Journal of Traumatic Stress, Vol. 21, No. 2, April 2008, pp. 190–198 ( C  2008) Resting Electroencephalogram Asymmetry and Posttraumatic Stress Disorder Stewart A. Shankman Department of Psychology and Psychiatry, University of Illinois at Chicago, Chicago, IL Steven M. Silverstein Department of Psychiatry, University of Illinois at Chicago, Chicago, IL Leanne M. Williams, Patrick J. Hopkinson, Andrew H. Kemp, and Kim L. Felmingham Brain Dynamics Centre, Westmead Millennium Institute, Westmead Hospital, University of Sydney, Australia Richard A. Bryant Department of Psychology, University of New South Wales, Australia Alexander McFarlane Department of Psychiatry, University of Adelaide, Australia C. Richard Clark School of Psychology, Flinders University, Adelaide, Australia The valence-arousal (W. Heller, 1993) and approach-withdrawal (R. J. Davidson, 1998a) models hypothesize that particular patterns of hemispheric brain activity are associated with specific motivational tendencies and psy- chopathologies. We tested several of these predictions in two groups—a posttraumatic stress disorder (PTSD) and a “supercontrol” group, selected to be maximally different from those with PTSD. Contrary to almost all hypotheses, individuals with PTSD did not differ from controls on resting electroencephalogram (EEG) asymmetry. Particular aspects of PTSD were also not related to EEG hemisphere differences. Our null findings are consistent with the few studies that have examined resting EEG asymmetries in PTSD and suggest that PTSD may be associated with different processes than psychopathologies previously examined in studies of hemispheric brain activity (e.g., major depressive disorder, panic disorder). Mood and anxiety disorder researchers have long been inter- ested in neurobehavioral markers for different psychiatric condi- tions. Over the last 20 years, researchers have examined whether these conditions are associated with specific patterns of electroen- cephalogram (EEG) activity recorded at rest. Two theories that have guided much of this research are the approach–withdrawal (Davidson, 1994; 1998a) and valence-arousal models (Heller, 1993; Heller & Nitschke, 1998; see Shankman & Klein, 2003 for review). The approach–withdrawal model is a neuropsychological model that posits two separate systems of motivation and emotion—one for approach behaviors and one for withdrawal. The approach system is hypothesized to control appetitive We acknowledge the generous support of the Brain Resource International Database (BRID; under the auspices of The Brain Resource Company) for data reported in this study. Access to BRID for scientific purposes is coordinated independently via a scientific network (BRAINnet; www.brainnet.org.au). Correspondence concerning this article should be addressed to: Stewart Shankman, Department of Psychology; University of Illinois at Chicago, 1007 W. Harrison, Room 1062D; M/C 285, Chicago, IL 60607. E-mail: stewarts@uic.edu. C  2008 International Society for Traumatic Stress Studies. Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/jts.20319 behavior and is viewed as being responsible for the generation of certain forms of positive affect and related emotions. The with- drawal system is proposed to facilitate behavior that removes an organism from potentially threatening stimuli (Davidson, 1998a; Gray, 1994). This system is also responsible for the generation of negative affects such as fear or disgust (Davidson, 1994). Both the approach and withdrawal systems are proposed to be responsible for individual differences in motivation, or “affective styles.” For example, a person with a “high approach affective style” is purported to have a tendency to be motivated to approach positive stimuli. The approach–withdrawal model posits that the approach and withdrawal systems are represented by separate neural circuits that 190