Neurophysiological Mechanisms of Acupuncture
To the age-old question “Where should the needle be placed, and how should it be stimulated for maximum benefit?” there is no one, single answer—it depends on what mechanism needs to be activated and what desired physiological outcome is determined. In this chapter we will look at five mechanisms: local, spinal segmental, endogenous opioid circuit, CNS, and neuromuscular.
1. Local mechanism
What is going on at the focal point of the acupuncture needle at the time of insertion and stimulation?
Why is it that when an acupuncture needle alone is inserted, incredible healing occurs locally? In Korea, a protocol has been introduced in which acupuncture needles are inserted all around the border and directly into second- and third-degree burns. This leads to incredible faster healing of the burn and much less scarring, if any, and results in little to no post-pathological neuropathy. I have utilized this theory style with tremendous success in the treatment of burns, post-op, stubborn, non-healing incisions, and skin infections. And why has simply inserting acupuncture needles directly into the plantar fascia resulted in the resolution of plantar fasciitis? How about needling around or directly into affected areas of slow-healing traumatic injuries?
At the site of the insertion, the special design of the needle (microscopically round, filiform, sterile, etc.) and the insertion technique produce a unique, healing, biochemical soup. The body’s complex reaction to the simple insertion of an acupuncture needle is really quite remarkable. The instant an acupuncture needle is inserted, and then stimulated, an “axon reflex” occurs throughout the meshwork of surrounding nerves. This reflex results in the stimulation of specific fibers located in the terminal network of the primary nociceptive afferent A-delta fibers (including A-gamma and sometimes A-beta) and II and III muscle fibers. This in turn triggers the release of the CGRP (see Chapter 2), one of the body’s most powerful vasodilators. This in turn dilates the surrounding local capillaries and leads to the release of other powerful neuropeptides. Locally, neuropeptides are released as a result of this local neuro-tissue stimulus. These chemicals have several specific therapeutic effects on the local tissues. It has been discovered that this local neurochemical accumulation consists of prostaglandins, red and white blood cells, glutamate, other excitatory amino acids, Substance P, and even serotonin from the local mast cells. This chemical soup begins to down-regulate the pain cascade, aids in reducing inflammation, starts the healing process of local and surrounding tissues, fights infections, and increases local circulation (Filshie & White, 1998; Marieb & Hoehn, 2009; White et al., 2008).
There is an interesting technique I have learned and used called “osteopuncture.” In this technique, you gently needle directly into accessible periosteum. This is a wonderful technique that directs that chemical soup to the bone level to treat such conditions as arthritis, stubborn fractures, ligament injuries, and shin splints. You do not needle deeply into the bone, just superficially into the periosteum or attaching ligament. The local chemical soup that is produced helps to heal bone injuries and ligament inflammatory injuries.
What is actually happening when a De Qi sensation has been obtained locally?
When a De Qi sensation has been achieved, we are certain that, based on the type of sensation the patient reports, we can determine which specific afferent sensory nerves have been stimulated. Those neuropeptides that are released locally (mentioned above) are what stimulate the afferent fibers and result in the De Qi sensation. Different needle stimulation techniques result in different sensations due to different neuropeptides being released as a result of the technique employed. The different techniques also have an effect on the amount of chemicals released (stronger techniques yield more). Hence different sensations lead to the stimulation of different afferent fibers and different outcomes. In other words, the local cutaneous afferent nerve fibers when stimulated elicit a specific sensation and reaction referred to as “axon reflex,” which results with the initial stimulation of the “acupoint.”
When we are training, our teachers constantly remind us, as do the TCM classics, of the importance of the De Qi sensation. For either the patient or we the practitioners feeling “the Qi gripping the needle,” De Qi is important for the outcome of the treatment. We can now explain through neurochemistry what our patients are feeling, as described above, and it is an interesting fact that under electro-microscopic imaging a sterile, disposable, microscopically round acupuncture needle has been shown to grasp and wrap tiny nerve fibers (A-delta) around its shaft during rotation techniques, explaining why practitioners feel the “Qi grasping” the needle.
Here are some quotes from classical TCM texts that illustrate the connection between a De Qi sensation, needling, and the desired effective clinical outcomes:
Needling is effective when one obtains De Qi. (Ling Shu, Chapter 3)
Needling is effective when Qi arrives. (Ling Shu, Chapter 1)
When the patient inhales, twist the needle to get De Qi. (Su Wen, Chapter 2)
Throughout my researching and reviewing of clinical trials on the efficacy of acupuncture in scientific environments, I have found that the more concrete findings, highest success rates, and consistent reproducible outcomes are achieved when the patient obtains a De Qi sensation. I have read in so many texts: “The needle was stimulated until a De Qi sensation was obtained.” So, seeing that pattern and putting it into clinical practice and theory, we find a systematic approach to yield better outcomes.
