Chronic pain is one of the most common conditions in the world. In the United States, about one in five adults—or 50.2 million people—experience it. This persistent pain can last for weeks, months or years, despite treatment.
“It is the number one reason why patients see a doctor,” Robert Jason Yong, the medical director of the pain management center at Brigham and Women’s Hospital, told Healthline’s Jamie Reno in 2021. “The impact of chronic pain on people’s lives is enormous.”
But chronic pain is difficult to measure and treat. Doctors often rely on patients to self-report pain levels using a numeric or visual scale, which may not always be reliable, especially for children or adults who have difficulty communicating.
Now, a team of scientists has discovered a new way to objectively measure chronic pain by reading brain signals from volunteers. They say this research could eventually be used to create personalized therapies for those with severe pain, such as electrodes that can intercept the brain’s pain signals to give a patient relief, writes Nicoletta Lanese for Live Science. The team published their findings Monday in the journal Nature Neuroscience.
To measure chronic pain, the researchers implanted electrodes in the brains of four volunteers who were experiencing pain after an amputation (phantom limb pain) or a stroke. As the participants went about their usual days, the devices recorded activity in two brain regions where researchers think pain responses occur: the anterior cingulate cortex and the orbitofrontal cortex.
Several times a day for up to six months, the patients rated their pain levels on standard scales and then pressed a button that would cause the electrode implants to record their brain signals for 30 seconds. The research team then built machine learning models that could find patterns in the data to predict each patient’s pain level based on the signals in their brain.
“From these models, we found that [electrical waves with] low frequencies in the orbitofrontal cortex corresponded with each of the patients’ subjective pain intensities, providing an objective measure of chronic pain,” Prasad Shirvalkar, a neurologist at the University of California, San Francisco and a co-author of the study, writes in the Conversation. “The larger the shift in low-frequency activity we measured, the more likely the patient was experiencing intense pain.”
Importantly, Shirvalkar tells Live Science, identifying an objective pain signal is meant to inform treatments, not undermine a patient’s subjective experience of pain.
While previous research has involved scanning brains of patients to document blood flow in a lab setting, “this is the first time ever chronic pain has been measured in the real world,” Shirvalkar tells the New York Times’ Priyanka Runwal. “Every patient actually had a different fingerprint for their pain.”
Next, the researchers wanted to compare these results with brain signals for short-term pain, so in the lab, they applied heat to the patients’ bodies and recorded how their brains responded. They found that acute pain was more associated with the anterior cingulate cortex, providing the first direct evidence that chronic pain and acute pain involve different areas of the brain, per the Conversation.
While this research might eventually help doctors find new targets for treatment and assess treatment responses, so far, data has only been collected on four participants, and all of them had chronic pain caused by nerve damage.
“We would need to know if these findings can generalize to other patients and pain conditions,” neuroscientist Chelsea Kaplan of the Chronic Pain and Fatigue Research Center at the University of Michigan, who was not involved with the study, tells Science News’ Laura Sanders.
The research team is now trying to treat chronic pain by using mild electrical currents near the electrodes, reports the Times. They hope to eventually expand their study to include 20 or 30 people, per the publication.
“We’re just getting started,” Edward Chang, a neurosurgeon at the University of California, San Francisco, and co-author of the study, tells the Times. “This is just chapter one.”