[Functional localization of the somatomotor area by magnetoencephalography]

Precise localization of the current dipole by the magnetoencephalography (MEG) has enabled us to combine the functional information onto the anatomical landmarks. This merit can be best exhibited when the dipole is situated in the superficial cortex and directed parallel to the skull surface. However, before utilizing MEG extensively as a clinical tool, it is inevitable to confirm the precision of the source localization by comparing the estimation with the actual sources. Somatosensory evoked field (SEF) following the electric shock to the peripheral nerve and movement-related cortical field (MRCF) associated with self-paced movement can show us the estimated sources at the postcentral and precentral cortex, respectively, with somatotopic organization. These localizations were confirmed by the direct recordings from the human brain surface during the operation, even if the corresponding areas were anatomically distorted by some lesion occupying the central area. In addition, MEG can localize second somatosensory area (SII) over the superior bank of the Sylvian fissure as well as posterior parietal cortex (PPC), which are difficult to be detected by the EEG recording. These reliable estimation enables us to apply MEG to clarification of pathogenesis of various diseases and source localization for higher brain function.