Background
A clinical characteristic of posttraumatic stress disorder (PTSD) is persistently
elevated fear responses to stimuli associated with the traumatic event. The objective
herein is to determine whether extinction of fear responses is impaired in PTSD and
whether such impairment is related to dysfunctional activation of brain regions known
to be involved in fear extinction, viz., amygdala, hippocampus, ventromedial prefrontal
cortex (vmPFC), and dorsal anterior cingulate cortex (dACC).
Methods
Sixteen individuals diagnosed with PTSD and 15 trauma-exposed non-PTSD control subjects
underwent a 2-day fear conditioning and extinction protocol in a 3-T functional magnetic
resonance imaging scanner. Conditioning and extinction training were conducted on
day 1. Extinction recall (or extinction memory) test was conducted on day 2 (extinguished
conditioned stimuli presented in the absence of shock). Skin conductance response
(SCR) was scored throughout the experiment as an index of the conditioned response.
Results
The SCR data revealed no significant differences between groups during acquisition
and extinction of conditioned fear on day 1. On day 2, however, PTSD subjects showed
impaired recall of extinction memory. Analysis of functional magnetic resonance imaging
data showed greater amygdala activation in the PTSD group during day 1 extinction
learning. During extinction recall, lesser activation in hippocampus and vmPFC and
greater activation in dACC were observed in the PTSD group. The magnitude of extinction
memory across all subjects was correlated with activation of hippocampus and vmPFC
during extinction recall testing.
Conclusions
These findings support the hypothesis that fear extinction is impaired in PTSD. They
further suggest that dysfunctional activation in brain structures that mediate fear
extinction learning, and especially its recall, underlie this impairment.
Key Words
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Article info
Publication history
Published online: September 14, 2009
Accepted:
June 26,
2009
Received in revised form:
June 25,
2009
Received:
March 16,
2009
Identification
Copyright
© 2009 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.
