How Does Acupuncture Work?

Modern Theories of the Anatomical Basis and Effects of Acupuncture

Acupuncture has a long history that disappears into the mists of antiquity, yet for all its perseverance through time no one has ever really managed to explain its actions effectively. The first attempts at this were in China around 300BCE when the Yellow Emperor's Classic of Internal Medicine was compiled and the most significant theory, that of meridians containing a mysterious energy known as qi, was formulated. This energy seems to be more like a word to describe conscious sensation and perception, hence its immaterial, paradoxical and all pervading nature. In modern times we have become unable to accept qi as a philosophical principle and insisted on finding material proof for the mechanisms of acupuncture. Here I am going to summarise some of the major theories.

Trigger Points
Trigger points are a medical observation made by two doctors of pain and rehabilitation medicine, Travell & Simons (1998), in their Trigger Point Manual that parallels acupuncture in many ways. Trigger points are a tender localised hardening in a skeletal muscle which is palpably tense and evokes a familiar sense of pain when pressed. Most people are familiar with these, as hard knots of muscle that they often get in the same place and can often cause pain radiating far away from the knot itself. Sometimes they are latent and not actively hard but still produce that familiar ache when pressed firmly. To understand them we must look at how muscles tense and relax in normal functioning. When a muscle receives a signal to tense, its cells releases calcium into their cytoplasm from a store called the sacroplasmic reticulum. This causes the long proteins in the muscle, actin and myocin, to slide against each other shortening the muscle. When the signal has stopped the calcium is pumped back to the store and the proteins slide back, relaxing the muscle. If a muscle becomes damaged its ability to pump the calcium back can be compromised. This continuously raised calcium content makes it permanently tense, draining more energy making it even more difficult to rebalance the calcium levels until the muscle becomes noticeably short, hard and painful. Needling creates a tiny lesion that is detected by the body which releases its injury response mechanisms, helping to break the loop, relax the muscle, increase blood flow, reduce inflammation and initiate healing in the damaged tissues. It has been noted that more than 70% of classic acupuncture points overlap with trigger points and have the same characteristics as trigger points but there is a significant difference. Acupuncture points are related to nerves and are often located away from muscles. The reason they coincide is because nerves supply muscles and so have a natural overlap. Trigger points can certainly explain some of acupuncture's more simple musculoskeletal effects, but trigger points on their own are not a good explanation for acupoints.

Gate Control Theory
Gate Control theory tries to explain one of the simplest actions of acupuncture: its ability to control and regulate pain. This is the area that originally brought the West to look at the ancient Chinese medical practice when President Nixon's delegation to China in 1972 was shown on television viewing open chest surgery with the patient still fully awake. Doctors Melzack and Wall (1965) developed this theory independently in their own work on pain relief but it is often cited to explain the mechanism of acupuncture. It is based on the anatomical understanding that we have three basic types of nerves involved in peripheral sensation, called the A-beta, A-delta and C fibres. Each one is responsible for a different sensation, A-beta for gentle pressure, A-delta for heavy pressure and temperature and C fibres for pain. Both types of A fibre nerves have a myelin sheath which enables their signal to travel faster than the thinner C fibres, so if we stimulate the A fibres then their signal will effectively block out the pain signals from the slower C fibres. The image is of a crowd trying to get through a small gate: only a few can get through at a time. So the more we stimulate the A fibres then the fewer C fibres will be able to reach the brain. Dr Wall went on to develop the system of electrical stimulation for pain control known today as TENS used for physiotherapy and pain control, which has its own parallel in electro-acupuncture where needles are stimulated with mild electricity. Standard acupuncture is thought by many to rely on the same principle because the sensations of needling, often described as dull aching, heaviness, numbness or distension are all properties of A fibres. More advanced understandings of the nervous system has meant that most elements of gate control theory have been replaced with more detailed explanations but the principle of its mechanism is still thought hold merit.

