How it works – The Science
Acupuncture really began to come to the attention of the western world following US President Nixon’s visit to China in 1972 and a successful acupuncture treatment for post-operative pain received by a senior New York Times reporter who had had an emergency appendix operation in Beijing whilst preparing to cover Nixon's visit. The reporter wrote up his experience with acupuncture in his newspaper column, thus stimulating a lot of interest.
Since then there has been an increasing amount of energy spent, both in the west and in the far east, in trying to explain how acupuncture works in modern scientific terms. (Of course the Chinese already have a sophisticated understanding of the way acupuncture works, but not in terms which western science understands or recognises.) The result of these efforts so far suggest that there are a number of mechanisms involved, which are listed below.
In traditional Chinese acupuncture, the needle is inserted into the patient’s skin so as to produce a sensation called ‘deqi’, which is a heavy, dull or numb sensation which often comes as a surprise to first-time acupuncture patients who may be expecting sharpness. This deqi sensation is accompanied by the stimulation of local free nerve endings, particularly a type of nerve known as an A-delta nerve. This leads to the local release of several chemicals called neuropeptides which in turn produce vasodilation (i.e. an increase in the diameter of local blood vessels) and thus an increase in local blood flow, as well as the formation of new blood vessels, thus facilitating repair after an injury – it is the blood which brings the nutrients essential to the body’s repair mechanisms. This neuropeptide release can also affect other structures in the vicinity; for example, facial acupuncture can regulate the action of the salivary glands.
One of the most common uses of acupuncture is for pain relief (analgesia), and there are at least two major mechanisms used to explain this.
a) Segmental Analgesia
When we feel pain, what is happening is that certain kinds of nerves called C-fibres are transmitting pain signals from the area in question to the spinal cord, and from there upwards to the brain, where the pain is registered. These nerves enter the spinal cord at different places; for instance, if we have painful arthritis in our big toe, the pain signal travels along nerves which ascend the leg and enter the spinal cord at the level of the fourth lumbar vertebra (L4) in our lower back; if we have tennis elbow, pain signals travel in nerves which ascend the arm to enter the spinal cord at the level of the fifth cervical vertebra (C5) in our upper back.
The parts of the body served by nerves enter the spinal cord at the same level – the level of L4 or the C5, in our examples – are referred to as segments. Injury at any point in a segment will involve pain signals entering the spinal cord at the same level.
One way of killing pain, therefore, is to somehow block these pain signals. In the case of the big toe, if we were to insert an acupuncture needle into any point on the segment in question, that of L4, and if we obtain the deqi sensation mentioned above, we stimulate A-delta nerves which also enter the spinal cord at the L4 level, where they stimulate the release of a substance called enkephalin (a neuromodulator) which blocks the transmission of pain from C-fibres in the L4 segment, thus stopping the big toe hurting. (This is a similar mechanism to that used in TENS pain relief).
One interesting application of this form of acupuncture analgesia is that a needle inserted into the L4 segment of the left leg can stop pain coming from the L4 segment of the right leg!
Although this mechanism does not involve any actual improvement in the condition of the big toe, it may have knock on effects which do lead to improvement: in particular, a decrease in pain may lead to less muscle tension in the affected area, hence increased mobilisation and thus increased blood flow, which will speed up and facilitate the body’s healing processes.
This mechanism can also account for the use of acupuncture to treat visceral pain (pain arising from one of the internal organs.) Once again, a needle inserted in the appropriate segment – in this case the level of the spinal cord where nerves enter from the organ in question – can block pain signals arising from that segment. This can partly explain, for example, why one of the traditional uses of Sp6, an acupuncture point about” above the ankle on the inner lower leg, is for the treatment of period pain. It goes without saying, of course, that any treatment aiming at pain control should only be happening after the cause of the pain has been diagnosed – pain is basically a message from the body to say that something is wrong, and that message should not be blindly blanked out by pain relief, whether acupuncture or pain killers, without recognising that something is wrong somewhere.
