Temporal interference stimulation over the motor cortex enhances cortical excitability in rats

Area of Science:

• Neuroscience
• Neuromodulation
• Non-invasive Brain Stimulation

Background:

• Temporal Interference Stimulation (TIS) is a novel technique for deep brain region targeting.
• Understanding TIS effects on cortical excitability is crucial for its application.
• Previous research has not fully elucidated TIS effects at various frequencies.

Purpose of the Study:

• To investigate the neuromodulatory effects of TIS at different beat frequencies on rat motor cortex excitability.
• To evaluate the impact of alpha (10 Hz), beta (20 Hz), and gamma (70 Hz) TIS on cortical excitability and inhibition.
• To assess neural biomarker activation and astrocyte responses following TIS.

Main Methods:

• Rats received TIS (alpha, beta, gamma, or sham) targeting the motor cortex for 20 minutes under anesthesia.
• Cortical excitability was measured using motor-evoked potentials (MEPs) and input-output (I/O) curves.
• Intracortical inhibition was assessed via long-interval intracortical inhibition (LICI).
• Immunohistochemistry was performed for c-Fos, GAD-65, and GFAP to evaluate neural and glial responses.

Main Results:

• Alpha and gamma TIS significantly increased MEP amplitudes compared to sham.
• I/O curve analysis showed enhanced area under the curve (AUC) in alpha and gamma TIS groups.
• Gamma TIS significantly reduced intracortical inhibition, indicated by an increased LICI ratio.
• TIS significantly increased c-Fos-positive cells in the motor cortex (35% increase vs. sham).
• No significant changes were observed in GAD-65 or GFAP expression.

Conclusions:

• A single session of alpha or gamma TIS effectively modulates cortical excitability in rats.
• TIS demonstrates potential for targeted neuromodulation applications.
• Gamma TIS specifically impacts intracortical inhibition, suggesting frequency-dependent effects.