High-Definition Fiber Tracking Study of the Executive Control Network in Blast-Related Traumatic Brain Injury
Ware, Ashley L.
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Blast-induced traumatic brain injury (bTBI) is common in Iraq and Afghanistan war veterans. However, subtle neural alterations and lack of a definitive biomarker impede clinical detection. The current study evaluated structure and functional correlates of executive control network (ECN) white matter tracts in veterans with and without bTBI to investigate the clinical utility of using High Definition Fiber Tracking (HDFT) to identify a biomarker of chronic bTBI. For the current study, male veterans (N = 38) between 24 and 50 years old completed a standardized neuropsychological evaluation that included the Stop Signal Task (SST) and structural magnetic resonance imaging. HDFT was used to derive quantitative metrics of tracts between the dorsolateral prefrontal cortex (DLFPC) and the putamen, caudate, and thalamus. Groups had similar demographic characteristics, and medical histories. Relative to the comparison group, moderate to strong effects indicated that bTBI was associated with: elevated quantitative anisotropy (QA) and reduced right hemisphere volume across tracts; reduced right DLFPC-putamen tract count and greater generalized fractional anisotropy (GFA); greater right DLPFC-thalamus tract count. A strong Group×Age interaction effect was observed on DLPFC-caudate tract count, indicating worse outcomes with older age in the bTBI group. Groups had similar SST performance, which strongly correlated with HDFT metrics across tracts in the comparison group; go and stop signal reaction time correlated positively with QA and negatively with tract volume and count; errors of commission correlated negatively with QA. Overall results support anomalous density and integrity of ECN white matter tracts in bTBI, particularly in the right putamen and thalamus tracts. In line with the literature, veterans with bTBI showed worsening DLPFC-caudate density with older age. Although ECN dysfunction was not apparent via behavioral testing, faster and more accurate task performance related to higher QA and lower tract count and volume in the comparison group, respectively. Spared ECN function, despite anomalous white matter microstructure, could indicate functional compensation in bTBI, although alternate interpretations are being explored.