Effects of tACS on electrophysiological signals are task-dependent

47 

Abstract Submission 

Abhijit Chinchani¹, Rafal Skiba², Todd Woodward²

¹The University of British Columbia (UBC), Vancouver, British Columbia (BC), ²University of British Columbia, Vancouver, British Columbia

Abhijit Chinchani  
The University of British Columbia (UBC)
Vancouver, British Columbia (BC)

Rafal Skiba  
University of British Columbia
Vancouver, British Columbia

Todd Woodward  
University of British Columbia
Vancouver, British Columbia

Transcranial alternating current stimulation (tACS) is a non-invasive technique that delivers low-intensity alternating currents intending to affect neural activity and behavior (Liu et al., 2018). Recent research has shown that the effects of tACS are often inconsistent and not replicable (Kasten et al., 2019; B. Krause & Kadosh, 2014). In this study, we investigated the effects of 10Hz alpha (vs 41Hz gamma) stimulation on alpha oscillations during a vigilance-oddball paradigm. Similar tasks involving sustained attention are used to study the effects of tACS on electrophysiology and behavior (Zaehle et al., 2010, Vossen et al., 2015). Here, we aimed to test whether electrophysiology is reliably modulated by neurostimulation.

In this study, participants (n=38) underwent occipital (Fig. 2A) alpha (10Hz) and gamma (41Hz) stimulation, on separate days. During each session, participants performed three blocks of a vigilance-oddball task: the first without stimulation (PRE), the second with either alpha or gamma stimulation (STIM), and the third without stimulation (POST). In each block, participants performed a vigilance-oddball task (Fig. 1A); where they were instructed to fixate on a white cross in the center of the screen and respond to color changes to the fixation cross using a button press on a keyboard. The color of the cross changed from white to either red or green, one of which occurred 80% of the time (DEFAULT color change) and the other 20% of the time (ODDBALL color change). Half the participants were instructed to use their left index finger for the DEFAULT color change (Left-hand dominant group, see Fig. 1B) and the other half their right index finger (Right-hand dominant group, see Fig. 1B). Simultaneous EEG was recorded from 256 electrodes during all the blocks.

Due to the lateralized nature of the responses, we checked whether tACS affected alpha power in a lateralized manner. We observed that enhancement in alpha power (Δ = POST - PRE) was greater for alpha stimulation than gamma stimulation but only for the contralateral electrodes (Fig. 2C, right; t(37)=-2.55, p=0.015) to the dominant response hand (response hand for DEFAULT color change) and not for the ipsilateral electrodes (Fig. 2C, left; t(37)=1.45, p=0.156). Moreover, the difference in the enhancement of alpha power between alpha and gamma stimulation (ΔΔ = alpha stim - gamma stim) was significantly higher for the contralateral electrodes as compared to the ipsilateral ones (Fig. 2D; t(37)=-3.68, p<0.001).

Our findings reveal that alpha tACS enhances alpha power but this enhancement is more pronounced in the electrodes contralateral to the dominant hand involved in the task. It is noteworthy that this lateralized effect is observed even though our tACS electrode montage (Fig. 2A) wasn't lateralized. This implies that the effect is likely driven by the motor planning aspects involved during the task paradigm. Thus suggesting that the effects of tACS on electrophysiological signals depend on the nature of the task being performed.

Non-invasive Electrical/tDCS/tACS/tRNS ¹

EEG/MEG Modeling and Analysis

Visuo-Motor Functions ²

Attention: Visual

Cognition

Electroencephaolography (EEG)

Motor

Other - Transcranial alternating current stimulation (tACS)