Somatotopic organization of cortical fields in the lateral sulcus of Homo sapiens: Evidence for SII and PV

The human somatosensory cortex in the Sylvian fissure was examined using fu nctional magnetic resonance imaging to describe the number and internal org anization of cortical fields present. Somatic stimuli were applied to the l ips, face, hand, trunk, and foot of 18 human subjects. Activity patterns we re transposed onto three-dimensional magnetic resonance images of the brain so that the location of activity associated with the different stimuli cou ld be related to specific regions of the cortex. There were several consist ent findings. First, there were three regions of activity in the lateral su lcus associated with stimulation of the contralateral body. The most consis tent locus of activation was on the upper bank of the lateral sulcus, conti nuing onto the operculum. The other two areas, one rostral and one caudal t o this large central area, were smaller and were activated less consistentl y. Second, when activity patterns in the large central area resulting from stimulation of all body parts were considered, this region appeared to cont ain two fields that corresponded in location and somatotopic organization t o the second somatosensory area (SII) and the parietal ventral area (PV). F inally, patterns of activation within SII and PV were somewhat variable acr oss subjects. Repeated within-subject stimulus pre-ii sentation indicated t hat differences across subjects were not due to inconsistent stimulus prese ntation. Comparisons with other mammals suggest that some features of organ ization are found only in primates. It is hypothesized that these features may be associated with manual dexterity and coordination of the hands, a ch aracteristic generally restricted to the primate lineage. (C) 2000 Wiley-Li ss, Inc.