Memory Repression: Brain Mechanisms underlying Dissociative Amnesia

Abstract

Dissociative amnesia usually follows a stressful event and cannot be attributable to explicit brain damage. It is thought to reflect a reversible deficit in memory retrieval probably due to memory repression. However, the neural mechanisms underlying this condition are not clear. We used fMRI to investigate neural activity associated with memory retrieval in two patients with dissociative amnesia. For each patient, three categories of face photographs and three categories of people's names corresponding to the photographs were prepared: those of "recognizable" high school friends who were acquainted with and recognizable to the patients, those of "unrecognizable" colleagues who were actually acquainted with but unrecognizable to the patients due to their memory impairments, and "control" distracters who were unacquainted with the patients. During fMRI, the patients were visually presented with these stimuli and asked to indicate whether they were personally acquainted with them. In the comparison of the unrecognizable condition with the recognizable condition, we found increased activity in the pFC and decreased activity in the hippocampus in both patients. After treatment for retrograde amnesia, the altered pattern of brain activation disappeared in one patient whose retrograde memories were recovered, whereas it remained unchanged in the other patient whose retrograde memories were not recovered. Our findings provide direct evidence that memory repression in dissociative amnesia is associated with an altered pattern of neural activity, and they suggest the possibility that the pFC has an important role in inhibiting the activity of the hippocampus in memory repression.

Autobiographical Memory in a Fire-Walking Ritual

“…Studies on traumatic experiences show that stressful events may sometimes lead to memory repression (Loftus and Kaufman, 1992;Bowman, 1996;Brown et al, 1998;Joseph, 1999;Bourget and Whitehurst, 2007;Kikuchi et al, 2010), and it has been proposed that such disruptions form part of an adaptive memory-repression response system designed to cope with traumatic memories by keeping them out of awareness (Freyd, 1994). This interpretation, however, does not correspond with the participants' claim that they felt calm during the fijire-walk or with the qualitative interviews, where they describe the event as inherently positive.…”

Towards a Cognitive and Neurobiological Model of Motivated Forgetting

“…Could psychogenic amnesia sometimes be the result of spontaneous, involuntary application of the mechanisms identifi ed here, as suggested by the earlier reviewed work of Tramoni et al ( 2009 ) ? There is intriguing preliminary evidence that this involuntary control may happen. In a recent study, Kikuchi et al ( 2010 ) studied two patients with dissociative amnesia. Both patients were well educated, and neurologically normal, and of normal intelligence, but both had undergone a recent stressful event or period of time that lead to extensive retrograde amnesia.…”

Neuroimaging and Dissociative Disorders

“…In other reports on patients with dissociative amnesia glucose-PET, single photon emission computed tomography (SPECT) or fMRI, or combinations of several of these methods were used (Sellal, Manning, Seegmuller, Scheiber, & Schoenfelder, 2002, Glisky et al, 2004Botzung, Denkova, & Manning, 2007;Hennig-Fast et al, 2008;Serra, Fadda, Buccione, Caltagirone, & Carlesimo, 2007;Stracciari, Fonti, & Guarino, 2008;Yang et al, 2005;Piolino et al, 2005;Yasuno et al, 2000;Thomas-Antérion, Guedj, Decousous, & Laurent, 2010 ;Arzy, Collette, Wissmeyer, Lazeyras, Kaplan, & Blanke, in press;Kikuchi et al, 2010). In most cases brain metabolic and functional changes were found, which involved areas that are agreed upon to play crucial roles in mnemonic processing.…”