BILATERAL HAND REPRESENTATION IN THE POSTCENTRAL SOMATOSENSORY CORTEX

IN accordance with its important role in prehensile activity, a large cortical area is devoted to representation of the digits. Within this large cortical zone in the macaque somatosensory cortex, the complexit y of neuronal receptive field characteristics increases from area 3b t o areas 1 and 2 (refs 1-7). This increase in complexity continues into the upper bank of the intraparietal sulcus, where the somatosensory c ortex adjoins the parietal association cortex. In this bank, callosal connections are much denser than in the more anterior part of this cor tical zone(8-17). We have now discovered a substantial number of neuro ns with receptive fields on the bilateral hands. It was previously tho ught that neuronal receptive fields were restricted to the contralater al side in this cortical zone. Neurons with bilateral receptive fields were not found after lesioning the postcentral gyrus in the contralat eral hemisphere. The majority of these neurons had receptive fields of the most complex types, representing multiple digits, indicating that the interhemispheric h anser of information occurs at higher levels o f the hierarchical processing in each hemisphere.