Diffusion tensor imaging evidence of white matter disruption associated with loss versus alteration of consciousness in warfighters exposed to combat in Operations Enduring and Iraqi Freedom.

The effects on the human brain of mild traumatic brain injury (mTBI), which is defined as a brief alteration (AOC) or loss of consciousness (LOC), are incompletely understood. Major psychiatric illnesses such as major depressive disorder (MDD) and posttraumatic stress disorder (PTSD) are common after mTBI. Prior research suggests that individuals who develop MDD after blast-related mTBI versus those who do not show significant white matter disruption and higher rates of LOC, suggesting that LOC might be uniquely associated with brain changes that increase the risk of developing mental illness after neurotrauma. Therefore, the objective of this study was to examine the effects of LOC, MDD, and PTSD on white matter integrity in individuals who reported experiencing mTBI during combat in Operations Enduring and Iraqi Freedom. We hypothesized that LOC would be associated with significant disruption of white matter, above and beyond putative effects of MDD and PTSD. To test this hypothesis, 46 individuals who experienced blast-related mTBI underwent a detailed clinical assessment and diffusion tensor imaging. As hypothesized, LOC versus AOC individuals displayed significantly lower fractional anisotropy (FA) in 14 regions, which included the superior longitudinal fasciculus and corpus callosum. No regions of significant FA difference were identified between individuals with and without PTSD, or between individuals with and without MDD. These preliminary results show that LOC is associated with detectable alterations in brain microstructure and may suggest a brain basis for psychiatric symptoms and mental illness after mTBI.