What is being stimulated in acupuncture: evaluation of the existence of a specific substrate.

This review surveys the available publications from within and without China on the question of "What is being stimulated in acupuncture?" Although a definite answer is not yet forthcoming, indirect evidence is available to afford a few speculations. By far, the most convincing results indicate that expression of acupuncture effects definitely involves the nervous system. Answers to how acupuncture is linked to the nervous system, however, are still equivocal. On one extreme, acupuncture is equated to direct nerve stimulation. On the other, circumstantial evidence from biophysical, physiologic and pathologic approaches implicates some form of specificity for the acupuncture points, although no well-defined anatomic entity is available. It is proposed that an open-minded attitude towards acupuncture is essential for establishing the valid aspects of this practice.