Increasing working memory capacity with theta transcranial alternating current stimulation (tACS).

The study aimed to investigate the influence of transcranial alternating current stimulation (tACS) on working memory's (WM) storage capacity. Sham/verum tACS with individually determined theta frequency was applied to the left parietal (target electrode=P3) or frontal (target electrode=F3) brain areas (return electrode above the right eyebrow). After sham and verum stimulation, 24 respondents solved a task measuring the scope of attention while their electroencephalogram (EEG) was recorded. Verum tACS with the target electrode positioned over the left parietal brain area significantly increased WM storage capacity, as compared to sham tACS. No such influence was observed for tACS with the target electrode positioned over the left frontal area. Increased WM storage capacity was accompanied by event-related potential (ERP) P300 latency decrease in the left hemisphere. The obtained behavioral and neuroelectric data emphasize the causal relationship between WM storage capacity and theta frequency oscillations in the left parietal brain area.