All mammalian species appear to have two major somatic sensory projection areas in the sensorimotor region of the cerebral cortex, SmI and SmII. Both projection areas receive low-threshold cutaneous input from the contralateral body surface, but most prominantly from the hand. Unilateral lesions of the SmI or SmII hand areas produce severe behavioral deficits in texture discrimination capacity. However the response properties of cells in these two areas in non-primate species suggest they may contribute differently to the ability to discriminate the spatiotemporal features of textured surfaces. With a continuing interest in sensorimotor cortex and tactile function in primates, we intend to study Galago to determine: 1) the physiological organization and cytoarchitectonic features of SmII; 2) texture discrimination deficits following selective removal of SmI or SmII glabrous hand areas; 3) the response properties of SmI and SmII neurons to hand-held punctate stimuli and to drum-rotated textured surfaces in normal animals. In these multidisciplinary studies we will examine the conributions of SmI and SmII to texture discrimination capacity, as suggested by behavioral consequences of cortical lesions and by the physiological properties of constituent neurons. We proposed these studies in Galago, as it is a primate species in which both SmI and SmII are more simply organized and more easily accessible than in Macaca and other anthropoid primates. However, we expect the findings of SI and SII in Galago to be generalizable to more complex and recently-evolved primates. These studies of the physiological basis of tactile discrimination are expected to demonstrate specific neural mechanism in perceptual phenomenon. An understanding of neural basis for somatic sensation has significance for perceptual abnormalities so common in psychiatric and neurological disorders.
