The Relationship between Social Defiance, Vindictiveness, Anger, and Brain Morphology in Eight-year-old Boys and Girls Cherine Fahim, University of Lausanne, Montreal Neurological Institute and Sainte-Justine Hospital Research Centre, Marina Fiori, University of Lausanne, Alan C. Evans, Montreal Neurological Institute and McGill University and Daniel Pérusse, Sainte-Justine Hospital Research Centre and University of Montreal Abstract The goal of this study is twofold: (1) to assess brain anatomical differences between children meeting diagnostic criteria for oppositional defiant disorder (ODD) and healthy controls, and (2) to investigate whether morphological brain characteristics associated with ODD differ in boys and girls. Eight-year-old participants (N = 38) were scanned using magnetic resonance imaging. ODD symptoms were assessed using the Dominic-R interactive. In ODD participants, we observed a significant reduction of gray matter density in the left orbitofrontal cortex—a prefrontal region that plays a pivotal role in emotional self-regulation and impulse control—and, conversely, an increase in the left temporal area—an area that has been associated with aggressive, impulsive, and antisocial personality. Furthermore, ODD boys showed a reduction of both gray matter density in the left orbitofrontal cortex and of white matter density in the left superior frontal area.The structural abnormalities found in the present study, in particular, the correlation between ODD symptoms and reduction of gray matter density in the left orbitofrontal cortex, may present some evidence for the existence of neuropathology associated with ODD symptoms during childhood. Furthermore, our findings indicate morphometric differences between boys and girls with ODD, which may be associated with gender differences in social behavior in children showing ODD symptoms. Keywords: oppositional defiant disorder; voxel-based morphometry; emotional self-regulation; gender differences Introduction It is bath time, dinnertime, or shopping time; a child is with his parents and suddenly explodes in response to a parental demand. Children may lack the social, cognitive, or Correspondence should be addressed to Daniel Pérusse, Sainte Justine Research Centre, 3175, Chemin de la Côte-Sainte-Catherine, Montréal H3T 1C5, Canada. Email: Daniel.Perusse@ umontreal.ca doi: 10.1111/j.1467-9507.2011.00644.x © Blackwell Publishing Ltd. 2012. Published by Blackwell Publishing, 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA.