“…Indeed, the serotonin level is thought to be decreased in human OCD, which would explain the effect of SSRIs (Aouizerate et al, 2005;Westenberg et al, 2007), and has been shown to be affected by physical manipulation of the OFC (Schilman et al, 2010). The role of dopamine is not as clear, as cases of OCD have been reported in both High-frequency stimulation of deep brain structures in obsessive-compulsive disorder 1123 hypodopaminergic and hyperdopaminergic pathologies [Parkinson's and Huntington's diseases (Cummings & Cunningham, 1992;Maia et al, 1999;Alegret et al, 2001;Harbishettar et al, 2005)]; in rats, injection of quinpirole, a D2 ⁄ D3 agonist, provokes compulsive action (Szechtman et al, 1998;Winter et al, 2008c;Mundt et al, 2009), and dopamine transporter knockout mice develop 'superstereotyped' behaviours (Berridge et al, 2005). There is therefore a strong and complex dysfunction in the basal ganglia-thalamocortical loop, in its associative and limbic parts.…”