Inverse effects of tDCS over the left versus right DLPC on emotional processing: A pupillometry study

Abstract

Background The Dorsolateral prefrontal cortex (DLPFC) is implicated in the top-down modulation of emotional responses. Research that investigates the causal role of the left versus right DLPFC on emotional responding, both during the anticipation and confrontation with emotional stimuli, is lacking. In the current study, transcranial direct current stimulation (tDCS) was used to investigate the DLPFC functional lateralization regarding spontaneously exerted effort to control emotional responses during the anticipation of, and confrontation with emotional stimuli in healthy volunteers. Methods Forty-eight subjects received both active and sham (on separate days) anodal tDCS over either the left (n = 24) or right (n = 24) DLPFC. Subjects’ pupil dilation (PD; i.e., a physiological marker for cognitive effort to control emotional responses) was recorded while performing an appraisal task in which negative and positive emotion eliciting images were presented, each preceded by an informative cue indicating the valence of the upcoming stimulus. Results Left DLPFC anodal tDCS (compared to sham tDCS) resulted in increased PD when confronted with negative emotional images, whereas right DLPFC anodal tDCS (compared to sham tDCS) resulted in decreased PD when confronted emotional pictures, irrespective of valence. Conclusion This study established a basic proof of concept for inverse lateralized DLPFC effects on cognitive effort to control automatic emotional responses (as measured by pupillary responses) when attending, but not preparing for, emotional stimuli. The current findings may shed some light on mechanisms that explain the antidepressant effects of non-invasive brain stimulation of the left DLPFC. However, further research is warranted to investigate these processes more closely.