Nonequivalent After-Effects of Alternating Current Stimulation on Motor Cortex Oscillation and Inhibition: Simulation...

Area of Science:

• Neuroscience
• Neurophysiology
• Brain Stimulation

Background:

• Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation technique.
• The precise effects of tACS frequency on brain oscillations and cortical excitability remain debated.
• Understanding frequency-specific modulation is crucial for optimizing tACS applications.

Purpose of the Study:

• To investigate how different tACS frequencies differentially modulate cortical oscillations and inhibition in the human motor cortex.
• To identify an optimal electrode configuration for tACS delivery to the hand motor area using electric field simulations.

Main Methods:

• Electric field simulations based on MRI data were used to determine the optimal Cz-CP1 tACS electrode configuration for the precentral gyrus.
• tACS was applied to the hand motor area at 10 Hz (alpha-tACS) or 20 Hz (beta-tACS) with sham-tACS as a control.
• Cortical oscillations and motor evoked potentials (MEPs) were measured to assess changes in cortical excitability and inhibition.

Main Results:

• Both alpha-tACS and beta-tACS significantly increased their respective brain oscillations (alpha and beta) compared to sham-tACS.
• Alpha- and beta-tACS decreased the amplitude of conditioned motor evoked potentials, indicating enhanced cortical inhibition.
• The Cz-CP1 electrode configuration provided higher electric field values and reduced inter-individual variability.

Conclusions:

• tACS frequency differentially modulates motor cortex oscillations, with alpha-tACS enhancing alpha oscillations and beta-tACS enhancing beta oscillations.
• tACS at specific frequencies (alpha and beta) effectively enhances cortical inhibition.
• These findings highlight the importance of tACS frequency selection for targeted neuromodulation of motor cortex excitability and inhibition.