Pain is a hard thing to measure, and also quite mysterious: Two people may experience very similar injuries and similar levels of initial pain, but where one may recover the other may go on to experience a crippling chronic condition.
Why does pain persist for some but not others?
Scientists at the Northwestern University Feinberg School of Medicine took an interesting look at this. Their work, just published in the journal Nature Neuroscience, tracked brain activity in 40 people with new back injuries and found a pattern of activity that could predict -- with 85% accuracy -- which patients were destined to develop chronic pain and which weren't.
Study subjects, all of whom had an episode of back pain that had lasted four to 16 weeks, were tracked for one year. Images of their brains were taken at the study start and then several more times over the year. After one year, they were divided into two groups: ones whose pain appeared to be resolving and those whose pain was persisting.
At the start, there wasn't much difference between the levels of pain reported by the two groups. However, the persistent-pain group did differ from the recovering group in terms of their emotional feelings about the pain.
And when senior author neuroscientist A. Vania Apakarian and colleagues looked at the brain patterns in these two groups, they found differences that had been there right from the start.
Two parts of the brain -- the nucleus accumbens and the medial prefrontal cortex -- were key in the pattern. The more connected these two regions were, the more likely a person in the study was to develop chronic pain later on, the authors found.
The nucleus accumbens "trains the whole rest of the brain as to values, judgments and motivations," Apakarian said in a phone interview. And the medial prefrontal cortex includes regions known to be involved in both acute and chronic pain.
The scientists speculate that strong connections between the nucleus accumbens and the medial prefrontal cortex might somehow teach the brain to develop chronic pain -- and that this process deserves more attention from researchers trying to develop better pain therapies. They note that most of the focus on chronic pain to date has been on damage in the peripheral nervous system and spinal cord that might set up nerves to send “I’m hurting” signals long past the time when an injury actually happened.
The scientists also found -- as had others before them -- that people with chronic pain lost more gray matter in their brains over time compared with healthy controls and the people whose pain was getting better.
There are two ways in which the new findings could be useful, Apakarian says.
One is with prediction: "If you could tell a patient, 'Don't worry, your pain will go away in a few weeks,' that would be fantastic," he said.
And the people whose brain scans portend chronic problems?
Doctors could focus therapeutic efforts on them -- although, Apakarian said, treatments are not yet very good.
Which brings us to his second hope -- that the findings in his lab could help improve matters. Identifying the crucial brain regions offers clues to neurotransmitters that might be involved in setting up chronic pain, and therefore ways to potentially interfere with targeted medications.
Apakarian has received money from the National Institutes of Health to investigate potential drug therapies, first in animal studies.
WebMD and the National Institute of Neurological Disorders and Stroke offer additional resources on chronic pain management.