Development of the Somatic Sensory System

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This three.year project will examine the development of tactile discrimination. It is known that information on touch projects to a region of the brain labelled S1, the primary somatosensory cortex. Single nerve cells in S1 respond to touch applied to particular local areas of the body, and the area eliciting a response is called the "receptive field" of that cell. The most effective tactile stimulus for the receptive field of a given cell may have particular spatial features (such as preference for small points, or separation distance between points) and temporal features (such as rapidly vibrating or moving points, or a maintained touch). In recent studies in kittens, the responses of cortical cells appeared to be limited compared to those in adults. Yet in monkeys, infants show touch discrimination that is at least equal to adults. This study will examine S1 neurons and psychophysical thresholds in response to patterned tactile stimulation, in macaque monkeys during the first year of age. Response types will be classified by their capacity to code spatial and temporal features of geometric dot patterns applied to the skin of the hand. The stimuli will be presented by an automated discrimination apparatus. Both behavioral discriminations (using a "same or different" decision) and neuronal firing patterns will be quantitatively measured. It is expected that the capacity of neurons to signal differences between different surfaces will relate to the capacity to make behavioral discriminations among these same surfaces.