T108. Magnetic recordings of sensory action currents in the cervical cord

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A prototype magnetospinography (MSG) system with highly sensitive SQUID sensors for humans has been developed to noninvasively measure spinal cord activity by our lab. Here, we report neural activity in dorsal column and dorsal horn in the cervical cord using MSG. Eleven healthy volunteers participated in this study. Participants were laid in a magnetically shielded room and neuromagnetic fields were measured from the neck in response to electrical stimulation of the median nerve at wrist, using a newly developed 124-channel MSG system. Two thousand responses between −5 and 30 ms after the stimulation were averaged. Evoked action currents were reconstructed by a spatial filter, recursive null steering beamforemer and superimposed on the X-ray image of individual participant’s cervical spine. Just before magnetic recordings, somatosensory evoked potentials (SEP) also were recorded with the same stimulus setting. The recording places were set at ipsilateral-to-contralateral Erb’s point and C5 posterior-anterior cervical derivation. In all 11 healthy subjects, estimated “horizontal” electrical currents in the cervical canal which indicates depolarization in dorsal column were ascending sequentially. Their peak latency at C5 level and the N11 peak latency of SEP recorded with C5S-ACmontage matched well (r = 0.96, p < 0.0001). In 7 of 11 participants, the waveform of estimated electrical currents from dorsal to ventral at C5 level displayed high similarity to SEP wave recorded with C5S-AC montage which contains the cervical N13-P13 potential. Across 7 participants, the estimated electrical current peak latency around C5 and the N13-P13 peak latency of SEP matched well (r = 0.95, p = 0.001). MSG could visualize sequential electrical activities in dorsal column and dorsal horn in the cervical cord.