Does transcranial direct current stimulation enhance visual working memory? A replication study

Abstract In recent years, non-invasive brain stimulation has been highlighted as a possible intervention to induce cognitive benefits, including on visual working memory (VWM). However, findings are inconsistent, possibly due to methodological issues. A recent high-profile study by Wang et al. (2019) reported that anodal transcranial direct current stimulation (tDCS) over posterior parietal cortex (PPC), but not over dorsolateral prefrontal cortex (DLPFC), selectively improved VWM capacity but not precision, especially at a high VWM load. Given the broad implications of this finding, it is imperative to test its replicability. Thus, in the current pre-registered conceptual replication study, we accounted for the key potential methodological issues in the original study and tested an adequate number of subjects required to demonstrate the previously reported effects (n = 48 compared to n = 20). Participants underwent counterbalanced PPC, DLPFC and sham stimulation before completing 360 trials of a continuous orientation-reproduction task. We failed to replicate the selective effect of PPC stimulation. Instead, our results showed little credible evidence for effects of tDCS regardless of stimulation region and VWM load. The absence of tDCS effects was largely supported by substantial to strong Bayesian evidence. Therefore, our results challenge previously reported benefits of anodal PPC-tDCS on VWM.