Segment Theory
Segment theory attempts to explain some of the effects of needling points distant to the site of a pathology and the effects of certain points on the organs. Its basic premise is that all our nerves come from our brain, through the spinal cord and leave the spine in groups at the level of each vertebra where they are known to innervate specific sections of muscle, skin, bone and organs. This is evident in the phenomena of referred pain where many organs which are incapable of feeling pain themselves will project their disease onto sections of muscle or skin in the same segment and result in pain at this site. The most well known example of this is the pain felt down the inside of the left arm during a heart attack due to both the heart and the inner arm being supplied by nerves from C8 and T1 segments. It is suggested that points selected on the same dermatome segment of skin, or myotome segment of muscle will send signals to the spine that will release endorphins and inhibit the pain response for the entire segment. So if we needle points along the inner arm and little finger side of the hand we may have an effect on calming the heart. Needling the back points next to the spine is also thought to work on this same principle, by simply selecting the spinal segment responsible and needling where the entire segment travels close to the surface. This could explain some of the effects of acupuncture, such as the reported effects on urinary bladder pain from refractory interstitial cystitis by stimulating the points on the sacrum (Katayama et al., 2013), for which there is even a surgical intervention that involves permanently stimulating the nerves on the sacrum with an implanted device, but many of the most tested and validated points do not fit this model. Neiguan pericardium-6 is known for its ability to reduce nausea and has been subject to many trials, yet it has no real relationship to the segments that innervate the stomach.

Fascial Release
This relatively new theory posits that the anatomical basis for acupuncture meridians may be the bands of fascia that wrap around the muscles and organs in our body in an almost continuous sheath. Langevin, a neurology professor, has observed that 80% of the acupoints in the arm were located at inter- or intramuscular connective tissue planes and noted that the phenomena of needle grip, when the skin appears to grasp the needle, that is associated with sensations of deqi occurs more readily at the sites of fascia because it winds around the needle and then responds to mechanical stimulation with sensation. This could certainly explain how points may affect a quite distant site since the bands of fascia do run almost continuously from head to toe, often in patterns that loosely resemble the traditional meridians and stress in one area may exert an influence on the entire band. This theory has considerable merits regarding the anatomical locations and mechanisms of points but it still leaves something of a black box between the stimulation of fascia and the observed reactions to acupuncture such as increased resilience to pain or reduction in symptoms like nausea.

'Homunculus' Theory
The thalamic neuronal theory builds on the work of Dr. Wilder Penfield who proposed that every part of the body had to be mapped onto a corresponding part of the brain. This helped to explain some unusual medical phenomena such as phantom limb pains, when amputees experienced pain or unusual sensations in the missing limb. His theory was that the brain still had perception areas for those limbs, even though the actual limb was missing and the brain, starved of sensory input, would begin to generate hallucinatory feelings seeming to come from a "ghost" limb, similar to how sensory deprivation of other sense organs can produce hallucinations. Moreover, these areas are not strictly defined and frequently overlap so stimulation in one area can affect sensations in the neighbouring areas of the brain. This makes the action of a point such as Hegu L.I.-4 to help with problems of the face not so far fetched as the area of the brain responsible for perceiving the thumb is actually quite close to the area that perceives the face. Points in the hands and feet, where many of the most powerful acupuncture points are located, have the largest representation in the brain due to them being the most sensitive, along with the mouth and sexual organs, also common places for piercing and bleeding rites in other cultures.

Recent advances in technology have allowed us to examine the brain's response acupuncture using fMRI scanners which have shown a decreased response to a painful stimulus after an acupoint was needled in both the thalamus, the relay center of the brain which refers messages on for processing, and the anterior cingulate cortex, involved in emotional responses to painful stimuli indicating that it may actually be encouraging our brains to ignore pain in some way. In other studies using PET scans the insular cortex, responsible for various roles involved in consciousness including emotion, bodily homeostasis and where pain in judged or imagined when thinking about painful events, has been shown to be affected by real acupoints and not by non-points. If the area this works on is not just local but overlaps with another area of bodily perception, which may be likely since the radiating sensations produced are more likely happening in the brain than in the peripheral nerves, which are only being stimulated at one point, then it may downtune our perception of pain in a distant part of the body too. This certainly adds a new dimension for modern scanners such as the fMRI to investigate and provides potential frameworks in which to place acupuncture, as a tool for stimulating and re-educating the nervous system to behave in a better fashion, but we still know so little about the brain that it will be difficult to prove these assertions for a long time yet.

