Neurocircuitry of disgust and anxiety in obsessive-compulsive disorder: a positron emission tomography study

Disgust and fear are basic emotions that have different elicitors and expressions, and that appear to be mediated by different neurocircuits. Although obsessive-compulsive disorder (OCD) is classified as an anxiety disorder, disgust may be involved in its pathogenesis. Functional magnetic resonance imaging (fMRI) studies of disgust-inducing visual stimuli in OCD have suggested disorder specific alterations in brain activation during these tasks.

Subjects with OCD and healthy controls (HC) underwent positron emission tomography (PET) brain scanning after injection of H(2) (15)O. During PET, subjects either watched slides designed to evoke feelings of disgust (OCD = 5, HC = 11), expected the delivery of an electrical shock (OCD = 11, HC = 13), or rested (OCD = 11, HC = 14). After the anticipatory anxiety and resting tasks, anxiety ratings, heart rate, and electrodermal measures were obtained. Statistical parametric mapping (SPM) was used to analyze regional cerebral blood flow (rCBF) data.

Comparison of OCD subjects with controls on differences in rCBF across the disgust-inducing and resting tasks showed that OCD was characterized by greater rCBF in the left insula. In OCD the disgust-inducing task increased right lateral orbitofrontal cortex rCBF compared to resting, whereas in controls there was no difference in rCBF between these tasks. Anxiety ratings, heart rate, and electrodermal activity increased during anticipatory anxiety in both groups, and comparison of rCBF in OCD subjects with controls in anticipatory anxiety versus resting state also found no significant differences.

OCD may be characterized by a disruption in disgust processing, such that there is a decrease in appropriate disgust (such as that evoked by observing disgust in others) and an increase in inappropriate disgust (such as that evoked by contamination stimuli). The insula may play a particularly important role in mediating such putative disruptions. The sample studied here was small, and further work is required to determine whether disgust-induced activation patterns in OCD are more apparent in specific subtypes of this disorder, whether they are specific to OCD, and whether they are normalized by treatment.