In a controlled brain imaging study, PTSD patients showed abnormal activity in several areas of the prefrontal cortex and ventral regions when they were deliberately distracted while performing cognitive tasks, said Rajendra Morey, M.D., of Duke University and the Durham (N.C.) VA Medical Center.
The results point to PTSD as at least partly a disorder of cognitive processing, Dr. Morey said in an interview.
Some of the results were published online in the Journal of Psychiatric Research. A portion of the research is also being presented Friday at the World Psychiatric Association's International Congress in Florence, Italy, by another researcher on the study, Florin Dolcos, Ph.D., of the University of Alberta.
The scientists studied 22 soldiers diagnosed with PTSD who had served in Iraq and Afghanistan, as well as 20 others with similar levels of combat exposure but no PTSD.
Participants underwent functional MRI scans while being shown photographs of human faces, which they were told to remember.
During this procedure, participants also were shown other types of pictures intended as distractions. These included combat scenes from Iran and Afghanistan, noncombat scenes, and digitally scrambled nonsense pictures.
Compared with the controls, PTSD patients showed enhanced activity in ventral regions associated with emotion processing when they were shown the distracting pictures.
Brain areas in the prefrontal cortex that are believed to house working memory and attention functions showed deactivation relative to controls.
Additionally, the dorsal medial prefrontal cortex -- related to information about the self -- was relatively hyperactivated in the PTSD patients.
Dr. Morey said this latter effect was consistent with the clinical aspects of PTSD. One of the condition's hallmarks is that patients regard innocuous situations as personally threatening.
That brain areas involving self-information processing would be inordinately activated during ordinary cognitive tasks would, therefore, be expected, he said.
In many cases, the differing reactions to distraction between PTSD patients and controls were seen regardless of whether or not the distractor was combat-related.
Dr. Morey said that finding suggests that PTSD involves a relatively extensive disruption in cognitive function.
The research may have implications for PTSD psychotherapies, he added.
Such symptoms as hypervigilance reflect misinterpretation of information, he pointed out.
He said it may make sense in cognitive-behavioral or exposure therapy to focus on "recalibrating" the way patients interpret information, Dr. Morey said.
Eventually, it may be possible to use drugs to normalize brain function in the affected regions, he said, "but that's a long way away."
The researchers identified several limitations to the study, including the fact that several participants were on antidepressant medications, and the diagnosis of PTSD versus other psychiatric conditions could be questioned.
The methodology also could not exclude the possibility that the differences in brain activity preceded the combat exposure and PTSD.
|The study was funded by the Department of Veterans Affairs, the National Institute of Mental Health, NARSAD, and NSERC.
Zalman S. Agus, MD Emeritus Professor
University of Pennsylvania School of Medicine