In order for a feedback to occur, there must be a means for the viscera and autonomic nervous system to become activated.
Clinical neuropsychology
By Kenneth M. Heilman, Edward ValensteinOxford University Press
"Sympathectomy is a technique about which we have limited knowledge, applied to disorders about which we have little understanding." Associate Professor Robert Boas, Faculty of Pain Medicine of the Australasian College of Anaesthetists and the Royal College of Anaesthetists, The Journal of Pain, Vol 1, No 4 (Winter), 2000: pp 258-260