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Deployment and Post-Deployment Experiences in OEF/OIF Veterans: Relationship to Gray Matter Volume

September 24, 2013

Deployment and Post-Deployment Experiences in OEF/OIF Veterans: Relationship to Gray Matter Volume
Source: PLoS ONE

Recent wars and political conflicts have exposed United States military men and women to increased levels of combat trauma. These experiences often lead not only to posttraumatic stress disorder (PTSD) but also to other highly comorbid mental health conditions, such as alcohol use disorders or major depressive disorders. It is estimated that approximately 20% of military veterans develop PTSD [1], [2] while approximately 7–10% develop alcohol use disorders and 17% develop major depressive disorder [1], [3]. Previous research has established a relationship between severity and amount of traumatic experiences (e.g., combat or other previous trauma) with subsequent development of PTSD and other mental health symptoms [4]–[9]. However, recent research suggests that there may be other experiences that may influence the likelihood or severity of subsequent mental health disorders. With respect to combat-related PTSD, identified resiliency factors include quality of non-combat deployment experiences (i.e., unit support or cohesion), as well as family and social support, among others [4], [5], [9]–[12].

Magnetic resonance imaging (MRI) has been helpful in delineating how trauma experiences and PTSD may relate to structure of various brain regions. PTSD has repeatedly been associated with reduced volume of hippocampal regions (see recent meta-analyses, [13], [14]), which may relate to severity of combat experiences [15] and/or severity of PTSD symptoms [16]. Studies have also identified reduced amygdala volume for PTSD versus non-PTSD with and without trauma exposure [14], though findings with this region have not been as consistently reported. Functional activation of the insula cortex (and its role in monitoring internal bodily states) has been increasingly implicated in PTSD and other anxiety disorders [17] and recent studies have also associated PTSD with reduced gray matter volume in this region [18]–[20]. Studies have additionally identified decreased volume within the temporal cortex and several frontal cortical regions, including anterior cingulate, orbitofrontal, middle frontal, and inferior frontal regions, for PTSD compared to non-PTSD groups [14], [21]–[24].

While there has been a plethora of studies focused on identifying structural abnormalities related to trauma exposure or PTSD, there has been a relative lack of research examining the impact of other factors, such as comorbid symptoms or factors related to resiliency. Alcohol use disorders in particular have been associated with structural differences that overlap with those identified for PTSD – including reduced volume within cortical regions, hippocampus, amygdala, and insula, as well as striatal regions [25]–[28]. However, a recent meta-analysis suggests that at least the hippocampal volumetric differences in PTSD cannot be fully attributed to alcohol use disorders [29].

Several investigators [30]–[34] have proposed that combat trauma and PTSD do not occur in a vacuum and that other life experiences – either good or bad, recent or long past – influence neural development and post-traumatic behavioral responses. The current study was designed to investigate how risk and resiliency factors related to deployment experiences and post-deployment symptoms of Operation Iraqi Freedom (OIF) and Operation Enduring Freedom (OEF) veterans relate to differences in gray matter volume. Specifically, we utilize MRI and voxel-based methods to investigate gray matter volumes related to the severity of combat experiences and deployment-related social support, as well as to post-deployment PTSD symptoms and level of alcohol use. In light of previous literature, we hypothesized that combat experiences and PTSD symptoms would relate to reduced hippocampal, amygdala, insula, and temporal and frontal cortical volumes.

Further, we hypothesized that greater quality of deployment social support would be a protective factor, serving as a moderator to reduce these volumetric effects. Lastly, we hypothesized that level of current alcohol use would relate to further volumetric reductions in hippocampal, amygdalar, and cortical regions as well as to volumetric reductions in striatal regions. Greater understanding of how these risk and resiliency factors relate to structural brain differences could provide insight concerning the development of post-traumatic mental health symptoms and potential strategies for prevention and treatment.

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