LAUSR

BACKGROUND The majority of existing clinical studies used active transcranial direct current stimulation (tDCS) over the superficial areas of pain neuromatrix to regulate pain, with conflicting results. Nevertheless, few studies have investigated the effect of tDCS on pain thresholds by focusing on targets in deep parts of the pain neuromatrix. METHODS This study applied single session of high-definition tDCS (HD-tDCS) targeting the anterior cingulate cortex (ACC) with a parallel and sham-controlled design, to compare the antinociceptive effects in healthy individuals through assessing changes in pain thresholds. Sixty-six (mean age, 20.5 ± 2.4) female individuals were randomly allocated into the anodal, cathodal, or sham HD-tDCS groups. The primary outcome of the study was pain thresholds (pressure pain threshold, heat pain threshold, and cold pain threshold), which were evaluated before and after stimulation by the quantitative sensory tests. RESULTS Only cathodal HD-tDCS targeting the ACC significantly increased heat pain threshold (p < 0.05) and pressure pain threshold (p < 0.01) in healthy individuals compared with sham stimulation. Neither anodal nor cathodal HD-tDCS showed significant analgesic effects on cold pain threshold. Furthermore, no statistically significant difference was found in pain thresholds between anodal vs. sham HD-tDCS (p > 0.38). Independent of HD-tDCS protocols, the positive and negative affective schedule scores were decreased immediately after stimulation compared with baseline. CONCLUSIONS The present study has found that cathodal HD-tDCS targeting the ACC provided a strong antinociceptive effect (increase in pain threshold), demonstrating a positive biological effect of HD-tDCS. CLINICAL TRIALS REGISTRATION An RCT was carried out at Shanghai University of Sport, China, from December 2021 to March 2022. Trial registration: ChiCTR2100053531. Registered 24 November 2021, http://www.chictr.org.cn/index.aspx.