Sensory potentials evoked by magnetic stimulation of the cervical spine

Magnetic stimulation of cervical spinal roots was shown to elicit sensory potentials (MESP) which could easily be recorded at the fingers with ring electrodes. The latency of the MESP recorded at digit I was significantly shorter and the amplitude higher than of digits III and V. The latencies were largely independent of stimulus strength. In an attempt to localize the place of depolarization, the latencies of these potentials were compared with the N11 of the SEP (reflecting the arrival in the spinal cord) and with F-wave latencies and motor evoked potentials (MEP) to abductor pollicis brevis. The MESP latencies showed a very constant difference with the N11, being 0.6 ms faster. The mean difference between F latency and MEP was 1.2 ms. It is concluded that the origin of these MESPs is very near the spinal foramina, possibly in the sensory ganglia.