The Root Cause: Unlocking the Brain's Role in Pain

CHICAGO, May 18, 2016 /PRNewswire/ -- Why do some people develop chronic pain following an injury while others do not? The question has long puzzled scientists and doctors alike. Now, a new study led by researchers at the Rehabilitation Institute of Chicago (RIC) and Northwestern University Feinberg School of Medicine has found that certain brain anatomical properties, and not the initial injury, determine the most risk of a patient developing chronic pain.

Today, chronic pain is deemed an epidemic in the United States, affecting 100 million Americans. It is commonly believed that a condition such as chronic back pain is the consequence of either ongoing inflammation of the back muscles or a manifestation of injury to major peripheral nerves of the spine.

"While simple, the logic of addressing problems at the site of an injury to remove pain has resulted in only limited success," said senior study author Marwan Baliki, PhD, research scientist at RIC and an assistant professor of physical medicine and rehabilitation at Feinberg. "The central processes of chronic pain have largely been ignored, so our research team set out to better understand the brain's role."

The researchers conducted the first longitudinal brain imaging study tracking patients following an acute injury to the back. As part of the study, they followed 159 patients for three years as their pain either ceased or persisted. They found that patients who developed chronic pain had a smaller hippocampus and amygdala compared with those who recovered and healthy subjects. The hippocampus is the primary brain region involved in memory formation and retention, while the amygdala is involved in the processing of emotions and fear. In addition to changes in size, these regions also showed differences in connections to the rest of the brain, particularly to the frontal cortex, an area involved in judgment.

"Together, these brain properties accounted for 60 percent of the variance for pain persistence and, for the first time, have enabled a mechanistic model for chronic pain development," said first author Etienne Vachon-Presseau, PhD, a visiting postdoctoral fellow in physiology at Feinberg. "As the anatomical risk factors were stable across three years, they were presumably hardwired and present prior to the onset of back pain."

The study's results challenge long-standing views of the science of pain, establishing that the gross anatomical properties of the brain determine the most risk for developing chronic pain.

"These results pave the way for the development of novel and distinct approaches for the prevention and treatment of chronic pain," said A. Vania Apkarian, professor of physiology at Feinberg and senior author of the study.

The full study, "Corticolimbic anatomical characteristics predetermine risk for chronic pain," will be published in the June edition of Brain. In addition to Apkarian, Baliki and Vachon-Presseau, study authors include Pascal Tétreault, Bogdan Petre, Lejian Huang, Sara E. Berger, Souraya Torbey, Alexis T. Baria, Ali R.Mansour, Javeria A. Hashmi, James W. Griffith, Erika Comasco, and Thomas J. Schnitzer.

About the Rehabilitation Institute of Chicago (RIC)
The Rehabilitation Institute of Chicago (RIC) is the nation's leading provider of comprehensive physical medicine and rehabilitation care to patients from around the world. Founded in 1953, RIC has been designated the "No. 1 Rehabilitation Hospital in America" by U.S. News & World Report every year since 1991. RIC sets the standard of care in the post-acute market through its innovative applied research and discovery programs, particularly in the areas of neuroscience, bionic medicine, musculoskeletal medicine and technology transfer. The AbilityLab — RIC's new, state-of-the-art research hospital, will open in Spring 2017. For more information, go to www.ric.org.

SOURCE Rehabilitation Institute of Chicago

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