Peripheral and cortical neural mechanisms underlying the cutaneous perception of shape and texture will be studied in primates. Transparent surfaces that differ in shape or contain spatial patterns or textures will be stroked across the passive fingertip with precise control over compressional force and the direction and velocity of stroking. Evoked responses in single glabrous skin primary mechanoreceptive afferents will be recorded in the anesthetized monkey. We will examine their responses to a) simple vertical skin indentations, using mechanical sinusoids or step indentations produced by cylindrical bars - as a function of ramp velocity and radius of curvature of the bars, and b) more complex stimuli with shaped surfaces (a curvature pattern or single steps of different shape) stroked across the skin. We will use a theoretical framework to test whether the responses of a fiber to the simple stimuli can be used to predict responses to the complex stimuli. In studies of texture, responses of afferent fibers to a """"""""simplified"""""""" texture, i.e. a single string of raised dots (less than or equal to 40Mum high) stroked across the skin will be recorded. In correlated human psychophysical studies, we will test whether sensory discrimination of spatial period depends on an accurate representation of spatial period in neuronal responses. In parallel experiments the same stimuli will be delivered to the restrained hand of the awake, behaving monkey while recording evoked responses in single tactually driven cortical neurons in the contralateral postcentral gyrus (SI: areas 3b, 1 and 2). The use of both the simple (indentation) and complex (curvature patterns and step-shapes) stimuli - the latter applied along different axes of movement, will provide a comprehensive and quantitative study of both the """"""""simple"""""""" (touch sensitive) neurons and possible """"""""complex"""""""" neurons selective for movement, direction, curvature, orientation, or texture. We will test the hypothesis of hierarchical processing (rostrocaudal gradient in complexity of neuronal responses) and obtain new information on the cortical neural representations of cutaneous shape and texture in SI of the awake, behaving monkey.
