Visual working memory performance after the theta cycle length modulation using transcranial alternating current

We tested whether presumed extending vs. shrinking the theta cycle in a given hemisphere by using transcranial alternating current stimulation (tACS) could affect working memory maintenance during the change detection task. In Experiment 1, 30 young healthy adults received tACS at fixed frequency of 4 vs. 7 Hz, but no changes in change detection hit rate were observed. In Experiment 2, individual theta frequency was estimated from EEG resting state for each of 50 young healthy adults, who then received tACS either decreased or increased by 1.5 Hz relative to this individuated theta frequency. Stimulating at the decreased frequency led to a significant change detection hit rate increase for the contralateral but not the ipsilateral hemifield, as compared to stimulating at the increased frequency. These differences were consistently matched by the tACS effects on Phase-Locking Value (cross-channel synchrony) and Modulation Index (cross-frequency synchrony) derived from the resting-state EEG data recorded after the stimulation. No analogous modulation was observed for the n-back task.