The Combination of Transcranial Alternating Current Stimulation and Electroencephalogram

Summary

This protocol establishes a practical approach for combining HD-tACS with EEG to examine stimulation effects on neural oscillations during cognitive tasks, using theta-frequency stimulation in working memory as an exemplar.

Abstract

Neural oscillations are integral to various cognitive processes, including working memory, attention, and perception. Transcranial alternating current stimulation (tACS) has emerged as a noninvasive tool for investigating causal relationships between brain oscillations and cognitive functions. By targeting specific frequencies, tACS can modulate oscillatory activity, providing insights into the role of neural rhythms in cognitive performance. To understand the impact of tACS on oscillatory dynamics and cognitive processes, it is essential to combine physiological measurements such as EEG with behavioral data. High-definition tACS (HD-tACS) improves the spatial precision of stimulation, enabling more localized targeting of specific cortical areas. This protocol outlines a method for combining HD-tACS with EEG to assess changes in theta-frequency (4 Hz) oscillations in the left parietal cortex. EEG recordings are taken before and after stimulation during a 2-back working memory task to examine theta activity. This approach offers a powerful tool for exploring the neural mechanisms that underlie cognitive modulation via rhythmic brain stimulation.

Introduction

Transcranial alternating current stimulation (tACS) is a noninvasive neuromodulation method that delivers weak sinusoidal electrical currents to the brain at specific frequencies, or combinations of frequencies^1,2. As part of the broader category of transcranial electrical stimulation (tES), which also includes transcranial direct current stimulation (tDCS), transcranial random noise stimulation (tRNS), and transcranial pulsed current stimulation (tPCS)³, tACS is particularly notable for its capacity to modulate endogenous brain rhythms. Unlike other tES modalities....

Protocol

The protocol was approved by the Institutional Review Board of Southwest University and conducted in accordance with institutional guidelines. This protocol demonstration presents data from one healthy adult participant (age = 25, female) to illustrate the protocol procedures. The participant provided written informed consent prior to the experiment. The equipment used are listed in the Table of Materials.

1. Determination of stimulation parameters

Based on prior research investigating neural oscillations underlying working memory^16,

Results

EEG data can be analyzed in the time domain (e.g., event-related potentials), frequency domain (e.g., spectral analysis), or time-frequency domain (e.g., time-frequency analysis). In this case, time-frequency analysis was used to examine changes in oscillatory activity associated with stimulation. EEG data acquired pre- and post-stimulation from a representative subject were pre-processed using the EEGLAB toolbox in MATLAB. The pre-processing steps included the following: The continuous EEG was filtered with 40 Hz low-pa.......

Discussion

Transcranial alternating current stimulation (tACS) offers a noninvasive approach to modulate specific brain rhythms. Due to its excellent resolution, EEG is well-suited for examining both spontaneous and externally entrained neural oscillations. Combining tACS with EEG provides a multimodal approach to investigate the function and structure of the brain, and to further explore the underlying neural mechanisms of tACS effects. Thus, this protocol presents a practical method for integrating HD-tACS with EEG.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
EEG Braincap	BRAIN PRODUCTS	BC-64-X42-UAMW-56	64 channels based on 10-20 system
4´1 HD-tES	Soterix medical	4´1-C3A	The Soterix 4×1 HD-tDCS / HD-tES adaptor converts any 2-channel Soterix Medical tDCS stimulator into an HD-tDCS / tES device. The 4×1 HD-tES adaptor is not a stand-alone stimulator, and during stimulation does not generate any current. Rather, the 4×1 HD-tES adaptor intelligently divides and guides current generated by a 2-channel device, converting it to HD-tES (HD-tDCS, HD-tACS, HD-tRNS, HD-tPCS, HD-tODCS).