Entrainment of Brain Oscillations by Transcranial Alternating Current Stimulation

Abstract

Novel methods for neuronal entrainment [1-4] provide the unique opportunity to modulate perceptually relevant brain oscillations [5, 6] in a frequency-specific manner and to study their functional impact on distinct cognitive functions. Recently, evidence has emerged that tACS (transcranial alternating current stimulation) can modulate cortical oscillations [7-9]. However, the study of electrophysiological effects has been hampered so far by the absence of concurrent electroencephalogram (EEG) recordings. Here, we applied 10 Hz tACS to the parieto-occipital cortex and utilized simultaneous EEG recordings to study neuronal entrainment during stimulation. We pioneer a novel approach for simultaneous tACS-EEG recordings and successfully separate stimulation artifacts from ongoing and event-related cortical activity. Our results reveal that 10 Hz tACS increases parieto-occipital alpha activity and synchronizes cortical oscillators with similar intrinsic frequencies to the entrainment frequency. Additionally, we demonstrate that tACS modulates target detection performance in a phase-dependent fashion highlighting the causal role of alpha oscillations for visual perception.

Pre-stimulus alpha oscillations over somatosensory cortex predict tactile misperceptions

“…Ai & Ro, 2014;Lakatos, Karmos, Mehta, Ulbert, & Schroeder, 2008;Sherman et al, 2016) and may have other relationships with performance than the overall state as indexed here. Future investigations which directly manipulate ongoing oscillations through methods such as transcranial alternating current stimulation (Helfrich et al, 2014;Herrmann, Murray, Ionta, Hutt, & Lefebvre, 2016;Vosskuhl, Huster, & Herrmann, 2016) would help to answer these questions more directly.…”

Exploring prefrontal cortex functions in healthy humans by transcranial electrical stimulation

“…Different from tDCS, tACS has no major plasticity-inducing effect [22] , although recent studies suggest that exceptions do exist [23] . Modelling and animal and human studies have shown that relatively focal AC stimulation can lead to widespread entrainment of oscillatory activity at the induced frequency [24,25] . The main effect of tACS in humans is a modulation of oscillatory frequency bands in the EEG, if these match the stimulation frequency.…”

Imaging human brain networks to improve the clinical efficacy of non-invasive brain stimulation

“…Finally, an oscillatory variant of tDCS, referred to as transcranial alternating current stimulation (tACS) applies a regular oscillating current (c.f., tRNS) across the two electrodes. This stimulation approach is thought to be efficient in changing neural oscillations in the targeted region (Marshall and Binder, 2013;Helfrich et al, 2014) and is discussed in more detail later in the review.…”

“…The task-related boosting (or suppression) of neural oscillations at specific frequencies between cortical regions can enhance performance in processes involved in task selection, attention and memory (Marshall et al, 2004;Lakatos et al, 2008;Bauer et al, 2012;Helfrich et al, 2014). Both rTMS and tDCS can modify ongoing oscillatory activity, and in so doing, may mimic or augment the amplitude of normal endogenous neural oscillations to promote task performance and cortical connectivity.…”

“…Recently, a different brain stimulation technique called transcranial alternating current stimulation (tACS) has been used to selectively modify ongoing oscillatory activity at a particular frequency (Marshall and Binder, 2013;Helfrich et al, 2014). This method alters the current density produced at the two electrodes in an oscillatory manner.…”