Assessing cortical excitability with electroencephalography: A pilot study with EEG-iTBS.

Area of Science:

• Neuroscience
• Neurophysiology
• Biophysics

Background:

• Cortical excitability reflects neural reactivity, often measured by Transcranial Magnetic Stimulation (TMS).
• The balance between neural excitation and inhibition (E/I) is crucial for brain function.
• Electroencephalography (EEG) offers non-invasive methods to estimate intrinsic E/I balance.

Purpose of the Study:

• To determine how different EEG-derived E/I estimates correlate with TMS-measured cortical excitability.
• To assess the inter-consistency of various EEG E/I measures.

Main Methods:

• Assessed primary motor cortex (M1) excitability using TMS before and after intermittent theta burst stimulation (iTBS).
• Recorded resting-state EEG to calculate multiple E/I estimates.
• Compared TMS excitability measures with EEG E/I estimates.

Main Results:

• Increased TMS M1 excitability correlated with enhanced gamma band phase synchrony in EEG.
• Other EEG E/I measures showed some expected outcomes but lacked correlation with TMS measures or inter-consistency.

Conclusions:

• EEG-based E/I estimates provide a promising, non-invasive tool for mapping cortical excitability with high resolution.
• Spatial phase synchrony in the gamma band emerges as the most reliable EEG measure for capturing M1 excitability changes induced by neuromodulation.