A generalized theory for current-source density analysis in brain tissue

TL;DR

This paper introduces a comprehensive theoretical framework for current-source density analysis in brain tissue that accounts for complex extracellular properties and source configurations, extending beyond traditional resistive and dipolar assumptions.

Contribution

It develops a generalized mean-field formalism that incorporates non-resistive media and multipolar sources, enhancing the accuracy of CSD analysis in neural tissue.

Findings

The formalism recovers classic CSD results as a special case.

It provides new expressions for non-resistive media and complex source configurations.

Power spectrum analysis reveals source and medium properties from experimental data.

Abstract

The current-source density (CSD) analysis is a widely used method in brain electrophysiology, but this method rests on a series of assumptions, namely that the surrounding extracellular medium is resistive and uniform, and in some versions of the theory, that the current sources are exclusively made by dipoles. Because of these assumptions, this standard model does not correctly describe the contributions of monopolar sources or of non-resistive aspects of the extracellular medium. We propose here a general framework to model electric fields and potentials resulting from current source densities, without relying on the above assumptions. We develop a mean-field formalism which is a generalization of the standard model, and which can directly incorporate non-resistive (non-ohmic) properties of the extracellular medium, such as ionic diffusion effects. This formalism recovers the classic results of the standard model such as the CSD analysis, but in addition, we provide expressions to generalize the CSD approach to situations with non-resistive media and arbitrarily complex multipolar configurations of current sources. We found that the power spectrum of the signal contains the signature of the nature of current sources and extracellular medium, which provides a direct way to estimate those properties from experimental data, and in particular, estimate the possible contribution of electric monopoles.