Neuronal effects of epicranial current stimulation in macaque cortex
Boateng Asamoah1, Ahmad Khatoun1, Maria C Romero2
1Department of Neurosciences, ExpORL, KU Leuven and the Leuven Brain Institute, Leuven, Belgium.
Frontiers in Neuroscience
|October 9, 2025
Summary
Epicranial current stimulation (ECS) shows promise for brain neuromodulation. This study found ECS can entrain neural activity and increase spike rates, offering a potential alternative to invasive methods for certain patients.
Area of Science:
- Neuroscience
- Biomedical Engineering
Background:
- Transcranial electrical stimulation (TES) is safe and inexpensive but delivers weak brain electric fields (E-fields) due to scalp shunting.
- Invasive neuromodulation like deep brain stimulation (DBS) and invasive cortical stimulation (ICS) are effective but costly and risky.
- Epicranial current stimulation (ECS) offers a novel, less invasive approach by placing electrodes on the skull.
Purpose of the Study:
- To investigate the effects of epicranial current stimulation (ECS) on neural activity in non-human primates.
- To compare the efficacy of focused versus unfocused ECS montages.
- To explore the potential of ECS as a bridge between non-invasive TES and invasive DBS/ICS.
Main Methods:
- Two macaque monkeys were implanted with concentric ring electrodes on the skull targeting the PFG area of the parietal cortex.
- Neural activity was recorded while stimulating with 10 or 40 Hz sinewaves using focused or unfocused montages at varying intensities (0.25–4 mA).
- A functional magnetic resonance imaging (fMRI) experiment was conducted using unfocused stimulation at 10 Hz.
Main Results:
- Electric field strengths varied based on montage and stimulation intensity.
- Focused and low-amplitude unfocused stimulation led to neural entrainment.
- High-amplitude unfocused stimulation increased spike rates, mimicking ICS/DBS effects.
- fMRI revealed distributed brain activation patterns, suggesting a network response to ECS.
Conclusions:
- ECS can modulate neural activity, inducing both entrainment and increased firing rates.
- ECS demonstrates potential as a standalone neuromodulation technique for larger brains.
- ECS may offer a viable treatment option for patients unresponsive to TES but not suitable for ICS/DBS.
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