Monday, April 28, 2008

Scientific theories and mechanisms of Acupuncture

Many hypotheses have been proposed to address the physiological mechanisms of action of acupuncture. To date, more than 10,000 scientific research studies have been published on acupuncture as cataloged by the National Library of Medicine database.

Neurohormonal theory
Modern acupuncture model.

Pain transmission can also be modulated at many other levels in the brain along the pain pathways, including the periaqueductal gray, thalamus, and the feedback pathways from the cerebral cortex back to the thalamus. Pain blockade at these brain locations is often mediated by neurohormones, especially those that bind to the opioid receptors (pain-blockade site).

Some studies suggest that the analgesic (pain-killing) action of acupuncture is associated with the release of natural endorphins in the brain. This effect can be inferred by blocking the action of endorphins (or morphine) using a drug called naloxone. When naloxone is administered to the patient, the analgesic effects of morphine can be reversed, causing the patient to feel pain again. When naloxone is administered to an acupunctured patient, the analgesic effect of acupuncture can also be reversed, causing the patient to report an increased level of pain. It should be noted, however, that studies using similar procedures, including the administration of naloxone, have suggested a role of endogenous opioids in the placebo response, demonstrating that this response is not unique to acupuncture.

One study performed on monkeys by recording the neural activity directly in the thalamus of the brain indicated that acupuncture's analgesic effect lasted more than an hour. Furthermore, there is a large overlap between the nervous system and acupuncture trigger points (points of maximum tenderness) in myofascial pain syndrome.

Evidence suggests that the sites of action of analgesia associated with acupuncture include the thalamus using fMRI (functional magnetic resonance imaging) and PET (positron emission tomography) brain imaging techniques, and via the feedback pathway from the cerebral cortex using electrophysiological recording of the nerve impulses of neurons directly in the cortex, which shows inhibitory action when acupuncture stimulus is applied. Similar effects have been observed in association with the placebo response. One study using fMRI found that placebo analgesia was associated with decreased activity in the thalamus, insula and anterior cingulate cortex.

Recently, acupuncture has been shown to increase the nitric oxide levels in treated regions, resulting in increased local blood circulation. Effects on local inflammation and ischemia have also been reported.

Histological studies

In the 1960s, Bonghan Kim (medical scientist, North Korea) proposed that meridians and acupuncture points exist in the form of distinctive anatomical structures in his Bonghan Theory.

Issues in study design

One of the major challenges in acupuncture research is in the design of an appropriate placebo control group. In trials of new drugs, double blinding is the accepted standard, but since acupuncture is a procedure rather than a pill, it is difficult to design studies in which both the acupuncturist and patient are blinded as to the treatment being given. The same problem arises in double-blinding procedures used in biomedicine, including virtually all surgical procedures, dentistry, physical therapy, etc.

Blinding of the practitioner in acupuncture remains challenging. One proposed solution to blinding patients has been the development of "sham acupuncture", i.e., needling performed superficially or at non-acupuncture sites. Controversy remains over whether, and under what conditions, sham acupuncture may function as a true placebo, particularly in studies on pain, in which insertion of needles anywhere near painful regions may elicit a beneficial response.

A study by Ted Kaptchuk et. al. showed that sham acupuncture exerted a stronger effect on pain than an inert pill did, and concluded: "Placebo effects seem to be malleable and depend on the behaviours embedded in medical rituals."