Lasting Enhancements in Neural Efficiency by Multi-session Transcranial Direct Current Stimulation in Working Memory Training

Abstract

The neural basis for long-term behavioral improvement resulting from multi-session transcranial direct current stimulation (tDCS) combined with working memory training (WMT) remains unclear. In this study, we used task-related electroencephalography (EEG) measures to investigate the lasting neurophysiological effects of anodal high-definition (HD)-tDCS applied over the left dorsolateral prefrontal cortex (dlPFC) during a challenging WMT. Thirty-four healthy young adults were randomized to sham or active tDCS groups and underwent ten 30-minute training sessions over ten consecutive days, preceded by a pre-test and followed by post-tests performed one day and three weeks after the last session, respectively, by performing high-load WM tasks along with EEG recording. Multi-session HD-tDCS significantly enhanced the behavioral benefits of WMT. Compared to the sham group, the active group showed facilitated increases in theta, alpha, and beta task-related oscillations at the end of training and significantly increased P300 response 3 weeks post-training. Our results suggest that anodal tDCS over the left dlPFC during multi-session WMT enhances the behavioral benefits of WMT and facilitates a sustained improvement in WM-related neural efficiency.