The functional organization of somatosensory cortex in primates.

Our understanding of the functional organization of somatosensory cortex and thalamus in primates and other mammals has greatly increased over the last few years. It is now clear that higher primates have four strip-like representations of skin and muscle receptors corresponding to areas 3 a, 3b, 1 and 2 of anterior parietal cortex. Areas 3b and 1 receive cutaneous information from the ventroposterior nucleus, while a ventroposterior superior nucleus provides areas 3a and 2 with information from muscle receptors. Area 3b is the homolog of S-I in prosimians and non-primates and it provides most of the activating cutaneous inputs to areas 1 and 2. Most of the further processing that allows tactile recognition of objects involves somatosensory areas of the lateral sulcus, where both S-II and the parietal ventral area (PV) receive activating inputs from areas 3a, 3b, 1 and 2. S-II also projects to PV and to a parietal rostral area where further connections with the amygdala and hippocampus may occur to allow the formation of tactile memories. Areas of anterior parietal cortex also project to posterior parietal cortex, where regions of cortex are largely somatosensory, but the functional subdivisions remain uncertain. All of the somatosensory fields have access to motor areas of the frontal lobe, but the magnitude and targets of the projections differ.