Topography of the secondary somatosensory cortex in humans: a magnetoencephalo-graphic study

THE topography of the secondary somatosensory cortex (SII) responses to som atosensory stimulation applied to various parts of the body of normal volun teers was analyzed using magnetoencephalography (MEG). Although there were large inter-individual differences, the following orders of a location of e quivalent current dipoles (ECDs) were found; (1) Anterior-posterior directi on: lower lip-upper lip-thumb-middle finger-foot, (2) Medial-lateral direct ion: foot-middle finger-thumb-upper lip-lower lip, and (3) Lower-upper dire ction: lower lip-upper-lip-thumb-middle finger-foot. In general, these find ings are similar to those obtained in studies of monkeys. However, the diff erentiation was not as clear as that seen in the homunculus in the primary somatosensory cortex (SI). The auditory cortex is located at a site more po sterior, lateral and lower than the SII. (C) 1999 Lippincott Williams & Wil kins.