Discussion
In this study, we investigated the modulation effects of different tDCS modes (anodal, cathodal, and sham) on two important brain networks involved in cognitive control, the DAN and FPN, as well as the association between the FC changes evoked by tDCS with the placebo and nocebo effects. We found that compared to sham tDCS, 1) both cathodal and anodal tDCS could increase the FC between the right parietal operculum and DAN, and the cathodal tDCS was also associated with increased FC between the DAN and right postcentral gyrus; 2) anodal tDCS led to increased FC between the FPN and right parietal operculum, while cathodal tDCS was associated with increased FC between the FPN and left superior parietal lobule/precuneus; and 3) the FC increase between the DAN and right parietal operculum (derived from cathodal and sham tDCS comparison) was significantly correlated to placebo analgesic effects.