Addiction-related process may keep people hurting long after an injury heals

By Laura Sanders

Web edition: July 1, 2012
Print edition: August 11, 2012; Vol.182 #3 (p. 10)

A signal in the brain can predict who will continue to suffer back pain more than a year after an initial injury. This early warning sign could reveal new ways to reverse or prevent pain that lingers long after an injury heals, scientists report online July 1 in Nature Neuroscience.

“We’re very excited about these results,” says study coauthor A. Vania Apkarian of Northwestern University in Evanston, Ill. “We think they open up a whole new way of looking at chronic pain.”

The study included 39 people with newish back pain, about half of whom still suffered a full year later. These people’s pain had turned chronic, morphing from the pain associated with the original problem to something more devastating. At the start, pain intensity was similar in people with chronic pain and in those who recovered.

But people whose pain turned chronic had an unusually strong connection between two parts of their brains: the nucleus accumbens and the prefrontal cortex. These two regions behaved in tandem, brain scans revealed, so that when one was busy the other was too. The strength of this connection predicted which participants would have lingering pain a full year later: The stronger the connection, the more susceptible a person was to chronic pain.

“This is something we can study,” says neuroscientist Laura Stone of McGill University in Montreal. “We can figure out how to target this to prevent that transition.”

Earlier studies have catalogued brain differences in people with chronic pain and healthy controls, but researchers never knew whether such differences were the cause of chronic pain or an effect of living with it. This study is the first to uncover a signal that’s present before pain becomes chronic, Stone says.

The study may also link chronic pain development to the brain’s addiction machinery, which includes the nucleus accumbens. “This is certainly part of the addiction pathway,” Apkarian says. Though the idea hasn’t been tested, he says, chronic pain may stem from the brain essentially becoming addicted to pain.

Stone says the concept of pain co-opting the addiction circuitry in the brain makes a lot of sense, but it’s too early to say whether that idea is right.