A brain imaging study suggests improper neural connections cause women with anorexia nervosa to have poor perceptual awareness of body shape.
German researchers also discovered that the weaker the brain connection, the greater the misjudgement of a body’s profile.
Normally, when people see pictures of bodies, a whole range of brain regions are active. This network is altered in women with anorexia nervosa.
Using functional magnetic resonance imaging (fMRI), researchers were able to determine that two regions important for the processing of body images were more weakly connected in anorexic women than in healthy women.
The stronger this “connection error” was, the more overweight the respondents considered themselves.
“These alterations in the brain could explain why women with anorexia perceive themselves as fatter, even though they are objectively underweight” said Prof. Dr. Boris Suchan.
In the study reported in the journal Behavioral Brain Research, researchers tested 10 anorexic and fifteen healthy women of similar age.
To begin, all the women were asked to view several different silhouettes and then document on a computer which silhouette corresponded best to their own body shape.
Ten control subjects who did not participate in the MRI scan answered the same question by matching a photo of the test subject to the right silhouette.
Both healthy and anorexic women estimated their body shape differently than outsiders: healthy subjects rated themselves as thinner than the control subjects. Anorexic women on the other hand perceived themselves to be fatter than the control subjects did.
Researchers then scanned and recorded the brain activity of the 25 participants while they observed photos of bodies.
Scientists paid particular attention to activity in the “fusiform body area” (FBA) and the “extrastriate body area” (EBA) of the brain because previous studies showed that these brain regions are critical for the perception of bodies.
Researchers then calculated the so-called effective connectivity between the FBA and EBA in both hemispheres. This is a measure of how much the activity in several brain areas is temporally correlated.
A high degree of correlation is indicative of a strong connection.
The scientists discovered the connection between the FBA and EBA was weaker in women with anorexia nervosa than in healthy women.
In addition, the researchers found a negative correlation between the EBA-FBA connection in the left hemisphere and the misjudgement of body weight: the weaker the effective connectivity between the EBA and FBA was, the fatter the subjects with anorexia falsely estimated themselves to be.
“In a previous study we found that there are structural changes in the brains of patients with anorexia,” Suchan said. “They have a lower density of nerve cells in the EBA. The new data shows that the network for body processing is also functionally altered.”
The EBA, which has a lower cell density in anorexics, is also the area that stood out in the connection analysis: it receives reduced input from the FBA.
“These changes could provide a mechanism for the development of anorexia,” Suchan said.
Source: Ruhr-University Bochum