Dissociative responses to conscious and non-conscious fear impact underlying brain function in post-traumatic stress disorder

Abstract

Background. Dissociative reactions in post-traumatic stress disorder (PTSD) have been regarded as strategic responses that limit arousal. Neuroimaging studies suggest distinct prefrontal responses in individuals displaying dissociative and hyperarousal responses to threat in PTSD. Increased prefrontal activity may reflect enhanced regulation of limbic arousal networks in dissociation. If dissociation is a higher-order regulatory response to threat, there may be differential responses to conscious and automatic processing of threat stimuli. This study addresses this question by examining the impact of dissociation on fear processing at different levels of awareness.Method. Functional magnetic resonance imaging (fMRI) with a 1.5-T scanner was used to examine activation to fearful (versus neutral) facial expressions during consciously attended and non-conscious (using backward masking) conditions in 23 individuals with PTSD. Activation in 11 individuals displaying non-dissociative reactions was compared to activation in 12 displaying dissociative reactions to consciously and non-consciously perceived fear stimuli.Results. Dissociative PTSD was associated with enhanced activation in the ventral prefrontal cortex for conscious fear, and in the bilateral amygdala, insula and left thalamus for non-conscious fear compared to non-dissociative PTSD. Comparatively reduced activation in the dissociative group was apparent in dorsomedial prefrontal regions for conscious fear faces.Conclusions. These findings confirm our hypotheses of enhanced prefrontal activity to conscious fear and enhanced activity in limbic networks to non-conscious fear in dissociative PTSD. This supports the theory that dissociation is a regulatory strategy invoked to cope with extreme arousal in PTSD, but this strategy appears to function only during conscious processing of threat. IntroductionPost-traumatic stress disorder (PTSD) is characterized by abnormal fear reactions, ranging from hyperreactivity to dissociative responses to threat. Dissociative phenomena occur in a substantial proportion of individuals with PTSD, and include emotional numbing, psychogenic amnesia, depersonalization and derealization symptoms. It is argued there may be a subtype of PTSD that involves an ongoing 'dissociative ' rather than 'hyperarousal ' reaction to threat (Bremner, 1999). In this context, dissociation has been conceptualized as an avoidant strategy to reduce awareness of aversive emotions such as extreme anxiety (Griffin et al. 1997).The neural mechanisms underlying dissociative responses in PTSD are insufficiently known. Neuroimaging studies suggest there may be distinctive prefrontal responses to trauma memories in individuals with dissociative and non-dissociative PTSD responses (Lanius et al. 2006). Individuals displaying a 'hyperarousal ' PTSD response to traumatic narratives, with heightened autonomic and emotional reactivity to trauma scripts, have reduced bilateral medial frontal activity [Brodmann area (BA) et al. 2002). Consistent with this propo...

Pain sensitivity and neural processing during dissociative states in patients with borderline personality disorder with and without comorbid posttraumatic stress disorder: a pilot study

“…16 In contrast, Felmingham and coworkers 17 found a significant positive correlation between dissociative responses and activation in the left parahippocampal gyrus during nonconscious fear in patients with PTSD. Our results are consistent with previous findings; 16,17 nevertheless, there are differences in hemispheres or contrary correlations that might result from the different patient sample, the fact that we did not use explicit trauma scripts to induce dissociation, or the different study design (e.g., compared with Felmingham and colleagues 17 ). The fact that we did not use explicit trauma scripts in our study may be seen as an advantage because our findings are not confounded by the effects of traumatic remembrance.…”

“…Finally, we did not assess the awareness of fear, which appears to play a crucial role in the activation pattern of dissociation. 17 Future studies should examine whether the enhanced activation in frontal regions is a correlate of a control mechanism following the presentation of the script or a neural reflection of dissociation.…”

“…Based on previous findings, 16,17 we hypothesized that there would be increased activation in the prefrontal cortex and anterior cingulate cortex as well as altered activation in the temporal cortex during presentation of the dissociation-inducing scripts as compared with the neutral scripts. In addition, we hypothesized that the fMRI blood oxygen level-dependent (BOLD) signal in these brain areas would be correlated with the intensity of the dissociative experience.…”

“…It is unclear whether the enhanced frontal activity during dissociative states reflects a control mechanism initiated to regulate an automatic process of hyperarousal involving limbic structures. Therefore, Felmingham and coworkers 17 investigated the activation pattern of dissociative responses to conscious and nonconscious fear impact in patients with PTSD. They used the masked fear paradigm to compare conscious and unconscious processing of fearful facial expressions.…”

The Dissociative Subtype of Posttraumatic Stress Disorder: Unique Resting-State Functional Connectivity of Basolateral and Centromedial Amygdala Complexes

“…Numerous studies point towards differential patterns of neural activation of the amygdala, prefrontal cortex (PFC), anterior cingulate cortex (ACC), precuneus, and parietal lobe in PTSD patients who exhibit dissociative responses during traumatic script-driven imagery or fear processing as compared with those who instead demonstrate re-experiencing symptoms (Felmingham et al, 2008;Hopper et al, 2007;Lanius et al, 2002;2010a). This observation led to the identification of two types of emotion and amygdalar dysregulation among PTSD patients, proposed to occur at baseline as well as in response to trauma reminders: undermodulation and overmodulation (Lanius et al, 2010b;2012).…”