For all montages, stimulation was applied for 10 blocks of trials (i.e., 5 memory blocks and 5 control blocks, alternating in order, lasting approximately 25 minutes). In the frontotemporal montages (i.e., theta-tuned and 8-Hz nontuned) across Experiments 1, 2, and 4, the alternating current was inphase, meaning it was delivered with 0° relative phase difference across the two targeted cortical locations. We specifically used inphase stimulation because it has been shown to facilitate network synchronization between targeted regions and improve cognitive performance 21–23, 46, 58. In contrast, for Experiment 3, subjects were challenged with a frontotemporal theta-tuned antiphase montage, in which alternating current was delivered with 180° relative phase difference across targeted areas, with the goal of impeding network synchronization and impairing performance 21. The current intensity values for the antiphase montage were set to: E12 = 0.267, E27 = 0.267, E29 = 0.267, G32 = −0.267, L4 = −0.267, K5 = −0.267. Although induction of peripheral flicker perception is typically only reported when using higher frequency tACS 59–61, we nonetheless used post-experiment questionnaires to confirm that our low-frequency stimulation
