The Nature of Traumatic Memories: A 4-T fMRI Functional Connectivity Analysis
Lanius RA, Williamson PC, Densmore M, Boksman K, Neufeld RW, et al.;
Commented by , 28 Jan 2004
Aims of the study
To assess the functional connections between brain regions activated by traumatic memories in traumatized subjects with and without post-traumatic stress disorder (PTSD).
Method
Study participants included 24 subjects who had experienced an extreme traumatic event meeting criterion A of PTSD according to DSM-IV. All subjects were assessed using the Structured Clinical Interview for DSM-IV (SCID-IV) and the Clinician-Administered PTSD-Scale (CAPS).
Subjects who had developed PTSD as a result of the traumatic experience (N=11) were compared with subjects who had not developed PTSD (N= 13) during script-driven traumatic and neutral symptom provocation. Brain activity correlations during script-driven imagery were determined using functional magnetic resonance imaging (fMRI) and functional connectivity analyses. The data were analysed using statistical parametric mapping (SPM).
Results
Patients with PTSD experienced traumatic memories in the form of flashbacks whereas subjects without PTSD recalled the traumatic event as an ordinary autobiographical memory.
Comparison of connectivity maps for the two groups showed that subjects with PTSD had greater correlations than subjects without PTSD in the
- right posterior cingulate gyrus
- right caudate
- right parietal lobe
- right occipital lobe
And that subjects without PTSD had greater correlations than subjects with PTSD in the
- left superior frontal gyrus
- left anterior cingulate gyrus
- left caudate
- left parietal lobe
- left insula
Discussion
The study shows that the brain regions that are activated by traumatic memories, as well as the functional connections between brain regions when traumatic memories are activated, are different in traumatized subjects according to whether they have or have not developed PTSD as a consequence of the traumatic experience.
Subjects with PTSD showed a right hemisphere dominance effect and a much more nonverbal pattern of memory retrieval. Subjects without PTSD showed a left hemisphere dominance effect and a pattern more consistent with verbal episodic memory retrieval.
The study has a number of limitations, concerning in particular the small number of study participants, the variability of comorbid disorders, and the range of different traumata that had been experienced by the participants.
In spite of these limitations, this is an important study with important implications. In particular, the functional connections revealed in subjects with PTSD provide a better understanding for the flashbacks experienced by these subjects, whereas the connections shown in subjects without PTSD are in line with previous findings concerning the mecanism underlying ordinary autobiographical memories.
As such the study is first of all an important contribution toa better understanding of PTSD. In addition, the results suggest that further functional connectivity analyses may identify not only other mechanisms underlying PTSD, but that such analyses may also contribute to a better understanding of other anxiety disorders, such as panic disorder, the various phobias, or obsessive-compulsive disorder, as well as of depression.