Brain activation changes during working memory training: Individual capacity effects on functional near-infrared spectroscopy measures

Working memory (WM) training has shown promise for cognitive enhancement, but the neural mechanisms underlying training effects and offline consolidation processes remain unclear. This study examined the correspondence between behavioral and neural changes during WM training and how individual differences in WM capacity influence these processes. Twenty-eight young adults completed two visual n-back training sessions separated by a 24-h interval. Behavioral measures and Brain activity in bilateral dorsolateral and ventrolateral prefrontal cortices were measured using functional near-infrared spectroscopy (fNIRS), before and after each session. Participants became more proficient in performing the n-back task, with accuracy improvements occurring during active training sessions and reaction time improvements reflecting increased automaticity occurring also during the offline consolidation period. Group-level neural changes were not significant, but individual differences in behavior were associated with neural activation changes: accuracy improvements were consistently associated with increased neural activation across all training phases, while reaction time improvements showed non-significant trends with variable relationships across intervals. Interestingly, individual WM capacity shaped neural adaptation patterns: higher-capacity individuals showed greater neural activation increases during the first training session and neural activation decrease during the second session. Although we found a behavioral effect for offline consolidation at the group level, this was not associated with specific neural activation changes. Our results highlight the complex relationship between individual capacity and training-related neural plasticity, with higher-capacity individuals showing both increased and decreased activation patterns at different time points during training. These findings support personalized training approaches that consider individual cognitive profiles.