Effect of the anodal transcranial Direct Current Stimulation (atDCS) on the attentional networks: A systematic review and meta-analysis

The prominent multifaceted models of attention posit the existence of three independent but functionally related attentional networks, namely the alerting, orienting, and executive conflict networks. Researchers have recently started to envision strategies to enhance the attentional networks, and transcranial Direct Current Stimulation (tDCS) has emerged as a promising tool. Yet, these studies have led to mixed findings, precluding any strong conclusion regarding the impact of tDCS on the three attentional networks. Moreover, this research field has been characterized by many study-to-study variations in terms of targeted samples, stimulation parameters, and electrodes placement. In this project, we thus aimed, in a preregistered fashion (https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=201199), at auditing this research’s field. To do so, we conducted a systematic review and a meta-analysis. We also assessed the quality of these studies using Cochrane tools. Only sham-controlled studies published (in English) in international peer-reviewed journals were included (number of studies = 12). A systematic search in bibliographical databases uncovered ten studies that compared a tDCS active stimulation to a sham stimulation. Our meta-analytic results suggest that tDCS produced a small and not significant modulation of the attentional networks. Yet, some meta-moderators were identified (e.g., clinical status). Although there was no indication of significant publication bias, the quality of the studies was substandard and modulated the effect sizes. We give possible explanations for these null findings and discuss the moderators, in order to provide guidelines for further studies in this research field.