An index to probe cortical excitability.

Area of Science:

• Neuroscience
• Computational Neuroscience
• Systems Neuroscience

Background:

• Cortical excitability, the brain's response to stimuli, is crucial for understanding neural function.
• Current methods like transcranial magnetic stimulation (TMS) offer global or local probing but lack dynamic range quantification.
• Intracranial electroencephalography (iEEG) in epilepsy patients provides a unique opportunity for detailed cortical analysis.

Purpose of the Study:

• To establish a novel framework for quantifying cortical excitability across its dynamical range.
• To develop a method for characterizing cortico-cortical connection strength and dynamics.
• To introduce a practical excitability index (ExI) for comparing neural responsiveness.

Main Methods:

• Utilized iEEG data from epilepsy patients undergoing electrical stimulation.
• Developed a stimulation-response curve analysis framework incorporating Spearman correlation and multi-parameter fits.
• Calculated the excitability index (ExI) as the normalized area under the stimulation-response curve.

Main Results:

• Identified 974 effective cortico-cortical connections (34.5%) with significant correlations.
• Demonstrated predominantly non-linear stimulation-response relationships, often requiring complex sigmoid fits.
• Showcased the framework's clinical relevance by analyzing excitability changes pre- and post-clonazepam administration.

Conclusions:

• Presented a robust framework for probing, measuring, and quantifying cortico-cortical connection excitability.
• The proposed excitability index offers a standardized metric for comparing neural excitability across diverse conditions and participants.
• This approach enhances our ability to understand and potentially modulate brain function.