Subjective imagery in obsessive-compulsive disorder before and after exposure therapy. Pilot randomised controlled trial.

Background Distressing mental imagery is hard to study experimentally in obsessive-compulsive disorder (OCD). Aims To develop a way to assess mental imagery in OCD during functional magnetic resonance imaging (fMRI). Method A small randomised study, controlled for type and order of mental imagery and for treatment condition (exposure therapy guided by a computer or by a therapist, or relaxation guided by audio-tape). Before and after treatment, during fMRI scanning, patients imagined previously-rehearsed scenarios that evoked an urge to ritualise or non-OCD anxiety or a neutral state, and rated their discomfort during imagery. Results The method evoked greater discomfort during OCD imagery and anxiety (non-OCD) imagery than during neutral imagery. Discomfort was reduced by cancelling imagery. Discomfort during OCD imagery (but not during anxiety non-OCD imagery) fell after exposure therapy but not after relaxation. Conclusions Results showed differences between OCD and non-OCD images and their change after successful treatment, and confirmed clinical suggestions that cancelling images reduced OCD discomfort. The method's success paves the way for further studies of mental imagery in OCD: for instance, during fMRI.