Doctors used to measure a person’s chronic pain based on self-reported pain scales or with emojis to understand the severity of discomfort for a person living with a chronic pain disorder.

For the first time, researchers have studied pain data from inside the brains of four patients who developed chronic pain following either a stroke or amputation.

Chronic pain is defined by the National Institutes of Health (NIH) as pain that continues for three to six months without improvement.

The researchers are hoping to discover that brain-stimulating therapies that are already used for patients with diseases like Parkinson’s and severe depression could also ease the chronic pain that is part of life for 1 in 5 American adults, according to the Centers for Disease Control and Prevention.

The researchers surgically inserted an electrode device into four patients that then recorded brain activity in the anterior cingulate cortex and orbital frontal cortex of the brain during outbursts of pain. All the patients had to do was push a button that would signal the electrode to then record the brain activity during the painful episode.

“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,” Dr. Prasad Shirvalkar, a neurologist and lead researcher on the project at the University of California, San Francisco, told The Guardian.

The study, published in the journal Nature Neuroscience, is seen as a major breakthrough for researchers studying the growing population of people with chronic pain who rely on painkiller medication in order to function.

“When you think about it, pain is one of the most fundamental experiences an organism can have,” Shirvalkar told NIH.

“Despite this, there is still so much we don’t understand about how pain works. By developing better tools to study and potentially affect pain responses in the brain, we hope to provide options to people living with chronic pain conditions,” he added.

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Once scientists were given the brain data collected by the patients, they were able to feed it into machine learning models that were able to identify the different ranges of pain the participants were feeling, based solely on the brain signals.

What they discovered is that the best predictors of pain were coming from the orbital frontal cortex of the patient’s brain.

“The study’s authors also noted that other brain regions may be involved. ‘We’re just getting started,’ said Dr. Edward Chang, a neurosurgeon at the University of California, San Francisco. ‘This is just chapter one,’” he told The New York Times.