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Original Articles
Introduction
Experiencing a traumatic event can result in the development of a post-traumatic stress disorder (PTSD; Breslau et al. 1998). PTSD is characterized by re-experiencing the traumatic event, avoiding and numbing symptoms, and hyperarousal symptoms (APA, 2013). The amygdala is a brain structure involved in emotional processing, and is particularly associated with fear (LeDoux, 2000). Heightened amygdala responsivity in general was hypothesized to be an important neurobiological characteristic of PTSD (Shin et al. 2006). However, this hypothesis is mainly based on specific findings regarding the brain response to trauma/fear-related stimuli. An increased amygdala response to trauma-related stimuli (e.g. Shin et al. 1997; 2004) or fearful faces (e.g. Rauch et al. 2000; Shin et al. 2005; Bryant et al. 2008) was often, but not always (e.g. Bremner et al. 1999a , b ; Lanius et al. 2001; Britton et al. 2005), observed in PTSD patients, using different imaging techniques. Trauma reminders elicit strong fear responses in PTSD patients, mediated by the amygdala (Rauch et al. 2006). Fearful faces may represent indicators of danger, and provoke a larger amygdala response than emotional pictures (Hariri et al. 2002). Three studies investigated the response to trauma-unrelated emotional pictures (Phan et al. 2006; Brohawn et al. 2010; Brunetti et al. 2010), but study samples were small and results opposing: a hyper- and hyporesponsive amygdala to negative stimuli was observed. To test the hypothesis that the amygdala of PTSD patients is hyperresponsive in general, a thorough investigation of trauma-unrelated emotional processing in PTSD is required.
Other areas involved in emotional processing are the hippocampus, the insula (Phillips et al. 2003a ), and the anterior cingulate cortex (ACC), in particular the dorsal ACC (dACC) and subgenual ACC (sgACC) (Beckmann et al. 2009). Structural MRI studies have implicated the hippocampus (Gilbertson et al. 2002; Bremner et al. 2003; Karl et al. 2006), insula (Herringa et al. 2012), and ACC (Dickie et al. 2013) in PTSD. PTSD was associated with hippocampal hyperactivity (Werner et al. 2009; St. Jacques et al. 2011) as well as decreased hippocampal activity (Bremner et al. 2003; Milad et al. 2009). Increased insula was demonstrated in PTSD patients (Etkin & Wager, 2007; Fonzo et al. 2010; Aupperle et al....