Reducing Disgust and Moral Rigidity through Transcranial Direct Current Stimulation (tDCS): A Promising Therapeutic Tool for Obsessive-Compulsive Disorder (OCD)

Background: Previous studies supported the existence of a distinctive relation between deontological guilt and both disgust and obsessive-compulsive (OC) symptoms. Specifically, the experience of deontological guilt has been found to selectively activate the insula, a structure implicated in disgust processing, which seems to be more easily activated in OCD patients. The present study hypothesized that indirect inhibition of the insula via cathodal tDCS would decrease disgust and moral rigidity. Correlational analyses were also performed driven by the hypothesis that these expected results would be larger in individuals with higher levels of OC tendencies. Methods: A randomized, sham-controlled, within-subject design was used. 36 healthy students (18 women) underwent 15-min anodal, cathodal, and sham tDCS over T3 in three different days. Levels of trait anxiety, depression, disgust sensitivity, scrupulosity, and altruism as well as pre- and post- stimulation momentary emotional states were assessed. Heart rate (HR) was recorded to derive measures of parasympathetic activity (HR Variability, HRV). After the first 10-min of tDCS stimulation, participants were asked to 1) rate the immorality of a series of vignettes, 2) complete a word-stem completion task with either disgust-related words or neutral alternatives. Results: Taking into account baseline levels, results showed a main effect of condition (anodal, cathodal, sham) on self-reported disgust (p = .007) and HRV (p = .02), as well as deontological morality (p = .016). Compared to sham, anodal stimulation significantly (all ps < .01) enhanced self- reported disgust (d = 0.18), HRV (d = 0.24) and deontological morality (d = 0.09), whereas cathodal stimulation decreased self-reported disgust (d = 0.54), HRV (d = 0.30) and deontological morality (d = 0.26). Interestingly, changes in self-reported levels of disgust following cathodal tDCS were inversely correlated with the Fear of Sin subscale of the PIOS (r= –.48; p = .003), and with the washing (r= -.49; p = .002) subscale of the OCI-R. Conclusion: A decrease in self-reported and physiological disgust (HRV), as well as deontological moral rigidity were found after cathodal tDCS over T3. As suggested by the correlational analyses, the inhibitory effect of cathodal tDCS on subjective levels of disgust were stronger in individuals with higher OC tendencies, thereby advising for future investigations of the long-term impact of this intervention on OCD symptoms.