Editors' ChoiceNeuroscience

Pain in the Brain

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Science Translational Medicine  18 Jul 2012:
Vol. 4, Issue 143, pp. 143ec127
DOI: 10.1126/scitranslmed.3004591

Some patients suffering from acute pain will undergo pain “chronification” and develop chronic pain, a condition that affects more than 100 million people in the United States alone. It is, however, difficult to predict who will progress in this way, and the result is inappropriate administration of drugs and interventions that do not work—or that even make things worse. A new study by Baliki and colleagues may help clinicians forecast chronic pain by looking in the brain.

The investigators studied patients who had been experiencing acute back pain for 4 to 16 weeks and then followed them for another full year. About half of the patients recovered, whereas the other half developed chronic back pain. Chronic pain patients showed a lower density of gray matter in the nucleus accumbens, a brain area that is involved in our sense of reward or punishment. In chronic pain patients, but not those who had recovered, the nucleus accumbens showed a more robust functional connection to the prefrontal cortex. This finding was critically important because unlike the loss of gray matter in the nucleus accumbens, this excess connectivity was present prior to pain chronification. It also persisted for the year-long study and varied directly with pain severity.

The magnitude of the connectivity between the nucleus accumbens and the prefrontal cortex may therefore have prognostic value in determining which patients with acute pain will go on to have chronic pain. This information could change the treatment for pain in those at risk of chronification. For example, opiates—the mainstay drug for acute analgesia—may be ineffective in those at risk for chronic pain, whereas other strategies aimed at central pain might be more effective. Such a prognostic tool could potentially eliminate trial-and-error treatment of pain and lead to more personalized approaches. Nevertheless, functional magnetic resonance imaging is expensive and impractical for clinicians at the point of care; portable and cost-effective signatures of this cortical-subcortical connection will have to be discovered.

The work of Baliki et al. also has mechanistic significance. The excessive and unhealthy communication between the executive prefrontal cortex and the reward/punishment–mediating nucleus accumbens may be the cause of the “pain in the brain” that persists even after the pain in the back has long since gone.

M. N. Baliki et al., Corticostriatal functional connectivity predicts transition to chronic back pain. Nat. Neurosci., 1 July 2012 (10.1038/nn.3153). [PubMed]

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