So far as we know, three studies demonstrated that that the right ventrolateral prefrontal cortex (RVLPFC) plays an important role in down-regulating the emotional response to social exclusion. In a previous study, we explored the causal relationship between transcranial direct current stimulation (tDCS) and dominant emotional regulation in the context of social exclusion. Depression is an disorder that shows deficits of social functions. Compared with healthy controls, depressive individuals enjoy less in social interaction and the activation of the lateral prefrontal lobe of depressive subjects usually reduces. The current study aimed to explore whether the anodal tDCS targeting at RVLPFC could also improve the emotional regulation of social exclusion in subjects with high depressive levels. Furthermore, this study added individual negative images as a baseline to test the specificity of the RVLPFC on emotional regulation of social exclusion. Before the experiment, we classified the participants with a Beck Depression Inventory score of < 3 as low depressive tendency group and those with a score of >= 18 as high depression tendency group. Participants also completed a Self-Rating Depression Scale (SDS) on the day of the tDCS experiment. Finally, a total of ninety-eight participants were included. They were randomly divided into anodal tDCS group (including 25 high depressive and 25 low depressive subjects) and sham tDCS group. All participants viewed social exclusion images and individual negative images separately in two blocks. In the no-reappraisal condition, participants were instructed to passively view images; in the reappraisal condition, they reappraised images so to down-regulate the negative emotional responses. Ratings of negative emotion experience were provided at the end of each trial. There was a significant three-way interaction of group, tDCS type, and task. Simple simple effect analysis showed that in the reappraisal condition, anodal tDCS over the RVLPFC resulted in a decreased negative emotion rating in subjects with low-depressive levels, while this task effect (i.e., emotional regulation) was not significant in subjects with high-depressive levels. Another three-way interaction was found among image type, tDCS type, and task: when participants were presented with social exclusion images, in the reappraisal condition, anodal tDCS over the RVLPFC resulted in a decreased negative emotion rating in the emotional regulation condition; however this task effect was less significant when participants were presented with individual negative images. Besides the two three-way interactions, this study also observed significant main effects of task, group, and tDCS type, as well as two-way interactions of group and task, tDCS type and task, image type and task, and group and tDCS type. The current findings indicate that the improvement of emotion regulation via tDCS targeting at RVLPFC may be invalid for depressive patients if only one session of tDCS is performed; thus multiple sessions are highly suggested for clinical practice. Furthermore, this is the first tDCS study that compared the RVLFPC role of emotional regulation of social versus individual based negative experiences. The result provides evidence of direct causal relationship between RVLPFC and emotional regulation in the context of social exclusion, highlighting the functional specificity of this brain region on emotional regulation.
