Efficacy of anodal suboccipital direct current stimulation for endogenous pain modulation and tonic thermal pain control in healthy participants: a randomised 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: Randomised 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 randomised 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 = 0.011, mean [SD]: -0.76±0.88 points) and M1-DCS (p < 0.002: -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.