TUESDAY, April 24 (HealthDay News) -- The brains of patients with chronic fatigue syndrome -- an often misunderstood condition marked by unexplained, incapacitating exhaustion -- don't respond to rewards in the same way as the brains of healthy people do, a new study suggests.

Researchers performed functional MRI scans on the brains of 18 people with chronic fatigue syndrome (CFS) and 41 healthy volunteers, finding that those with chronic fatigue experienced significantly less change in blood flow to the basal ganglia in response to winning a simple card game meant to stimulate feelings of reward.

Previous research has shown that the basal ganglia, a region at the base of the brain associated with motor activity and motivation, is affected in diseases associated with fatigue. Participants with the most severe chronic fatigue had the smallest change in basal ganglia activity, the study showed.

"We don't know if these changes are involved in causing CFS or are found as a result of CFS," said study author Dr. Elizabeth Unger, chief of the chronic viral diseases branch of the U.S. Centers for Disease Control and Prevention. "Every carefully controlled scientific study on CFS helps raise the credibility of this very complex illness. Even though our findings are preliminary . . . they do support a biologic [theory] about this illness."

The study is to be presented Tuesday in San Diego at the Experimental Biology 2012 meeting, a conference sponsored by six scientific societies.

An estimated 1 million Americans suffer from CFS, also known as chronic fatigue and immune dysfunction syndrome (CFIDS). The condition has no known cause, diagnostic test or universally effective treatment. More common in women, chronic fatigue symptoms last at least six months and can include sleep difficulties, memory and concentration problems, and joint and muscle pain.

During the experiment -- which is considered preliminary since it hasn't yet been peer-reviewed or published -- Unger and her team told participants undergoing brain scans that they'd win a small amount of money if they correctly guessed whether a pre-selected card was red or black. After choosing, they were presented with the card while researchers measured blood flow to the basal ganglia during winning and losing hands.

Participants with chronic fatigue syndrome experienced significantly less change in blood flow to the basal ganglia between winning and losing hands than did the healthy volunteers. The results support prior research that also demonstrated biological differences among patients with chronic fatigue syndrome, Unger said.

"This is what we need -- validation of these biological underpinnings of CFS," said Suzanne Vernon, scientific director of the CFIDS Association of America in Charlotte, N.C. "These imaging studies are tricky because they only show a correlation, which doesn't necessarily translate to causation, but it's nice to see validation and a number of different studies pointing [to this brain area]."

Unger said additional studies are needed, but she hoped the current results would entice other scientists to become interested in investigating chronic fatigue syndrome.

"A strength of the study is that we used some of the newest technology available to look at the function of regions of the brain that may be involved with CFS," she said. "We hope the impact of our study will be to encourage further basic science investigation of CFS."

More information

The U.S. National Library of Medicine has more about chronic fatigue syndrome.