Gaining Clarity: New Insights into Chronic Pain from Brain Implants
In a groundbreaking study published in Nature Neuroscience on May 22, researchers have achieved a remarkable level of understanding about chronic pain by examining the brains of four individuals through implanted electrodes. This detailed examination offers fresh possibilities for alleviating this debilitating condition.
Katherine Martucci, a neuroscience at Duke University School of Medicine, remarked that this approach "provides a way into the brain to track pain." Chronic pain affects a significant number of individuals, with recent research published in JAMA Network Open on May 16 revealing that more American adults were diagnosed with chronic pain than with diabetes, depression, or high blood pressure in 2019-2020.
Chronic pain is a complex phenomenon influenced by various factors such as the body, brain, context, emotions, and expectations, explains Martucci. This complexity makes chronic pain elusive to external observation and challenging to treat effectively.
One treatment avenue involves electrical brain stimulation. As part of a clinical trial, researchers at the University of California, San Francisco implanted electrode wires in the brains of four volunteers experiencing chronic pain. These electrodes served the dual purpose of monitoring and stimulating nerve cells in two brain regions: the orbitofrontal cortex (OFC) and the anterior cingulate cortex (ACC).
Although OFC is not typically associated with pain regulation, it exhibits extensive neural connections to pain-related areas, including the ACC, which is believed to be involved in the experience of pain.
Before initiating brain stimulation, the researchers needed to comprehend how chronic pain affected the brain. Over a period of three to six months, the implanted electrodes monitored the brain signals of the participants as they went about their daily lives. During this time, the volunteers rated their pain levels on standardized scales multiple times per day.
By employing advanced machine-learning techniques, the researchers established links between each individual's pain ratings and their patterns of brain activity, ultimately identifying distinct signatures of chronic pain for each person.
While the patterns were largely unique to each participant, certain commonalities emerged. Brain activity in the OFC, a region located at the front of the brain behind the eyes, corresponded with the individuals' chronic pain levels. Notably, unexpected pain patterns were also observed, such as pain fluctuations occurring on a three-day cycle for two of the volunteers.
"Brain activity in OFC could serve as a reliable biomarker for chronic pain, enabling doctors to track treatment responses and identify new targets for intervention," suggests neuroscientist Chelsea Kaplan from the Chronic Pain and Fatigue Research Center at the University of Michigan in Ann Arbor.
It is important to note that the study focused on four individuals, three of whom experienced pain from a stroke and one with phantom limb pain following a leg amputation. Kaplan emphasizes the need to determine whether these findings can be generalized to other patients and different types of chronic pain.
If brain activity patterns prove to be consistent among individuals with chronic pain, they could potentially be utilized in the future to assess pain levels in individuals who cannot communicate, including those in non responsive states like locked-in syndrome, according to Martucci.
However, the goal of identifying reliable markers of chronic pain is not necessarily to establish the presence or absence of pain as a diagnostic test. Rather, it aims to guide treatment decisions. Study co-author Prasad Shirvalkar, a neurologist at UCSF, highlighted this during a news briefing, stating that the team is currently conducting a clinical trial involving brain stimulation to treat chronic pain.
