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fMRI shows trauma affects neural circuitry.

CHICAGO -- Functional MRI studies of 39 patients with a range of stress-related psychiatric disorders have added new neurobiologic weight to theories about the complementary roles of the prefrontal cortex and the hippocampus in managing memory suppression and retrieval.

Data from the images point to an impairment in the neural circuitry between these two structures in patients with major depressive disorder, borderline personality disorder, panic disorder, and generalized anxiety disorder who have experienced trauma, such as sexual abuse, at some point in their lives.

This impairment, which appears to lie in the prefrontal cortex, interferes with the ability to actively suppress memories, even neutral memories, reported Dr. Nivedita Agarwal, a research fellow at McLean Hospital of Harvard Medical School, Boston, and a resident in radiodiagnostics at the University of Udine (Italy).

Previous research has posited an increase in prefrontal cortex activation and a decrease in hippocampal activation as the neural basis for an ability to suppress unpleasant past experiences (Science 2004;303:232-5).

"Controlling unwanted memories was associated with increased dorsolateral prefrontal activation, reduced hippocampal activation, and impaired retention of those memories," according to the authors. "Both prefrontal cortical and right hippocampal activations predicted the magnitude of forgetting. These results confirm the existence of an active forgetting process and establish a neurobiological model for guiding inquiry into motivated forgetting."

In the present study, impairments in this active forgetting process were manifested on fMRI in an overactivation of the hippocampus and an insufficient activation of the prefrontal cortex in ill patients, compared with healthy controls during the memory suppression portion of a task involving neutral word pairs.

Subjects included 11 patients with major depressive disorder, 5 with borderline personality disorder, 10 with panic disorder, 13 with generalized anxiety disorder, and 20 healthy controls.

Dr. Agarwal and her associates used a "think/no think" paradigm in which subjects were shown 36 pairs of neutral words on a computer screen (e.g., monkey-banana) and were asked to exert executive control to retrieve the associated word when one of the words was flashed on the screen. During fMRI, subjects then were provided with the same words and instructed to recall the word if it appeared in green or to suppress the word if it appeared in red.

Patients showed significantly greater levels of hippocampal activation and significantly lower levels of prefrontal cortex activation than healthy controls when asked to actively suppress the memory of a word from a pair, said Dr. Agarwal, who presented the findings at the annual meeting of the Radiological Society of North America. Patients showed greater hippocampal activation and less prefrontal cortex activation than did healthy subjects during the recall portion of the task as well.

"These data suggest that the prefrontal cortex is dysfunctional in the patients studied" and that these individuals may have alterations in their brain circuitry, Dr. Agarwal and her colleagues concluded.

"Is it genetic differences, environmental differences or the fact that they have suffered trauma? These are questions that longitudinal studies will have to answer," Dr. Agarwal said in an interview. "Our study is really a snapshot of what's going on."

It is worth noting, she added, that "the circuitry that we're looking into has nothing to do with emotional circuitry. We're looking at how traumatic events can affect a circuitry that is very much vital for normal living." Dr. Agarwal said the results of this study also point to fMRI's enormous potential as a tool for exploring the neurobiologic underpinnings of psychiatric disorders. "In 5-10 years, I'm quite sure fMRI and other modalities will be used to diagnose psychiatric illness," she said.

Dr. Agarwal disclosed that she had no financial conflicts of interest related to this study.
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Author:Birk, Susan
Publication:Clinical Psychiatry News
Date:Mar 1, 2009
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