Obsessive-compulsive disorder (OCD) is a severe and debilitating condition that occurs in 2–3% of the population1. It is characterized by recurrent, intrusive, irrational and distressing thoughts (obsessions) and repetitive behaviors or mental acts (compulsions)2. So far, no biomarkers that aid differential diagnosis are available, and diagnosis relies entirely on recognition of characteristic symptoms assessed by clinical interview3. Many neuroimaging studies have provided evidence for abnormalities in cortico-striato-thalamo-cortical (CSTC) circuits, as well as distributed changes in limbic, parietal and cerebellar regions4,5. These findings have recently been confirmed by different meta-analyses and mega-analyses of neuroimaging studies, based on results that were reported in the literature or by using original data within different consortia6–10. However, inference has been at the group-level, and the small effect sizes reported preclude clinical application.
