EEG Spectral Exponents and Visual Chirp Responses Mirror Anti-Seizure Medication Load in Refractory Focal Epilepsy

Area of Science:

• Neuroscience
• Clinical Electrophysiology
• Pharmacology

Background:

• Quantitative markers of cortical excitability are crucial for identifying optimal anti-seizure medication (ASM) responders.
• Refractory epilepsy presents challenges in treatment selection, necessitating objective biomarkers.

Purpose of the Study:

• To investigate the relationship between ASM load and electroencephalography (EEG) markers of cortical excitability.
• To assess how changes in ASM load affect specific EEG measures in individuals with refractory epilepsy.

Main Methods:

• Participants with refractory focal epilepsy underwent ASM tapering and sleep deprivation during presurgical evaluation.
• Resting state EEG and EEG responses to visual stimulation (10-40 Hz chirp) were recorded.
• Aperiodic exponent from EEG power spectra and harmonic responses to chirp stimulation were analyzed and related to ASM load using regression models.

Main Results:

• Reduced ASM load was associated with less negative spectral exponents (p=0.02), primarily due to decreased low-frequency power.
• Lowering ASM load increased harmonic responses to chirp stimulation (p=0.004), independent of sleep deprivation.
• ASM tapering specifically enhanced harmonic responses to high-frequency stimulation (27-40 Hz, p=0.01).

Conclusions:

• Resting state EEG spectral exponents and visual chirp responses dynamically reflect ASM load in refractory epilepsy.
• Visual chirp stimulation reveals enhanced harmonic EEG responses at lower ASM loads, potentially indicating increased high gamma activity.
• Normative values for these EEG markers are needed for timely, individualized treatment optimization.