While most chronic-pain disorders lack ... established, objective outcomes of disease, this is not true for carpal tunnel syndrome (CTS), a neuropathic pain disorder that can be validated by measuring electrical conduction across the median nerve, which passes through the wrist. Interestingly, the slowing of nerve conduction at the wrist does not occur in isolation – it’s not just the nerve in the wrist that’s affected in CTS. My own department’s research and others’ has clearly demonstrated that the brain, and particularly a part of the brain called the primary somatosensory cortex (S1), is re-mapped by CTS. Specifically, in functional magnetic resonance imaging (fMRI) brain scans, the representation of fingers innervated by the median nerve are blurred in S1. We then showed that both real and placebo acupuncture improved CTS symptoms. Does this mean that acupuncture is a placebo? Maybe not. While symptom relief was the same immediately following therapy, real acupuncture was linked to long-term improvement while sham acupuncture was not. And better S1 re-mapping immediately following therapy was linked with better long-term symptom reduction. Thus, sham acupuncture might work through an alternative route, by modulating known placebo circuitry in the brain, while real acupuncture rewires brain regions such as S1, along with modulating local blood flow to the median nerve in the wrist.
Where you stick the needle might matter as well. While site-specificity is one of the key features of acupuncture therapy, it has been controversial. Interestingly, in the S1 region of the brain, different body areas are represented in different spatial areas – this is how we localise the mosquito that’s biting us, and swat it. Different S1 areas might also pass along information to a diverse set of other areas that affect different bodily systems such as the immune, autonomic and other internal motor systems. As far as acupuncture is concerned, the body-specific map in S1 could serve as the basis for a crude form of point specificity. In our study, we compared patients receiving real acupuncture locally to the wrist with patients receiving real acupuncture far from the wrist, in the opposite ankle. Our results suggested that both local and distal acupuncture improved median nerve function at the wrist. This suggests that the brain changes resulting from acupuncture might not just be a reflection of changes at the wrist, but could also drive the improved median nerve function directly by linking to autonomic brain regions that control blood vessel diameter and blood flow to the median nerve.
This new research clearly demonstrates that bodily response is not the only means by which acupuncture works; response within the brain might be the most critical part. Once we better understand how acupuncture works to relieve pain, we can optimise this therapy to provide effective, non-pharmacological care for many more chronic-pain patients.