Understanding the sodium cation conductivity of human epileptic brain tissue

David Emin; Aria Fallah; Noriko Salamon; William Yong; Andrew Frew; Gary Mathern; Massoud Akhtari

doi:10.1063/5.0041906

Understanding the sodium cation conductivity of human epileptic brain tissue

AIP Adv. 2021 Apr 16;11(4):045118. doi: 10.1063/5.0041906. eCollection 2021 Apr.

Authors

David Emin¹, Aria Fallah², Noriko Salamon³, William Yong⁴, Andrew Frew⁵, Gary Mathern², Massoud Akhtari⁶

Affiliations

¹ Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131, USA.
² Departments of Neurosurgery and Pediatrics, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA.
³ Department of Radiology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA.
⁴ Department of Pathology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA.
⁵ Human Brain Mapping Center, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA.
⁶ Semel Institute for Neuroscience and Human Behavior, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA.

Abstract

Transient and frequency-dependent conductivity measurements on excised brain-tissue lesions from epilepsy patients indicate that sodium cations are the predominant charge carriers. The transient conductivity ultimately vanishes as ions encounter blockages. The initial and final values of the transient conductivity correspond to the high-frequency and low-frequency limits of the frequency-dependent conductivity, respectively. Carrier dynamics determines the conductivity between these limits. Typically, the conductivity rises monotonically with increasing frequency. By contrast, when pathology examinations found exceptionally disorganized excised tissue, the conductivity falls with increasing frequency as it approaches its high-frequency limit. To analyze these measurements, excised tissues are modeled as mixtures of "normal" tissue within which sodium cations can diffuse and "abnormal" tissue within which sodium cations are trapped. The decrease in the conductivity with increasing frequency indicates the predominance of trapping. The high-frequency conductivity decreases as the rate with which carriers are liberated from traps decreases. A relatively low conductivity results when most sodium cations remain trapped in "abnormal" brain tissue, while few move within "normal" brain tissue. Thus, the high densities of sodium nuclei observed by ²³Na-MRI in epilepsy patients' lesions are consistent with the low densities of diffusing sodium cations inferred from conductivity measurements of excised lesions.