The brain needs no introduction; it makes us who we are. And yet, this organ that lets us understand the world understands so little about ourselves.

Scientists are currently researching the brain in relationship to the eating disorder, anorexia nervosa, a psychiatric disorder of unknown etiology. Although there is still much to learn about anorexia, it is clear that a patient's nervous system, which includes the brain and nerves, is negatively impacted by restrictive behaviors.

In the United States, at least 30 million people of all ages, genders, races and ethnic groups suffer from an eating disorder. About 0.9 percent of American women suffer from anorexia, and 1 in 5 anorexia deaths are by suicide.

Roughly 50 to 80 percent of the risk for anorexia is genetic, and 33 to 50 percent of those with anorexia have a comorbid mood disorder, such as depression. Half of anorexia patients have comorbid anxiety disorders, including obsessive-compulsive disorder (OCD) and social phobia.

Individuals with anorexia tend to find that restricting food intake provides a temporary respite from their dysphoric mood. Because there are no proven treatments, anorexia has high rates of relapse, chronicity and death, statistics that underline the importance of understanding the associations between behavior and neurobiology.

In a recent study, researchers wanted to see if heightened brain activity would normalize once patients regained their weight. Using a novel monetary reward task during functional magnetic resonance brain imaging, a recent study tested how brain reward learning in adolescent anorexia nervosa changes with weight restoration.

The researchers examined 21 female adolescents with anorexia nervosa about 16 years of age before and after treatment, compared to 21 participants without the eating disorder. Brain function was tested using the reward prediction error construct, a computational model for reward receipt and omission related to motivation and neural dopamine responsiveness.

The results showed that reward responses were higher in the adolescents with anorexia than in those without it. The anorexia group exhibited greater brain response 1) for prediction error regression within the caudate, ventral caudate/nucleus accumbens, and anterior and posterior insula, 2) to unexpected reward receipt in the anterior and posterior insula, and 3) to unexpected reward omission in the caudate body.

The more severely the brain was altered, the more difficult it was to treat the illness — to gain weight. Even after treatment, the brains of anorexia patients had not fully recovered.

According to Guido Frank, M.D., senior author of the study and associate professor of psychiatry and neuroscience at the University of Colorado School of Medicine, the neurotransmitter dopamine might be key mediating reward learning and possibly playing a major role in the pathology of the disorder.

The reward responses normalized after weight gain but still remained elevated, indicating that those with anorexia were not cured. Although anorexia nervosa is difficult to treat, studies such as this are revealing more and more exactly what is happening in the brain. By understanding the system, better strategies can be developed to treat the disorder.