Manipulating Neural Oscillations in Frequency and Phase Shifting Using Transcranial Alternating Current Stimulation: An Investigation into the Oscillatory Neural Mechanisms of Visual Working Memory

Visual working memory (VWM) is a specific memory system that bridges the gap between our information-rich but short-lived perceptual memory and high-capacity but effortful visual long-term memory. Recent neuroimaging studies have suggested that successful VWM relies on a network of brain regions that are functionally connected and whose activities are well-coordinated. However, how such coordination is achieve among various brain regions still remains unclear. In the human brain, such functional connectivity can be artificially “entrained” via noninvasive electrical stimulation, called the transcranial alternating current stimulation (tACS), that ramps voltage up and down in a sinusoidal manner, thereby entraining the neural populations with amplitude (amperage), frequency (number of cycles per second), and phase information (the alignment of phase among the electrodes). Today, a growing number of studies have begun to demonstrate a positive effect of tACS on VWM, but many conflicting results have been reported, and such lack of agreement in the field strongly suggest that our understanding of the mechanisms behind tACS and VWM need to be updated and reevaluated. To this end, we have been the first in the field to propose a complex model that includes interregional and intraregional phase coherence, or the likely combination of the two, to explain the many seemingly-contradictory effects that tACS in theta and gamma frequency has on VWM. In this proposal, we have designed a series of experiments to further refine such model by systematically manipulating tACS frequency, phase shift, and electrode placements to map out the independent contribution of intra- and interregional synchronization. As such, the goal of the present proposal is twofold: 1) based on what we already know about VWM and its neural correlates, we can build on such information to explore and better understand the effect and mechanisms behind tACS, and 2) importantly, we in turn use what we learn from Point 1 to modulate the oscillation between different brain areas to investigate the neural mechanisms behind spatial, featural, and binding VWM. In summary, this proposal contains a series of 9 experiments that use both tACS and EEG to investigate the temporally-precise oscillatory mechanisms behind VWM.