Transcranial direct current stimulation enhances soothing positive affect and vagal tone.

Transcranial Direct Current Stimulation (tDCS) is a promising tool for the treatment of depression and the dorsolateral prefrontal cortex (dlPFC) is often targeted when exploring tDCS effects on mood. However, the basic effects of tDCS on momentary emotions are inconsistent. We tested whether a single-session of anodal tDCS over the left temporal lobe (T3), topographically closer to the insular cortex than dlPFC, had effects on both vagally-mediated heart rate variability (HRV) and momentary affect in healthy participants. Thirty-four subjects underwent both sham and active tDCS in a counterbalanced random order. ECG was continuously recorded to derive both time and frequency domain HRV indexes. Before and after the tDCS protocol, participants completed momentary affect assessments. Results showed that HRV and soothing positive affectivity were both enhanced after a single-session of tDCS over T3, while negative and activating positive affect were not modulated by the stimulation. After controlling for sex, age, and levels of anxiety and depression a significant association emerged between increases in soothing positive affect and concomitant increases in vagally-mediated HRV. Deficits in soothing positive emotions have consistently been associated with psychopathology and psychotherapeutic approaches aimed to develop this type of emotionality have shown to improve psychological well-being. Thus, present exploratory results may impact future research investigating potential moderators (site of stimulation) and mediators (specificity for a determined type of momentary affect) of the effects of tDCS on psychopathological conditions such as depression.