Apparent extracellular current density and extracellular space: basis for the current source density analysis in neural tissue

TL;DR

This paper establishes a theoretical framework linking macroscopic neural signals like EEG and LFP to cellular electrophysiological processes, incorporating Maxwell's equations and concepts of apparent extracellular properties.

Contribution

It introduces the concepts of apparent extracellular current density and space, deriving a general equation for current source density analysis in biological tissue.

Findings

Derived a general CSD equation considering frequency-dependent properties

Connected extracellular space to dielectric dispersion phenomena

Provided a theoretical basis for interpreting neural electrical signals

Abstract

This article provides a theoretical basis for relating macroscopic electrical signals recorded from biological tissue, such as electroencephalogram (EEG) and local field potential (LFP), to the electrophysiological processes at the cellular level in a manner consistent with Maxwell's equations. Concepts of the apparent extracellular current density and the apparent extracellular space with apparent permittivity and conductivity are introduced from the conservation of current and Gauss's theorem. A general equation for the current source density (CSD) analysis is derived for biological tissue with frequency-dependent apparent permittivity and conductivity. An intuitive account of the apparent extracellular space is given to relate the concept to the dielectric dispersion of biological tissue.