Reinnervation of peripheral receptors following peripheral nerve lesions results in a variety of sensory deficits. These include a decrease in general sensory acuity and the loss of the ability to correctly localize peripheral stimuli. Other common symptoms include several hypersensitivity reactions such as, Hyperesthesia, Dysesthesia, Hyperalgesia and Causalgia which can be very disabling to individuals. Although some of these deficits can be permanent, others can be reversed following reinnervation of peripheral receptors. Recent studies in primates have demonstrated that reinnervation following peripheral nerve transection elicits organizational changes in the somatosensory cortex. It has been suggested that these organizational changes may parallel in some manner the clinically observed recovery from sensory deficits following these lesions. The long term objective of this project is to assess the contributions of the regenerative process and possible changes in subcortical structures, specifically the spinal dorsal horn, to these changes. Newly developed single fiber recording and stimulation procedures will be employed to examine: 1) how specific sensory inputs from individual characterized primary sensory afferents are processed by both the population of dorsal horn cells receiving input from single fibers and by individual identified dorsal horn neurons; 2) the specificity of the regenerative process (e.g. do regenerating fibers reinnervate the same type of receptor they had originally innervated?); 3) the affect of reinnervation on the central processing of these identified inputs during the recovery period. This information will allow the identification of those processes which can contribute to the recovery seen after disruption of sensory inputs. Once identified, these processes can then be studied further to determine if certain manipulations could enhance their efficacy.