Psychophysical measurements will be made in humans of the absolute thresholds and magnitude scaling functions for pricking and aching pain using punctate probes of different shapes indented into the skin and of """"""""abrasive"""""""" pain using textured surfaces consisting of raised dots of different heights and spacing stroked across the skin. A less intense variety of similar stimuli will be used to measure itch. These measurements will be obtained for normal skin and for two types of cutaneous dysesthesia: secondary hyperalgesia (in skin surrounding an intradermal injection of capsaicin) and secondary """"""""hyperknesia"""""""" (itchy skin) surrounding an intradermal injection of histamine. Evoked responses to the same cutaneous stimuli will be recorded electrophysiologically in single low threshold and nociceptive peripheral nerve fibers in vivo from anesthetized monkeys and in vitro from skin-nerve preparations from rat, monkey and human. In other experiments, evoked responses to the same stimuli will be recorded in single identified low-threshold and nociceptive neurons in the dorsal horn of the spinal cord in anesthetized monkeys. Correlating the discharges of single neurons in animals with sensory measures of pain or itch in humans will reveal the peripheral and central neuronal processes contributing to normal mechanically evoked pain and to the dysesthesias to mechanical stimuli that can develop with cutaneous injuries or peripheral nerve disorders.
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