2. Prospects. Pain of many types is responsive acutely to stimulation in the periaqueductal/periventricular gray region (PAG/PVG; our anatomical target). There is a large confirmatory literature on this in both animals and man, going back 3-4 decades. A review analyzing PAG/PVG stimulation in prior clinical studies for all types of drug-refractory pain uncovered 148 cases with a 79.1% success rate after lead internalization.