The effects of transcranial direct current stimulation on cognitive function for mild cognitive impairment: a systematic review and meta-analysis of randomized controlled trials

Background Transcranial direct current stimulation (tDCS) emerged as a potential modality for enhancing cognitive functions in patients with cognitive decline, including mild cognitive impairment (MCI). Our systematic review and meta-analysis aim to synthesize the available randomized controlled trials (RCTs) on the effects of tDCS on cognitive functions in patients with MCI. Methods Our review protocol was registered on PROSPERO with ID: CRD42022360587. We conducted a systematic database search until September 2022. Standardized mean difference (SMD) and pooled effect size (ES) for robust variance estimation (RVE) method were used as effect estimates for our meta-analysis. Results We included 11 RCTs with a total of 429 participants. The meta-analysis showed that, compared to sham groups, tDCS did not improve global functioning (measured by MOCA) (SMD = 0.02, CI = − 0.30 to 0.35; p = 0.88), memory domain (ES = 0.681, CI = − 2.15 to 3.51, p = 0.576), sustained attention (measured by TMT-A) (SMD = − 0.21, CI = − 0.52 to 0.10, p = 0.19), and executive function (measured by TMT-B) (SMD = − 0.53, CI = − 1.56 to 0.50, p = 0.20). Conclusion Our meta-analysis found no significant effect of tDCS on cognitive functions in MCI patients, including effects on global functioning, memory, sustained attention, and executive function. Therefore, an important change to be tested in future studies is to look for a better combination with tDCS for patients with MCI.