Of all the things that scientists still don’t understand about pain, one of the biggest questions is where in the brain it lives. As Science of Us reported earlier this month, past research has shown that the parts of the brain that process chronic pain can change over time, even as the pain itself still feels the same to the person experiencing it. Emotional pain and physical pain and physical pain, meanwhile, may or may not be products of the same neurological processes. And in a study published earlier this week in JAMA Neurology, a team of British and Chinese researchers threw some shade at the so-called “pain matrix,” the network of areas in the brain that that respond to pain.
The study authors took fMRI scans of the brains of six people – including two who were born without the ability to feel pain – as they received 24 jabs on the hand. The subjects rated each one on a scale of zero to ten on both the level of pain and the overall intensity of the sensation. In the end, the two groups had roughly equal ratings for the intensity, with an average of 4.6 among the four with normal sensation and 4.4 for the pain-free people. For the pain itself, the people who could feel it rated it an average of 3.2; the ones who couldn’t, unsurprisingly, called it a zero.
When the researchers looked at the subjects’ scans, though, they found nearly identical patterns across the two groups – meaning that people who couldn’t feel pain still had normal-looking activity in the parts of the brain associated with the pain matrix. Which, in turn, may mean that the pain matrix doesn’t do what we thought it did. Instead, the study authors suggest, it may process sensory stimuli more broadly.
This isn’t the first time the pain matrix has been called into question in recent months: In January, a small study published in the journal PLOS Biology found that one part of the pain matrix, the posterior insula, also responds to other types of stimuli, casting doubt on the idea that the brain contains specific structures dedicated to pain processing.
“Now, no one is denying that these regions do respond to painful stimuli,” the Discover blogger Neuroskeptic wrote at the time. “The question is whether they are, in any sense, functionally specific to pain.”
To better understand where pain comes from, future research should look beyond brain imaging to study pain response at the cellular level, JAMA study co-author John Wood, a biologist at University College London, said in a statement. “The precise location of pain sensation in the brain remains elusive for now,” he said. “It would be therefore misguided to use brain scans to inform diagnosis or drug discovery relating to pain management.” In the meantime, this study doesn’t bring researchers any closer to pinpointing where pain lives, but it does suggest they may have to rethink how they hunt.