Magnetoneurography to investigate the mechanisms underlying the P9 far-field potential.

OBJECTIVE

The mechanism underlying the generation of P9 far-field somatosensory evoked potentials (SEPs) is unresolved. Accordingly, we used magnetoneurography to visualize the current distribution in the body at the P9 peak latency and elucidate the origin of P9 generation.

METHODS

We studied five healthy male volunteers without neurological abnormalities. We recorded far-field SEPs after median nerve stimulation at the wrist to identify the P9 peak latency. Using magnetoneurography, we recorded the evoked magnetic fields in the whole body under the same stimulus conditions as the SEP recording. We analyzed the reconstructed current distribution at the P9 peak latency.

RESULTS

At the P9 peak latency, we observed the reconstructed current distribution dividing the thorax into two parts, upper and lower. Anatomically, the depolarization site at the P9 peak latency was distal to the interclavicular space and at the level of the second intercostal space.

CONCLUSIONS

By visualizing the current distribution, we proved that P9 peak latency originates in the change in volume conductor size between the upper and lower thorax.

SIGNIFICANCE: We clarified that magnetoneurography analysis is affected by the current distribution due to the junction potential.