Session-dependent effects of 6-Hz frontoparietal tACS on visuospatial working-memory accuracy

Visuospatial working memory (VSWM) is supported by distributed fronto-parietal networks and is critically dependent on coordinated neural oscillations, particularly in the theta band (4-8Hz). Non-invasive neuromodulation via transcranial alternating current stimulation (tACS) has been proposed to enhance cognitive function by entraining these oscillations. The present study investigated the effects of theta-frequency (6Hz) tACS applied over the left fronto-parietal network (F3/P3) on VSWM performance using the Corsi Block Tapping Task. In a within-subjects design, participants completed four sessions under in-phase, anti-phase, tRNS and no-stimulation conditions. Linear mixed-effects modeling indicated higher accuracy during both in-phase and anti-phase tACS relative to the no-stimulation condition, whereas the tRNS effect was not statistically significant. In the interaction model, the stimulation-related differences were most pronounced during the first session and attenuated thereafter. No stimulation-related effects were observed on response speed. The results suggest that frontoparietal theta tACS may modulate visuospatial working-memory accuracy, particularly during initial task exposure. However, the present findings do not demonstrate a selective behavioral advantage of anti-phase over in-phase stimulation.