Table 1.
Inclusion and exclusion criteria for identified studies.
Table 2.
Study characteristics and outcome measure in healthy individuals.
Table 3.
Study characteristics and outcome measure in patients with chronic pain.
Fig 1.
Risk of bias graph: Review authors’ judgments about each risk of bias item presented as percentages across all 10 included studies.
Table 4.
Quality assessment of included studies.
Table 5.
c-tDCS parameters in healthy individuals.
Fig 2.
Flowchart study selection.
Fig 3.
Forest plots of sensory threshold changes in healthy individuals.
mparison of percentages of sensory threshold changes before and after c-tDCS (A), and comparison of after effects of sensory threshold changes between active and sham c-tDCS (B). Subgroup analysis: studies of M1 and S1 stimulation. ■ = the effect size for one trial; horizontal line = 95% of confidence interval; ◆ = pooled effect size for all trials. CI: confidence interval, IV: inverse variance.
Fig 4.
Forest plots of pain threshold changes in healthy individuals.
Comparison of percentages of pain threshold changes before and after c-tDCS (A), and comparison of after effects of pain threshold changes between active and sham c-tDCS (B). Subgroup analysis: studies of M1 and S1 stimulation. ■ = the effect size for one trial; horizontal line = 95% of confidence interval; ◆ = pooled effect size for all trials. CI: confidence interval, IV: inverse variance.
Fig 5.
Forest plots of pain level changes in patients with chronic pain.
Comparison of percentages of pain level changes before and after c-tDCS (A), and comparison of after effects of pain level changes between active and sham c-tDCS (B). Subgroup analysis: studies of M1 and dorsolateral prefrontal cortex (DLPFC) stimulation. ■ = the effect size for one trial; horizontal line = 95% of confidence interval; ◆ = pooled effect size for all trials. CI: confidence interval, IV: inverse variance.
Fig 6.
Assessment of the individual influence of included studies evaluating the after effects of c-tDCS on outcome measures.
The Impact of single studies on overall effect size in studies evaluating the effect of c-tDCS of S1 (A) and M1 (B) on sensory threshold, c-tDCS of S1 (C) and M1 (D) on pain threshold in healthy individuals, and pain level (E) in patients with chronic pain were evaluated. The effect sizes are Cohen’s d (SMD) and error bars represent the 95% confidence interval. The left, middle, and right vertical lines are indicator for the minimum, mean, and maximum value of total effect size respectively.
Fig 7.
Assessment of the individual influence of included studies evaluating the effect of active and sham c-tDCS on outcome measures.
The Impact of single studies on overall effect size in studies evaluating the effect of active and sham c-tDCS of S1 (A) and M1 (B) on sensory threshold, c-tDCS of S1 (C) and M1 (D) on pain threshold in healthy individuals, and pain level (E) in patients with chronic pain were evaluated. The effect sizes are Cohen’s d (SMD) and error bars represent the 95% confidence interval. The left, middle, and right vertical lines are indicator for the minimum, mean, and maximum value of total effect size respectively.
Fig 8.
The funnel plots representative of publication bias.
After effects of c-tDCS on sensory threshold (A), pain threshold (B), and pain level (C) in patient group. Also the publication bias in studies investigating sham effects of c-tDCS on sensory threshold (D), pain threshold (B), and pain level (E) in patient group are evaluated. In Figures A, B, D, and E, circles indicates S1 subgroup analysis and squares show M1 subgroup analyses.