ABSTRACT
Certain somatic stimuli, such as electrical stimulation, can produce analgesia. Therapeutic electrical stimulation has a long history. As early as 46 ad, during the period of the ancient Romans, shock from electric rays were used for pain relief in patients with gout and headache (1). Several forms of therapeutic stimulation, including acupuncture, acupressure, transcutaneous electrical nerve stimulation (TENS), and spinal cord stimulation (SCS) have been widely applied to the treatment of intractable pain. Beginning in the 1960s, Shealy (2) and co-workers (3) showed that electrodes implanted on the dorsal surface of the cord could produce an analgesic effect. Their results were partly explained by gate control theory proposed by Melzack and Wall in 1965 (4). Although the details of the mechanism underlying therapeutic stimulation still remains unclear, recent studies of diffuse noxious inhibitory controls (DNIC) (5,6) and the descending inhibitory system (7) have begun to elucidate the process in greater detail.
