title: Neuromagnetic evidence of pre- and post-central cortical sources of somatosensory evoked responses.
abstract: Somatosensory evoked magnetic fields (SEFs), corresponding with electrical median nerve stimulation, were measured using an MRI-linked, whole-head MEG system. In total 184 hemispheres, SEFs were measured, involving 22 normal volunteers and 70 patients with intracranial lesions. The first SEF peak appeared 20.2 +/- 1.5 msec (mean +/- S.D.) after stimulation. The first peak was followed by a second and third peak, 7.7 +/- 3.2 msec and 14.6 +/- 5.4 msec respectively after the first. Corresponding isofield maps suggested a single current dipole oriented in the anterior direction for the first peak, posterior for the second and either anterior or posterior for the third. Using a spherical model and a single current dipole source, the localization of each peak was estimated and superimposed on individually determined MRI images. On a grand average basis, the first-peak dipole was localized on the posterior surface of the central sulcus, "area 3b." The second-peak dipole was localized 3.7 mm medial (P < 0.001) and 2.0 mm superior (P < 0.001) to the first-peak dipole, on the anterior wall of the central sulcus, "area 4." This study with a large number of subjects was able to statistically distinguish two adjacent cortical sources, located on opposite walls of the central sulcus, and within a few millimeters of each other.
authors.affiliation: Department of Neurosurgery, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Kawamura
authors.forename: N
authors.initials: N
authors.lastname: Nakasato
authors.forename: K
authors.initials: K
authors.lastname: Seki
authors.forename: A
authors.initials: A
authors.lastname: Kanno
authors.forename: S
authors.initials: S
authors.lastname: Fujita
authors.forename: S
authors.initials: S
authors.lastname: Fujiwara
authors.forename: T
authors.initials: T
authors.lastname: Yoshimoto
mesh_terms: D000328:Adult; D000368:Aged; D001921:Brain / Q000473:pathology; D001927:Brain Diseases / Q000175:diagnosis / Q000503:physiopathology; D002648:Child; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008280:Magnetics; D008297:Male; D008475:Median Nerve / Q000502:physiology; D008875:Middle Aged; D011930:Reaction Time; D012016:Reference Values