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Focal brain damage - 2008 Nature Publishing Group...

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Focal brain damage protects against post-traumatic stress disorder in combat veterans Michael Koenigs 1 , Edward D Huey 1 , Vanessa Raymont 1,2 , Bobby Cheon 2 , Jeffrey Solomon 3 , Eric M Wassermann 1 & Jordan Grafman 1 Post-traumatic stress disorder (PTSD) is an often debilitating mental illness that is characterized by recurrent distressing memories of traumatic events. PTSD is associated with hypoactivity in the ventromedial prefrontal cortex (vmPFC), hyperactivity in the amygdala and reduced volume in the hippocampus, but it is unknown whether these neuroimaging findings reflect the underlying cause or a secondary effect of the disorder. To investigate the causal contribution of specific brain areas to PTSD symptoms, we studied a unique sample of Vietnam War veterans who suffered brain injury and emotionally traumatic events. We found a substantially reduced occurrence of PTSD among those individuals with damage to one of two regions of the brain: the vmPFC and an anterior temporal area that included the amygdala. These results suggest that the vmPFC and amygdala are critically involved in the pathogenesis of PTSD. PTSD is characterized by re-experience of a traumatic event (for example, flashbacks), emotional numbing, avoidance of reminders of the event and hyperarousal (for example, excessive vigilance) 1 . With an estimated prevalence of over 15 million, PTSD is a major global health problem and is among the ten medical conditions most likely to cause sufferers to miss work 2,3 . Yet the biological mechanism of the disorder is unclear. Prevailing neurobiological models of PTSD focus on the interaction between the vmPFC, amygdala and hippocampus 4,5 . The role of the amygdala in fear and anxiety is well documented 6 , as is the role of the hippocampus in episodic memory 7 . The vmPFC projects directly to the amygdala 8,9 , and is thought to provide inhibitory input that regulates emotion 10 . PTSD patients have reduced hippocampus and vmPFC volumes 4,5,11 . When exposed to reminders of traumatic events, PTSD patients show diminished hemodynamic responses in the vmPFC 12–14 , but exaggerated hemodynamic responses in the amyg- dala 5,15–17 . Taken together, these data suggest that PTSD is associated with overactivation of the amygdala as a result of a lack of inhibitory control by vmPFC, as well as by deficient hippocampal function. However, imaging data cannot determine whether any of these neuroa- natomical findings reflect an underlying cause of the disorder (such as a pre-existing risk factor for the development of PTSD or trauma-induced neuropathology that engenders PTSD symptoms) or a secondary effect of the disorder (such as an artifact of primary dysfunction in other brain areas or the neural response to the experience of PTSD symptoms).
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