Since the 1980s, obsessive–compulsive disorder (OCD) researchers worldwide have made extensive use of neuroimaging (Behar et al., 1984; Luxenberg et al., 1988). OCD has a distinctive phenotype, with characteristic repetitive thoughts and intrusions (obsessions) and habitual behaviors (compulsions), and there was early evidence of the involvement of specific brain circuits and systems (Cummings, 1995). Early hypotheses regarding brain systems involved were based on clinical observations, including descriptions of OCD‐like behaviors in patients with subcortical disorders, such as Huntington's disease (Cummings & Cunningham, 1992), Sydenham's chorea (Swedo, Rapoport, Cheslow, & Ayoub, 1989), and pallidal (Laplane et al., 1989) and frontal lobe (Eslinger & Damasio, 1985) lesions. Data obtained with human brain imaging in the late 1980s allowed detailed neurobiological models of OCD to be developed. These models initially focused on the striatum and orbitofrontal cortex, but were later refined to include more broadly interacting fronto‐striatal, fronto‐parietal, fronto‐limbic, and cerebellar circuits (Stein et al., 2019; Van den Heuvel et al., 2016).