Neurohormonal Theories
If the previous theories centre of the effects of acupuncture on the nervous system neurohormonal theories go one step further and examine the effects of acupuncture stimulation on the release of hormones using the nervous system as a medium. Considerable research has been done into these mechanisms since the discovery of endorphins which have helped explain the natural pain control systems of our bodies and how acupuncture helps us to release this opiate. But it is possible to explain more through neurohormonal theory than just pain relief. The autonomic nervous system in the brain controls most of our basic body functions either directly or indirectly by activating endocrine glands which then effect target organs. Evidence is being compiled indicating acupuncture is able to modulate these systems by stimulating these unconscious parts of the brain. The main pathway for this is the hypothalamus-pituitary-adrenal axis, an ancient and major part of the neuroendocrine system in many animals that controls reactions to stress and regulates many body processes including digestion, the immune system, mood and emotions, sexuality, and energy storage and expenditure. This theory has gone a long way to explain the possible mechanisms of acupuncture in modern language and has the great advantage of being quantifiable in clinical trials as raised or lowered levels of hormones which can be clearly measured but systemic effects are often general in nature and give little indication of which points are best to use, only that acupuncture of some kind will trigger a change in hormone balance. Thomas Lundeberg, a Swedish doctor, has suggested that the heavy aching feelings of deqi are paralleled by the muscular aches experienced in prolonged exercise and that acupuncture may cause the brain to respond in the same way causing decreased airway resistance, lower blood pressure, improved mood and immunological alterations and pain suppression.

Quantum Theories
Quantum mechanics are quite a buzzword among alternative disciplines seeking to sound scientific and tend to raise my scepticism quite quickly but there are a few ideas relating to acupuncture that are worth a mention here. Some imaging methods have demonstrated a lattice of electrically charged lines running through the body that seem to mirror the acupuncture meridians of Chinese medicine. It has long been noted that acupoints have a lower electrical resistance than non-acupoints and various devices can be used to 'detect' points using this discovery. Biophysicists in Germany also claim to have revealed these lines using infrared imaging after points were treated with moxa (Schlebusch, Maric-Oehler & Popp, 2005). The quantum theorists propose that the entire body generates minute electrical forces through cellular respiration which form subtle fields that condense in certain areas to form the meridian lines. Injury or disease is accompanied by a change in organic function and a subsequent change in the charges which make up these fields and leads to pain at certain areas. Needling at certain points can discharge the potential differences and assist our body return to its optimal state of functioning. This theory maintains the original character of Chinese medicine with its holistic focus and the idea that a problem may generate symptoms and respond to treatment that are quite distant to the actual site of injury but they often feel like they are restating the ancient theories using popular scientific terminology to sound convincing. Lower electrical resistance at acupoints could equally be explained by the fact that they often near nerve junctions and neuromuscular attachment zones and since nerves are designed to conduct electricity they should have a lower resistance in areas where they are most dense. The most likely aspect of quantum theories that can apply to manual therapies is that they may be introducing a certain amount of chaos into a pattern that has become stuck in a bad way, giving it the opportunity to settle in a different, hopefully better form.

Psychological Effects
The placebo effect is often a derogatory term in medicine implying that a treatment does nothing but in recent times this has been questioned. Even placebo medication most definitely does have effect which is why they have to be used in medical trials. Daniel Moerman (2002), a medical anthropologist, has called for the term 'placebo' to be rethought and outside of the strict definition, of an inert pill used in a controlled trial, it should be referred to as a 'meaning response' as it clearly does have effects. A lot of modern research on manual therapies of all kinds is coming to similar conclusions, that instead of 'fixing' a problem like a mechanic, what is really happening is a communication between patient and practitioner, causing 'top down' changes to happen. This is actually much closer to the acupuncture described in classical sources that originating as part of a meditation tradition and used massage, acupuncture and tai chi style movements as rituals to make the visualisations come to life. This would imply that perhaps we should stop looking for mechanical actions caused by needling but consider it to be more like a psychotherapy where the language used is one of touch and sensation.

This concludes my review of modern theories of how acupuncture works. The end result is that we don't know yet and part of this reason is because scientific testing becomes very difficult when applied to complex things like organisms and especially people. What scientific trials attempt to do is report what happens when you insert a needle into a specific part of the body, which gives us some interesting data and ideas to think about. Without the context of Chinese philosophy it is much like documenting the effect of hearing a word and then assuming we understand all talking therapy as just that response repeated multiple times. There is probably an element of truth in most of them but the most likely is that they work on a systemic level, engaging some physiological and some psychological responses to create an experience, and experiences can certainly change our lives.

