Transcranial Magnetic Stimulation enhances working memory

Cognitive decline associated with aging affects a large proportion of America’s progressively older population. To remedy this decline, various working memory (WM) training protocols are emerging, the most novel of which utilize Transcranial Magnetic Stimulation (TMS) to excite neuronal activity, induce long-term potentiation, and enhance cognitive functioning. Ultimately aiming to remediate WM decline in aging adults by using TMS, this study first sought to establish ideal TMS parameters to induce WM improvements. Using a delayed match-to-sample (DMS) WM task with both maintenance and manipulation conditions, it was hypothesized that active TMS, relative to sham TMS, would differentially impact task performance depending on its timing of administration, either before encoding or at the end of the delay phases. Following screening and practice, subjects trained on the DMS task for 4 hours over 2 days, receiving 5s of either active 5Hz TMS at 100% of motor threshold to the dorsolateral prefrontal cortex (DLPFC) or sham TMS. The phase of active versus sham TMS stimulation was counterbalanced across participants. The results suggest that active TMS improved DMS reaction time and accuracy as compared to sham TMS. Specifically, maintenance task performance improved with TMS before encoding, while manipulation task performance was aided by TMS during the delay period. Although promising, these results should be bolstered by increased sample sizes and individualized fMRI-based DLPFC targeting before deciding on the optimal timing of TMS for each DMS task condition in aging adults.