Psychological Medicine

Original Articles

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

K. Felminghama1a2 c1, A. H. Kempa1a2, L. Williamsa1a2, E. Falconera1a3, G. Olivieria4, A. Pedutoa4 and R. Bryanta1a3

a1 Brain Dynamics Centre, Westmead Millennium Institute, Westmead Hospital, Australia

a2 Division of Psychological Medicine, Western Clinical School, University of Sydney, Australia

a3 School of Psychology, University of New South Wales, Australia

a4 MRI Unit, Department of Radiology, Westmead Hospital, Australia


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.

(Received April 20 2007)

(Revised December 04 2007)

(Accepted December 14 2007)

(Online publication February 25 2008)


c1 Address for correspondence: Dr K. Felmingham, Brain Dynamics Centre, Westmead Hospital, Westmead, NSW 2145, Australia. (Email: