High-Definition Transcranial Direct Current Stimulation Improves Pain Empathy: A Randomized, Double-Blind, and Sham-Controlled Study Based on Event-Related Potentials (ERPs)

The impact of transcranial direct current stimulation (tDCS) on pain empathy is a subject of debate and controversy. The variations in the results could be attributed to differences in the stimulus parameters. This study aimed to examine the impact of high-definition transcranial direct current stimulation (HD-tDCS) with different intensities on pain empathy through event-related potentials (ERPs). Thirty-nine participants were recruited for the experiment, and a parallel control design was used. The participants were randomly assigned to the sham group, 1 mA stimulation group, or 2 mA stimulation group. Before the experiment, all the participants provided basic information, completed relevant questionnaires and then wore an EEG cap for the first pain empathy task. After completing the task, each group received 20 minutes of HD-tDCS stimulation over the left DLPFC region at different intensities (2 mA, 1 mA, or sham), followed by a second pain empathy task. The findings from the pain-judgment and hands-counting tasks (task 1) demonstrated that both 1- and 2-mA stimulation increased Δ-N1 amplitudes, suggesting that anodal stimulation enhances early empathic responses. The results of the pain rating task (task 2) indicate that HD-tDCS stimulation did not improve the ratings of others' pain. However, the application of 2-mA tDCS significantly increased the Δ-intensity of unpleasantness compared with that of the other two groups. This suggests that 2-mA tDCS stimulation had a notable effect on the affective dimension of empathy, specifically the perception of unpleasantness. This finding indicates that 2mA stimulation primarily enhances affective empathy, whereas its influence on cognitive empathy appears to be limited. By employing different intensities of HD-tDCS, our findings build upon and extend previous findings in the field of pain empathy. These results have the potential to offer dose recommendations for future studies employing tDCS as an intervention to increase pain empathy.