References and Further Reading:

Andersson, S. and Lundeberg, T. (1995): Acupuncture- from Empiricism to Science: Functional Background to Acupuncture Effects in Pain and Disease in Medical Hypotheses 45, 271-281

Carrell, S. (2005): At last the truth about acupuncture: it's as good as drugs for treating pain in The Independent: 1/5/2005

Cho, Z.H. et al (2002): fMRI Neurophysiological Evidence Of Acupuncture Mechanisms in Medical Acupuncture 14(1):16-22

Cleary, T. (2003): Wen-Tzu: Understanding the Mysteries in Taoist Classics, Vol. 1, Shambhala

Ernst, E. and White, A. (1999): Acupuncture: A Scientific Appraisal: Butterworth-Heinemann Ltd

Eshkevari L. et al (2011): Acupuncture at ST36 prevents chronic stress-induced increases in neuropeptide Y in rat in Experimental Biology and Medicine (Maywood)

Filshie, J. and White, A (1998): Medical Acupuncture, A Western Scientific Approach: Elvesier, Churchill Livingstone

Katayama, Y., K. Nakahara, T. Shitamura, S. Mukai, H. Wakeda, Y. Yamashita, K. Inoue, K. Nose, and T. Kamoto (2013): Effectiveness of Acupuncture and Moxibustion Therapy for the Treatment of Refractory Interstitial Cystitis Hinyokika kiyo. Acta urologica Japonica 59, no. 5 (2013): 265-269.

Langevin HM, Yandow JA. Relationship of acupuncture points and meridians to connective tissue points in The Anatomical Record 2002;269:257-265.

Lee, T.N. (1977): Thalamic Neuron Theory: A Hypothesis Concerning Pain and Acupuncture in Med Hypotheses 3(3):113-21

Lee, T.N. (1994): Thalamic Neuron Theory: Theoretical Basis for the Role Played by the Central Nervous System (CNS) in the Causes and Cures of all Diseases in Med Hypotheses 43(5):285-302

Levi-Strauss, C. (1974): Structural Anthropolgy: Basic Books

Levine, J.D., et al (1981): Analgesic responses to morphine and placebo in individuals with postoperative pain in Pain 10(3):379-89

Ma, Y.T., Ma, M and Cho, Z.H. (2005): Biomedical Acupuncture for Pain Management: Elvesier, Churchill Livingstone.

Macdonald, A.J. (1983): Segmental Acupuncture Therapy in Acupuncture Electrotherapy Resource 8(3-4):267-82

Melzack R., Wall P.D. (1965): Pain Mechanisms: A New Theory in Science 150(3699):971-9

Moerman, D. (2002): Meaning, Medicine and the 'Placebo Effect', Cambridge University Press

Peters, K. M. (2002): Neuromodulation for the Treatment of Refractory Interstitial Cystitis in Reviews in Urology 4(Suppl 1): S36–S43.

Ramachandran, V.S. (1999): Phantoms in the Brain: Human Nature and the Architecture of the Mind: Fourth Estate

Schlebusch K-P, Maric-Oehler W, Popp F-A. (2005): Biophotonics in the Infrared Sprectral Range Reveal Acupuncture Meridian Structure of the Body. in The Journal of Alternative and Complementary Medicine, Volume 11, Number 1, 2005, pp. 171-173.

Starwynn, D.: Electrophysiology And The Acupuncture Systems in Medical Acupuncture, Volume 13, Number 1.

Travell J.G. and Simons, D.G. (1998): Travell & Simons' Myofascial Pain and Dysfunction: Vol 1 & 2: The Trigger Point Manual: Lippincott Williams and Wilkins

Wu, M.T. et al (1999): Central Nervous Pathway for Acupuncture Stimulation: Localization of Processing with Functional MR Imaging of the Brain—Preliminary Experience in Radiology 212:133-141

Yu Bai, Jun Wang, Jin-peng Wu, et al. (2011), Review of Evidence Suggesting That the Fascia Network Could Be the Anatomical Basis for Acupoints and Meridians in the Human Body, Evidence-Based Complementary and Alternative Medicine

Zylka, M.J. (2010): Needling adenosine receptors for pain relief in Nature Neuroscience 13:783–4