b) Descending Inhibitory Pain Control
As well as providing pain relief within a certain segment, acupuncture also induces generalised analgesia throughout the body; this it does by activating an area of the brain called the periaqueductal grey (PAG). A number of the A-delta nerves mentioned above, which are stimulated by the deqi sensation produced by acupuncture needles, terminate in another part of the brain called the hypothalamus, where they stimulate the release of a substance called beta-endorphin. Beta-endorphin causes the PAG to release serotonin, met-enkephalin and noradrenaline down the entire spinal cord, and these cause pain signals to be blocked in every segment.[4,5]
Myofascial Trigger Points
Another mechanism which can partly explain how acupuncture treats some painful conditions (and some associated symptoms), but which this time involves resolving the problem that is causing the pain rather than simply blocking the pain signals, involves myofascial trigger points. These are tender spots within a muscle (or its associated fascia), which has become slightly damaged, causing pain, restricted movement and sometimes, depending on the muscle, other symptoms as well. These muscles, on examination, may be found to have a particularly tight band of muscle fibre, on which is located the trigger point. Pressing the trigger point will trigger what the patient recognises as the typical pain they suffer from.
Again, to some extent, trigger points often correspond with traditional Chinese acupuncture points, and also with the traditional Chinese concept of the ‘ah shi’ point. (’Ah shi’ is what a Chinese person may exclaim when the point is pressed, variously translated as ’ouch!’ or even ’oh yes!’, perhaps pointing to the patient’s recognising of their typical pain pattern.) Drs Janet Travell and David Simons]6], western physicians from rheumatology and pain management backgrounds, have carried out extensive research to map the typical symptoms caused by trigger points in all of the major skeletal muscles of the human body.
One of the ways of releasing trigger points, restoring the muscle to its proper functioning and thus resolving the symptoms it is causing, is the insertion of an acupuncture needle into the trigger point, again corresponding to the traditional Chinese approach to needling ’ah shi’ points. Sometimes some manipulation of the needle, perhaps quite vigorous, is needed to fully release the trigger point.
A muscle with one or more trigger points may not only cause the typical referred pain as mapped by Travell and Simons, but may cause secondary problems, particularly by the muscle pressing on or trapping a nerve. For instance, a trigger point in the piriformis muscle of the buttock will cause pain in the buttock, lower back and perhaps the upper thigh; but it may also cause the piriformis to trap the sciatic nerve, leading to what is commonly known as sciatica. Skilled acupuncture treatment will release the trigger point, relaxing the piriformis, stopping the referred pain pattern and freeing the sciatic nerve.
Central Regulatory Effects
As well as the specific effects described above – increase in local blood flow, analgesia and trigger point release – acupuncture appears to have effects on the patient as a whole. For instance, after acupuncture treatment patients often report feeling relaxed and sleeping particularly well on the night of the treatment. Most of these effects seem to be mediated through the central nervous system, but as yet the specific mechanisms involved are unclear.
For example, there is now good evidence that acupuncture produces definite changes in the limbic system, a group of interconnected structures within the brain that, among other things, seem to be involved in emotion. One consequence of this is that our affective response to pain and illness – how being ill makes us feel – may be modulated by acupuncture, so that it does not get us down so much.
Other studies[8,9] appear to show that acupuncture can, for example, boost the immune system and regulate the sympathetic nervous system. Over the past ten years or so, there have been a number of studies using functional magnetic resonance imaging (fMRI) to study the way different parts of the brain respond to acupuncture: a meta-analysis of this literature concluded that acupuncture can modulate the activity within specific brain areas, affecting not merely somatosensory but also affective and cognitive processing. For example, two acupuncture points on the lower leg and ankle traditionally used for eye problems showed deactivation of areas of the brain, such as the cuneus, used for visual processing.
Qi, Acupuncture Points and Meridians
Of course, as acupuncture evolved in China, it did so with its own theoretical underpinning. Central to this is the classical Chinese concept of Qi (sometimes spelt Chi), which is virtually impossible to translate effectively into English. What we can say is that Qi flows through a living individual, and that illness involves some problem, or nest of problems, with aspects of that flowing Qi. Acupuncture is envisaged as a way of regulating the Qi, and traditional Chinese medicine maps out several hundred key spots on the body, called acupuncture points, where the Qi can be influenced in different ways. Most of these points lie on meridians, which are envisaged as important routes of the flow of Qi, and which criss-cross the body and connect its surface with its interior, thus enabling regulation of what happens in the organ systems, for instance, by intervening on the surface with acupuncture.
This raises the question, which is a separate question from the efficacy of acupuncture, as to whether Qi, acupuncture points and meridians exist, in what sense they exist, and whether they can be mapped and recognised by modern science.
