Background. Failure to resist chronic obsessive–compulsive symptoms may denote an altered state of cognitive control. We searched for the cerebral regions engaged in this dysfunction.

Method. Differences in brain regional activity were examined by event-related functional magnetic regional imaging (fMRI) in a group of adolescents or young adults (n=12) with childhood-onset obsessive–compulsive disorder (OCD), relative to healthy subjects. Subjects performed a conflict task involving the presentation of two consecutive and possibly conflicting prime and target numbers. Patients' image dataset was further analysed according to resistance or non-resistance to symptoms during the scans.

Results. Using volume correction based on a priori hypotheses, an exploratory analysis revealed that, within the prime-target repetition condition, the OCD subjects activated more than healthy subjects a subregion of the anterior cingulate gyrus and the left parietal lobe. Furthermore, compared with ‘resistant’ patients, the ‘non-resistant’ OCD subjects activated a bilateral network including the precuneus, pulvinar and paracentral lobules.

Conclusions. Higher regional activations suggest an abnormal amplification process in OCD subjects during the discrimination of repetitive visual stimuli. The regional distribution of functional changes may vary with the patients' ability to resist obsessions.