Brain signals that reveal how much pain a person is in have been discovered by scientists who say the work is a step towards radical new treatments for people living with debilitating chronic pain.
It is the first time researchers have decoded the brain activity underlying chronic pain in patients, raising hopes that brain stimulation therapies already used for Parkinson’s and major depression can help those who have run out of other options.
“What we’ve learned is that chronic pain can successfully be tracked and predicted in the real world, while patients are walking the dog, or at home, when they get up in the morning, and when they are going about their lives,” said Prasad Shirvalkar, a neurologist and lead researcher on the project at the University of California, San Francisco.
A “silent epidemic” of chronic pain affects nearly 28 million adults in the UK alone, meaning nearly 44% of the population have experienced pain for at least three months despite medication or treatment. The causes are manifold, ranging from arthritis, cancer and back problems to diabetes, stroke and endometriosis.
But while chronic pain has fuelled a rise in prescriptions of powerful opioids, no medical treatments work well for the condition, prompting experts to call for a complete rethink in how health services handle patients with lasting pain.
For the latest study, published in Nature Neuroscience, Shirvalkar and his colleagues surgically implanted electrodes into four patients with intractable chronic pain after a stroke or the loss of a limb. The devices allowed the patients to record activity in two brain regions – the anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC) – at the press of a button on a remote handset.
Several times a day, the volunteers were asked to complete short surveys on the strength and type of pain they were experiencing, and then record snapshots of their brain activity. Armed with the survey responses and brain recordings, the scientists found they could train an algorithm to predict a person’s pain based on the electrical signals in their OFC. “We’ve developed an objective biomarker for that type of pain,” said Shirvalkar.
Separate work by the team found that very different brain activity accompanied acute or short-term pain, such as that produced by a hot object touching the skin. The finding may explain, at least in part, why routine painkillers are less effective for chronic pain than the short stab of agony from a stubbed toe.
“Chronic pain is not just a more enduring version of acute pain, it is fundamentally different in the brain,” Shirvalkar said. “The hope is, as we understand this better, that we can use the information to develop personalised brain stimulation therapies for the most severe forms of pain.”
The findings could have an immediate impact on clinical trials that are investigating a procedure called deep brain stimulation to control chronic pain. Deep brain stimulation sends electrical pulses into the brain to disrupt problematic signals. Because it involves brain surgery, DBS is a treatment of last resort, but it is already used for Parkinson’s disease and major depressive disorder. To be effective, doctors need to know precisely which signals to target.
Prof Blair Smith, an expert in chronic pain at the University of Dundee who was not involved in the research, said the lack of objective measures for pain make it difficult for doctors to assess whether treatments are effective. “If this research is successfully extended, it offers not only the opportunity to develop objective measurement of some types of pain, but also to enhance our understanding of the biological mechanisms,” he said.
But pain is a complex phenomenon, Smith warned, with psychological, social and cultural factors, previous experiences of pain and expectations all feeding in. “As [the essayist] Nassim Taleb wrote: ‘studying neurobiology to understand humans is like studying ink to understand literature.’”