The acupuncture needle can be inserted utilizing traditional hand insertion or guide-tube insertion. In either event, the needle after insertion should be stimulated until the patient feels a De Qi sensation. Remember, this should be a comfortable Qi sensation, not a sharp or stabbing/burning/painful sensation. A dull, achy, warm, heavy, distended, traveling, fullness sensation, or even a small muscle fasciculation, is fine. (Also, keep in mind that certain medications can amplify pain, such as with hyperalgesia.) As explained above, those classical sensations are the peripheral afferent nerve fibers firing and eventually hitting their mark: the brain and specific receptors. For a patient to feel those sensations, or any sensation for that matter, the afferent fibers of the A-delta, II and III muscle fibers, or C-fibers must have been stimulated (see Chapter 1 for the neuro-breakdown of De Qi sensations).
One thing is clear: patients who report feeling a comfortable De Qi sensation yield better outcomes in scientific clinical trials and clinically. However, there is no need to overstimulate, or vigorously treat, to the extent that patients feel uncomfortable. There has been no scientific or clinical evidence of higher efficacy with excessive stimulation—actually the opposite has been recorded. The A-delta fibers and II and III muscle fibers are the target fibers. They are the fibers that transmit more pleasant sensations, because they have been known to have neural tracts that terminate in specific areas of the brain, and specific receptors, and they then release specific neurotransmitters when stimulated (White et al., 2008).
This section has outlined the beneficial mechanisms behind local needling and provided a neural description of De Qi sensations. We can utilize this scientific evidence to needle locally with the sole purpose of creating a local, chemical, natural, healing soup!
Does every TCM acupuncture point have this local healing potential?
For the local mechanism, the answer is quite often “yes.” However, out of the 364 classical TCM acupuncture points, less than half have been evaluated and have a collection of neural tissue that when stimulated has a deeper, more profound effect on the nervous system and stimulates the CNS for a systemic, visceral therapeutic effect. The specific location of a TCM “acupuncture point” is difficult to determine. It is the neural tissue that we aim for, and although the classical location of TCM acupuncture points can give us a general area to examine, further understanding leads to accessing other areas of the body where this neurophysiological phenomenon occurs to access the inner workings of our elaborate nervous system.
2. Spinal segmental mechanism
For this mechanism, we examine the neuroanatomy of the spinal cord. We study where and how the peripheral nerves innervate the spinal segments and conclude with three important findings. First, it is important to recognize that all primary afferent nociceptive fibers (A-delta group, C-fibers, and II and III muscle fibers) enter the spinal column via the dorsal horn. Second, it is at this specific entrance that the somatic and visceral afferent nerve fibers converge and then cross over and travel up the same single tract (spinothalamic tracts, either paleo or neo). Third, these tracts terminate at various areas of the brain, yielding different neurological outcomes.
At the level of the dorsal horn, small intermediate cells are stimulated and the neuromodulator/endorphin, enkephalin, is released and blocks the transmission of pain in the substantia gelatinosa. Additional neurotransmitters are released at the dorsal horn of the spinal cord, namely serotonin and noradrenaline. These neurotransmitters have a general depression effect on the activity of the dorsal horn. This, in turn, immediately begins to reduce and modify the signaling of pain. So, we see segmentally at the specific level of neural innervation of the nociceptives that there is depression of the transmission of pain but also anything now under this level will feel the effects of the depression of the ascending pain system. This means that if you needle and stimulate an acupoint whose neuroanatomy enters the cervical spine, everything below that innervation will benefit from the depression of ascending pain signals. This effect takes some time to develop (10–20 minutes) but outlasts the duration of the stimulation and has been reported to last several days (Filshie & White, 1998; Marieb & Hoehn, 2009; White et al., 2008).
Figure 4.1 The dorsal horn
By depressing the dorsal horn activity, we affect both somatic and visceral afferent nerves because they converge at the dorsal horn into the same neurotract. What this does is inhibit any visceral dysfunctional autonomic reflexes of the leveled segment (Marieb & Hoehn, 2009). This results in the relaxation of the visceral smooth muscles. The relaxation of the visceral smooth muscle spasms will inherently release excessive, undesired stress on the targeted organ, increase healthy circulation, and aid in enhancing that organ’s function.
