Behavior funnels the electrophysiological effects of tACS to specific brain areas.
Poster No:
22
Submission Type:
Abstract Submission
Authors:
Abhijit Chinchani1, Rafal Skiba2, Yvette Ni2, Sage Radlmeier2, Dan Vuong2, Yudan Chen2, Todd Woodward2
Institutions:
1University of British Columbia, Vancouver, British Columbia, 2UBC, Vancouver, BC
First Author:
Co-Author(s):
Introduction:
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). However, the effects of tACS are often inconsistent and not replicable (Kasten et al., 2019; B. Krause & Kadosh, 2014). The main reason for this inconsistency is that more than 70% of the electric current applied passes through the scalp without reaching the cortex (Vöröslakos et al., 2018). This raises a conundrum - we need to place the anode and cathode far apart to induce large electric fields. However, placing them far apart will lead to the induced electric fields being non-localized and spreading out in most brain parts. Thus, to address this issue, we investigated whether behavior could assist in achieving more localized effects of tACS even when the anode and cathodes are placed further apart.
Methods:
Participants (n=74) underwent occipital 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. One group of participants (LEFT biased group, n=23) were instructed to respond using their left-hand index finger for the DEFAULT color change and their right-hand index finger for the ODDBALL color change. Another group (n=29) used the opposite configuration to respond (i.e., right-hand for DEFAULT and left-hand for ODDBALL color change). We also conducted a control experiment where the red and green color changes were equally likely to occur (Unbiased group, n=23). Simultaneous EEG is recorded from 256 electrodes during all the blocks.
Results:
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 (Figure 1C, right; Paired Cohen's d=0.372 [95.0% CI 0.000, 0.711], p=0.048) to the biased response hand (response hand for DEFAULT color change) and not for the ipsilateral electrodes (Figure 1C, left; Paired Cohen's d=-0.259 [95.0%CI -0.506, -0.010], p=0.084). 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 (Figure 1D; Paired Cohen's d=0.514 [95.0%CI 0.282, 0.705], p<0.001).
Next, we tested whether the lateralized effect of tACS systematically changes for different response groups. The difference in the enhancement of alpha power for gamma and alpha stimulation (ΔΔ alpha power) for left vs right electrodes is maximum for the left-biased group (Figure 2, left, Paired Cohen's d=0.721 [95.0%CI 0.335, 1.0], p=0.001), almost zero for the unbiased group (Figure 2, center, Paired Cohen's d=0.108 [95.0%CI -0.23, 0.424], p=0.566), and opposite for the right-biased group (Figure 2, right, Paired Cohen's d=-0.347 [95.0%CI -0.635, -0.0811], p=0.037).
Next, we tested whether the lateralized effect of tACS systematically changes for different response groups. The difference in the enhancement of alpha power for gamma and alpha stimulation (ΔΔ alpha power) for left vs right electrodes is maximum for the left-biased group (Figure 2, left, Paired Cohen's d=0.721 [95.0%CI 0.335, 1.0], p=0.001), almost zero for the unbiased group (Figure 2, center, Paired Cohen's d=0.108 [95.0%CI -0.23, 0.424], p=0.566), and opposite for the right-biased group (Figure 2, right, Paired Cohen's d=-0.347 [95.0%CI -0.635, -0.0811], p=0.037).
·Figure 1
·Figure 2
Conclusions:
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 (Figure 1A) wasn't lateralized. This implies that the effect is likely driven by the motor planning aspects involved during the task paradigm. Thus, behavioral tasks could be used to funnel the effects of tACS on electrophysiology to specific brain areas.
Brain Stimulation:
Non-invasive Electrical/tDCS/tACS/tRNS 1
Motor Behavior:
Motor Planning and Execution
Novel Imaging Acquisition Methods:
EEG 2
Keywords:
Electroencephaolography (EEG)
Motor
Other - tACS
1|2Indicates the priority used for review
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Provide references using APA citation style.
Krause, B., & Kadosh, R. C. (2014). Not all brains are created equal: The relevance of individual differences in responsiveness to transcranial electrical stimulation. Frontiers in Systems Neuroscience, 8. https://doi.org/10.3389/fnsys.2014.00025
Liu, A., Vöröslakos, M., Kronberg, G., Henin, S., Krause, M. R., Huang, Y., Opitz, A., Mehta, A., Pack, C. C., Krekelberg, B., Berényi, A., Parra, L. C., Melloni, L., Devinsky, O., & Buzsáki, G. (2018). Immediate neurophysiological effects of transcranial electrical stimulation. Nature Communications, 9(1), Article 1. https://doi.org/10.1038/s41467-018-07233-7
Vöröslakos, M., Takeuchi, Y., Brinyiczki, K., Zombori, T., Oliva, A., Fernández-Ruiz, A., Kozák, G., Kincses, Z. T., Iványi, B., Buzsáki, G., & Berényi, A. (2018). Direct effects of transcranial electric stimulation on brain circuits in rats and humans. Nature Communications, 9(1), 483. https://doi.org/10.1038/s41467-018-02928-3