Non-invasive magnetoneurography for 3D-monitoring of human compound action current propagation in deep brachial plexus.

Compound action current (CAC) propagation along nerve fibers running deep in the human brachial plexus was 3D-visualized based on non-invasive 49-channel superconducting quantum interference device (SQUID) magnetoneurography. Spatio-temporal mappings over the upper thoracal quadrant of magnetic fields (<100 fT) evoked upon alternating median and ulnar nerve stimulation in seven healthy volunteers showed consistently smoothly propagating dipolar patterns for both the CAC depolarization and repolarization phases. Multipolar current source reconstructions (i) distinguished spatially CAC propagation pathways along either median or ulnar plexus fibers, allowed (ii) to calculate local conduction velocities ( approximately 56 m/s) and (iii) even to estimate the CAC extension along the nerve fibers (depolarization phase: approximately 11 cm). Thus, for deep proximal nerve segments magnetoneurography can provide a detailed tracing of neural activity which is a prerequisite to localize non-invasively focal nerve malfunctions.