HealthDay News — Greater connectivity between two areas of the brain  increases the likelihood that subacute back pain will not recover and will become chronic instead, study findings suggest.

To better understand mechanisms of the brain responsible for chronic pain, Marwan N. Baliki, PhD, from Northwestern University’s Feinberg School of Medicine in Chicago, and colleagues enrolled 40 patients with a documented episode of subacute back pain lasting at least four to 16 weeks. They performed brain scans at study entry and followed neurological markers of pain during a one-year follow-up period.

Compared with patients who recovered from their pain, those whose pain became chronic had greater connectivity between the medial prefrontal cortex (mPFC) and the nucleus accumbens (NAc), the area of the brain responsible for reinforcement learning, the researchers reported in Nature Neuroscience.

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These patients also had loss of gray matter density in the bilateral striatum and insula and in the left sensorimotor cortex. Furthermore, patients with persistent pain had significantly greater positive functional connectivity in the NAc at baseline and one year.

This greater functional connectivity of the NAc with the mPFC at baseline was predictive of persistent pain, suggesting that corticostriatal circuitry may be involved in the transition from acute to chronic pain.

“That motivation-valuation circuitry predicts pain persistence raises the intriguing possibility that, as with positive reinforcement learning, the NAc contributes to an aversive teaching signal that leads to sustained pain intensity over time following a static peripheral injury,” the researchers wrote.

Baliki MN et al. Nature. 2012; doi:10.1038/nn.3153.