Chronic Pain Signature Unveiled through Brain Implants

Scientists have gained new insight into chronic pain by using electrodes implanted in the brains of four participants to detect specific signs of their persistent pain over time. Revealed in a study published in Nature Neuroscience, this detailed view of chronic pain offers new avenues for preventing or dealing with this debilitating condition.

Katherine Martucci, a Duke University of Medicine neuroscientist and a researcher of chronic pain, says, “The approach provides a way into the brain to track pain.” Chronic pain is an incredibly common affliction in the US, with more adults diagnosed with it than with diabetes, depression, or high blood pressure in 2019 and 2020 according to a May report on a JAMA Network Open study. It is also an incredibly complex condition influenced by a variety of factors including the mind, body, context, emotions, and expectations, all of which compound to make chronic pain seem invisible to outsiders and difficult to treat.

Among the treatments proposed is electrical brain stimulation. Electrified wires were implanted into the brains of four volunteers as part of a clinical trial conducted by researchers at the University of California, San Francisco, with the wires able to take readings from nerve cells in two brain areas linked to pain. These were the orbitofrontal cortex (OFC), and the anterior cingulate cortex (ACC). The OFC is not regarded as a critical pain influencer, but it has many neural connections to areas of the brain linked to pain, including the ACC, which experts believe is a critical component of how people experience pain.

Before the team could stimulate the brains of their volunteers, they needed to establish how chronic pain was affecting their brains. During a period of up to six months, the implanted electrodes monitored the volunteers’ brain activity patterns as they went about their daily lives. At the same time, the participants recorded their pain levels on standard pain scales between two and eight times per day. This data was then analyzed using analytical machine learning processes to determine unique signatures for each participant’s chronic pain.

While the patterns were unique to each individual, there was some overlap. Brain activity in the OFC, located at the front of the brain, behind the eyes, correlated notably with the chronic pain levels reported by each participant. During the study, some unexpected pain patterns emerged, for example, with two volunteers reporting that their pain fluctuated on a three-day cycle.

Chelsea Kaplan of the Chronic Pain and Fatigue Research Center at the University of Michigan in Ann Arbor stated that brain activity patterns in the OFC may represent a dependable biomarker for chronic pain, which could help track responses to treatment and provide new targets for treating pain.

The study was conducted on only four people: three with pain resulting from stroke, and one with phantom limb pain stemming from a leg amputation. Kaplan believes that the findings need to be checked to see if they generalize across other patient and pain conditions.

Martucci, however, suggested that if the brain activity patterns were shared by others with chronic pain, they might one day help measure pain in those who cannot communicate it, such as those with locked-in syndrome.

Prasad Shirvalkar, a co-author of the study, said that identifying reliable chronic pain markers is not intended to diagnose if a person is in pain but to guide their treatment. Shirvalkar and his colleagues are now conducting a trial, in which they are stimulating the brains of patients to ease chronic pain. As he said in a May 18th news briefing, “I think of the biomarker as one tool to actually help treat a patient, to actually make them feel more seen.”

The success of our mission to provide accurate and accessible scientific news to the public depends on you, as we are a non-profit news organization. We cannot achieve our goals without your support, which enables us to keep our content free and available to the next generation of scientists and engineers. Donate today to invest in quality science journalism.