Brain activity in individuals with chronic pain studied

Researchers have identified a brain area associated with chronic pain, along with biomarkers, through analysis of data collected over months using machine learning tools. The researchers, including those from University of California, San Francisco, US, recorded pain-related data from inside the brain of individuals with chronic pain disorders caused by stroke or amputation.

They are hopeful that the findings, published in the journal Nature Neuroscience, would help understand how pain is represented by brain activity and how modulating this activity could help relieve suffering from chronic pain.

Chronic pain is one of the largest contributors to disability worldwide. Neuropathic pain is caused by damage to the nervous system itself. While it most commonly occurs due to injury to the nerves in our bodies, for the individuals in this study, their pain was thought to originate from the brain itself. This kind of pain does not respond well to current treatments and can be debilitating for people living with it.

"When you think about it, pain is one of the most fundamental experiences an organism can have," said Prasad Shirvalkar, associate professor of anaesthesia and neurological surgery at the University of California, San Francisco, and lead author of this study.

"Despite this, there is still so much we don't understand about how pain works," said Shirvalkar.

In this study, the researchers looked directly at changes in brain activity in two regions where pain responses are thought to occur - the anterior cingulate cortex (ACC) and the orbitofrontal cortex (OFC) - as participants reported their current levels of chronic pain.

"Functional MRI studies show that the ACC and OFC regions of the brain light up during acute pain experiments. We were interested to see whether these regions also played a role in how the brain processes chronic pain," said Shirvalkar.

"We were most interested in questions like how pain changes over time, and what brain signals might correspond to or predict high levels of chronic pain?" said Shirvalkar.

Four participants, three with post-stroke pain and one with phantom limb pain, were surgically implanted with electrodes targeting their ACC and OFC. Several times a day, each participant was asked to answer questions related to how they would rate the pain they were experiencing, including strength, type of pain, and how their level of pain was making them feel emotionally.

They would then initiate a brain recording by clicking a remote-control device, which provided a snapshot of the activity in the ACC and OFC at that exact moment. Using machine learning analyses, the research team was able to use activity in the OFC to predict the participants' chronic pain state.

In a separate study, the researchers looked at how the ACC and OFC responded to acute pain, and found that brain processes acute vs. Chronic pain differently, though more studies were needed to establish that, they said.

The study said it represented an initial step towards uncovering the patterns of brain activity underlying our perception of pain. Identifying such a pain signature will enable the development of new therapies that can alter brain activity to relieve suffering due to chronic pain, it said.

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