In Spain, around 32% of adults suffer from some type of pain, according to experts from the Spanish Society of Neurology (SEN), who also point out that recent studies show that 20% of Europeans suffer from chronic pain, and that in Spain could affect at least 17% of the population. Pain is not just a symptom of disease or trauma, but is itself a disease when our brain continues to send pain signals, even though there is no injury or other identifiable cause.
An adequate diagnosis of this serious public health problem is difficult because its origin cannot always be determined, and the sensation experienced by patients is subjective; thus, patients with chronic back pain whose magnetic resonance imaging yields similar results may report very different levels of pain intensity and location. Findings from a new study, in which researchers have for the first time recorded pain-related data from inside the brain of people with chronic pain disorders caused by stroke or amputation (phantom limb pain) , can now help to obtain objective biomarkers of pain that will be useful both to guide diagnosis and to develop personalized and more effective treatments for chronic pain.
“Because the way chronic pain reorganizes neural networks is so unique to each individual, we need more personalized treatment strategies to manage it,” said Prasad Shirvalkar, MD, associate professor of anesthesia, neurology, and neurological surgery at the University of California at San Francisco (UCSF), and one of the directors of the work, who adds: “To address the pain of an individual patient, we first need objective biomarkers of a subjective experience.”
Record neural activity to measure and predict pain
Pain is not only linked to the brain’s somatosensory cortex, where this organ receives and processes sensory information such as touch and temperature, but also to cognitive and emotional processing areas, and is closely linked to circuits expectations and rewards, as well as those related to mood and attention, all of which vary constantly based on information, environment, and individual biology.
“This is the first time that neural activity related to chronic pain has been measured in the real world over a clinically relevant period of time.”
In order to find objective biomarkers of pain, the researchers implanted an intracranial neural recording device; specifically, in the anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC) – areas of the brain related to pain – of four people (three suffering from post-stroke neuropathic pain and another with phantom limb pain).
The electrodes recorded the brain activity of the four participants for several months, during which they led a normal life and three times a day noted in detail the episodes of pain, their intensity and how they felt. In addition, immediately after recording this information, they used a remote control to record the neural activity of the device implanted in their brains for 30 seconds.
The researchers used machine learning models to develop an analysis method that enabled them to accurately predict reported pain levels with specific neural activity patterns in each patient, and to define a unique neural signature for each individual’s pain experience. They were also able to differentiate between types of pain and found that changes in activity in the brain’s orbitofrontal cortex were more strongly correlated with chronic pain episodes, while acute pain was more closely related to activity in the anterior cingulate cortex.
The results of the research have been published in Nature neuroscience and, although the data has been obtained in a very small sample of patients, the authors believe that they can be very useful to develop tools that identify pain circuits in the brain and help to guide the diagnosis or find out why the symptoms become chronic in some cases. They also believe that they can be used to guide the treatment of chronic pain problems, such as the phantom limb syndrome experienced by many patients after limb amputation, or suffered by many patients after a stroke.
“This is a huge milestone because it marks the first time that chronic pain-related neural activity has been measured in the real world over a clinically relevant period of time.” “And although the biomarkers we found were individual-specific, their location in the OFC appeared to be common across subjects,” concludes Shirvalkar.
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