Does anodal transcranial direct current stimulation modulate sensory perception and pain? A meta-analysis study

• Anodal tDCS (a-tDCS) of the primary motor cortex increases sensory and pain threshold in healthy individuals.
• a-tDCS of the primary sensory cortex increases pain threshold significantly.
• a-tDCS of both primary motor cortex and dorsolateral prefrontal cortex decreases pain level in patients with chronic pain.

ObjectiveThe primary aim of this systematic review was to evaluate the effects of anodal transcranial direct current stimulation (a-tDCS) on sensory (STh) and pain thresholds (PTh) in healthy individuals and pain levels (PL) in patients with chronic pain.MethodsElectronic databases were searched for a-tDCS studies. Methodological quality was examined using the PEDro and Downs and Black (D&B) assessment tools.Resultsa-tDCS of the primary motor cortex (M1) increases both STh (P < 0.005, with the effect size of 22.19%) and PTh (P < 0.001, effect size of 19.28%). In addition, STh was increased by a-tDCS of the primary sensory cortex (S1) (P < 0.05 with an effect size of 4.34). Likewise, PL decreased significantly in the patient group following application of a-tDCS to both the M1 and dorsolateral prefrontal cortex (DLPFC). The average decrease in visual analogue score was 14.9% and 19.3% after applying a-tDCS on the M1 and DLPFC. Moreover, meta-analysis showed that in all subgroups (except a-tDCS of S1) active a-tDCS and sham stimulation produced significant differences.ConclusionsThis review provides evidence for the effectiveness of a-tDCS in increasing STh/PTh in healthy group and decreasing PL in patients. However, due to small sample sizes in the included studies, our results should be interpreted cautiously. Given the level of blinding did not considered in inclusion criteria, the result of current study should be interpreted with caution.SignificanceSite of stimulation should have a differential effect over pain relief.