It is clear that meridians, for example, do not always correspond to any obvious western anatomical structures such as nerves or blood vessels, which has led some to conclude that they do not exist, despite the fact that acupuncture patients quite frequently report sensations travelling along the lines of the meridians during treatment. It is worth pointing out also that western medicine is not wholly unfamiliar with the idea of something happening in one part of the body having an effect at a distant part – for instance most people would be surprised to learn that stretching the hamstring muscles can lead to immediate effects on the jaw muscles and thus a capability of being able to open the mouth further, something which the meridian theory of classical Chinese medicine would be able to explain relatively simply. Others maintain that the meridians are purely functional and energetic and it is missing the point to search for them anatomically. It is also worth noting here that the courses of the meridians were not formalised until the early Song dynasty (11th century C.E.) and before this time they were found by palpation; many practitioners of traditional acupuncture would still perhaps maintain that the courses of the meridians, and the location of the acupuncture points, found in textbooks are only a starting point, and careful palpation is necessary to locate them on each individual patient.
Qi poses particular problems for scientific investigation in that it is not easily defined. Borrowing an expression from an ancient Chinese classic, one might be tempted to say that the Qi that can be spoken of is not the true Qi. One attempt to define Qi has that it is.
“both a principle of unity and coherence that connects all things and a potential, an immanent life force in the world that is knowable only in the various changing aspects it assumes.”
It is not clear how such an entity could be measured. Nevertheless, there have been a number of avenues pursued in an attempt to measure meridians, acupuncture points and Qi scientifically.
i. Electrical resistance
Much early investigation of acupuncture points, meridians and Qi focused on the analogies between Qi and electricity, and some researchers have shown that acupuncture points are loci of decreased electrical resistance, and that meridians are pathways of low resistance along which electrical micro currents flow. Indeed there are a number of devices available which are designed to help clinicians locate acupuncture points ‘scientifically’ by detecting points of low resistance. A systematic review14 of the studies investigating the electrical properties of acupuncture points and meridians, done on human subjects and written in the English language, concludes that the findings are suggestive of acupuncture points and, in particular, meridians being electrically distinguishable from surrounding tissue.
One problem with many of the studies reviewed is the process of identifying the acupuncture points in the first place – as mentioned previously, the textbook location of an acupuncture point may only be a guide to locating it by palpation, and it may be debatable whether they may be found by any method other than palpation by a skilled clinician.
ii. Neural Structures
In the 1970’s and 80’s some research investigated the correspondence between acupuncture points, meridians and neural structures. For example19, some acupuncture points were found to correspond closely to the location of muscle motor points (the most electrically excitable area of a muscle, usually where the motor nerve enters the muscle); the commonly used acupuncture point Hegu (LI-4), for instance, correlates strongly with the motor point of the first dorsal interosseus muscle. Moreover it is clear from the above that the nervous system is heavily involved in acupuncture mechanisms, when viewed from a western viewpoint. Whilst no macroscopic anatomical neural structure has been identified as clearly linked to acupuncture meridians and points, any western explanation of these must realistically include reference to the nervous system.
iii. Myofascial trigger points and pain referral patterns.
As outlined above, one of the ways in which western science explains acupuncture mechanisms is in its use in deactivating myofascial trigger points. Some traditional acupuncture points are located in common locations of trigger points, and the typical referred pain pattern of these may correspond with meridians. For example, a common location of a trigger point in the supraspinatus muscle is at the acupuncture point Tianliao (SJ-15), and the typical referred pain pattern down the arm matches with the Shaoyang meridian of the arm, on which Tianliao is located.
iv. Fascia and Connective Tissue
The most promising recent research focuses on fascia, which is an uninterrupted web of connective tissue that maintains structural integrity and provides support and protection to the human body. It fills the space between the internal organs, the bones and the flesh, and according to some researchers may function as a body-wide signalling network constituting a method in which the body maintains homeostasis independently of the brain and central nervous system. Traditional acupuncture points are often found at locations which give access to this tissue, and research suggests that it may be important in accounting for acupuncture mechanisms. The contact the needle makes with collagen fibres in connective tissue may explain the typical way in which the needle is ‘grasped’ upon insertion.
Pathways in the connective tissue may relate to the meridians. For example, one study used ultrasound to show how an acupuncture needle inserted in to a point on the Shaoyang meridian of the leg caused connective tissue displacement further up that meridian. Recent Chinese research suggests a strong correlation between intramuscular connective tissue and traditional meridians. Pathways in the connective tissue can provide migratory tracks for cells such as mast cells and fibroblasts, for electrolytes, oxygen, carbon dioxide and proteins; influencing the flow in these channels can thus cause significant modification and regulation of numerous physiological functions.
