tACS on, tACS off: entrainment of neural oscillations during WM
Kevin Jones1,2, Hector Arciniega1, Jennifer Shepack1, Carlos Carrasco1, Marian Berryhill1; 1University of Nevada, Reno, 2Colorado State University
Efforts to improve working memory (WM) by pairing training with noninvasive neurostimulation reveal behavioral improvements in younger and older adults. We previously found that WM training paired with transcranial direct current stimulation (tDCS) was associated with pre-/post- changes in EEG signals. Specifically, we observed changes in both anterior-posterior theta (7 Hz) and posterior alpha (11 Hz) oscillations during WM maintenance, but only in those who received active tDCS. Here, we tested the hypothesis that directly modulating these frequencies using transcranial alternating current (tACS) might elicit behavioral change without requiring WM training. In Experiment 1 we applied 7 Hz in/out phase tACS targeting left or right frontoparietal networks during several 2-back WM tasks (verbal, object, spatial stimuli). In Experiment 2, we provided in phase 7 Hz or 11 Hz tACS targeting right frontoparietal sites using more difficult 3-back WM tasks (object, spatial stimuli). The results were mixed. Experiment 1 replicated previous findings, showing that tACS had a modest effect on WM performance on the tasks. A limitation was that the 2-back tasks were not sufficiently difficult for our young adult population. Experiment 2 revealed mixed effects depending on stimulation frequency and stimulus type. Surprisingly, 7 Hz tACS impaired WM performance across 3-back stimuli. In contrast, 11 Hz tACS improved performance on the spatial 3-back task and impaired performance for the verbal 3-back task. These data provide little support for the ability of single-session tACS to shortcut WM training paired with tDCS.
Topic Area: EXECUTIVE PROCESSES: Working memory