The Combination of Transcranial Alternating Current Stimulation and Electroencephalogram
October 10th, 2025
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.
The current protocol aims to demonstrate how to combine high definition transcranial alternating current stimulation with EEG. By recording EEG before and after stimulation, this protocol enables researchers to assess neural physiological effects of stimulation. To begin, clean the participant's scalp before the experiment.
Place the 64-channel EEG brain cap, with electrodes arranged according to the 10-20 system on the participant's head. Monitor electrode impedance by selecting impedance in the software interface. Set the impedance display range to zero to five kilo ohms, to ensure high recording quality.
Interpret orange or green signals on the display as below five kilo ohms. Use the syringe tip to part the hair through the electrode openings, then inject the gel to ensure direct contact between each electrode and the scalp. Gently rub the scalp with the syringe tip until the impedance of each electrode drops below five kilo ohms.
Once impedance is confirmed for all electrodes, initiate EEG recording by pressing start in the software as the participant performs the two-back task. Visualize EEG signals during the task. Clean the participant's scalp again before stimulation.
Prepare all necessary materials in advance. Install batteries and confirm they are fully charged. Use the input cable to connect the two-channel transcranial electrical stimulation stimulator to the four-by-one stimulation interface.
Connect the output cable to the four-by-one interface and attach five silver or silver chloride electrodes to the output cable. Power on the two-channel stimulator and the four-by-one system after completing all connections. Now, embed five plastic high definition casings into designated sites in the EEG brain cap at the sites P3, CP3, P1, PO3, and P5.Then place the EEG cap on the participant's head.
Apply conductive gel to the scalp through each HD casing opening, using a syringe tip. Part the hair to expose the scalp and apply gel directly. Insert five electrodes into the casings with electrode five at P3, and the rest surrounding it.
Fill all EEG electrodes with conductive gel again and confirm impedance values below five kilo ohms. Confirm that the default mode on the stimulator is set to scan. Then view impedance values of each electrode individually by pressing the numbered buttons on the four-by-one interface.
If impedance exceeds 1.5, open the cap and scrub the scalp with a syringe tip to reduce impedance. Set stimulation parameters on the two-channel stimulator, including waveform, duration, and intensity, using four knobs. Use the joystick to toggle the sham condition.
Set parameters to alternating current waveform, two milliamperes, and four hertz for 10 minutes. Switch the relaxed level to full current. Next, change the stimulator mode from scan to pass, using the mode select button.
Start stimulation by pressing the start button on the stimulator. Observe current ramp-up on the screen until target intensity is reached. If discomfort occurs, reduce intensity with the relaxed lever, and resume once the participant is comfortable.
Terminate stimulation if necessary by pressing the abort button. Remove the HD casings and stimulation electrodes from the EEG cap. Reinsert the original EEG electrodes at sites P3, CP3, P1, PO3, and P5.Use the syringe tip to part the hair and apply conductive gel directly to each reinserted electrode.
Confirm impedance values are below five kilo ohms before starting post-stimulation EEG recording. Ocular artifacts were successfully removed during EEG pre-processing, as illustrated by the absence of typical eye movement signals in the post-artifact rejection traces. Time-frequency spectrograms revealed a reduction in theta band power following stimulation compared to pre-stimulation.
This protocol presents a practical method for integrating HDTACS with EEG. We hope this protocol will facilitate broader applications of TACS and EEG integration, and promote more regular exploration of neuro-entrainment dynamics. This protocol can be extended to larger sample sizes with tailored stimulation parameters to investigate a broader range of cognitive and affective functions.
View the full transcript and gain access to thousands of scientific videos
Overview
This protocol establishes a practical approach for combining high definition transcranial alternating current stimulation (HD-tACS) with EEG to examine the neural oscillations during cognitive tasks, specifically using theta-frequency stimulation in working memory as a case study. The integration of these methods enables researchers to assess the physiological effects of stimulation on neural activity before and after cognitive tasks.
