Validating non-invasive EEG source imaging using optimal electrode configurations on a representative rat head model

TL;DR

This study validates non-invasive EEG source imaging in rats using optimal electrode configurations derived from a template-based head model, demonstrating potential for accurate localization of brain activity despite anatomical variability.

Contribution

It adapts human EEG source imaging methods to rats, establishing electrode spacing and sensitivity parameters for effective non-invasive brain activity localization.

Findings

Electrodes should be at least 3-3.5 mm apart for optimal configuration.

Sensitivity resolution varies across the scalp, better at the center.

Theoretical localization accuracy can reach the level of specific brain structures.

Abstract

The curtain of technical limitations impeding rat multichannel non-invasive electroencephalography (EEG) has risen. Given the importance of this preclinical model, development and validation of EEG source imaging (ESI) is essential. We investigate the validity of well-known human ESI methodologies in rats which individual tissue geometries have been approximated by those extracted from an MRI template, leading also to imprecision in electrode localizations. With the half and fifth sensitivity volumes we determine both the theoretical minimum electrode separation for non-redundant scalp EEG measurements and the electrode sensitivity resolution, which vary over the scalp because of the head geometry. According to our results, electrodes should be at least ~3-3.5 mm apart for an optimal configuration. The sensitivity resolution is generally worse for electrodes at the boundaries of the scalp measured region, though, by analogy with human montages, concentrates the sensitivity enough to localize sources. Cram\'er-Rao lower bounds of source localization errors indicate it is theoretically possible to achieve ESI accuracy at the level of anatomical structures, such as the stimulus-specific somatosensory areas, using the template. More validation for this approximation is provided through the comparison between the template and the individual lead field matrices, for several rats. Finally, using well-accepted inverse methods, we demonstrate that somatosensory ESI is not only expected but also allows exploring unknown phenomena related to global sensory integration. Inheriting the advantages and pitfalls of human ESI, rat ESI will boost the understanding of brain pathophysiological mechanisms and the evaluation of ESI methodologies, new pharmacological treatments and ESI-based biomarkers.