Scientists discover that heightened levels of communication between different parts of the brain increase your chances of developing chronic pain after an injury.   

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Whether you are a construction worker, a nurse, or an accountant, back pain is something to be feared. Nothing can ruin a day like the sting of a pinched nerve or a sore muscle along your spine. But what happens when a day of pain turns into weeks, or months? Why does some people’s pain persist while others with similar injuries heal?

A new study published in Nature Neuroscience has elucidated the differences between people who heal quickly after suffering a back injury, and those who do not. According to a team of Northwestern University researchers, the difference lies in the level of connectivity, that is the amount of communication that occurs, between the brain’s nucleus accumbens and the prefontal cortex.

This study not only marks an important step towards identifying patients who are more likely to develop chronic pain, but also lends support to the age-old saying that pain really is all in your head.

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 In the study, back pain sufferers with similar injuries underwent four brain scans over the course of a year, each time discussing how their pain and their mood were evolving with medical professionals.

At the end of the year, the participants were subdivided into two categories, recovering or persisting, depending on how each patient’s pain had progressed.

When the researchers compared the brain scans of both groups, they noticed that the recovering group tended to have much lower levels of connectivity between the nucleaus accumbens – a small collection of neurons located in the lower middle part of the brain that plays an important role in reinforcement learning – and the medial prefrontal cortex,  the front part of the brain responsible for coordinating emotions, thoughts, and actions.

In addition, the chronic pain sufferers’ brain connectivity increased over the course of the year. The researchers think this is a symptom of the brain’s adaptation to unrelenting pain.

These results are exciting because the connectivity demonstrated by the patients with persisting pain could be used as a predictor of whether or not a patient is likely to transition from subacute pain – pain that lasts less than three months – to chronic pain.

Incidentally, this is not the only effect that chronic pain can have on your brain. When faced with a continuous signal, your brain has to adapt. So, when it comes to chronic pain, the brain responds by losing gray matter volume over time (Rodriguez-Raecke et al., 2009; Baliki et al., 2011). Gray matter, or grey matter, is the part of the brain that contains neural cell bodies. It is found on the surface of the brain, enveloping the brain’s white matter, which contains the cell body projections, the axons.

This loss of gray matter volume, which implies a “shrinking” of the brain, is not yet understood. Despite our current ignorance, pain researchers have come to expect to see this loss of volume in their patients.

Unsurprisingly, the patients in the persisting group also experienced an early decrease in whole-brain gray matter volume.

“We think gray matter loss is a direct reflection of the brain changing into a network that reflects chronic pain perception,” explains Dr. Vania A. Apkarian, senior author of the paper and professor of physiology at Northwestern University Feinberg School of Medicine.

Dr. Vania A. Apkarian believes the study was a huge success, stating that it was “much better than I anticipated.” The researchers hope that understanding the underlying mechanisms behind chronic pain will precipitate the future development of pain therapies, thus saving us all the headache.

Baliki MN, Petre B, Torbey S, Herrmann KM, Huang L, Schnitzer TJ, Fields HL, & Apkarian AV (2012). Corticostriatal functional connectivity predicts transition to chronic back pain. Nature neuroscience PMID: 22751038

Additional References:

Baliki M, Schnitzer T, Bauer W, & Apkarian A (2011) Brain morphological signatures for chronic pain. PloS one 6(bd8d78af-7994-dd7c-4396-4e5b6e025492).

Rodriguez-Raecke R, Niemeier A, Ihle K, Ruether W, & May A (2009) Brain gray matter decrease in chronic pain is the consequence and not the cause of pain. The Journal of neuroscience : the official journal of the Society for Neuroscience 29(5f8597d2-7060-5859-9ef0-4f9e53a70d0b):13746-13796.

This work by Arielle Duhaime-Ross is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported