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Effectiveness assessment of repetitive transcranial alternating current stimulation with concurrent EEG and fNIRS measurement

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Abstract

Transcranial alternating current stimulation (tACS) exhibits the capability to interact with endogenous brain oscillations using an external low-intensity sinusoidal current and influences cerebral function. Despite its potential benefits, the physiological mechanisms and effectiveness of tACS are currently a subject of debate and disagreement. The aims of our study are to (i) evaluate the neurological and behavioral impact of tACS by conducting repetitive sham-controlled experiments and (ii) propose criteria to evaluate effectiveness, which can serve as a benchmark to determine optimal individual-based tACS protocols. In this study, 15 healthy adults participated in the experiment over two visiting: sham and tACS (i.e., 5 Hz, 1 mA). During each visit, we used multimodal recordings of the participants’ brain, including simultaneous electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS), along with a working memory (WM) score to quantify neurological effects and cognitive changes immediately after each repetitive sham/tACS session. Our results indicate increased WM scores, hemodynamic response strength, and EEG power in theta and delta bands both during and after the tACS period. Additionally, the observed effects do not increase with prolonged stimulation time, as the effects plateau towards the end of the experiment. In conclusion, our proposed closed-loop scheme offers a promising advance for evaluating the effectiveness of tACS during the stimulation session. Specifically, the assessment criteria use participant-specific brain-based signals along with a behavioral output. Moreover, we propose a feedback efficacy score that can aid in determining the optimal stimulation duration based on a participant-specific brain state, thereby preventing the risk of overstimulation.

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Data availability

The dataset and materials used for current study are available from the corresponding author on reasonable request.

Abbreviations

EEG:

Electroencephalography

fNIRS:

Functional near-infrared spectroscopy

HbO:

Concentration changes of oxyhemoglobin

HbR:

Concentration changes of de-oxyhemoglobin

HD-tACS:

High-definition transcranial alternating current stimulation

NIBS:

Non-invasive brain stimulation

PFC:

Prefrontal cortex

tACS:

Transcranial alternating current stimulation

tDCS:

Transcranial direct current stimulation

tES:

Transcranial electrical stimulation

TMS:

Transcranial magnetic stimulation

tRNS:

Transcranial random noise stimulation

WM:

Working memory

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Funding

This study was supported by the National Research Foundation (NRF) of Korea under the Ministry of Science and ICT, Republic of Korea (grant no. RS-2023–00207954).

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Authors and Affiliations

  1. School of Mechanical Engineering, Pusan National University, Busan, 46241, Republic of Korea

    Dalin Yang, Usman Ghafoor & Keum-Shik Hong

  2. Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO, 63100, USA

    Dalin Yang & Adam Thomas Eggebrecht

  3. Department of Biomedical Engineering, Washington University, St. Louis, MO, 63130, USA

    Adam Thomas Eggebrecht

  4. Institute for Future, School of Automation, Qingdao University, Qingdao, 266071, Shandong, China

    Keum-Shik Hong

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Contributions

DY—Designed the study, supervised its execution, analyzed the data and drafted the manuscript; UG—participated in designing the study and drafting the manuscript; AE—provided iterative critical commenting on the drafts of the manuscript. K-SH—suggested the theoretical aspects of the current study, corrected the manuscript, and supervised the entire process leading to the manuscript generation. All authors read and approved the final manuscript.

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Correspondence to Keum-Shik Hong.

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The research paradigm was approved by the Human Research Ethics Committee of Pusan National University in compliance with the latest Declaration of Helsink.

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Yang, D., Ghafoor, U., Eggebrecht, A.T. et al. Effectiveness assessment of repetitive transcranial alternating current stimulation with concurrent EEG and fNIRS measurement. Health Inf Sci Syst 11, 35 (2023). https://doi.org/10.1007/s13755-023-00233-y

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