The P50 auditory evoked potential in violent and non-violent patients with schizophrenia Ana Fresán a , Rogelio Apiquian b , María García-Anaya a , Camilo de la Fuente-Sandoval c , Humberto Nicolini b,d , Ariel Graff-Guerrero e,f, ⁎ a Subdirección de Investigaciones Clínicas. Instituto Nacional de Psiquiatría Ramón de la Fuente, Mexico City, Mexico b Grupo Médico Carracci, Mexico City, Mexico c Laboratorio de Psiquiatría Experimental, Instituto Nacional de Neurología y Neurocirugía Manuel Velasco Suárez, Mexico City, Mexico d Departamento de Medicina Genómica, Universidad de la Ciudad de México, Mexico City, Mexico e Centre for Addiction and Mental Health, PET Centre, Schizophrenia Research Programme, Toronto ON, Canada f Instituto de Neurobiología, Universidad Nacional Autónoma de México, Juriquilla, Qro., Mexico Received 17 April 2007; received in revised form 10 September 2007; accepted 16 September 2007 Available online 22 October 2007 Abstract Background: Emotionally driven violence is facilitated by increased arousal. It may be a consequence of an information-processing deficit and the cognitive attributions for the stimuli given by the subject. The aim of this study was to compare the P50 evoked potential responses of violent patients with schizophrenia with non-violent patients with schizophrenia and healthy controls. Method: Patients were classified into violent and non-violent in accordance to the Overt Aggression Scale. P50 auditory evoked potentials of 32 unmedicated patients with schizophrenia (violent = 14, non-violent = 18) and 17 healthy controls were recorded during five runs of 30 click pairs. Results: Healthy controls exhibited a lower S2/S1 ratio when compared to violent (p b 0.001) and non-violent (p = 0.04) patients. Using a cutoff point of 0.50 for S2/S1 ratio to define abnormal gating a significant proportion of violent patients did not show P50 suppression (71.4%) in comparison to non-violent patients (38.9%) and healthy controls (23.5%) (p = 0.02). Conclusions: Violent behavior in patients with schizophrenia could be associated with a disturbed information sensory gating. Violence in patients with schizophrenia may be facilitated by an increased arousal which may in turn be the result of an information-processing deficit. © 2007 Elsevier B.V. All rights reserved. Keywords: Schizophrenia; Arousal; Auditory P50 gating; Evoked potentials; Violence; Electrophysiology 1. Introduction Schizophrenia is one of the main psychiatric disorders associated with violent behavior (Coid, 1996; Modestin and Ammann, 1996; Stueve and Link, 1997; Swanson et al., 1990). This behavior arises out of multiple causes involving biological, psychological, and environmental factors (Angermeyer, 2000; Martin et al., 2000; Mon- ahan et al., 2000; Wessely, 1997; Wessely et al., 1993; Wessely and Taylor, 1991), although recent evidence emphasizes neurobiological mechanisms influencing the development of violent behavior (Bernat et al., in press; Volavka, 1999). Available online at www.sciencedirect.com Schizophrenia Research 97 (2007) 128 – 136 www.elsevier.com/locate/schres ⁎ Corresponding author. Centre for Addiction and Mental Health, PET Centre, 250 College St. Toronto, Ontario, Canada M5T 1R8. Fax: +1 416 260 4164. E-mail address: ariel_graff@yahoo.com.mx (A. Graff-Guerrero). 0920-9964/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.schres.2007.09.017