Noninvasive measurement of sensory action currents in the cervical cord by magnetospinography

Abstract

Objective: To obtain magnetic recordings of electrical activities in the cervical cord and visualize sensory action currents of the dorsal column, intervertebral foramen, and dorsal horn.

Methods: Neuromagnetic fields were measured at the neck surface upon median nerve stimulation at the wrist using a magnetospinography system with high-sensitivity superconducting quantum interference device sensors. Somatosensory evoked potentials (SEPs) were also recorded. Evoked electrical currents were reconstructed by recursive null-steering beamformer and superimposed on cervical X-ray images.

Results: Estimated electrical currents perpendicular to the cervical cord ascended sequentially. Their peak latency at C5 and N11 peak latency of SEP were well-correlated in all 16 participants (r = 0.94, p < 0.0001). Trailing axonal currents in the intervertebral foramens were estimated in 10 participants. Estimated dorsal-ventral electrical currents were obtained within the spinal canal at C5. Current density peak latency significantly correlated with cervical N13-P13 peak latency of SEPs in 13 participants (r = 0.97, p < 0.0001).

Conclusions: Magnetospinography shows excellent spatial and temporal resolution after median nerve stimulation and can identify the spinal root entry level, calculate the dorsal column conduction velocity, and analyze segmental dorsal horn activity.

Significance: This approach is useful for functional electrophysiological diagnosis of somatosensory pathways.

Keywords: Dorsal column; Dorsal horn; Evoked magnetic field; Magnetospinography; Somatosensory evoked potential; Superconducting quantum interference device (SQUID).