Orthopedic application
Here we apply Hilton’s law. The large muscles that surround and affect anatomical joints converge with those same nerves at the same segment of the spine. In this, one can modify the pain signaling from any joint. For example, the vastus medialis (SP10) is one of the large muscles that surround and affect the knee joint, as does the anterior tibialis (ST36). The nerves that innervate those muscles and the nerves that innervate the knee joint both converge at the second, third, and fourth lumbar vertebral segments. So, needling into these acupuncture points will directly affect the neurophysiology of the knee joint. How about the trapezius (GB21) and the splenius capitis muscles (BL10) and the cervical column and the treatment of cervical conditions? The trapezius muscles innervate the cervical spine at level C4–C5, as does the splenius capitis (Marieb & Hoehn, 2009; Rohen et al., 2003).
It is important to remember that Neuropuncture acupoints have local effects as well as segmental ones. We can capitalize on both effects when needling and stimulating the points.
3. Endogenous opioid circuit (EOC) mechanism
Above we discussed the spinal segmental mechanism, which explained how the afferent nerve fibers, after being stimulated, travel to a specific level of the spinal segments and release enkephalins and other neurotransmitters, which depress the transmission of pain signaling. It is at these segments that the nerves that innervate muscles and the viscera also merge, affecting both directly. This impulse, or stimulation, does not end there. Acupuncture needling techniques also have an effect on our cerebral tissue. From the intermediate cells in the dorsal horn to the transmission cells, they then travel up the spinothalamic tract and have ends that terminate on the hypothalamus and other regions dependent on the acupoint. The hypothalamus is one of the largest manufacturers of beta-endorphins, which is another endogenous poly-opioid (natural pain killer). When the hypothalamus is stimulated, beta-endorphins are released that then travel immediately to the PAG (see Chapter 2). The PAG is simply the body’s pain station. The beta-endorphins stimulate the PAG to depress all pain signaling that is being sent in from the peripheral.
We know that there are three main general groups of endogenous endorphins (the body’s self-made pain killers). They are beta-endorphins, enkephalins, and dynorphins. Each of these groups has subsets but they are the three main endorphins that are mostly referred to in acupuncture research. They have affinities to specific receptors: mu, delta, and kappa, respectfully. We now also know that certain hertz with specific frequencies stimulate the specific release of targeted endorphins (Filshie & White, 1998; Marieb & Hoehn, 2009; Rohen et al., 2003; White et al., 2008). (Please see Table 4.2 and the protocols in Chapter 8.)
|
Endorphin |
Receptor |
Frequency/amperage |
Location |
|
Beta-endorphins |
Mu |
2–4 Hz millicurrent |
Midbrain/PAG/pituitary |
|
Enkephalins |
Delta |
2–4 Hz millicurrent |
Dorsal horn of spinal cord |
|
Dynorphins |
Kappa |
50–100 Hz millicurrent |
Brainstem/spine |
|
Orphanin |
Mu |
2/15 Hz millicurrent |
Widespread |
|
Source: Filshie & White, 1998 |
|||
Serotonin is another neurotransmitter that acts as a powerful component in the pain control matrix. Serotonin also is released in the brainstem, which is involved in the descending pain inhibitory system. Not only does serotonin get released in the brainstem but it also stimulates the release of more serotonin in the dorsal horn, as well as noradrenalin. Both of these neurotransmitters strongly inhibit pain signaling in both directions. Now there is some evidence that certain pharmaceuticals can positively influence the effects of acupuncture. Tricyclic antidepressants increase the release of both serotonin and noradrenalin in the CNS. There is some evidence that these medications can amplify and reinforce the effects of acupuncture (Filshie & White, 1998; White et al., 2008).
Neuroscience may help to explain, and legitimize, why acupuncture treatments have a cumulative effect, so that the patient receives better results the more they come. Opioid peptide metabolism illustrates that when there is a release of opioid peptides, there is also enhancement of gene expression, which leads to the manufacture of more opioid peptides to be stored at the terminal. So, when there is stimulation for a second time, the release is greater, resulting in a greater effect and better outcome. The increased gene expression decays back to normal after about 3–5 days (White et al., 2008).
4. CNS mechanism
We see several mechanisms for the effect of pain management with acupuncture via the PAG region of the brain. In addition, when the PAG is stimulated, the neural activity continues throughout the cerebral cortex, stimulating the thalamus, amygdala, and other centers of the brain. How does this affect its role on the immune system, drug dependency, endocrinology, nausea and vomiting, hypertension, and diabetes? All of these areas or conditions have been shown to respond favorably to acupuncture by the findings of fMRI and other imaging, illustrating how acupuncture neurophysiologically affects multiple regions of the brain, thereby correcting the pathology.
