Perceived treatment assignment influences the effects of transcranial direct current stimulation on anxiety during an internet-based psychosocial stressor.

Social anxiety disorder is the most prevalent anxiety disorder. Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that represents a promising tool for modulating anxiety-related cortical activity. Psychosocial stressors, such as the InterneT-based Stress test for Social Anxiety Disorder (ITSSAD), are useful tools for controlled induction of acute social anxiety symptoms. We tested whether tDCS might reduce anxiety induced by the ITSSAD. This was a randomized, sham-controlled, double-blinded study. Ninety-six university students were randomized to receive 20 min of active or sham 2 mA tDCS over the dorsolateral prefrontal cortex (dlPFC) in a unilateral (anodal left dlPFC only) or bilateral (anodal left and cathodal right dlPFC) montage. Participants then underwent a challenging social interaction with an experimenter over videoconferencing software (ITSSAD). Subjective anxiety and mood, and autonomic nervous system activity measures were taken. Perceived treatment assignment was measured after the interaction. The ITSSAD increased subjective anxiety and negative mood, as reported previously. No differential effects of active versus sham tDCS were found on any of the subjective or autonomic measures. Significant effects of perceived treatment were found on subjective anxiety, such that participants who believed they had received active stimulation reported smaller increases following the ITSSAD. The findings of this study do not provide support for the effectiveness of tDCS for anxiety symptoms in response to an acute psychosocial stressor but instead suggest that perceived treatment plays an important role in observed outcomes. This study highlights the importance of measuring treatment expectations and blinding integrity in tDCS trials.