The goal of the current study is to more fully characterize the neurobiological sequelae of exposure to primary blast forces, extending our previous findings of white matter injury in primary blast exposed Veterans both with and without acute symptoms of concussion at the time of exposure. Department of Defense (DoD) surveillance data reported 287,861 total diagnosed traumatic brain injuries (TBI) from 2000 through November, 2013, 82.5% of which were mild in severity. It is estimated that 75% of mild TBI sustained during deployment are blast-related. It is likely that many more individuals are exposed to blast during deployment but do not display symptoms consistent with mild TBI.
Most combat-related TBIs are classified as mild on the basis of symptoms at the time of injury. Preliminary evidence suggests that early evolution of blast-related mild TBI may differ from other injury mechanisms. Differences in injury mechanism(s) and/or injury evolution make it essential to determine the effects in the human brain of exposure to primary blast. Adding to the complexity of the situation, a growing body of evidence demonstrates the potential of sub-concussive events to injure the brain. Recently, our group demonstrated the use of diffusion tensor imaging (DTI) to identify spatially heterogeneous areas of white matter injury on an individual basis that were due to primary blast alone, with no other possible mechanisms of head injury present.
This project will investigate the microstructural nature and functional effect of diffuse heterogeneous white matter abnormalities present in post-deployment Veterans exposed only to primary blast, without exposure to other mechanisms likely to injure the brain. We hypothesize that post-deployment Veterans exposed to primary blast will display a greater number of white matter abnormalities than healthy unexposed post-deployment Veterans. We expect the extent of white matter abnormalities to be directly related to increased blast exposure history.
Specific Aims: 1) We will characterize white matter abnormalities present in Veterans exposed to primary blast using multimodal neuroimaging. 2) We will investigate how history of primary blast exposure and mild TBI are related to the presence of white matter abnormalities. 3) We will characterize the sequelae of white matter abnormalities present in Veterans exposed to primary blast, including effects on brain function, cognitive processes, and symptom presentation.
There is growing evidence that repetitive subconcussive events can injure the brain. Our recent findings suggest that subconcussive exposure only to primary blast forces also has the potential to injure the brain. The proposed study will provide a better understanding of the microstructural nature of white matter abnormalities present following primary blast exposure, as well as insights into the relationship between severity of blast exposure history and presence of white matter abnormalities. Further, the effect on brain networks, cognitive function, and symptom presentation will be investigated. These results will provide vital information to better understand the effect of blast exposure on the brain at all levels, possibly improving identification of at risk active duty service members and diagnosis of affected Veterans.