The Effect of Prior Parameters on Standardized Kalman Filter-Based EEG Source Localization

TL;DR

This paper investigates how prior parameter choices in the Standardized Kalman Filter improve EEG source localization, especially for deep sources, by optimizing Gaussian priors and smoothing techniques based on synthetic data experiments.

Contribution

It introduces optimized Gaussian prior parameters within the SKF framework and demonstrates their effectiveness in improving depth localization accuracy.

Findings

Raising the standardization exponent to 1.25 enhances depth localization.

RTS smoothing improves source separability.

Optimal prior parameters depend on noise levels.

Abstract

EEG Source localization is a critical tool in neuroscience, with applications ranging from epilepsy diagnosis to cognitive research. It involves solving an ill-posed inverse problem that lacks a unique solution unless constrained by prior knowledge. The Bayesian framework enables the incorporation of such knowledge, typically encoded through prior models. Various algorithms have been proposed for source localization, and they differ significantly in how prior knowledge is incorporated. Some approaches rely on anatomical or functional constraints, while others use statistical distributions or sampling-based techniques. In this landscape, the Standardized Kalman Filter (SKF) represents a dynamic Bayesian approach that integrates temporal modeling with a Gaussian prior structure. It addresses the depth bias, a common limitation in source localization, through a post-hoc standardization step that equalizes sensitivity across cortical depths and makes deep activity detection feasible. This study focuses on the development and optimization of Gaussian prior models within the SKF framework for simultaneous cortical and sub-cortical activity detection. Synthetic data similar to the P20 / N20 component of the somatosensory evoked potentials (SEP) was used to identify effective prior parameter configurations for reconstructing both deep and superficial sources under different noise levels. We also investigated the role of RTS smoothing in enhancing source separability. Our results indicate that raising the standardization exponent to 1.25, along with smoothing, significantly improves depth localization accuracy at low noise levels.