Brain-behavior relationships in obsessive-compulsive disorder.

Advances in neuroimaging have led to a greater understanding of brain-behavior relationships in obsessive-compulsive disorder (OCD). This article provides an updated review and analysis of the structural and functional neuroimaging studies in OCD published to date and discusses how evidence from various types of neuroimaging studies has been synthesized to generate and test hypotheses regarding these relationships. We also review the basic science literature on the functional neuroanatomy of cortico-basal ganglia-thalamo-cortical circuits and integrate this information with neuroimaging data in OCD, to present a theoretical model of brain mediation of OCD symptoms and response to treatment. Taken together, neuroimaging studies indicate that OCD symptoms are mediated by hyperactivity in orbitofrontal-subcortical circuits, which may be attributable to an imbalance of tone between direct and indirect striato-pallidal pathways. Serotonergic drugs may ameliorate OCD symptoms by changing the relative balance of tone through the indirect versus direct orbitofrontal-subcortical pathways, thereby decreasing activity in the overall circuit that exists in the symptomatic state.