Groundbreaking research indicates a person’s experience of chronic pain originates in the brain.
This is the first longitudinal brain imaging study to track chronic pain. The Northwestern Medicine study shows for the first time that chronic pain develops when two sections of the brain – those related to emotional and motivational behavior – communicate with each other. The more they communicate, the greater the chance a person will develop chronic pain, according to a Northwestern press release..
A total of 40 participants who had an episode of back pain that lasted four to 16 weeks, but with no prior history of back pain, were studied. All subjects were diagnosed with back pain by a clinician. Brain scans were conducted on each participant at study entry and for three more visits during one year.
Chronic pain costs an estimated $600 billion a year, according to a 2011 National Academy of Sciences report, and back pain is the most prevalent chronic pain condition.
Researchers were able to predict, with 85 percent accuracy at the beginning of the study, which participants would go on to develop chronic pain based on the level of interaction between the frontal cortex and the nucleus accumbens, according to the press release.
“For the first time we can explain why people who may have the exact same initial pain either go on to recover or develop chronic pain,” said A. Vania Apakarian, senior author of the paper and professor of physiology at Northwestern University Feinberg School of Medicine.
“The injury by itself is not enough to explain the ongoing pain. It has to do with the injury combined with the state of the brain,” Apakarian said. “This finding is the culmination of 10 years of our research.”
The more emotionally the brain reacts to the initial injury, the more likely the pain will persist after the injury has healed. “It may be that these sections of the brain are more excited to begin with in certain individuals, or there may be genetic and environmental influences that predispose these brain regions to interact at an excitable level,” Apkarian said in the press release.
The nucleus accumbens is an important center for teaching the rest of the brain how to evaluate and react to the outside world, Apkarian noted, and this brain region may use the pain signal to teach the rest of the brain to develop chronic pain.
Chronic pain participants in the study also lost gray matter density, which is likely linked to fewer synaptic connections or neuronal and glial shrinkage, Apkarian said in the press release. Brain synapses are essential for communication between neurons.
The finding provides a new direction for developing therapies to treat intractable pain, which affects 30 to 40 million adults in the United States, according to the press release. The study is published in the journal Nature Neuroscience.