The effect of cathodal tDCS on fear extinction: a cross-measures study

Extinction-based procedures are often used to inhibit maladaptive fear responses. However, because extinction procedures show efficacy limitations, transcranial direct current stimulation (tDCS) has been suggested as a promising add-on enhancer. In this study, we tested the effect of cathodal tDCS over extinction, to unveil the processes at play that boost the effectiveness of extinction procedures and its translational potential to the treatment of anxiety disorders. We implemented a fear conditioning procedure whereby 41 healthy women (mean age = 20.51 ± 5.0) were assigned to either cathodal tDCS (n=27) or sham tDCS (n=16). Fear responses were measured with self-reports, autonomic responses, and implicit avoidance tendencies. Cathodal tDCS shows no statistically significant effect in extinction, according to self-reports, and seems to even negatively affect fear conditioned skin conductance responses. However, implicit avoidance tendencies, assessed one-to-three months after the tDCS session and extinction, reveal a group difference in the avoidance tendencies towards the neutral stimuli ( F (1, 41) = 12.04, p = .001, ηp 2 = .227), with the active cathodal tDCS groups showing a positive bias but not the sham group. This suggests a decreased generalization effect in the tDCS group with a moderate effect size. That is, cathodal tDCS may have enhanced long-term distinctiveness between threatening cues and perceptively similar neutral cues through a disambiguation process of the value of the neutral stimuli – a therapeutic target in anxiety disorders. Future studies should confirm these results and extend the study of cathodal tDCS effect on short term avoidance tendencies.