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

Concurrent spinal and brain imaging with optically pumped magnetometers

“…The latency of the peak components of the SCEF were extracted using the peak activity of the absolute maximum T-values across all spinal channels (both radial and tangential) that surpassed the false discovery rate (FDR) threshold. Previous MSG studies have found evoked spinal responses to MNS at the wrist occurring 9.7 ms after stimulation 21 . We found peak activity in the early period (< 12 ms post-stimulation) at 10, 9 and 10 ms, for right MNS in sessions 2 and 3 (Figure 2Dii and 3Aii) and left MNS in session 3 (Figure 3Ai), respectively.…”

“…OPM sensors uniquely allow for non-invasive imaging of the brain and spinal cord simultaneously, facilitating electrophysiology recording over the entire human central nervous system (CNS; Figure 1). Here, we chose median nerve stimulation (MNS) to probe the CNS, due to the time-locked nature of the expected response and the wealth of previous literature providing strong priors about the latency of the evoked field 17,21,40,41 .…”

“…Recent work using MSG has described very fast spinal responses occurring 5.5 ms following MNS at the elbow 22 and 9.7 ms following MNS at the wrist 21 . Here, we saw evidence for early components 10 ms after wrist MNS.…”

“…Commonly used non-invasive techniques for measuring spinal electrophysiology generally rely on surface electrodes, which, for example, can detect spinal cord evoked potentials (SCEPs) following electrical stimulation of peripheral nerves 17–20 . SCEPs recorded with skin and scalp electrodes, while non-invasive and easy to record, can be difficult to interpret due to the distortion of the volume currents caused to surrounding tissue which in turn limits precise estimates of the underlying sources 21 .…”

“…The magnetic fields detected with MSG are not as distorted by the tissue surrounding the spinal cord or muscle artefacts, meaning source analysis is more reliable 23,27 . Recent MSG systems are based upon custom-built arrays of SQUID sensors within rigid cryogenic vessels (dewars) filled with liquid helium 21 . Both reclining and supine position scanning systems have been developed, optimized to record from the cervical spine 22,28 .…”