The images showed that the former anorexia patients had increased activity in brain areas that make dopamine.
Dopamine is a chemical involved in weight, feeding behaviors, reinforcement, and reward.
"This finding might help explain why individuals with anorexia nervosa are able to lose weight, resist eating, overexercise, are protected from substance abuse, and are insensitive to normal rewards," write the researchers.
Their study appears in Biological Psychology's online edition.
Anorexia is an eating disorder with both physical and emotional traits including:
- Severely limited food intake
- Distorted body image
- Refusal to maintain a normal body weight
- Intense fear of gaining weight despite being very underweight
Long-term or severe anorexia can lead to serious health problems. It can even be fatal.
Anorexia's cause is not known. Recovery is possible with proper treatment.
Both men and women can have anorexia or other eating disorders.
Women with anorexia may have infrequent or absent menstrual periods. They may not be able to have normal menstrual cycles until they regain a healthy weight.
An estimated 0.5% to 3.7% of women have anorexia at some point during their lives, states the web site of the National Institute of Mental Health (NIMH). The NIMH does not provide numbers for men with anorexia.
"When they are ill, people with anorexia don't seek or respond to the kinds of comforts and pleasures most of us enjoy, including food," says researcher Walter Kaye, MD, in a news release.
"They also resist and ignore feedback that signifies their precarious state of health," he continues. "They don't see an emaciated figure in the mirror. They ignore the most obvious warning signs and dismiss comments from loved ones that suggest they are seriously and medically ill.
"People with anorexia nervosa have extreme self-denial, not only of food, but often of many comforts and pleasures in life, yet [they] can be very energetic and productive," Kaye says.
"Taken together, the alterations in the dopamine system may help explain the tell-tale symptoms of anorexia."
Kaye works at the University of Pittsburgh's medical school.
About the Study
None of the women had active anorexia. The researchers took that approach because malnourishment alters brain chemistry, the news release states.
Former anorexia patients had to have been recovered from the eating disorder for at least one year prior to the study. They had maintained a healthy weight and had regular menstrual periods.
The women also had not taken psychological drugs (such as antidepressants) or abused alcohol or drugs for at least three months before the study.
Flip Side of Brain-Obesity Pattern
When other researchers scanned the brains of obese people in the past, they found the opposite pattern.
Obesity was linked to decreased activity in the brains' dopamine reward centers, write Kaye and colleagues.
The findings support the possibility that dopamine binding might be inversely related to weight and eating with anorexia on one end, and obesity on the other end of the spectrum.
They call for larger studies on the topic.