTBI and PTSD are challenging due to significant symptom overlap and the absence of clearly established biomarkers. The objective of this work is to examine how post-traumatic stress influences task-free default mode network in chronic mTBI subjects. Control subjects (N= 44) were compared with chronic mTBI subjects with low (N= 58, PTSD Checklist-Civilian Version [PCL-C] total < 30), medium (N=124, PCL-C total = 31-49), and high (N= 105, PCL-C total >= 60) post-traumatic stress symptoms (PTSS). The results indicate significant differences in Brodmann area 10 for all mTBI subject groups, indicating potential mTBI-related disruptions with regulation of emotions and decision-making. The effects of PTSS were observed in the anterior cingulate and parahippocampus, suggesting possible disruptions pertaining to memory regulation, encoding, and retrieval. The overall results indicate the presence of aberrant connectivity patterns between controls and chronic mTBI subjects with low, medium, and high PTSS. Furthermore, the findings suggest a disruption in attention relating to a network of brain regions involved with emotional regulation and memory coding, rather than a fear-related response. Taken together, the results suggest these regions form a network that could be a target for future research pertaining to PTSD and chronic mTBI. Furthermore, the use of clinical measures, task-based imaging studies, or multimodal imaging could help further elucidate specific neural correlates of PTSS and mTBI.