ABSTRACT
The evaluation of averaged electroencephalography (EEG) following somatosensory stimulation, i.e. somatosensory evoked potential, is one of the most useful methods for investigating the human somatosensory system. magnetoencephalography (MEG) has several theoretical advantages over EEG in localizing cortical sources, because the magnetic fields recorded on the scalp are less affected by volume currents and anatomical inhomogeneities. MEG has excellent spatial and temporal resolution in the order of mm and msec. The spatial resolution of MEG is almost the same as that of functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), but its temporal resolution is much better than fMRI and PET. The magnetic fields recorded from the human brain are very small, approximately ten thousand to a million times smaller than the Earth’s steady magnetic field and environmental fields. Electrical stimulation is used, since its stimulus onset is very sharp, and it generates much larger magnetic field than cutaneous stimulation.
