People with chronic back pain may experience shrinkage in the ‘thinking’ part of the brain, according to preliminary results of a small study presented this week at a meeting of the American Pain Society in Chicago.

The decrease in brain tissue remains a chicken-or-the-egg question for researchers, since they do not know which comes first — the back pain or the shrinkage.

But if chronic pain turns out to cause parts of the brain to shrink, “the urgency to cure chronic pain becomes more important,” according to Dr. A. Vania Apkarian at Northwestern University in Chicago, who heads the ongoing study.

In previous research, Apkarian and his colleagues uncovered evidence that people with chronic pain may experience changes in brain tissue called gray matter. Unlike white matter, which mainly holds the brain together, gray matter contains active “thinking cells” that are involved in processing information and memory. It makes up the largest proportion of the brain.