Face representation in the human primary somatosensory cortex.

Abstract

To investigate the representation of facial skin areas in the primary somatosensory cortex (SI), we recorded magnetic fields evoked by air pressure-induced tactile stimulation applied to six points on the face, lower lip and thumb. The thumb area in the SI was located more medial and superior to the lip area, which was consistent with Penfield's homunculus. However, the representations of all skin-covered areas including forehead, cheek, nose and chin in the SI were located between the thumb and lower lip area. There was no significant difference in location among the six facial points. Our results imply that lips occupy a large area of the face representation in the SI, whereas only a small area located between the thumb and lip areas is devoted to skin-covered surfaces. This is the first study showing that the facial skin areas in the human SI are located between the thumb and lower lip areas and close together.