YOU'RE not imagining the pain. But your brain might be behind it, nonetheless. For the first time, it is possible to distinguish between brain activity associated with pain from a physical cause, such as an injury, and that associated with pain linked to your state of mind.
A fifth of the world's population is thought to experience some kind of chronic pain – that which has lasted longer than three months. If the pain has no clear cause, people can find themselves fobbed off by doctors who they feel don't believe them, or given ineffective or addictive painkillers.
But a study led by Tor Wager at the University of Colorado, Boulder, now reveals that there are two patterns of brain activity related to pain. One day, brain scans could be used to work out your relative components of each, helping to guide treatment.
"Pain has always been a bit of a puzzle," says Ben Seymour, a neuroscientist at the University of Cambridge. Hearing or vision, for example, can be traced from sensory organs to distinct brain regions, but pain is more complex, and incorporates thoughts and emotions. For example, studies have linked depression and anxiety to the development of pain conditions, and volunteers put in bad moods have a lower tolerance for pain.
So does this mean we can think our way into or out of pain? To find out, Wager and his colleagues used fMRI to look at the brain activity of 33 healthy adults while they were feeling pain. First, the team watched the changing activity as they applied increasing heat to the volunteers' arms. As the heat became painful, a range of brain structures lit up. The pattern was common to all the volunteers, so Wager's team called it the neurologic pain signature.
The group then examined whether the volunteers could control the pain by thought alone. "We asked them to rethink their pain, either as a blistering heat, or as a warm blanket on a cool day," Wager says. Although the volunteers couldn't change the level of activity in the neurologic pain signature, they could alter the amount of pain they felt. As they did this, a distinct set of brain structures linking the nucleus accumbens and ventromedial prefrontal cortex became active (PLoS Biology, doi.org/x55).
"It's a major finding," says Vania Apkarian at Northwestern University in Chicago. "For the first time, we've established the possibility of modulating pain through two different pathways."
The upshot is that brain scans comparing the strength of activation in the two brain networks could help work out how much of someone's pain has a physical cause, and how much is down to their thoughts and emotions. This could benefit those with conditions such as fibromyalgia, which is poorly understood and characterised by pain all over the body.
About a quarter of those with chronic pain who contact UK charity Action on Pain say that their doctors don't believe them. "The problem is that chronic pain is invisible," says chairman Ian Semmons.
"Doctors may tell people with chronic pain that they're hysterical, or think that they are making it up," Wager says. "But [the new work] can help us to put a physical basis on the emotional and cognitive contributions."
The findings build on recent work by Apkarian's team, who discovered that chronic back pain seems to be associated with a pattern of brain activity not usually seen with physical pain. In fact, the brain regions active in Apkarian's volunteers were the same as those active in the volunteers controlling pain with their thoughts in Wager's study.
This suggests that in chronic pain conditions, psychological pain may overtake physical pain as the main contributor to the overall sensation. This may explain why traditional pain relief such as opioids don't offer much reprieve.
Wager's study suggests that cognitive therapies and techniques such as neurofeedback – where people learn to control their brain activity by watching how it changes in real time – might offer a better approach. Semmons, of Action on Pain, thinks many people with chronic pain will be open to these alternative therapies. "We always encourage people to be open-minded about their pain," he says. "Painkillers aren't always the answer."
"In the next five to 10 years, we'll see a huge change in the way clinicians deal with pain," says Seymour. "Rather than being based on what the patient says, we'll be building a richer picture of the connections in that person's brain to identify what type of pain they have."
This article appeared in print under the headline "Pain really can be all in your mind"
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