Health care professionals have long wondered why the same injury may resolve normally in some individuals yet become a lifelong battle with chronic pain for others.
After years of research, experts believe they have discovered the more emotionally the brain reacts to the initial injury, the more likely the pain will persist after the injury has healed.
Researchers say their findings show that chronic pain develops when two sections of the brain — related to emotional and motivational behavior — talk to each other. And, the more these brain areas communicate, the greater the chance a patient will develop chronic pain.
Experts say the discovery can lead to new therapies to treat intractable pain, which affects 30 to 40 million adults in the United States.
Investigators followed 40 participants who had an episode of back pain that lasted four to 16 weeks – but with no prior history of back pain.
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.
Brain imaging of the level of interaction between the frontal cortex and the nucleus accumbens allowed researchers to predict, with 85 percent accuracy, which participants would go on to develop chronic pain.
“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 Apkarian, Ph.D., 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. This finding is the culmination of 10 years of our research.”
“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.
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.
“Now we hope to develop new therapies for treatment based on this finding,” Apkarian added.
Interestingly, 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. Brain synapses are essential for communication between neurons.
“Chronic pain is one of the most expensive health care conditions in the U. S. yet there still is not a scientifically validated therapy for this condition,” Apkarian said.
Chronic pain costs an estimated $600 billion a year, according to a 2011 National Academy of Sciences report. Back pain is the most prevalent chronic pain condition.
The study is published in the journal Nature Neuroscience.
Source: Northwestern University