Differentiating cortical patterns of cognitive dysfunction in schizophrenia and posttraumatic stress disorder Cherrie A. Galletly a, ⁎ , Alexander C. McFarlane b , Richard Clark c a Discipline of Psychiatry, School of Medicine, University of Adelaide, Elanor Harrald Building, Frome Rd, Adelaide 5000, South Australia, Australia b The University of Adelaide Centre of Military and Veterans' Health, 122 Frome Street, Adelaide 5000, South Australia, Australia c Cognitive Neuroscience Laboratory, The Flinders University of South Australia, GPO Box 2100, Adelaide 5001, South Australia, Australia Received 5 May 2006; received in revised form 6 March 2007; accepted 6 April 2007 Abstract Comparative studies are needed to determine whether the cognitive impairments found in various psychiatric disorders are specific to those disorders, or are a more universal consequence of mental illness. This study compares the patterns of cognitive dysfunction in two conditions characterized by working memory dysfunction, schizophrenia and posttraumatic stress disorder (PTSD). Three matched groups (Schizophrenia, PTSD, Control) of 16 subjects had event related potentials recorded, using a 27 electrode array, while they performed a working memory auditory target detection task. Both disorders were associated with impaired task performance, with greater impairment in schizophrenia. Reduction in N1 amplitude was found only in schizophrenia, and an increase in target N2 amplitude and latency was found only in PTSD. Both patient groups showed a reduction in the amplitude of the non-target and target P3, but the groups were distinguished by a reduction in non-target parietal P3 amplitude in the schizophrenia group and a reduction in target P3 amplitude over the left posterior parietal region in the PTSD Group. This study demonstrates that there are specific patterns of cognitive dysfunction associated with schizophrenia and with PTSD. © 2007 Elsevier Ireland Ltd. All rights reserved. Keywords: Cognitive; Working memory; Event-related potentials; P3; N1; N2; Target detection; Latency; Amplitude; EEG 1. Introduction Cognitive dysfunction is a core feature of schizophre- nia (Bowie and Harvey, 2005), and is thought to reflect subtle abnormalities in the structure and function of the brain. However, impairments in cognition have been reported in other psychiatric disorders such as bipolar disorder (Bruno et al., 2006) and PTSD (Vasterling et al., 2002; Bremner, 2005). These findings raise the question of whether the cognitive impairments found in schizo- phrenia are specific to this condition, or are a nonspecific result of mental illness. This is crucial to our understand- ing of the neurobiology of schizophrenia. The present study was designed to compare measures of brain function in two psychiatric disorders, schizophre- nia and PTSD. PTSD was chosen as the comparator condition because, like schizophrenia, it is characterized by cognitive impairment and in particular working memory dysfunction (Weber et al., 2005). However, the etiology of the two conditions is very different. Schizo- phrenia is regarded primarily as a neurodevelopmental disorder, although factors such as social adversity and Available online at www.sciencedirect.com Psychiatry Research 159 (2008) 196 – 206 www.elsevier.com/locate/psychres ⁎ Corresponding author. Tel.: +61 8 82698144; fax: +61 8 82696187. E-mail address: cherrie.galletly@adelaide.edu.au (C.A. Galletly). 0165-1781/$ - see front matter © 2007 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.psychres.2007.04.001