What is pain? Ask a poet and they may tell you the never-ending torment of true love, but ask a scientist and they’ll likely struggle to give a direct answer. That’s because a new study recently cast doubt on a long-standing theory on the nature of pain known as the “pain matrix.” According to the theory, the “pain matrix” is a pattern of brain activity believed to be a reliable indicator for pain. However, the study found that the matrix still existed in patients born without a sense of pain – suggesting that the matrix simply responds to attention-grabbing stimuli, regardless of whether or not the personal actually feels.
For the study, now published in the online journal JAMA Neurology, researchers from both University College London and the University of Reading measured brain activity in response to painful “pinpricks” in two rare individuals born without the ability to feel pain, along with four age-matched healthy volunteers who could feel pain. Although the scientists expected to see different neuroimaging responses between the two groups, results showed that the volunteers with no sense of pain showed the same pattern of brain activity as the healthy volunteers.
While these findings may not mean much to the average layman, for scientists it could possibly call into question a fundamental theory on how humans sense pain. The pain matrix, also referred to as the pain center of the brain, is a pattern of brain activity widely considered to be the marker for pain in humans. According to a press release, this pain matrix theory is so widely accepted in the science community that it has even been used in research to reject the idea that social rejection or mental exertion can cause actual physical pain.
“By testing people with no sense of pain, we can categorically rule out that these are pain-specific responses,” explained lead author Dr. Tim Salomons in a statement. “These people still retain all other senses including non-painful touch, so the brain activity that has been dubbed the “pain matrix” is likely to represent these senses rather than actual touch.”
The team instead believe that the pain matrix brain pattern may instead be simply a response to attention-grabbing responses, regardless of whether or not individuals feel any actual pain. While this is not the first time the authenticity of the pain matrix has been called into question, the findings do further highlight the need to understand that correlation does not automatically imply causation.
“Every science student knows that correlation does not imply causation, and we should not forget this when interpreting brain scans,” says senior author Professor John Wood in a statement.
Finding the true origins of pain would be very useful for the development of pharmaceutical drugs used on individuals who suffer from chronic pain. Millions of Americans are reported to experience chronic pain per year, but there is no cure for the condition. In addition, although opioid pain medications remain an effective way to combat moderate to severe pain, these drugs are highly addictive and are largely cited as the reason for America’s current opioid addiction epidemic.
For this reason, understanding how pain sensations are interpreted in our brains could be the first step towards finding a different way to combat pain. However, Wood explained that for now, the true origins of pain in the brain remain elusive.
Source: Salomons TV, Iannetti GD, Liang M, Wood JN. The “Pain Matrix” in Pain-Free Individuals. JAMA Neurology . 2016
Correction: This story has been corrected to show that the research was conducted by University College London and the University of Reading.