The Combined Effects of Prefrontal tDCS and Slow-Paced Breathing on Stress Reactivity, Emotional Reactivity, and Emotion Regulation

Difficulties in stress and emotion regulation can undermine psychophysical well-being. Yet, they could be tackled through shifting autonomic balance toward parasympathetic dominance. Two promising interventions could achieve this via complementary pathways: slow-paced breathing (SPB), acting via peripheral mechanisms, and prefrontal transcranial Direct Current Stimulation (tDCS), targeting brain regions involved in autonomic regulation. Combining those techniques could therefore enhance their effects. This placebo-controlled study examined the effects of SPB and tDCS, alone and in combination, on stress, emotional reactivity, and emotion regulation. 187 healthy participants were randomly assigned to one of four groups in a 2 (Breathing: SPB vs. control) × 2 (tDCS: active vs. sham) design. They completed a baseline assessment, the intervention, a psychosocial stress task, a recovery phase and an emotional reactivity task with negative versus neutral images. We measured psychophysiological indices of stress and emotion regulation (heart rate variability, skin conductance, pupil dilation and blood pressure, appraisal of threat, affect, and the use of emotion regulation strategies). Surprisingly, combining SPB and tDCS may hinder their individual effects. Receiving tDCS decreased pupil dilation, and increased positive affects and distraction as emotion regulation strategy. Receiving SPB decreased skin conductance, pupil dilation, and increased positive affect and distraction. Surprisingly, combining them reduced the effects on positive affect, acceptance and pupil dilation. No other effects were found. Rather than enhancing outcomes, combining them may hinder each intervention. These findings highlight the independent efficacy of SPB and tDCS, caution against their concurrent use and highlight the need for further investigation.