Background: The majority of existing clinical studies used active transcranial direct current stimulation (tDCS) over superficial areas of the pain neuromatrix to regulate pain, with conflicting results. 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 a single session of high-definition tDCS (HD-tDCS) targeting the anterior cingulate cortex (ACC) and used a parallel and sham-controlled design to compare the antinociceptive effects in healthy individuals by assessing changes in pain thresholds. Sixty-six female individuals (mean age, 20.5 ± 2.4 years) 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 through the use of 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 and 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.
Keywords: Anterior Cingulate Cortex; High-Definition Transcranial Direct Current Stimulation; Neuromodulation; Noninvasive Brain Stimulation; Pain Threshold.
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