As well as mechanical mechanisms, the insertion of an acupuncture needle affects the flow of interstitial fluid through the fascia, and this in turn stimulates the flow of electric current through the collagen fibres of the connective tissue, regulating cell growth, division and repair. This in turn suggests that the flow of Qi is equivalent to a complex array of phenomena including electric currents, movements of cells and mechanical effects on the connective tissue.
v. MRI scans and meridians
A Chinese group used radioactive tracers in conjunction with MRI to investigate the existence of meridians – they injected minimal amounts of tracer into acupuncture points on some of the traditional meridians of the hand and foot. The MRI showed migration channels along which the tracer flowed, whereas when they injected into non acupuncture points, no such channels formed.
vi. Acupuncture Points and fMRI scans.
Although it is the most promising model to date for explaining meridians and acupuncture points, the fascia and connective tissue model does not as yet fully explain the traditional specific functions of acupuncture points in regulating, for example, the internal organs – although since the fascia is a continuous structure which encompasses these organs it may go some way to show how organs can be influenced from acupuncture at distant sites.
As mentioned above, there have been a number of interesting experiments using functional magnetic resonance imaging (fMRI) to measure brain activity during acupuncture treatment, and some of these point to the specificity of acupuncture points. For instance one study12 used fMRI to measure the effect of acupuncture stimulation of the traditional acupuncture point Erjian (LI-2) which lies on the radial side of the index finger and which is commonly used in the treatment of xerostomia (dry mouth). Needling of this point was associated with activation of areas of the brain called the insula and the operculum, which are believed to be involved with saliva production. Acupuncture needling at adjacent sites – not at an acupuncture point – neither activated or deactivated these areas of the brain. Furthermore, needling of Erjian was associated with increased saliva production. Studies such as this suggest that acupuncture points indeed exist as locations which can have specific effects on specific body functions. Of course such studies merely beg the question of how the acupuncture point can influence brain activity!
To date a number of mechanisms have been, or are being, discovered which help to explain how acupuncture works from a western scientific point of view. The picture is complex, and is likely to become more so as research progresses. There is certainly no one explanation, and it is likely that in any actual traditional acupuncture treatment some or all of the mechanisms above are involved, along with a few others that are yet to be clarified. The separate question of the scientific measurement of meridians, acupuncture points and Qi is similarly not susceptible of an easy answer.
These considerations raise a number of questions, especially for those with health problems. It has been pointed out that people choose the kind of healthcare they do (when indeed they have any kind of choice) based not upon the likely efficacy of treatment, but on whether the treatment accords with their own world view. Thus someone who regards themselves as scientific, or who believes that science describes the way things are more accurately than other systems, or perhaps who puts their faith in scientists and biomedical doctors as repositories of knowledge, will choose western medical treatment; whilst someone who thinks of themselves as somehow ‘alternative’, or who distrusts ‘the establishment’, or perhaps who is nostalgic for traditional ways of thinking which have been lost or superseded, may choose some kind of ‘alternative’ medicine; in both cases possibly regardless of the actual efficacy of the treatment. (Perhaps this distinction applies not just to individuals, but to governments and societies; western societies choose scientific forms of healthcare almost exclusively, not necessarily because they are always more effective, but because they accord with prevailing world views, which may be described as scientific, reductionist and materialist. Economic forces, such as the power of multi-national pharmaceutical companies, are also influential.)
Attempts to explain Traditional Chinese Medicine in terms of western science, such as those described above, partly cater for people (and societies) who believe that treatments can only be valid if they can be so described. Such people will tend to believe, for instance, that if acupuncture meridians exist, they must be measurable scientifically. Often this is not a considered philosophy (and the construction of a philosophy which could justify such a position is not so straightforward as such people might think) so much as an unexamined assumption, and indeed some people’s faith in science sometimes looks suspiciously like the uninformed religious faiths of earlier times, or indeed the sometimes equally uniformed faiths of many proponents of alternative medicine. At its worst, this position also often involves a rather simplistic and uninformed understanding of the body which in no way reflects the complex web of processes which science actually reveals.
