Since the 1970s there has been a good deal of research to find out
how acupuncture works. The early studies mostly focused on the
endogenous opioids, which had been discovered not long before and
seemed to provide a rational basis for acupuncture analgesia. While
these are still part of the story there is much interest these days
in other ideas, including the use of brain imaging techniques to
study central changes in acupuncture.
In outline, there seem to be five types of mechanism involved in
pain modulation by acupuncture.
Local changes in the tissues
Myofascial trigger points
Segmental analgesia (spinal cord)
Extrasegmental analgesia (spinal cord)
Central regulation (brain stem, thalamus, limbic system,
There is a good discussion of all this in Section 2 of Medical
Acupuncture: A Western Scientific Approach, edited by
Jacqueline Filshie, Adrian White, and Mike Cummings. Rather than try
to summarise it here I shall look at some aspects of
neurophysiology that seem to me to be of particular
importance. These mainly concern pain.
The modern view of pain
Our understanding of pain has undergone a major transformation
since the middle of the twentieth century. To put it at its
simplest, we have seen that pain processing is dynamic and active,
not passive and static. It depends on a balance between excitation
and inhibition. To modify pain we can either decrease excitation or
increase inhibition. Acupuncture for pain relief is largely a
means of increasing inhibition.
Another way of thinking about chronic pain is as a form of faulty
In this context 'memory' refers to a change
in an organism that affects its subsequent behaviour. It is not
necessarily a question of conscious memory, so acquired immunity is
an example of memory in this sense.
Not all kinds of memory are as useful as is acquired immunity.
Sometimes it's just the opposite—think of autoimmune disease.
Chronic pain is due to unwanted memory that has some resemblance to
autoimmunity. It can be thought of a form of faulty learning, in
which case pain relief by acupuncture is produced by erasure of the
unwanted memory. The mechanism by which this happens is still not
entirely clear but it may be connected with a phenomenon known as
Long-term potentiation (LTP) was discovered in 1968
in the rabbit hippocampus. It is now known to be widespread
throughout the central nervous system and is thought to be related
to memory formation. It depends on the strengthening of synaptic
links between neurons. It occurs in the pain pathways, where C-fibre
inputs increase LTP in the posterior horn cells.
Acupuncture may be a means of counteracting LTP in cases of chronic
Pain and the limbic system
The limbic system is involved in memory formation and this part of
the brain is affected by acupuncture, so here is another link with
memory. But parts of this system, particularly the anterior
cingulate cortex, are concerned with the emotional response to pain.
Acupuncture has been shown to reduce activity in the anterior
cingulate, which may help to explain the clinical observation that
acupuncture sometimes makes pain less unpleasant even when it does
not eliminate it completely.
'Just a placebo?'
The principal objection raised by
critics of acupuncture is that it is simply an elaborate placebo.
One answer to this is to point out that placebos must ultimately
work by modifying the way the nervous works (what else could they
do?) and acupuncture is a means of modifying the activity of the
nervous system, so to call acupuncture a placebo doesn't mean that
its effects are any sense unreal. But we need more than this.
The important thing to keep in mind is that there is more to
acupuncture than the needles. An acupuncture session usually
involves a preliminary examination for myofascial trigger points,
for example—in other words touching the patient. There
may also be the sight of the needles being inserted. And of course
there is the information aspect—what the patient understands
about what is happening. All these features, as well as others that
neither the acupuncturist nor the patient may be fully aware of,
influence the outcome. This means that acupuncture should be thought
of as a form of multisensory analgesia.
This is a relatively new idea although the first example, the gate
theory of pain, which gave rise to treatments such as transcutaneous
electrical nerve stimulation (TENS), dates from the 1960s. But we
now know that other sensory inputs can also modulate pain,including
stimulation of the cochlear vestibular apparatus and vision. These
observations have led to the concept of multisensory analgesia,
whose relevance to acupuncture seems likely to be far-reaching.
It is difficult if not impossible to isolate the contribution of the
needles from that of the other elements of acupuncture in the
clinical setting. Still, there is no doubt that needle stimulation has
particular effects that are not produced, or not so reliably
produced by other kinds of sensory stimulation. Moreover, not all
needle stimulation is of equal effect; for example, periosteal
(bone) needling and subcutaneous needling are not equivalent.
What this amounts to is that there is nothing magic about the
needles. Acupuncture is a form of manual therapy that has much in
common with steopathy, chiropractic, and physiotherapy, all of which
involve touching the patient and have effects which are often quite
similar to acupuncture effects. But needles can produce responses that
are difficult or sometimes impossible to produce in other ways.