Original ArticlesP300 Is Attenuated During Dissociative EpisodesKirino, Eiji MD Author Information Juntendo University School of Medicine Department of Psychiatry, Juntendo Institute of Mental Health, Koshigaya-shi Saitama, Japan. Send reprint requests to Eiji Kirino, Juntendo Shizuoka Hospital, Department of Psychiatry, 1129 Nagaoka Izunokunishi, Shizuoka 4102295 Japan. The Journal of Nervous and Mental Disease: February 2006 - Volume 194 - Issue 2 - p 83-90 doi: 10.1097/01.nmd.0000198145.18457.28 Buy Metrics Abstract The present study examined the pathophysiology of dissociative phenomena using the P300 component of event-related potentials, quantitative electroencephalography (QEEG), and morphology measures of computed tomography scan. Event-related potentials during an auditory oddball paradigm and QEEG in resting state were recorded. Patients exhibited attenuation of P300 amplitudes compared with controls during dissociative episodes, but exhibited recovery to control levels in remission. Patients had a larger Sylvian fissure-brain ratio than did controls. QEEG findings revealed no significant differences between the patients and controls or between episodes and remission in the patient group. Attenuation of the P300 can be interpreted as the result of a negative feedback loop from the medial temporal lobe to the cortex, which decreases the amount of information flow, allocation of attentional resources, and updating of working memory to avoid both excessive long-term memory system activity in medial temporal lobe and resurgence of affect-laden memories. © 2006 Lippincott Williams & Wilkins, Inc.