Effects of anodal transcranial direct current stimulation on experimentally induced heat pain in healthy volunteers

Abstract

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulatory technique that can reduce pain. Its side effects are milder than those of pharmacological treatments, and its analgesic effect on chronic pain has been demonstrated. In this study we investigated 1) the effects of anodal tDCS on pain intensity and threshold, 2) the placebo component of tDCS analgesic effect, and 3) whether stress and negative affect moderate the analgesic effect of tDCS. Sixty-four participants (32 females) received three blocks of heat stimuli, 43° C, 45° C, and 47° C in each block. The treatment group received anodal tDCS of 2 mA intensity for 7 minutes, the placebo group received sham stimulation for 30 seconds, and the natural history group received painful stimuli only. Participants rated pain intensity with CoVAS. Threshold was measured before the first and after the last block. Subjective stress was measured by two SACL items, and negative affect was measured by FPQ, PANAS, and BFI questionnaires. Compared to no treatment, tDCS reduced pain by 28%, for 47° C stimuli only. Compared to sham stimulation, tDCS reduced pain by 11%, but this reduction was only marginally significant. There was no placebo response, and no effect of tDCS on pain threshold. Fear of medical pain predicted pain reduction by tDCS, higher fear of medical pain was associated with larger pain reduction. Our findings confirm and extend those of earlier experimental and clinical studies.