(This post was originally posted on the 24th February 2014 and in light of new research has been updated on the 26th March 2017.)
To assist us in our understanding on the mechanisms of Medical Acupuncture I thoroughly recommend watching a recent presentation by a Professor Lundeberg. You can find the 23min video presentation at the bottom of this article.
In this post I offer some highlights from this presentation.
First a quick reminder as to how the nervous system centrally processes nociceptive input arising from the tissues. Nociceptive input travels via the thalamus and projects to
- The limbic structures - the amygdala and hippocampus, resulting in a primitive emotional response to pain
- The somatosensory cortex where pain intensity and location is registered
- The prefrontal cortex where the cognitive interpretive aspects of pain occur
- Recent research has also shown that pain activates the REWARD centres of the brain which is very relevant when pain becomes chronic
NB: Nociceptive information only registers as pain when ‘interpreted’ by the brain
This response can be influenced with the use of Acupuncture stimulation, but where best to place the needles?
We must remember that the Acupuncture effect, from a neurophysiological point of view takes place at three locations:
1. THE PERIPHERAL TISSUES
Usually muscle tissue, where Acupuncture stimulation of the intramuscular type III receptors results in release of ATP which is broken down to adenosine. Adenosine may bind to the peripheral A1 nociceptors and inhibit nociceptive signals arising in this area - a small anti-nociceptive effect. Adenosine also binds to epithelium of blood vessels resulting in a vasodilatory effect.
Acupuncture also stimulates ergo-receptors/proprioceptors (Type II) in the muscle tissue - this occurs when the de qi stimulus is evoked - and from these receptors we get CGRP released which is also a potent vasodilator. CGRP also has a trophic effects which stimulates the growth of the epithelium i.e. triggers healing and repair.
This combined effect explains why Acupuncture may be very effective when local muscle ischaemia occurs such as during or after mechanical overload.
If we want a longer lasting effect we need to repeat treatment when trying to assist wound or muscle healing for example. So where we place the needle is important when treating ischaemic conditions - such as trigger points for example.
Use local needling in the periphery to promote tissue healing and repair especially when tissue ischaemia suspected. For example trigger points, wounds and local tender areas.
2. THE SPINAL CORD
Where effects take place at the segmental level/s at which the nociceptive input from injured tissues is converging. This is mainly due to the activation of the intramuscular type II/III receptors.
This results in a segmental enkephalinergic pain inhibitory effect, as well as segmental sympathetic effects. Sympathetic tone is initially INCREASED within the segment being needled. This may result in a reduced feeling of coldness (if present) in the area, a mild increase in peripheral muscular blood flow due to a general vasodilatory effect and a functional effect on internal organ function i.e. a somato-visceral effect.
This sympathetic effect is time dependent and after about 20 minutes of needle stimulation the sympathetic tone then starts to DECREASE. This effect may be maintained for up to 18 hours. So the acute effect of shorter duration needling results in an increase in sympathetic tone, and the effect of longer duration needling results in a decrease in sympathetic tone. A decrease in sympathetic tone is associated with an increase in GIT activity which explains how Acupuncture used for a longer period may be effective in treating constipation for example. When attempting to influence the segmental activity within a segment, it is important to place the needle within the same spinal segment.
Use segmental needling for pain arising from joints, or to affect multiple areas of pain within a spinal segment. Also useful to affect sympathetic tone when treating musculoskeletal as well as visceral conditions.
3. THE CENTRAL SYSTEMS I.E. THE BRAIN
Basically the neurophysiological effects of Acupuncture seeks to reverse the effects of nociceptive input as it converges on the various parts of the brain.
In other words it ‘de-activates’ the limbic system and thereby may affect the emotional response to pain. It also blocks the impact of pain in the prefrontal cortex as well as the reward system. Another central effect of Acupuncture is to activate the descending pain inhibitory system which is controlled at the level of the hypothalamus.
It must be noted the activity in the brain is different when in a pain or illness state. When in a chronic pain state this may be a result of central sensitisation. This in turn may determine the response of the brain and central nervous system to Acupuncture stimulation. The stronger the stimulation in a healthy brain the greater the general decrease in brain activity, unless the stimulus registers as being painful in which case it has the opposite effect.
However in a brain which is centrally sensitised, light stimulation still results in a decrease in brain activity however any stimulation beyond light, i.e. medium/strong or painful will result in an increase in brain activity, potentially exacerbating central sensitivity. This explain why it is important to treat chronic pain e.g. fibromyalgia or migraine sufferers or illness patients very gently and not to overstimulate. This is essential to appreciate from a clinical perspective.
When considering the central effects of Acupuncture - placing needles in the painful segments results in a decrease in limbic system activity and prefrontal cortex activity. If needles are inserted outside the painful segment, i.e. extra segmentally, the effects are in the prefrontal cortex only. So in order to benefit from the combined central effect of Acupuncture needling, especially when treating pain, we need to combine segmental with extra segmental needling.
Using Acupuncture in this way to affect the central mechanisms is very useful when treating those with strong emotional response to pain such as fear, coupled with cognitive disturbances such as a tendency to catastrophize or be hypervigilant, which in turn may be impacting on behaviour resulting in fear avoidance.
The number of treatments given will determine the duration of pain relief. For example it has been shown that at least 5-6 sessions are needed to affect genomic expression leading to sustained activity within the descending pain inhibitory system.
Use segmental and extrasegmental points to affect central regulatory function when treating those with chronic pain, especially with a strong affective/ emotional or cognitive component.
I certainly found Prof. Lundeberg’s presentation very insightful and certainly feel more confident and up to date in my understanding of the mechanisms underpinning Acupuncture as a treatment technique. Once again, please watch the video to benefit from the drawings used to make this sometimes complex subject easier to digest.
Writted by Simon Coghlan
Presentation by Prof. Lundeberg