The purposes of this study are threefold: (1) assess the effectiveness of chronic electrocal stimulation of midbrain sites for the relief of chronic pain in humans; (2) evaluate the efficacy and mechanism of traditional narcotic analgesia and compare these to that found for chronic electrical stimulation of midbrain sites; and (3) validate experimental models of pain and their potential diagnostic use in chronic pain patients. In addition, this study will determine and compare the impact of both traditional narcotic and chronic electrical stimulation therapies on the functional, intellectual and emotional well-being of these patients. The three types of participants in this study will be chronic pain patients who will receive surgically implanted stimulating electrodes for pain control, chronic pain patients maintained on traditional narcotic analgesics who will not receive implanted stimulating electrodes, and healthy normal volunteers. The effects of chronic brain stimulation in surgical patients will be compared to the effects of narcotics previously administered to these patients and to effects of narcotic regimes in nonsurgical chronic pain patients.