Dissociative responses to conscious and non-conscious fear impact underlying brain function in post-traumatic stress disorder
Felmingham, KL and Kemp, AH and Williams, L and Falconer, E and Olivieri, G and Peduto, A and Bryant, R, Dissociative responses to conscious and non-conscious fear impact underlying brain function in post-traumatic stress disorder, Psychological Medicine, 2008, (38) pp. 1771-1780. ISSN 0033-2917 (2008) [Refereed Article]
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
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.