Transcranial Direct Current Stimulation Facilitates Insight Learning

Abstract Background After two decades of transcranial direct current stimulation (tDCS) research, it is still unclear which applications benefit most from which tDCS protocols. One prospect is the acceleration of learning, where previous work has demonstrated that anodal tDCS applied to the right ventrolateral prefrontal cortex (rVLPFC) is capable of doubling the rate of learning in a visual camouflaged target detection and classification task. Goals Questions remain as to the specific cognitive mechanisms underlying this learning enhancement, and whether it generalizes to other tasks. The goal of the current project was to expand previous findings by employing a novel visual classification task. Methods Participants learned to classify pictures of European streets within a discovery learning paradigm. In a double-blind design, 54 participants were randomly assigned to 30 minutes of tDCS using either 2.0 mA anodal (n=18), cathodal (n=18), or 0.1 mA sham (n=18) tDCS over the rVLPFC. Results A linear mixed-model revealed a significant effect of tDCS condition on classification accuracy across training (p=0.001). Compared to a 4.2% increase in sham participants, anodal tDCS over F10 increased performance by 20.6% (d=1.71) and cathodal by 14.4% (d=1.16). Conclusions These results provide further evidence for the capacity of tDCS applied to rVLPFC to enhance learning, showing a greater than quadrupling of test performance after training (491% of sham) in a difficult image classification task requiring insight. Combined with our previous studies, these results suggest a generalized performance enhancement. Other tasks requiring sustained attention, insight or categorization learning may also benefit from this protocol.