Cathodal tDCS enhances extinction-based procedures

Abstract

Background Extinction-based procedures are used to inhibit maladaptive fear responses. However, due to extinction efficacy limitations, transcranial direct current stimulation (tDCS) has been studied as a promising add-on enhancer. Previous fundamental research found anodal tDCS to have an adverse effect in increasing generalization of the fear response to safety cues. However, first stage clinical studies demonstrate cathodal tDCS effectiveness in reducing fear and anxiety related symptoms. Methods As of now, fear-conditioning studies almost exclusively observe SCRs and self-reports to index conditioned fear. Nonetheless, other fear measures, such as the pervasive implicit avoidance tendencies should be studied to better explain tDCS conflicting results. We used a 3-day fear conditioning procedure whereby forty-one healthy women were assigned to either cathodal tDCS or sham tDCS. To measure the fear response we collected three dependent measures: affective, contingency, expectancy and symptom self-reports; SCRs; and a symbolic approach-avoidance task that taps on the individual implicit avoidance tendencies. Results show that contrary to anodal stimulation, cathodal tDCS improves long-term discrimination processes, by enhancing distinctiveness between threatening and safety cues, inhibiting the generalization effect. Particularly interesting are the implicit avoidance tendencies that show stimuli and experimental group interaction [F(1,41) = 5.51, P = .024, P = 119], whereby for the cathodal group the action tendency towards the CS- follows the trend of positive stimuli. Conclusion Our findings support a cross-measures validation for the use of cathodal tDCS to enhance extinction effects. Together, the results show that cathodal tDCS increases discrimination between threat and safety cues and inhibits generalization effect–a therapeutic benchmark of anxiety disorders such as generalized anxiety disorders and phobias.