The long-term goal of this project is to understand how thermal stimulation is integrated within and among the sensory systems of the skin. The proposed research will test hypotheses stemming from three new findings during the present funding period that raise questions about current theories of thermoreception: First, that cutaneous cold fibers, many of which also discharge 'paradoxically' at high temperatures, may contribute to sensations of heat whenever warm fibers are also stimulated; second, that mild cooling between 31degrees -25 degrees C can produce nociceptive sensations of stinging and/or burning ('innocuous-cold nociception') during static, but not dynamic, contact cooling; and third, that much of summation of warmth and cold can be accounted for by the higher probability that larger stimuli will contact the most sensitive sites in the skin. Experiments are proposed that will take advantage of specially designed thermal stimulators to (1) test the hypothesis that the Heat Grill Illusion (Synthetic Heat) occurs because cool stimulation is encoded as heat, and even heat pain, when warm fibers are also stimulated; (2) determine the spatiotemporal properties of these warm-cold interactions via studies of Synthetic Heat and Paradoxical Heat using a linear thermode array; (3) test the hypothesis that 'innocuous-cold nociception' is suppressed by tactile stimulation produced by dynamic contact with the skin, and investigate its relationship to the nociceptive sensations associated with Synthetic Heat and Paradoxical Heat; and (4) provide further tests of the 'sensitive-site' explanation of spatial summation using a unique, handgrip thermal stimulator that will enable studies of thermal perception and integration throughout the hand under conditions that mimic haptic exploration of temperature. In addition to increasing our knowledge of how normal temperature sensitivity depends upon interactions among the senses of temperature, touch, and pain, the results of the proposed studies may help to explain how neuropathic pains that are triggered by temperature, such as cold dysesthesias and hyperalgesias, can arise from disruption of afferent processing in one or more of the cutaneous senses.
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