Connections of the fronto-parietal operculum and the postcentral gyrus with the posterior ventral thalamic nucleus, especially its medial nucleus, in monkeys.
In 22 crab-eating monkeys (Macaca irus), either lesions or HRP injections were made in the frontol parietal operculum and, for the purpose of contrast, in the postcentral gyrus to observe their fiber connectionl with the posterior ventral nucleus (VP). The exposed opercular part, reported to consist of areas 3b, 1, and 2 showed scanty fiber connections with VP. The buried parietal operculum had connections with the media (VPM) and lateral (VPL) nuclei of VP, corresponding to the second somatic sensory cortex (SII). This cortica area was connected, in VPM, to its ventromedial part, while the base of the postcentral gyrus, the ordinary face area of SI, was connected to its lateral-most part. This suggests that the ventromedial part of VPM is more intimately related to SII, and its lateral-most part to SI. In contrast, the SI and SII areas of VPL overlapped more extensively with each other. The cortical area which received fibers from the parvocellular part of VPM (VPMpc) lay in the frontal operculum, especially in its buried part. This area extended caudally beyond the precentral dimple and included areas 1 and 2 of the buried frontal operculum, indicating that its posterior extent was wider than the pure taste cortical area. Spinothalamic terminations in VPL and the PO nuclear group were discussed in relation to cortical connections of these thalamic nuclei. It was suggested that spinothalamic input could be relayed to both postcentral and opercular cortices. The relation of the spinothalamic input to the PO group appeared to be minor.