Neuromagnetic evidence of pre- and post-central cortical sources of somatosensory evoked responses

Tsuyoshi Kawamura, Nobukazu Nakasato, Kaoru Seki, Akitake Kanno, Satoshi Fujita, Satoru Fujiwara, Takashi Yoshimoto

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163 Citations (Scopus)


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 ( < 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.

Original languageEnglish
Pages (from-to)44-50
Number of pages7
JournalElectroencephalography and Clinical Neurophysiology - Evoked Potentials
Issue number1
Publication statusPublished - 1996


  • Dipole model
  • Functional anatomy
  • Magnetic resonance imaging
  • Somatosensory cortex
  • Somatosensory evoked response
  • Whole-head magnetometry


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