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Influence of tACS on neural dynamics at a targeted frequency in SSVEP

Poster No:

Submission Type:

Abstract Submission

Authors:

Nuri On¹, Jeonghui Kim², Chany Lee³, Do-Won Kim⁴

Institutions:

¹CHONNAM NATIONAL UNIVERSITY, Yeosu City, Jeollanam-do, ²CHONNAM NATIONAL UNIVERSITY, Yeosu, Jeollanamdo, ³Korea Brain Research Institute, Daegu, Korea, Republic of, ⁴Chonnam National University, Yeosu, Jeollanam-do

First Author:

Nuri On
CHONNAM NATIONAL UNIVERSITY
Yeosu City, Jeollanam-do

Co-Author(s):

Jeonghui Kim
CHONNAM NATIONAL UNIVERSITY
Yeosu, Jeollanamdo

Chany Lee
Korea Brain Research Institute
Daegu, Korea, Republic of

Do-Won Kim
Chonnam National University
Yeosu, Jeollanam-do

Introduction:

Steady-state visual evoked potential based brain-computer interface (SSVEP-BCI) is one of the most extensively studied types of BCIs, utilizing the neural responses that elicited when an individual gazes at a visual stimulus flickering at a specific frequency. However, widespread adoption is hindered by individuals known as "SSVEP illiteracy" who lack the ability to respond to these visual stimuli. To address this issue, recent studies have shown that applying transcranial direct current stimulation (tDCS) to the visual cortex can enhance SSVEP responses, but this enhancement is only observed in individuals with a low signal-to-noise ratio (SNR) (Kim, 2019). This study investigates whether SSVEP responses can be enhanced at specific frequencies using transcranial alternating current stimulation (tACS).

Methods:

A total of 24 participants (19 males, age: 22.70 ± 2.07) were recruited for the experiment. Each participant first recorded an initial SSVEP response before receiving tACS stimulation. SSVEP responses were recorded for 10 seconds while gazing at a flickering stimulus at 12 random frequencies, each presented 10 times. The frequency with the lowest SNR was chosen for tACS. tACS was applied for 20 minutes with a maximum current of 2 mA. Anodal electrodes were placed at O1, Oz, O2, and Pz; the cathodal electrode was at Fz. After tACS, SSVEP responses at 12 frequencies were recorded to assess the effects of tACS. All EEG recordings and tACS stimulation used a battery-driven current stimulator (Starstim R32, NeuroElectrics, Barcelona, Spain). All participants signed a written consent that was approved by the Institutional Review Board (IRB) of Chonnam National University prior to their participation in the study (IRB No. 1040198-210708-HR-103-03).

Results:

A significant increase in absolute power was observed in the post-stimulation condition (0.706 ± 0.309) compared to the pre-stimulation condition (0.588 ± 0.246), whereas in the non-stimulation condition, absolute power was not significantly different between pre- (0.678 ± 0.228) and post- (0.708 ± 0.245) TACS. Similarly, SNR was significantly improved in the post-stimulation (1.377 ± 0.307) condition compared to pre-stimulation (0.213 ± 0.292), but no significant difference was found in the non-stimulation condition. [Figure 1]

·Changes in (a) absolute power and (b) SNR as stimulation condition

Conclusions:

This study provides compelling evidence that frequency-specific transcranial alternating current stimulation (tACS) is a viable method to enhance steady-state visual evoked potential (SSVEP) responses, particularly at targeted stimulus frequencies. By applying tACS to the visual cortex at frequencies associated with the lowest initial signal-to-noise ratio (SNR), significant improvements in both absolute power and SNR of SSVEP responses were observed. These enhancements were specifically localized to the targeted frequencies, while non-stimulus frequencies remained unaffected, demonstrating the frequency-specific nature of tACS effects.

Brain Stimulation:

Non-invasive Electrical/tDCS/tACS/tRNS ¹

Novel Imaging Acquisition Methods:

EEG ²

Keywords:

Electroencephaolography (EEG)

Other - steady-state visual evoked potential (SSVEP); transcranial alternating current stimulation (tACS); signal-to-noise ratio (SNR); spectral power; visual cortex

^1|2Indicates the priority used for review

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Were any human subjects research approved by the relevant Institutional Review Board or ethics panel? NOTE: Any human subjects studies without IRB approval will be automatically rejected.

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Provide references using APA citation style.

Kim, D.-W. et al., (2019) Can anodal transcranial direct current stimulation increase steady-state visual evoked potential responses? Journal of Korean Medical Science, 34(43), e285.

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