Visualization of axonal and volume currents in median nerve compound action potential using magnetoneurography

Objective: Reconstruct compound median nerve action currents using magnetoneurography to clarify the physiological characteristics of axonal and volume currents and their relationship to potentials.Methods: The median nerves of both upper arms of five healthy individuals were investigated. The prop-agating magnetic field of the action potential was recorded using magnetoneurography, reconstructed in -to a current, and analyzed. The currents were compared with the potentials recorded from multipolar surface electrodes.Results: Reconstructed currents could be clearly visualized. Axonal currents flowed forward or backward in the axon, arcing away from the depolarization zone, turning about the subcutaneous volume conduc-tor, and returning to the depolarization zone. The zero-crossing latency of the axonal current was approx-imately the same as the peak of its volume current and the negative peak of the surface electrode potential. Volume current waveforms were proportional to the derivative of axonal ones.Conclusions: Magnetoneurography allows the visualization and quantitative evaluation of action cur-rents. The currents in axons and in volume conductors could be clearly discriminated with good quality. Their properties were consistent with previous neurophysiological findings.Significance: Magnetoneurography could be a novel tool for elucidating nerve physiology and pathophysiology.& COPY; 2023 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).