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

Dalin Yang; Usman Ghafoor; Adam Thomas Eggebrecht; Keum-Shik Hong

doi:10.1007/s13755-023-00233-y

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

Health Inf Sci Syst. 2023 Aug 2;11(1):35. doi: 10.1007/s13755-023-00233-y. eCollection 2023 Dec.

Authors

Dalin Yang^{1

2}, Usman Ghafoor¹, Adam Thomas Eggebrecht^{2

3}, Keum-Shik Hong^{1

4}

Affiliations

¹ School of Mechanical Engineering, Pusan National University, Busan, 46241 Republic of Korea.
² Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63100 USA.
³ Department of Biomedical Engineering, Washington University, St. Louis, MO 63130 USA.
⁴ Institute for Future, School of Automation, Qingdao University, Qingdao, 266071 Shandong China.

PMID: 37545487
PMCID: PMC10397167 (available on 2024-12-01)
DOI: 10.1007/s13755-023-00233-y

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.

Keywords: Brain stimulation; Electroencephalography (EEG); Functional near-infrared spectroscopy (fNIRS); Hemodynamic response (HR); Transcranial alternating current stimulation (tACS); Working memory (WM).

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