What are the generators of median nerve somatosensory evoked potential (SEP)?

Updated: Oct 25, 2019
  • Author: Andrew B Evans, MD; Chief Editor: Selim R Benbadis, MD  more...
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The generators of median nerve SEP are as follows:

  • Erb point – Brachial plexus

  • N11, N13 – Dorsal column, nucleus cuneatus

  • P14 – Medial lemniscus

  • N18 – Subcortical

  • N20 – Primary sensory cortex

  • P22 – Primary motor cortex

Buchner et al researched the origin of P16 of the median nerve SEP. [40] After median nerve stimulation, several monophasic peaks were recorded at the scalp in the 15- to 18-msec time range. Source analysis using 3 different methods modeled a source near the center of the head with an orientation toward the activated hemisphere and a peak activity at 16 msec after the stimulus. Magnetic recordings detected no signals in this time range, which confirmed that the source had a subcortical location.

From dipole localization, the exact origin of the P16 source could not be assigned to either the subthalamic level or the thalamocortical radiation, because of the limited spatial resolution at the center of the spherical head model. An estimate of the conduction velocity of the medial lemniscus suggested a subthalamic origin. [40] The P16 source was preserved in 2 patients with a lesion of the thalamocortical radiation and the ventral thalamus. Further evidence for a subthalamic location was derived from the physical mechanisms generating far-field potentials.

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