Modulation of connectivity and perception via phase-specific neurophysiological effects of tACS in humans

Abstract

Abstract The effects of transcranial alternating current stimulation (tACS) on neural activity have been debated extensively during the last years. With recent advances including unit recordings in macaques, it has been shown rigorously that neurons can entrain to the tACS rhythm. Nevertheless, it remains a challenge to uncover the complex dynamics of neurons embedded in various networks under the influence of weak electric fields, leading to state-dependencies and strongly non-linear effects, as well as how such complex dynamics translate into behavior and perception. In this talk, I will summarize several studies investigating the specificity of tACS in humans. We investigated if neural rhythms detected noninvasively via EEG can be phase-specifically modulated, and if these modifications resulted in behavioral changes. Although effects of tACS were highly state-dependent, we found rhythmic EEG modulations with varying phase between tACS and neural rhythms, also reflected in visual perception. Furthermore, dual-site tACS, supposedly phase-specifically affecting neural activity at two brain sites, was able to modulate functional connectivity between the targeted areas. In a computational model, we show that STDP can explain this connectivity modulation if neural activity is phase-specifically modulated. In sum, our studies show that tACS can phase-specifically modulate both neural activity and behavior in humans, and that this phase-specificity can be used to modulate functional connectivity. Further efforts will uncover whether such modulations can re-adapt pathological activity and relief impairment in disease. Research Category and Technology and Methods Basic Research: 8. Transcranial Alternating Current Stimulation (tACS) Keywords: EEG, Perception, Connectivity, Spike-timing Dependent Plasticity