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.
Highlights
The regulation of emotional responses is essential for subjective wellbeing [1], and plays an important part in dealing with daily life hassles
As compared to sham stimulation, left dorsolateral prefrontal cortex (DLPFC) anodal transcranial direct current stimulation (tDCS) resulted in increased PD when confronted with negative emotional images, whereas right DLPFC anodal tDCS resulted in decreased PD when confronted with emotional images, irrespective of valence
The interpretation of pupil dilation in response to emotional stimuli is limited. These findings suggest inverse lateralized DLPFC effects on cognitive resource allocation when confronted with emotional stimuli
Summary
The regulation of emotional responses is essential for subjective wellbeing [1], and plays an important part in dealing with daily life hassles. It has been shown that when individuals are instructed to down-regulate their emotional responses towards emotional stimuli (i.e., reappraisal), activity in the DLPFC increases, while activity in the amygdala and self-reported negative affect decreases [5]. Patients with mood disorders are characterized by a functional hemispheric imbalance of the DLPFC, with hyperactivity of the right DLPFC and hypoactivity of the left DLPFC [9]. By using non-invasive brain stimulation (NIBS) techniques, augmenting activity in the left DLPFC or reducing activity in the right DLPFC has been shown to decrease depressive symptoms (for a review, see [10]). Research in healthy volunteers showed that anodal (i.e., excitatory) tDCS over the left DLPFC decreased emotional reactivity towards negative stimuli, as measured by both behavioral [11, 12], and psychophysiological [13] assessment methods
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