The excellent blog, MindHacks (click link) had a great post today on

Hypnosis as a surgical tool. 

"Altering perception using hypnosis results in brain changes that literally reduce pain perception [rather than merely altering the response to pain]. Indeed, simply changing the wording of the hypnotic instruction from "you will feel cool, tingling numbness more than pain" to "the pain will not bother you" alters the brain location of the analgesia from the somatosensory cortex to the anterior cingulate gyrus."