Reducing Disgust and Moral Rigidity Through Transcranial Direct Current Stimulation (tDCS): Clinical Implications for Obsessive-Compulsive Disorder.

The experience of deontological guilt has been found to selectively activate the brain region of the insula, a well-known structure implicated in the processing of disgust. Moreover, previous studies showed a hyperactivity of the insula in persons with obsessive-compulsive disorder (OCD), in which deontological guilt and disgust play a pivotal role in pathogenesis and maintenance of symptoms. The present study tested the hypothesis that indirect inhibition of the insula via cathodal transcranial direct current stimulation (tDCS) would decrease disgust and moral rigidity. By using a randomized, sham-controlled, within-subject design, 36 healthy individuals (18 women) underwent 15-min anodal, cathodal, and sham tDCS over T3 in three different days. Levels of OC tendencies as well as pre and post-stimulation momentary emotional states were assessed. Subjects’ heart rate (HR) was recorded to derive measures of parasympathetic nervous system activity (Heart Rate Variability, HRV). After the first 10 minutes of tDCS stimulation, participants were asked to complete a computerized moral task and a word-stem completion task with either disgust-related words or neutral alternatives. Compared to sham condition, anodal and cathodal stimulation of T3 respectively enhanced and decreased self-reported disgust, severity of moral judgements in the deontological domain, and HRV. A positive correlation emerged in the anodal condition between scores on the Obsessive-Compulsive Inventory-Revised (OCI-R) and self-reported disgust, between deontological guilt and the Fear-of-Sin (FoS) subscale of the Pennsylvania Inventory of Scrupolosity (PIOS), and between deontological guilt and the washing and obsessing subscales of the OCI-R; in the cathodal condition, disgust inversely correlated with the FoS and the washing and obsessing subscales of the OCI-R. To conclude, results showed a decrease in self-reported and physiological disgust, and deontological moral rigidity following cathodal tDCS on T3, with stronger effects in individuals with higher levels of OC traits, thereby suggesting potential implications for OCD treatment.