Short latency somatosensory evoked potentials recorded around the human upper brain-stem

Eiichirou Urasaki, Sumio Uematsu, Ronald P. Lesser

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


We analyzed the intracranial spatiotermporal distributions of the N18 component of short median nerve somatosensosry evoked potentials (SSEPs) in 3 patients with epilepsy. In these patients, depth electrodes were implanted bilaterally into the frontal and temporal lobes, with targets including the amygdala and hippocampus; the latter two targets are close to the upper pons and midbrain. In this study N18 was divided into the initial negative peak (N18a) and the following prolonged negativity (N18b). Mapping around the upper pons and midbrain showed that: (1) the amplitude of the first negativity, which coincided with scalp N18a, was larger contralateral to the side of stimulation, but showed no polarity change around the upper brain-stem; and (2) the second negativity, which was similar to scalp N18b, did show an amplitude difference or a polarity change. This wave appeared to reflect a positive-negative dipole directed in a dorso-ventral as well as dorso-lateral direction from the midbrain, where positivity arises from the dorsum of the midbrain, contralateral to the side of the stimulation. Recordings from depth electrode derivations oriented in a caudo-rostral direction suggest that N18a and N18b may in part reflect neural activity originating from the upper pons to midbrain region which projects to the rostral subcortical white matter of the frontal lobe as stationary peaks.

Original languageEnglish (US)
Pages (from-to)92-104
Number of pages13
JournalElectroencephalography and Clinical Neurophysiology/ Evoked Potentials
Issue number2
StatePublished - 1993


  • Depth recordings
  • Median nerve stimulation
  • N18 component
  • Somatosensory evoked potentials

ASJC Scopus subject areas

  • General Neuroscience
  • Clinical Neurology


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