Representation of the ear in human primary somatosensory cortex

We studied 13 healthy subjects with a multichannel magnetoencephalography ( MEG) system to investigate the somatotopic representation of the ear in the primary somatosensory cortex (SI). We stimulated three parts of the left e ar: the helix, the lobulus, and the tragus, The somatosensory-evoked magnet ic fields (SEFs) were successfully measured in 7 of 13 subjects. Short-late ncy responses were analyzed using both single dipole and multidipole models (brain electric source analysis, BESA). From the single dipole model, the equivalent current dipole (ECD) following the helix stimulation was estimat ed to be near the neck area of SI in all the subjects. In the lobulus stimu lation, the ECDs were estimated around the neck area of SI in four subjects , in the face area in one subject, and in the deep white matter in two subj ects. In the tragus stimulation, the ECDs were estimated around the neck ar ea of SI in three subjects, in the hand area of SI in two subjects, and in the deep white matter in two subjects. When the ECDs were estimated to be l ocated in unlikely sites (hand area and deep white matter), a two-dipole mo del, (1) the neck area of SI and (2) face area of SI, was found to be the m ost appropriate. Although this might be a preliminary study due to a relati vely small number of subjects, it revealed that receptive fields of some pa rt of the ear, such as the lobulus and tragus, might be present in both the neck and face areas of SI. These findings suggested that the "ear area" of SI has variability between subjects, unlike the other areas of SI, possibl y because the ear is located on the border between the neck and face. (C) 2 001 Academic Press.