Magnetoencephalographic study for face representation in the human primary somatosensory cortex

To investigate the representation of facial skin area in the primary somatosensory cortex (SI), we recorded magnetoencephalography (MEG), the somatosensory-evoked magnetic fields (SEFs), by using tactile stimulation induced by air pressure applied to six points of facial skin (lateral and medial side of forehead, cheek and chin), lower lip and thumb. Equivalent current dipole (ECD) following thumb stimulation was located significantly more medial and superior to that following lip stimulation, which was consistent with Penfield's homunculus. In contrast, representation of six facial skin areas was located between the thumb and lip areas, and there was no significant difference of locations among six face points. This new finding was inconsistent with homunculus.