Many people with chronic pain are depressed, too. These two conditions both involve the brain, and there's been a lot of speculation and research on how they might interact. A group of American and German researchers used brain imaging to look at how pain is processed in people with and without fibromyalgia, a chronic disorder in which people are highly sensitive to pain induced by pressure. The causes of fibromyalgia are unknown.

What the researchers wanted to know: Are people who are more depressed more sensitive to pain?

What they did: The researchers recruited 33 women and 20 men with fibromyalgia and 20 women and 22 men without fibromyalgia. Each person had two days of tests at Georgetown University Medical Center. On the first day, they were assessed for symptoms of depression. On the second day, they had pain testing and scans of their brains. For the pain testing, a hard rubber probe pushed hard for five seconds on the left thumbnail, and the participants rated the intensity of the pain. Some of the fibromyalgia patients also had a functional MRI, or fMRI, scan, which shows the parts of the brain that are active. During the fMRI test, the patients experienced 25-second periods of pressure, set to a level they had rated before as "slightly intense pain."

What they found: People with fibromyalgia who were more depressed or had major depressive disorder did not rate pressure more painful than fibromyalgia patients who were less depressed. However, they had different brain responses to pain, with more activity in an area of the brain that, the researchers say, may process the negativity and unpleasantness of pain.

What the study means to you: The researchers conclude that in fibromyalgia, at least, sensing pain and processing the unhappiness of pain are two separate activities that occur in different regions of the brain. If this finding turns out to apply to different kinds of pain, it suggests that simply treating depression won't lessen patients' pain, although it might make them feel better about it.

Caveats: This still leaves the chicken-or-egg question about depression and chronic pain unanswered. (Are people depressed because they're always in pain, or does depression make pain chronic in certain conditions, such as fibromyalgia or chronic lower back pain that doesn't have a clear cause?) The researchers say a long-term study of fibromyalgia patients, which looked at them when they were and weren't depressed, might shed further light on the question.

Find out more: Read information about fibromyalgia from the National Fibromyalgia Association.

Read the article: Giesecke, T., et al. "The Relationship Between Depression, Clinical Pain, and Experimental Pain in a Chronic Pain Cohort." Arthritis & Rheumatism. May 2005, Vol. 52, No. 5, pp. 1577-1584.

Abstract online: http://www3.interscience.wiley.com