Neuroscientists have been studying how acupuncture affects the brain. It’s clear from many imaging studies that causing pain by inserting needles into the skin does influence brain activity, presumably by activating nerves close to the acupuncture point. Intriguingly, being pricked with needles seems to reduce activity in areas of the brain normally associated with pain, dubbed “the pain matrix”, says Hugh MacPherson, an acupuncture researcher at the University of York. “Rather than activating the pain matrix, it actually de-activates it.”
Sceptics argue that because of the lack of effect in clinical trials, such results are irrelevant. “It wouldn’t be at all surprising if being impaled with needles produced a signal in the brain,” says David Colquhoun, a pharmacologist at University College London and a prominent sceptic of alternative medicine. “It doesn’t tell you anything about how useful the needles are to patients.”
But a new generation of brain imaging studies is suggesting that perhaps researchers should refine their testing methods. There are now several trials showing that even when patients in acupuncture and placebo groups report similar drops in pain, the physical effects of treatment can be very different.
For example, Richard Harris, a neuroscientist at the University of Michigan, Ann Arbor, and colleagues used brain scans to investigate whether acupuncture triggers an endorphin hit in the same way that placebos do. They gave fibromyalgia patients – a condition characterised by chronic, widespread pain – either real or placebo acupuncture (using retractable needles at non-acupuncture points) then scanned their brains using positron emission tomography (PET) imaging. PET scans can’t see endorphins directly, but can detect the opioid receptors that these molecules target. Opioid receptors are present on the surface of nerve cells in the brain. When “locked” by endorphins (or other opioid molecules such as morphine), they prevent the cell from sending pain signals. In Harris’s experiment, a drop in the number of free, or unlocked, receptors in the patients’ brains would show that endorphins had been released.
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