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. …