Non-impact blast-related mild traumatic brain injury (mTBI) appears to be present in soldiers returning from deployments to Afghanistan and Iraq. Although mTBI typically results in cognitive deficits that last less than a month, there is evidence that disrupted coordination of brain activity can persist for at least several months following injury (Thatcher et al., 1989, 2001). In the present study we examined whether neural communication may be affected in soldiers months after blast-related mTBI, and whether coordination of neural function is associated with underlying white matter integrity. The investigation included an application of a new time-frequency based method for measuring electroencephalogram (EEG) phase synchronization (Aviyente et al., 2010) as well as fractional anisotropy measures of axonal tracts derived from diffusion tensor imaging (DTI). Nine soldiers who incurred a blast-related mTBI during deployments to Afghanistan or Iraq were compared with eight demographically similar control subjects. Despite an absence of cognitive deficits, the blast-related mTBI group exhibited diminished EEG phase synchrony of lateral frontal sites with contralateral frontal brain regions suggesting diminished interhemispheric coordination of brain activity as a result of blast injury. For blast injured (i.e., blast-related mTBI) soldiers we found that EEG phase synchrony was associated with the structural integrity of white matter tracts of the frontal lobe (left anterior thalamic radiations and the forceps minor including the anterior corpus callosum). Analyses revealed that diminished EEG phase synchrony was not the consequence of combat-stress symptoms (e.g., post-traumatic stress and depression) and commonly prescribed medications. Results provide evidence for poor coordination of frontal neural function after blast injury that may be the consequence of damaged anterior white matter tracts.
Bibliographical noteFunding Information:
This work was supported by grants from the Minnesota Veterans Medical Research and Education Foundation (formerly Minnesota Veterans Research Institute [MVRI]) and the Congressionally Directed Medical Research Program ( W81XWH-08-2-0038 ) to Scott R. Sponheim and a grant from the Minnesota Veterans Medical Research and Education Foundation to Kathryn A. McGuire. We are grateful for the contributions of Melanie Leuty and Joel W. Nelson in the collection of clinical, cognitive, EEG and MRI data. Michael Armstrong MD assisted in identifying individuals for study and Christie Clason Ph.D. assisted in the collection of neuropsychological data.
This work was supported by grants from the Minnesota Veterans Medical Research and Education Foundation (formerly Minnesota Veterans Research Institute [MVRI]) and the Congressionally Directed Medical Research Program (W81XWH-08-2-0038) to Scott R. Sponheim and a grant from the Minnesota Veterans Medical Research and Education Foundation to Kathryn A. McGuire.