Analgesia induced by anodal tDCS and high-frequency tRNS over the motor cortex: Immediate and sustained effects on pain perception

Abstract

Background: Many studies have shown effects of anodal transcranial direct current stimulation (a-tDCS) and high-frequency transcranial random noise stimulation (tRNS) on elevating cortical excitability. Moreover, tRNS with a direct current (DC)-offset is more likely to lead to increases in cortical excitability than solely tRNS. While a-tDCS over primary motor cortex (M1) has been shown to attenuate pain perception, tRNS þ DC-offset may prove as an effective means for pain relief.Objective: This study aimed to examine effects of a-tDCS and high-frequency tRNS þ DC-offset over M1 on pain expectation and perception, and assess whether these effects could be influenced by the certainty of pain expectation. Methods: Using a double-blinded and sham-controlled design, 150 healthy participants were recruited to receive a single-session a-tDCS, high-frequency tRNS þ DC-offset, or sham stimulation over M1. The expectation and perception of electrical stimulation in certain and uncertain contexts were assessed at baseline, immediately after, and 30 min after stimulation. Results: Compared with sham stimulation, a-tDCS induced immediate analgesic effects that were greater when the stimulation outcome was expected with uncertainty; tRNS induced immediate and sustained analgesic effects that were mediated by decreasing pain expectation. Nevertheless, we found no strong evidence for tRNS being more effective for attenuating pain than a-tDCS. Conclusions: The analgesic effects of a-tDCS and tRNS showed different temporal courses, which could be related to the more sustained effectiveness of high-frequency tRNS þ DC-offset in elevating cortical excitability. Moreover, expectations of pain intensity should be taken into consideration to maximize the benefits of neuromodulation.

Transcranial Direct Current Stimulation (tDCS) Effects on Quantitative Sensory Testing (QST) and Nociceptive Processing in Healthy Subjects: A Systematic Review and Meta-Analysis

“…Finally, 29 studies [5,9,17,[19][20][21][22][23][24][25][26][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] were included in the qualitative analysis, and 17 [5,9,17,[19][20][21]24,26,40,43,44,46,48,50,53,55,56] were included in the quantitative analysis, with a total of 700 subjects. The whole screening process is shown in the PRISMA flow diagram (Figure 1).…”

“…Among the selected studies, most of the studies applied a-tDCS over M1 [5,9,19,[21][22][23][24][25]40,[42][43][44][47][48][49][50][55][56][57], and other studies applied a-tDCS over DLPFC [9,22,26,43,47,[51][52][53][54], S1 [24,53], and SO [19]. Six studies applied c-tDCS over M1 [21,24,40,47,54,57], two over DLPFC [26,47], two over S1 [45,48], and one over ACC [17].…”

“…Regarding current density, five applied a current density of 0.028 mA/cm 2 [21,24,41,45], two applied 0.04 mA/cm 2 [19,44], nine applied 0.057 mA/cm 2 [5,25,26,40,46,47,50,57], and one applied 0.1 mA/cm 2 [53]; the rest of the studies did not report current density. Regarding stimulation time, one applied tDCS for 7 min [38], three for 10 min [23,52], five for 15 min [21,24,41,45,57], eighteen for 20 min [5,9,19,22,26,[42][43][44][47][48][49][50][51][53][54][55][56], and one for 40 min [46]. Most studies conducted single treatment sessions [5,17,19,21,23,25,26,…”

“…Regarding stimulation time, one applied tDCS for 7 min [38], three for 10 min [23,52], five for 15 min [21,24,41,45,57], eighteen for 20 min [5,9,19,22,26,[42][43][44][47][48][49][50][51][53][54][55][56], and one for 40 min [46]. Most studies conducted single treatment sessions [5,17,19,21,23,25,26,[40][41][42][43][45][46][47]50,52,[55][56][57], and the rest between three and five sessions [9,22,24,44,51,…”

“…Regarding outcome measures, 12 measured PPTs [9,17,19,[21][22][23]41,44,45,48,52,53,55], 13 measured VAS or NRS [5,21,24,40,43,46,47,49,51,54,56], 10 measured HPTs [5,9,17,21,24,26,40,41,45,48], and 13 measured CPTs [9,17,19,22,25,[41][42][43]45,[47][48][49]57].…”