I have found biofeedback helpful twenty percent of the time for those lacking the sensitivity to notice very small temperature changes. Imagery can help some times, but it will hinder progress many other times. I believe that a homeostatic reflex is the mechanism that allows warming triggered by sensory attention. That is, with the two major exceptions noted above, attention to the skin will automatically evoke warmth of the patient if encouraged to let attention linger over an area for as long as forty-five seconds or a minute. An example of this sensory principle gone awry is the increased blushing we have all seen when a blusher's attention is called to his or her cheeks.
Cognitive mediation is unnecessary much of the time.
In a sense, then, I no longer believe that the parasympathetic system is the exclusive mediator of skin temperature. In fact with adequate training vasodilation now seems possible much of the time just by doing it, with as much specificity and rapidity as is involved in moving a finger. That there is great applicability of peripheral vasodilation to skeletal muscle and arthritic pain, as well as to temporary reductions in paresthesias in the presence of protruding or herniated disks is remarkable when patients are well-equipped to follow through and learn the intricacies of this process. I am continually surprised by people's ability to learn to apply sensory attention to the task of warming, and to achieve results that please and surprise them as well. Note that passive attention is still an important part of this process.