An excerpt from Beyond Biofeedback by Elmer & Alyce Green, 1977 Knoll Publishing Co., Chapter II: Self-regulation: East and West, pp. 197 - 218.: https://www.swamij.com/pdf/swami-rama-beyond-biofeedback.pdf

"... The record shows that the temperature began going up at both locations on the palm of his hand, and then the thermistor went down to where it had been but the W thermistor kept increasing in temperature until it reached 95F. Eventually the two thermistors were 11F apart, an increase of 9F over the original temperature difference. The Swami told us that this differential control of temperature in one hand was one of the most difficult things that he had learned to do, more difficult than stopping his heart. That seemed unlikely to me at first, but on thinking about it I realized that the neural controls over the radial and ulnar arteries in the wrist and over the arterial shunts in the hand probably were located within a few millimeters of each other in a section of the central nervous system. The Swamiís demonstration showed exquisite differential control over this normally uncontrolled piece of the neural apparatus..."