Information requested on Buddhist monks self-immolation mental technique

Thích Quảng Đức was a monk who immolated himself to protest against the repression by the Vietnamese government in 1963. It was filmed how he adopted the full-lotus posture an fire was set on him. The picture which was awarded the Pulitzer was known worldwide. In that video he does not show any signs of pain at all and he doesn't seem to be under the effect of any drug. It is said this is some sort of deep meditation or self-hypnosis technique nevertheless Hypnosurgery lacks of scientific evidence. Plenty of other monks even younger have committed self-immolation in Tibet to protest against the Chinese occupation. A lack of fiscal pain is a common trait. Is there more information on how this technique is done, it's difficulties and knowing that some Buddhist organizations are collaborating with modern neuro-science is there a scientific explanation for this and its possibilities or medical potential to treat chronic pain diseases? Video here watcher discretion advised