THURSDAY, Aug. 5 (HealthDay News) -- Fibromyalgia patients have more "connectivity" between brain networks and regions of the brain involved in pain processing, which may help explain why sufferers feel pain even when there is no obvious cause, a new study suggests.

Researchers had 18 women with fibromyalgia undergo six-minute fMRI brain scans, and compared their results to women without the condition.

Participants were asked to rate the intensity of the pain they were feeling at the time of the test. Some people reported feeling little pain, while others reported feeling more intense pain.

Brain scans showed the connectivity, or neural activity, between certain brain networks and the insular cortex, a region of the brain involved in pain processing, was heightened in women with fibromyalgia compared to those without the condition.

The connectivity to the insular cortex was even stronger in participants who reported feeling more intense pain compared to milder pain, said study author Vitaly Napadow, a neuroscientist at Massachusetts General Hospital.

"We took advantage of the fact that there is a large discrepancy in the amount of pain patients happen to be in at the time they come in. Unfortunately some patients come in, and they are in a lot of pain. Other patients come in and they are not in pain," Napadow said.

The study, by researchers from Massachusetts General Hospital and the University of Michigan, is published in the August issue of Arthritis & Rheumatism.

Fibromyalgia is a chronic pain syndrome that's characterized by widespread pain, fatigue, insomnia, and the presence of multiple tender points. The syndrome can also cause psychological issues, including anxiety, depression and memory and concentration problems, sometimes called the "fibromyalgia fog."

Prior research has shown that people with fibromyalgia feel a given amount of pain more intensely than others, Napadow explained. In other words, studies have shown a typical person might rate a painful stimuli a "one" on a scale or one to 10, while a person with fibromyalgia might rate the pain a 5 or higher.

The new study is different in that fibromyalgia patients' pain responses were measured while they were at rest and not being exposed to anything painful, Napadow said.

The brain networks involved were the default mode network (DMN) and the right executive attention network (EAN). The DMN is involved in "self-referential thinking," when you think about yourself or what's happening to you, Napadow explained.

The EAN is involved in working memory and attention. When that brain network is occupied, or distracted, by pain, it may explain some of the cognitive issues that fibromyalgia patients experience, Napadow said.

Dr. Philip Mease, director of rheumatology research at Swedish Medical Center in Seattle and a member of the National Fibromyalgia Association medical advisory board, said the study provides insight into what may be going on in the brains of people with fibromyalgia.

"This work shows there is increased connectivity between different brain centers that connect the purely sensory pain processing centers of the brain with some of the emotional and evaluative parts of the brain, or areas of the brain that take a sensory stimulus and say, "How do I interpret this? How do I feel about this'?" Mease said.

For years, fibromyalgia has been a highly misunderstood syndrome, with some doctors doubting it even existed, and others attributing the pain to depression or other psychological issues.

That began to change early this decade, when brain scans showed pain-processing abnormalities in fibromyalgia patients, Mease said.

"That first neuroimaging study really demonstrated fibromyalgia patients were different than normal individuals, and at a neurobiological level, were truly experiencing more pain at lower intensities," Mease said.

The new research moves understanding of the condition a step further, by exploring what's happening in the brain during a resting state.

"Regardless of poking or prodding them, this study is trying to get at an understanding of what is crackling in the brain, intrinsically, such that they have this higher sensitivity," Mease said.

About 10 million Americans are believed to have fibromyalgia, almost 90 percent of whom are women, according to the National Fibromyalgia Association. Sufferers report a history of widespread pain in all four quadrants of the body for at least three months, and pain in at least 11 of 18 "tender points."

More information

Read more about fibromyalgia at the National Fibromyalgia Association.