Therapeutic effects of tDCS on cognitive functions in patients diagnosed with autism spectrum disorders: a systematic review and meta-analysis on randomized sham-controlled trials.

OBJECTIVE: This meta-analysis aimed at investigating the effectiveness of transcranial direct current stimulation (tDCS) in improving cognitive functions in individuals with autism spectrum disorder (ASD) and evaluating the effects of potential confounders on therapeutic outcomes. METHODS: Randomized placebo-controlled trials (RCTs) identified from major databases were reviewed. Continuous data were expressed as effect size based on standardized mean difference (SMD) with 95% confidence intervals. RESULTS: Meta-analysis of thirteen RCTs involving 347 participants diagnosed with ASD (mean age=15.76) revealed significant improvements in social cognition among those receiving tDCS treatment compared to sham controls (SMD=1.14, 95% CI=0.70-1.58, p<0.01, seven studies, n=172). Subgroup analysis showed no significant impact regarding location of anode placement, combination with cognitive/behavioral training, and number of sessions. Our secondary analyses demonstrated significantly greater improvements in processing speed of patients receiving tDCS than their sham controls (SMD=0.50, 95% CI=0.22-0.77, p<0.01, five studies, n=208) but not in attentional function, inhibitory control, and working memory. CONCLUSION: Our study supported the use of tDCS for improving social cognition and processing speed in individuals with ASD. Nevertheless, the impact of potential confounders on therapeutic outcomes, including treatment duration and target brain region, warrants elucidation by further large-scale investigations.