This chapter discusses the studies of periaqueductal gray (PAG)/ periventricular gray (PVG) stimulation for pain relief in humans. PAG electrical stimulation produce a profound analgesia without other obvious neurological effects. A major difference between stimulation of human PAC and techniques used in animal studies is that, it is not possible to determine whether a particular electrode is effective in relieving pain during the initial implantation procedure in human subjects. Early studies indicated that SPA could be at least partially blocked by systemically-administered naloxone. The analgesic effects seen in the animals are of immediate onset and are often short-lived, while those in humans have a slower onset and last longer. Electrical stimulation of the PAG is used for the treatment of patients with severe, medically-refractory pain problems. Well-designed prospective studies are essential for a better understanding of analgesic mechanisms in humans to improve success rates for this procedure.
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