# Comprehensive evaluation of EEG spatial sampling, head modelling and parcellation effects on network alterations in idiopathic generalized epilepsy

## TL;DR

Low-density EEG can detect brain network changes in idiopathic generalized epilepsy, though high-density EEG is better for detailed spatial mapping.

## Contribution

The study shows that low-density EEG arrays can reliably detect global alterations in idiopathic generalized epilepsy, particularly in signal power.

## Key findings

- Lower-density EEG arrays reliably identified global group differences in power and connectivity.
- Spatial similarity dropped for connectivity with fewer than 64 channels.
- Coarser brain parcellations increased stability for low-density maps.

## Abstract

Idiopathic generalized epilepsy is characterized by marked brain network alterations as assessed using electrophysiology. Logistical challenges and the need for a volumetric MRI often hinder the clinical application of high-density EEG or magnetoencephalography. This study investigates the influence of EEG channel density and the head model on brain metrics derived from 256-channel EEG and 19-channel routine EEG in two samples balanced for age and sex. First, we evaluated resting-state data from 35 individuals with idiopathic generalized epilepsy and 54 healthy controls collected using the 256-channel setup. Data were analysed at full density and then iteratively downsampled to lower densities. Source reconstruction was performed either using individual MRI data or a standard brain template and dynamic imaging of coherent sources. We assessed EEG power and connectivity (imaginary part of coherency) group differences at all channel compositions, head model types and parcellations (cortical vertices, anatomical and network parcellations). Second, a routine sample recorded with 19 channels was analysed to validate findings in a real epilepsy monitoring scenario (71 patients, 43 controls). We found that lower-density arrays reliably identified global group differences for both power and connectivity and in frequency bands for which the strongest effects were observed. The spatial similarity of the results for the 256 channels set and those with fewer channels were good to moderate for power (rspin ∼0.97 to 0.33), but dropped for connectivity with fewer than 64 channels (rspin ∼0.78 to −0.12). Comparing individual and canonical head models revealed consistent effects (rspin ∼0.77 to 0.5), with coarser brain parcellations increasing stability for low-density maps. In sum, low-density EEG arrays suffice for detecting global alterations in idiopathic generalized epilepsy, particularly in signal power. Our findings advocate for leveraging clinical EEG for brain-wide analyses in idiopathic generalized epilepsy while emphasizing the need for high-density coverage if spatial precision is needed. Canonical head models are a viable alternative if no individual MRI is available, especially for regional- or network-level assessments.

Stier et al. report that low-density EEG recordings reliably detect global theta-band power and connectivity alterations in idiopathic generalized epilepsy. Detailed spatial mapping of network connectivity, however, requires ≥64 channels and individual head models, with coarser parcellations mitigating template model limitations.

Graphical Abstract