Assessing interactions in the brain with exact low-resolution electromagnetic tomography

TLDR

EEG neuroimaging estimates cortical current density from scalp recordings, but the resulting measures are inflated by volume conduction and low spatial resolution. The study aims to provide an exact localization solution—eLORETA—and a decomposition method that separates instantaneous and lagged components to isolate physiologically relevant activity. eLORETA is an exact low‑resolution electromagnetic tomography technique that reconstructs cortical sources, and the decomposition approach partitions signals into instantaneous and lagged parts, with the lagged part reflecting almost pure physiological origin. The method delivers high‑time‑resolution intracranial signals enabling assessment of functional dynamic connectivity through coherence and phase synchronization.

Abstract

Scalp electric potentials (electroencephalogram; EEG) are contingent to the impressed current density unleashed by cortical pyramidal neurons undergoing post-synaptic processes. EEG neuroimaging consists of estimating the cortical current density from scalp recordings. We report a solution to this inverse problem that attains exact localization: exact low-resolution brain electromagnetic tomography (eLORETA). This non-invasive method yields high time-resolution intracranial signals that can be used for assessing functional dynamic connectivity in the brain, quantified by coherence and phase synchronization. However, these measures are non-physiologically high because of volume conduction and low spatial resolution. We present a new method to solve this problem by decomposing them into instantaneous and lagged components, with the lagged part having almost pure physiological origin.