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

## TL;DR

This study shows that brain activity measured by EEG changes with anti-seizure medication levels in people with hard-to-treat epilepsy.

## Contribution

The study identifies EEG markers that reflect ASM load changes during tapering in refractory epilepsy patients.

## Key findings

- Spectral exponents became less negative with reduced ASM load, mainly due to low-frequency power changes.
- Lowering ASM load increased harmonic responses to high-frequency visual stimulation (27–40 Hz).
- Harmonic responses increased during low ASM loads, possibly due to enhanced high gamma activity and visual perturbation responses.

## Abstract

Quantitative markers of cortical excitability may help identify responders to anti‐seizure medications (ASMs). We studied the relationship between ASM load and two electroencephalography (EEG) markers of cortical excitability in people with refractory epilepsy.

We included individuals with refractory focal epilepsy undergoing presurgical evaluation, involving ASM tapering and sleep deprivation. We obtained daily resting state EEG and EEG responses to visual stimulation at linearly increasing flash frequency (10–40 Hz chirp). We extracted the aperiodic exponent from resting state EEG power spectra and analysed chirp response at driving and second‐order harmonic frequencies. We modelled ASM load, which we related to the EEG markers using linear mixed‐effects regression.

Forty‐eight subjects (median age 34 years, age range 16–62 years, 19 females) participated. The spectral exponent became less negative with ASM load reduction (p = 0.02), mainly attributable to reduced low‐frequency power. Lowering ASM load increased the harmonic response to chirp stimulation (p = 0.004), also after accounting for sleep deprivation (p = 0.02), but did not affect the driving response. ASM tapering specifically increased harmonic responses to high stimulation frequencies (27–40 Hz, p = 0.01).

Resting state EEG spectral exponents and visual chirp responses reflect ASM load in refractory epilepsy. Low‐frequency spectral changes in resting state EEG may only mirror ASM‐induced spectral slowing. Visual chirp stimulation reveals enhanced harmonic EEG responses during low ASM loads, likely due to both increased high gamma activity and increased response to visual perturbations. Implementation of the markers would need normative values to reduce the delay to individually optimised treatment regimens.