Sometimes extracellular recordings fail for good reasons

Area of Science:

• Biophysics
• Computational Neuroscience
• Cellular Electrophysiology

Background:

• Excitable cells generate extracellular potentials (EPs) crucial for physiological signals like EEG and ECG.
• Some excitable systems exhibit minimal or undetectable EPs, a phenomenon lacking clear explanation.
• Understanding EP generation is vital for interpreting bioelectrical recordings.

Purpose of the Study:

• To mathematically elucidate the conditions under which excitable cells and tissues produce extracellular potentials.
• To explain the absence of detectable EPs in certain homogeneous excitable systems.
• To identify the key factors driving EP generation in biological tissues.

Main Methods:

• Development of mathematical models for excitable cells and tissues.
• Analysis of extracellular potential generation under conditions of spatial homogeneity and uniformity.
• Simulation of cellular and tissue-level electrophysiology, including Purkinje neurons, hiPSC-CMs, and pancreatic β-cells.

Main Results:

• Homogeneous excitable cells and tissues produce zero extracellular potentials during spatially uniform, non-propagating activity.
• Absence of EPs in isolated, autonomous cells with uniform membrane properties, irrespective of model complexity.
• EPs are generated solely by spatial inhomogeneities, propagating waves, or applied currents.
• Demonstrated physiological relevance in Purkinje neurons, where channel clustering enables synchronization and EP detection.

Conclusions:

• Spatial homogeneity is the primary reason for the absence of extracellular potentials in certain excitable systems.
• Heterogeneity, electrical waves, and external stimuli are necessary and sufficient for generating detectable EPs.
• The findings provide a fundamental principle for understanding bioelectrical signal generation and detection in diverse cell types.