title: Generators of tibial nerve somatosensory evoked potential: recorded from the mesial surface of the human brain using subdural electrodes.
abstract: The generators of the initial cortical component of somatosensory evoked potentials in response to tibial nerve stimulation (Tib-somatosensory evoked potentials) are still uncertain. The purpose of this study is to localize the generators of it. A 15-year-old boy with intractable parietal lobe epilepsy was studied. Subdural electrodes were chronically implanted for presurgical evaluation of epilepsy surgery, covering the primary motor, primary sensory, and supplementary sensorimotor areas of the right leg. Tib-somatosensory evoked potentials were recorded from these areas. Highly localized prominent positive activities were recorded from electrodes on the primary motor area of the leg at 32.4 to 34.0 milliseconds. No corresponding large negative peak was recorded in any other electrodes. Weak negative activities distributed widely around the postcentral area at 33.2 to 33.6 milliseconds, accompanied by similar but positive activities in the precentral area at 32.8 to 33.2 milliseconds. There was an independent positive field on supplementary sensorimotor areas at 34.0 to 34.8 milliseconds. A small negative peak was also recorded but only from a single electrode within supplementary sensorimotor areas at 34.0 milliseconds. Our data suggest that the initial response of Tib-somatosensory evoked potentials has at least three independent generators: a radial dipole on the primary motor, a tangential dipole on the primary sensory area, and a dipole on the supplementary sensorimotor areas oriented perpendicularly to the mesial hemispheric surface.
authors.affiliation: Department of Neurology, National Epilepsy Center, Shizuoka Institute of Epilepsy and Neurological Disorders, Aoi-ku, Shizuoka, Japan. kyht-terada@umin.net
authors.forename: Kiyohito
authors.initials: K
authors.lastname: Terada
authors.forename: Shuichi
authors.initials: S
authors.lastname: Umeoka
authors.forename: Koichi
authors.initials: K
authors.lastname: Baba
authors.forename: Yuji
authors.initials: Y
authors.lastname: Sakura
authors.forename: Naotaka
authors.initials: N
authors.lastname: Usui
authors.forename: Kazumi
authors.initials: K
authors.lastname: Matsuda
authors.forename: Takayasu
authors.initials: T
authors.lastname: Tottori
authors.forename: Tadahiro
authors.initials: T
authors.lastname: Mihara
authors.forename: Keiko
authors.initials: K
authors.lastname: Usui
authors.forename: Fumihiro
authors.initials: F
authors.lastname: Nakamura
authors.forename: Yushi
authors.initials: Y
authors.lastname: Inoue
mesh_terms: D000293:Adolescent; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D004828:Epilepsies, Partial / Q000503:physiopathology / Q000601:surgery; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D013003:Somatosensory Cortex / Q000502:physiology*; D013979:Tibial Nerve / Q000502:physiology*; D004561:Transcutaneous Electric Nerve Stimulation