In the new study, Apkarian's team continued to study the brains of people with chronic pain, in this case 10 people with chronic back pain. The researchers measured gray matter in the brains of people with chronic back pain and compared them to a group of 20 people who did not have chronic pain.

The measurements revealed that people with chronic pain had less gray matter -- overall and in a part of the brain called the thalamus. Not only was there less gray matter in terms of volume in pain sufferers, but the tissue was also less dense, Apkarian said.

The changes in people with chronic pain, Apkarian told Reuters Health in an interview, were particularly noticeable in parts of the gray matter that are known to be important in making "emotional assessments," including decision making and control of everyday social behavior.