Plasticity in the somatosensory system in mammals. Neural mechanisms whereby injury provokes sensory dysfunction and chronic pain. Pathophysiology of injured nerve and abnormal impulse generation. Synaptic reorganization in the brain and spinal cord after peripheral nerve injury. Regeneration and collateral sprouting of injured nerve fibers. Animal models of chronic pain states and pain relief. Heritability of chronic pain. Neural mechanisms of loss of pain response and of consciousness in general anesthesia.