| Obsessive-compulsive disorder (OCD) is a frequently occurring psychiatric disorder, with a world-wide life-time prevalence of 2-3%, which often results in considerable morbidity. According to current nosological systems OCD is classified as an anxiety disorder. However, recently it has been hypothesized that OCD may also share common features with a number of so-called obsessive-compulsive spectrum disorders, characterized by either over-controlled (compulsive, as in OCD) or under-controlled (impulsive, as in Tourette's syndrome (GTS)) behaviour. Recent developments in functional neuroimaging techniques have enabled visualisation of brain structures that are presumably implicated in the pathophysiology of OCD, in particular striatal-prefrontal circuits. The aim of the present project is to test the specificity of the hypothesis that in OCD patients the prefrontal-striatal system functions abnormally, compared with other OC-spectrum disorders. To address this issue, brain activation in OCD (compulsive behaviour with anxiety) will be compared with that in GTS (impulsive behaviour without anxiety) and somatoform disorder (anxiety without compulsive behaviour): (a) during provocation of OCD-specific (disgust, which is fear-associated) and GTS-specific (mental play, which is not fear-associated) symptom states in subjects with OCD and GTS, and in normal controls, using H2(15)O PET; (b) during performance of cognitive tasks designed to involve striatal-prefrontal systems in subjects with OCD, and somatoform disorder, and in normal controls, using functional MR; (c) during enhancing the postsynaptic dopaminergic system in OCD and GTS, using 11C Raclopride PET. |
