Neuromodulation of somatosensory pain thresholds of the neck musculature using a novel transcranial direct current stimulation montage: a randomized double-blind, sham controlled study

Abstract

Objectives Anodal transcranial direct current stimulation (tDCS) of primary motor cortex (M1) and cathodal of the primary sensory cortex (S1) have previously shown to modulate the sensory thresholds when administered with the reference electrode located over the contralateral supraorbital area (SO). Combining the two stimulation paradigms into one with simultaneous stimulation of the two brain areas (M1 + S1 − tDCS) may result in a synergistic effect inducing a prominent neuromodulation, noticeable in the pain thresholds. The aim of this study is to assess the efficacy of the novel M1 + S1 − tDCS montage compared to sham-stimulation in modulating the pain thresholds in healthy adults. Methods Thirty-nine (20 males) subjects were randomly assigned to either receiving 20 min. active M1 + S1 − tDCS or sham tDCS in a double-blinded single session study. Thermal and mechanical pain thresholds were assessed before and after the intervention. Results There were no significant differences in the pain thresholds within either group, or between the M1 + S1 − tDCS group and the Sham-tDCS group (p>0.05), indicating that the intervention was ineffective in inducing a neuromodulation of the somatosensory system. Conclusions Experimental investigations of novel tDCS electrode montages, that are scientifically based on existing studies or computational modelling, are essential to establish better tDCS protocols. Here simultaneous transcranial direct current stimulation of the primary motor cortex and primary sensory cortex showed no effect on the pain thresholds of the neck musculature in healthy subjects. This tDCS montage may have been ineffective due to how the electrical field reaches the targeted neurons, or may have been limited by the design of a single tDCS administration. The study adds to the existing literature of the studies investigating effects of new tDCS montages with the aim of establishing novel non-invasive brain stimulation interventions for chronic neck pain rehabilitation. North Denmark Region Committee on Health Research Ethics (VN-20180085) ClinicalTrials.gov (NCT04658485).

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]. Seven studies applied HD-tDCS [9,17,22,23,42,52,55].…”

“…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 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].…”

“…Sensitivity analysis eliminating studies for which the standard deviation (SD) was imputed with a correlation coefficient from other studies and in which a coefficient of 0.5 was used showed no significant differences between real and simulated stimulation (MD = −0.35; 95% CI: −0.92 to −0.21; n = 175; Z = 1.22; p = 0.22; I 2 = 0%; p = 0.93). The analysis was performed in the studies of Jürgens et al, 2012 [21], and Kold et al, 2022 [48]. The funnel plot showed asymmetry, indicating a possible risk of publication bias (Supplementary Material S4).…”