Hopefully, what this article may do is to help us to move beyond our often simplistic assumptions about the way things, and in particular human beings, are, the ways that illnesses arise, and the ways that medicines work, or fail to work. One thing that the kinds of research mentioned here certainly do prove, is that, at least from the point of view of western science, the human being is an extremely complex phenomenon, much more complex than most of us appreciate. Although western medical doctors may like to give the impression that the human being is largely understood by science, this is as yet far from being the case. It may be premature to think that we can explain acupuncture scientifically, and it is certainly premature to think that it cannot be so explained and is some kind of mumbo jumbo. Apart from anything else, western science is a constantly evolving undertaking, in which what are sometimes considered to be facts may at a later date come to be considered to be false. (For instance, consider the placebo effect, which is now universally recognised but would have been dismissed as impossible a few generations ago. Similarly, it used to be considered a fact that cancers are not caused by infection, but now we know that some cancers are so caused.)
1 Wang K et al (1985) A study of the receptive field of acupoints and the relationship between the characteristics of needling sensation and groups of afferent fibres. Scientia Sinca 28:963
2 Dawidson I. et al (1998) The influence of sensory stimulation (acupuncture) on the release of neuropeptides in the saliva of healthy subjects. Life Sciences 63(8): 659-674
3 White A. et al (2008) An Introduction to Western Medical Acupuncture Churchill Livingstone, Edinburgh
4 Pomeranz B. (2001) Acupuncture analgesia – basic research. In Stux g. & Hammerschlag R. (eds) Clinical Acupuncture – scientific basis. Springer, Berlin
5 Han J. & Terenius L. (1982) Neurochemical basis of acupuncture analgesia. Annual Review of Pharmacology & Toxicology 22. 193-220
6 Travell J. & Simons D. (1983) Myofascial pain and dysfunction: the trigger point manual. Volume 2 the lower extremities. 1st editon. Williams & Wilkins, Baltimore
7 Hui K.K et al (2000) Acupuncture modulates the limbic system and subcortical gray structures of the human brain: evidence from fMRI studies in normal subjects. Human Brain Mapping 9(1): 13-25
8 Lundeberg T. (1999) Effects of sensory stimulation (acupuncture) on circulatory and immune systems. In Ernst E. & White A. (eds) Acupuncture: a scientific appraisal. Butterworth-Heinemann, Oxford
9 Dyrehag L.E. et al (1997) Effects of repeated sensory stimulation sessions (electro acupuncture) on skin temperature in chronic pain patients. Scandinavian Journal of Rehabilitation Medicine 29: 243-250
10 Langevin H.M. et al (2006) Subcutaneous tissue fibroblast cytoskeleton remodelling induced by acupuncture; evidence for a mechanotransduction-based mechanism. Journal of Cell Physiology 207(3)
11 Wenjing Huang et al (2012) Characterizing Acupuncture Stimuli Using Brain Imaging with fMRI – A Systematic Review and Meta-Analysis of the Literature PLoS ONE 7(4): e32960. doi:10.1371/journal.pone.0032960
12 Deng G. et al(2008) Functional magnetic resonance imaging (fMRI) changes and saliva production associated with acupuncture at LI-2 acupuncture point: a randomized controlled study. BMC Complement Altern Med. 2008 Jul 7:8:37
13 Li H. et al (2008) Visualized regional hypodermic migration channels of interstitial fluid in human beings: are these ancient meridians? J Altern Complement Med 2008 Jul;14(6):621-8
14 Ahn A. et al (2008) Electrical properties of acupuncture points and meridians: a systematic review. Bioelectromagnetics 29:245-256
15 Robinet I. (1997) Taoism: Growth of a religion. Stanford. CA Stanford University Press
16 Langevin H.M. (2005) Connective tissue: A body-wide signalling network? Medical hypotheses, 66, (6):1074-7
17 Konofagou E.E. & Langevin H.M. (2005) Understanding Ultrasound to Understand Acupuncture. IEEE Engineering in Medicine and Biology Magazine (March/April):41-6
18 Yuan L. & Bai Y. (2009) Anatomical Discovery of Meridians and Collaterals in Huijing P.A. et al (2009) Ed. Fascia Research II; Vrije universiteit. Amsterdam NL: Elsevier, 99-100
19 Liu Y et al (1975) American Journal of Chinese Medicine. Oct;3(4):347-58.
20 Unschuld P. (1988 ) Medicine in China – A History of Ideas. University of California Press. Berkeley, Los Angeles and London
21 Bretischwerdt C et al (2010) Immediate Effect of Hamstring Muscle Stretching on Pressure Pain Sensitivity and Active Mouth Opening in Healthy Subjects Journal of Manipulative and Physiological Therapeutics 33 (1)