From Medscape Medical News

Brains of Veterans With and Without PTSD Differ, Imaging Study Shows

April 23, 2009 — Preliminary research showing distinct differences between the brains of veterans with and without posttraumatic stress disorder (PTSD) suggests that brain imaging may have the potential to enhance diagnosis, allow for early evaluation of treatment, and possibly act as a screening tool to identify at-risk individuals.

Results from functional magnetic resonance imaging (fMRI) scans during which veterans had to perform a visual working memory task while distracted by trauma- and non–trauma-related visual images showed that those with PTSD had markedly different neural activity from that of their counterparts without the disorder.

Specifically, veterans with PTSD had disruption in the dorsolateral prefrontal cortex, which is responsible for working memory, as well as the ventrolateral prefrontal cortex, the area of the brain that processes emotions, regardless of the type of visual distractor (trauma or nontrauma) images they were shown.

"As activity in the emotional system went up in response to processing the information of the distractors, the activity in the executive or cognitive system went down and so did task performance," study investigator Florin Dolcos, PhD, from the University of Alberta, in Edmonton, told Medscape Psychiatry.

"Our interpretation of this finding is that, as a result of responding to and processing the emotional stimuli, there was a reallocation of the processing resources from the dorsolateral prefrontal cortex to the ventrolateral system in individuals with PTSD," Dr. Dolcos added.

The study results, which were recently presented at the World Psychiatric Association International Congress, are published in the May issue of the Journal of Psychiatric Research.

Processing Deficits Explored

According to Dr. Dolcos, PTSD is associated with significant functional impairment and cognitive deficits, which include an inability to maintain concentration and focus, hypervigilance (where affected individuals are more likely to feel threatened in apparently neutral situations), and intrusive memories of the trauma.

While a number of neuroimaging studies have looked at emotion-processing systems by using trauma-related material to provoke symptoms, these studies have largely ignored the significant processing deficits associated with PTSD, the authors note.

To investigate how trauma-related environmental cues modulate working memory networks in PTSD, the researchers recruited 42 participants from a large registry of military service members and veterans who had recently served in Iraq or Afghanistan.

All study subjects had comparable levels of combat exposure. However, 22 individuals had developed PTSD and 20 subjects had not. To assess subjects' ability to stay focused, participants performed a 3-part short-term memory task that included distractions while undergoing fMRI.

Greater Distractibility

In the first stage, subjects were shown photographs of 3 similar faces. After a delay period, they were shown a single photograph of a face and had to indicate whether it was one they had seen earlier or whether it was new.

During the delay period, participants were randomly shown photos irrelevant to the faces — either 2 images depicting combat scenes, 2 images of noncombat (neutral) scenes, or 2 digitally scrambled images depicting nothing.

While all participants rated combat scenes as more distracting than noncombat scenes, those in the PTSD group reported higher distractibility ratings than controls.

In addition, the PTSD group had poorer performance than the control group on the memory task when the combat and noncombat distractors were presented.

The imaging findings revealed that the PTSD group showed greater activation than the control group for combat images, compared with noncombat images, in 3 ventral emotion-processing regions — the amygdala, the ventrolateral prefrontal cortex, and the fusiform gyrus.

In addition, the PTSD group showed greater simultaneous disruption of activation in the dorsolateral prefrontal cortex when exposed to both combat and noncombat distractors.

In contrast, the control group showed disruption in the dorsolateral prefrontal cortex only when exposed to combat distractors.

Heightened Response to Neutral Stimuli

The presence of any emotional distractor in PTSD patients is reflected in a reduction in brain activity in the dorsolateral prefrontal cortex and a subsequent reduction in their ability to stay focused, which, in this study, is reflected in reduced memory performance, explained Dr. Dolcos.

The bottom line, he said, is that individuals with PTSD are equally distracted by something that is very emotional and something that, for most people, would be perceived as neutral.

"This sensitivity to neutral information is consistent with the PTSD symptom of hypervigilance, where those afflicted are on high alert for threats and are more distracted by not only threatening situations that remind them of trauma but also by benign situations," principal investigator Rajendra Morey, MD, from Duke University Medical Center, in Durham, North Carolina, said in a statement.

While the study findings are still preliminary, Dr. Dolcos said they provide investigators with a target — the dorsolateral prefrontal cortex — that could lead to identification of a neurosignature that would have the potential to increase the sensitivity of current diagnostic methods by detecting changes before symptoms develop.

Further, he said, identification of neurosignatures could help clinicians monitor the effects of treatment and help optimize clinical outcomes. Finally, he said, this research could eventually help identify individuals at increased risk for PTSD, possibly leading to preventive strategies.

The research was funded by the Department of Veterans Affairs the National Institute of Mental Health, National Alliance for Research on Schizophrenia and Depression and the Natural Sciences and Engineering Research Council of Canada. The authors report no relevant conflicts of interest.

J Psychiatr Res. 2009;43:809-817. Abstract