Deficits in Visual System Functional Connectivity after Blast-Related Mild TBI are Associated with Injury Severity and Executive Dysfunction
Defense and Veterans Brain Injury Center Minneapolis United States
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Introduction Approximately, 275,000 American service members deployed to Iraq or Afghanistan have sustained a mild traumatic brain injury mTBI, with75 of these incidents involving an explosive blast. Visual processing problems and cognitive dysfunction are common complaints following blast-related mTBI. Methods In 127 veterans, we examined resting fMRI functional connectivityFC of four key nodes within the visual system lateral geniculate nucleusLGN, primary visual cortex V1, lateral occipital gyrus LO, and fusiform gyrus FG. Regression analyses were performed i to obtain correlations between time-series from each seed and all voxels in the brain, and ii to identify brain regions in which FC variability was related to blast mTBI severity. Blast-related mTBI severity was quantified as the sum of the severity scores assigned to each of the three most significant blast-related injuries self-reported by subjects. Correlations between FC and performance on executive functioning tasks were performed across participants with available behavioral datan 94. Results Greater blast mTBI severity scores were associated with lower FC between A LGN seed and i medial frontal gyrus, ii lingual gyrus, andiii right ventral anterior nucleus of thalamus B V1 seed and precuneus CLO seed and middle and superior frontal gyri D FG seed and i superior rand medial frontal gyrus, and ii left middle frontal gyrus. Finally, lower FC between visual network regions and frontal cortical regions predicted worse performance on the WAIS digit-symbol coding task. Conclusion These are the first published results that directly illustrate the relationship between blast related mTBI severity, visual pathway neural networks, and executive dysfunction results that highlight the detrimental relationship between blast-related brain injury and the integration of visual sensory input and executive processes.