The organization of somatosensory area II in tree shrews.

Microelectrode multiunit recording methods were used to determine the somatotopic organization of the second somatosensory area, S-II, in tree shrews. Neurons were activated by light tactile stimuli, and receptive fields were located on the contralateral body surface only. The orientation of S-II was such that the top of the head adjoined S-I and the distal limbs pointed away from S-I so that the representation could be characterized as "erect". In general, the distortions of the body surface in S-II were similar to those found in S-I of the tree shrew (Sur et al., '80), with the exception that proportionately less cortex was devoted to the glabrous nose. The representation in S-II was more continuous than that in S-I. Finally, cortex bordering S-II caudally was found to be responsive to generally more intense somatosensory stimuli such as taps to the body surface.