Anomalous frequency-dependent ionic conductivity of lesion-laden human-brain tissue

TL;DR

This study investigates how brain lesions affect ionic conductivity measurements, revealing that most lesion-affected tissues show increased conductivity with frequency, while some show decreased conductivity due to sodium ion trapping.

Contribution

It introduces a novel frequency-dependent analysis of ionic conductivity in lesion-laden brain tissue, linking electrical behavior to specific pathological features.

Findings

Most samples show increased conductivity with frequency.

Some samples exhibit decreased conductivity with frequency.

Frequency dependence correlates with lesion severity.

Abstract

We study the effect of lesions on our four-electrode measurements of the ionic conductivity of (1 cm3) samples of human brain excised from patients undergoing pediatric epilepsy surgery. For most (about 94 %) samples the low-frequency ionic conductivity rises upon increasing the applied frequency. We attributed this behavior to the long-range (0.4 mm) diffusion of solvated sodium cations before encountering impenetrable blockages such as cell membranes, blood vessels and cell walls. By contrast, the low-frequency ionic conductivity of some (6 %) brain tissue samples falls with increasing applied frequency. We attribute this unusual frequency-dependence to the electric-field induced liberation of sodium cations from traps introduced by the unusually severe pathology observed in samples from these patients. Thus, the anomalous frequency-dependence of the ionic conductivity indicates trap-producing brain lesions.