Immunology
Acupuncture in this area has only been recently studied, but the findings are positive. Possible mechanisms include generalized autonomic changes in the lymphoreticular system of the bone marrow and spleen. Also, the release of beta-endorphins into the bloodstream induces immune changes through the receptors on the leukocytes. There has also been evidence that acupuncture increases the natural killer cells, solubility of the IL-2 receptor, and changes in gamma interferon. Overall, what we discover does not provide a full explanation nor are the findings so far completely clear, but the area is promising.
Chemical dependency
There is an extensive amount of published literature in this area, particularly in the area of opioid dependency. The social effects are great and too political to discuss here. However, I have been told by professionals that, given the pharmaceutical opioid epidemic in the USA, we are now facing “opium wars” like the ones China experienced 200 years ago. The numbers of opioid addicts are staggering and reaching epidemic levels. So, with this in mind, let us look at how acupuncture can be applied to address this problem.
It has been shown that acupuncture is equally effective in many different areas of dependency or habituation. Auricular acupuncture has the most clinical and scientific research and has gained the most popularity. In the 1970s, China was utilizing auricular EA for opiate detoxing, utilizing bilateral Lung points in the concha, with EA for 30 minutes at 125 Hz millicurrent, for 2–3 consecutive days. The mechanism was at first thought to involve the stimulation of the vagus nerve that innervates the ear, resulting in a parasympathetic inhibition. However, there is yet another idea. Withdrawal symptoms are a result of an imbalanced adrenergic and cholinergic neurotransmitter system with an adrenergic predominance. So, EA actually stimulates the parasympathetic system back into balance. There is also evidence that EA also stimulates the enkephalins throughout the cerebral spinal fluid (CSF), resulting in a reduction in pain associated with a rapid detox. Chemical-dependent patients present significant alterations in extensive areas of the cortex (especially in the prefrontal and temporal cortex), subcortex (amygdala, hippocampus, and insular cortex), and basal regions (striatum). All of these areas have been researched and illustrate that EA stimulates these areas of the brain into homeostasis (Filshie & White, 1998; White et al., 2008).
Endocrinology
As previously stated, it has been proven that acupuncture can stimulate the hypothalamus. From this stimulation, the anterior pituitary can be influenced and then the adrenals, which complete the hypothalamic-pituitary-adrenal axis. There is evidence that both adrenocorticotropic hormone (ACTH) and beta-endorphins are released with acupuncture. The hypothalamus is also the site for the production of the gonadotropin pulse regulator. This affects menstrual flow and timing, and it has been suggested that this is why acupuncture is so effective in women’s health. Other studies suggest that the release of beta-endorphins modifies the CGRP, a strong vasodilator, which can aid in the reduction of hot flashes. 5-hydroxytryptophan (5-HTP) has also been proven to be released with acupuncture and this has a thermoregulatory effect.
Nausea and vomiting
This area has some of the most consistent positive outcomes in randomized clinical trials (RCTs) for nausea related to pregnancy, chemotherapy, and surgery. What has been consistent is the protocol ST36 (anterior tibialis), REN12, and PC6 (deep median nerve). This protocol seems to have an inhibition in emetic response and consistently produces positive outcomes.
Depression
D1 receptors of the prefrontal cortex have been shown to be stimulated with EA. There was a study concluded by the National Center for Complementary and Alternative Medicine (NCCAM) that illustrated a 90 percent success rate in the treatment of major depression (see protocols in Chapter 8).
Oxytocin
This has an interesting story. It was determined that infants nursing on their mothers’ breasts sucked at a mixed rhythm. They would suck at one pace and then increase at one point, which resulted in milk being released. It was later discovered that this “peripheral” slow then faster stimulation on the mother’s nipple stimulated the nervous system in a way that released the neuropeptide oxytocin from the brain. So, we apply a mixed frequency of 2–15 Hz, which mimics an infant breastfeeding and signals the brain to release oxytocin for many applications in obstetric and gynecological cases.
In the treatment of sport injuries and other orthopedic conditions, many times we are needling the MFTRP or motor points of large muscle groups, which stimulates the neural compartments of those muscles. What is actually happening when we needle these points? What we are stimulating is a specific neural loop, the PANS. These tracts have terminal endings throughout the limbic regions in the brain. When these acupoints are needled, they have a profound effect in relaxing and “resetting” the tight, wound-up muscle bundle. The local neurophysiological mechanism that produces the chemical soup also aids in the local healing of the muscle being needled. When these muscles are in spasm, they apply unnecessary pressure on the surrounding joints and tissues. When they are needled and “reset,” they release static tension, and the undue pressure disappears. This also helps to stimulate the muscle’s internal healing potential and fire neurons along its tract, leading to specific spinal segments and healing the entire “neural loop.”