Does Transcranial Direct Current Stimulation Improve Tactile spatial discrimination? A Systematic Review and Meta-Analysis

Background: Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique for modulating neural processes, enabling the direct investigation of how experimentally altered neural activity affects behavior. It has been suggested that using tDCS for targeted enhancement or attenuation of the excitability of the somatosensory cortex alters tactile perception; however, studies published so far have revealed contradictory findings. Objectives: Systematically determine the influence of tDCS on tactile perception in healthy adults. Methods: We performed a comprehensive literature search on PubMed and filtered the results following the Preferred Report Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Selection Criteria: To achieve a homogenous sample, we selected only studies that used tDCS for measuring tactile spatial discrimination, as revealed by two widely used standardized tests, the grating orientation task, and the 2-point orientation discrimination task. Data Collection and Analysis: Nine studies could be identified for which effect sizes and confidence intervals were either reported or could be calculated based on the statistics provided. Main Results: Our meta-analysis indicates a significant but small benefit from tDCS for tactile spatial discrimination in the experimental vs. control groups; however, there was a high level of heterogeneity. Remarkably, our subanalysis based on the target sites (primary somatosensory cortex or motor cortex) and duration of tDCS stimulation (i.e., >20 minutes) revealed a significant effect on tactile spatial discrimination. Conclusion: Because of the variability in the methodological protocols and the partly small sample sizes of the included studies, more empirical high-quality randomized controlled trials are required to verify these intervention effects further.