Secondary Somatosensory Cortex

The human secondary somatosensory cortex (S2, SII) is a functionally-defined region of cortex in the parietal operculum on the ceiling of the lateral sulcus.

Region S2 was first described by Adrian in 1940, who found that feeling in cats' feet was not only represented in the primary somatosensory cortex (S1) but also in a second region adjacent to S1. In 1954, Penfield and Jasper evoked somatosensory sensations in human patients during neurosurgery by electrically stimulating the ceiling of the lateral sulcus, which lies adjacent to S1, and their findings were confirmed in 1979 by Woolsey et al. using evoked potentials and electrical stimulation. Functional neuroimaging studies have found S2 activation in response to light touch, pain, visceral sensation, and tactile attention.

In monkeys, apes and hominids, including humans, region S2 is divided into several "areas". The area that adjoins S1 at the entrance to the lateral sulcus is called the parietal ventral area (PV). Adjacent and posterior to PV is area S2 - which must not be confused with region S2 (which designates the entire secondary somatosensory cortex, of which area S2 is a part). Deeper in the lateral sulcus lies the ventral somatosensory area (VS), whose outer edge adjoins PV and S2 and inner edge adjoins the insular cortex.

In humans, the secondary somatosensory cortex includes parts of Brodmann areas 40 and 43.

Areas PV and S2 both map the body surface. Functional neuroimaging in humans has revealed that in areas PV and S2 the face is represented nearest the entrance to the lateral sulcus, and the hands and feet deeper in the fissure, nearer the border with VS. Individual neurons in PV and S2 receive input from wide areas of the body surface (they have large "receptive fields"), and respond readily to stimuli such as wiping a sponge over a large area of skin.

Areas S2 in the left and right hemispheres are densely interconnected, and stimulation on one side of the body will activate area S2 in both hemispheres. Area S2 is interconnected with Brodmann area (BA) 1 and densely so with BA 3b, and projects to PV, BA 7b, insular cortex, amygdala and hippocampus. PV connects densely with BA 5 and the premotor cortex.

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