The effect of transcranial direct current stimulation of the dorsolateral prefrontal cortex on behavioral and brain activity indices of visuospatial attention in intrinsic reward contexts

Research indicates a connection between frontal brain activity asymmetry and self-regulation, particularly, approach and inhibitory tendencies. However, the underlying brain mechanism remains unclear. Our preregistered study used transcranial direct current stimulation (tDCS) to overcome limitations in prior correlational studies, investigating the link between frontal alpha asymmetry (FAA), a potential neuromarker and a treatment target for relevant psychiatric disorders, and the behavioral and brain activity components related to approach and avoidance tendencies, as observed in a visuospatial cueing (VSC) paradigm. We utilized a randomized sham-controlled design with 65 healthy participants. Participants resting-state EEG was recorded to calculate FAA scores before and after 2 mA anodal tDCS to the right frontal site. They also completed a VSC task with neutral and intrinsic reward-associated (food) conditions. Results indicated no impact of tDCS on FAA or behavioral attentional bias/disengagement. Surprisingly, secondary analyses revealed tDCS enhancing attentional bias for rewards, as seen in enhanced Late Directing Attention Positivity and P1 effect. However, these effects did not translate into observable behavioral changes. The observed effects are consistent with a noradrenergic mechanism rather than asymmetry of brain activity.