(Fig. 4b). This resulted in no significant difference in memory-specific gamma PLV across conditions (Fig. 4b). Both stimulation conditions showed no preferred direction of information flow among occipitotemporal gamma synchronization (ts41 < −1.221, ps > 0.229, dsz > 0.188). The results suggest occipitotemporal gamma connectivity in older adults was neither impaired at baseline, nor modulated by HD-tACS. It is possible that age-related preservation of occipitotemporal gamma plays a role in compensating for disconnected frontal control systems. Moreover, the preferential modulation of theta, but not gamma, synchronization by HD-tACS highlights the frequency specificity of this procedure, allowing us to potentially manipulate activity along a particular frequency channel of neural communication.
