Pain type matters to brain.

Chronic back pain affects different parts of the brain than acute back pain does, magnetic resonance images reveal. Researchers say that the area of the brain responding to chronic pain is also associated with emotional distress.

A. Vania Apkarian and his colleagues at Northwestern University Medical Center in Chicago asked people with chronic backaches to undergo magnetic resonance imaging of their brains. While in the scanner, the patients rated their pain levels, which fluctuated spontaneously.

During sustained periods of pain, nerve activity increased in the brain's medial prefrontal cortex, which has been associated with negative emotions, emotional memories, and self-image.

In another experiment, the researchers put a hot probe onto the backs of chronic-back-pain patients and volunteers with no history of back pain. The scientists scanned brain activity while escalating the intensity of the heat up to painful levels.

When either chronic-pain patients or healthy volunteers felt the painful heat, their medial prefrontal cortices were quiet. However, the scans showed activation of the insula, a brain area associated with acute pain.

These results show that chronic pain "impinges on a person's very sense of being," Apkarian says. He and his team report their findings in the Nov. 22 Journal of Neuroscience.--J.J.R.