Prefrontal tDCS-Augmented Brief Memory Training in Older Adults: A Randomized Controlled Trial of Cognitive and Brain Network Plasticity

Cognitive aging is characterized by declining memory and reduced segregation of large-scale brain networks. While memory training and transcranial direct current stimulation (tDCS) each show potential to support neurocognitive function in older adults, their combined effect on cognitive outcomes remains an active line of research and effects on whole-brain network modularity remain unclear. Additionally, recent studies suggest that tDCS may accelerate the cognitive benefits of memory training. We tested whether five days of training working memory (WM) and long-term memory (LTM), paired with anodal tDCS over the left dorsolateral prefrontal cortex, would enhance these memory domains and increase resting-state functional network modularity. 62 healthy older adults were randomly assigned to receive either active or sham stimulation during adaptive WM and LTM training, with resting-state fMRI collected at baseline, post-test, and follow-up 2-4 months after training. Behavioral results indicated no significant improvements in WM or LTM over time, and stimulation condition did not reliably modulate performance. Similarly, resting-state modularity did not change significantly across the training period, nor were there differences between stimulation groups. Exploratory analyses revealed that task-based modularity increased from post-test to follow-up in the active group, though this effect was not accompanied by behavioral gains. Further exploratory analyses revealed that across all outcomes, baseline measurements (irrespective of condition) emerged as strong moderators of change over the training period, emphasizing the importance of interindividual variability. By integrating memory training with tDCS and longitudinal fMRI, this study adds to the growing literature on stimulation-augmented cognitive training protocols and underscore the need for research on interindividual differences.