Key Study Components
Area of Science
- Neuroscience
- Electrophysiology
- Cognitive Neuroscience
Background
- High definition tACS is a method used to modulate brain activity.
- The role of neural oscillations in cognitive functions is increasingly recognized.
- EEG allows for real-time monitoring of brain activity.
- Combining these techniques can enhance understanding of cognitive processes.
Purpose of Study
- To provide a detailed protocol for integrating HD-tACS with EEG.
- To assess the effects of theta frequency stimulation on working memory.
- To promote broader applications of this dual-method approach in research.
Methods Used
- The platform used includes EEG and a transcranial electrical stimulation device.
- Participants perform a cognitive task while being stimulated to monitor EEG responses.
- Key steps include impedance checks and ensuring electrode contact for clear recordings.
- Stimulation parameters such as waveform, duration, and intensity are carefully calibrated.
Main Results
- EEG pre-processing successfully removed ocular artifacts, improving data quality.
- A reduction in theta band power was observed following stimulation compared to pre-stimulation baselines.
- The protocol facilitates a better understanding of neuro-entrainment dynamics related to cognitive tasks.
- This method can be applied to larger sample sizes for further exploration.
Conclusions
- The study presents a viable method for combining HD-tACS and EEG to investigate cognitive functions.
- The findings demonstrate the potential for HD-tACS to influence neural oscillations related to cognitive performance.
- This approach may lead to greater insights into neurological mechanisms underlying cognition.
Frequently Asked Questions
Executive Industry Relevance
Combining high-definition transcranial alternating current stimulation (HD-tACS) with EEG enables precise interrogation of neural oscillations underlying cognitive functions, supporting mechanistic de-risking in early neuroscience discovery. This integrated approach provides quantitative, frequency-specific readouts that inform target validation and predictive confidence for neuro-modulation strategies. The protocol's reproducibility and scalability position it as a reusable platform for advancing neurotechnology portfolios.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Enables direct assessment of causal links between neural oscillations and cognitive endpoints.
- Supports functional target validation by quantifying physiological effects of frequency-specific stimulation.
- Facilitates mechanistic de-risking for neuro-modulation targets in cognitive and affective domains.
Screening & Assay Development
- Establishes validated EEG-based assays for quantifying neural response to stimulation.
- Standardizes measurement of oscillatory power changes, supporting reproducible screening workflows.
- Provides quantitative outputs for evaluating compound or device effects on neural dynamics.
Translational & Preclinical Research
- Aligns neural oscillation biomarkers with cognitive task performance for translational continuity.
- Enables risk-adjusted advancement of neuro-modulation strategies based on physiological endpoints.
- Supports extension to larger cohorts and diverse cognitive paradigms for broader translational insight.
Pipeline & Workflow Integration
This protocol integrates into the neuroscience discovery continuum from early mechanistic studies to preclinical validation of neuro-modulation interventions.
- Discovery Biology: Provides a platform for hypothesis testing on neural oscillation-cognition relationships.
- Screening: Delivers standardized, reproducible EEG readouts for evaluating intervention effects.
- Analytics: Enables quantitative comparison of pre- and post-stimulation neural activity.
- Translational Research: Bridges discovery findings to preclinical models using cognitive and physiological endpoints.
- Enterprise Reuse: Offers a modular workflow adaptable to various stimulation parameters and cognitive tasks.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence and reduces mechanistic ambiguity in neuro-modulation research.
- Operational Value: Promotes standardization, reproducibility, and scalability across studies.
- Strategic Value: Informs go/no-go decisions and enhances capital efficiency in neurotechnology pipelines.
- Portfolio Impact: Supports risk-adjusted prioritization and advancement of neuromodulation assets.
Implementation Considerations
- Requires expertise in EEG acquisition, stimulation parameterization, and artifact rejection.
- Demands high-quality instrumentation for impedance monitoring and signal fidelity.
- Necessitates cross-team standardization of electrode placement and stimulation protocols.
- Adaptable to different cognitive tasks and stimulation frequencies with protocol modifications.
- Participant variability in neural response may affect generalizability and requires careful cohort design.
