Efficacy of Anodal Suboccipital Direct Current Stimulation for Endogenous Pain Modulation and Tonic Thermal Pain Control in Healthy Participants: A Randomized Controlled Clinical Trial

Objective. The aim of this study was to assess whether anodal DCS applied to the suboccipital (SO) target area could potentiate antinociception assessed primarily with conditioned pain modulation of tonic thermal test stimuli. Design. Randomized double-blinded control trial. Setting. Rehabilitation hospital. Subjects. Healthy participants. Methods. Forty healthy participants were randomized to receive either SO-DCS or M1-DCS. The 20-minute 1.5mA anodal or sham DCS intervention were applied to each participant in randomized order during two test sessions. The primary outcome measure included heterotopic cold-pressor conditioned pain modulation (CPM) of tonic heat pain. Secondary measures included pressure pain threshold and tonic thermal pain intensity. Results. Heterotopic CPM of tonic heat pain intensity was unaffected by either SO-DCS or active M1, including the secondary measures of pressure pain threshold and tonic thermal pain intensity. Although low-power non-significant interactions were identified for DCS intervention (active versus sham) and time (before and after), a significant within-group inhibition of tonic cold pain was identified following SO-DCS (P = .011, mean [SD]: -0.76 +/- 0.88 points) and M1-DCS (P<.002: -0.84 +/- 0.82 points), without a significant change following sham DCS. Conclusions. Although heterotopic CPM was not facilitated with either SO-DCS or M1-DCS, a general significant inhibition of tonic cold pain intensity was demonstrated following both interventions. The general effects of active DCS compared to sham on tonic cold pain-irrespective of the M1 or SO target-need to be confirmed using standard quantitative sensory testing.

Automated summary

The study aimed to assess the effects of DCS applied to the SO region on pain perception, finding that neither SO-DCS nor M1-DCS enhanced heterotopic CPM but both showed significant inhibitory effects on tonic cold pain. Further confirmation is needed on the general effects of active DCS compared to sham on tonic cold pain.