Chronic pain is associated with brain signals in the orbitofrontal cortex

Researchers have recorded the brain’s firing patterns for the first time when a person is in chronic pain, paving the way for implanted devices to one day be able to predict or short-circuit pain signals. cut open.

Scientists documented four patients who had been experiencing constant neuralgia for more than a year using pacemaker-like devices surgically placed in their brains. The device records several times a day for up to six months and provides clues as to where chronic pain resides in the brain.

The study, published Monday in the journal Nature Neuroscience, reported that pain is associated with electrical fluctuations in the orbitofrontal cortex, an area involved in emotion regulation, self-evaluation and decision-making. This study suggests that such patterns of brain activity will guide the diagnosis and treatment of millions of people with chronic shooting or burning pain associated with nervous system injury. It suggests that it may function as a marker.

“This study really advances a whole generation of research that has shown that brain function is critical to pain processing and perception,” said Ajay Wasan, a pain medicine expert at the University of Pittsburgh School of Medicine. said Dr. Not involved in research.

almost 1 in 5 American adults experience chronic pain, which is persistent or recurring pain that lasts longer than three months. To measure pain, doctors typically ask patients to rate their pain using a numeric scale or a visual scale based on pictograms. However, self-reported pain scales are subjective and can change throughout the day. Also, some patients, such as children and people with disabilities, may have difficulty accurately describing and scoring their pain.

“There is a big movement in the pain field to develop more objective markers of pain that can be used alongside self-reports,” says Stanford University neuroscientist Kenneth Weber, who was not involved in the study. said Mr. In addition to advancing our understanding of the neural mechanisms underlying pain, Dr. Weber said that these markers could be used because the pain experienced by some patients is either poorly understood or completely ignored by physicians. He added that it could help verify that

Previous studies have typically scanned the brains of chronic pain patients to look for changes in blood flow in different regions, an indirect measure of brain activity. However, such studies are limited to laboratory settings, requiring patients to make multiple visits to hospitals and laboratories.

In a new study, Dr. Prasad Silvarkar, a neurologist at the University of California, San Francisco, and his colleagues instead used electrodes to measure the collective firing patterns of thousands of neurons in close proximity to the electrodes.

Researchers surgically implanted recording devices in four people who had lived with pain for over a year and had no relief from medication. Three of his patients had pain onset after stroke. A fourth suffered from so-called phantom limb pain after losing a leg.

At least three times a day, patients rated the pain they felt and pressed a button that stimulated the implant and recorded brain signals for 30 seconds. “This is the first time chronic pain has been measured in the real world,” said Dr. Silvalkar, by following patients daily at home and at work.

The researchers placed electrodes in two brain regions, the orbitofrontal cortex, which is poorly studied in pain studies, and the anterior cingulate cortex, an area involved in processing emotional cues. a lot of research suggest that the anterior cingulate cortex is important in perceiving both acute and chronic pain.

Scientists fed data about a patient’s pain score and corresponding electrical signals into a machine learning model that can now predict high and low levels of chronic pain based solely on brain signals.

Researchers found that specific frequency fluctuations from the orbitofrontal cortex were the best predictors of chronic pain. Dr. Silvalker said that while the brain characteristics were common among patients, each patient also showed unique brain activity. “In practice, each patient had a different pain signature,” he said.

Given the variability and the study’s small number of four participants, Dartmouth College neuroscientist Thor Weiger, who was not involved in the study, still calls the orbitofrontal cortex signature a biomarker. suggested to be cautious.

“We definitely want to confirm this with other studies using other methodologies that can systematically cover the whole brain,” he said.

The study’s authors noted that other brain regions may also be involved. “We’re just getting started,” says Dr. Edward Chan, a neurosurgeon at the University of California, San Francisco. “This is only Chapter 1.”

Implants serve another purpose: deep brain stimulation. As part of a large clinical trial to treat chronic pain, Dr. Silvalker and his colleagues are using weak electrical currents to stimulate brain regions near electrodes. In addition to the four patients in the study who are receiving the treatment, the researchers hope to recruit two more and eventually expand the study to 20 or 30 people. By pulsing the electrodes to modify abnormal brain activity, researchers hope to alleviate lingering pain in patients.