Scientists have found that anorexic women misjudge their body shapes because of altered connectivity in the brain networks responsible for body perception.
When people see pictures of bodies, a whole range of brain regions are active. Researchers at Ruhr University Bochum in Germany found that this network is altered in women with anorexia nervosa, an eating disorder.
In a functional magnetic resonance imaging study, two regions that are important for the processing of body images were functionally 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 Professor Dr Boris Suchan.
Together with Professor Dietrich Gronemeyer (University of Witten-Herdecke), Professor Silja Vocks (University of Osnabruck) and other colleagues, Suchan tested ten anorexic and fifteen healthy women of similar age.
All the women judged on a computer which of the several different silhouettes 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.
In MRI scanners, researchers recorded the brain activity of the 25 participants while they observed photos of bodies.
Above all, they analysed the activity in the "fusiform body area" (FBA) and the "extrastriate body area" (EBA), because previous studies showed that these brain regions are critical for the perception of bodies.
The neuroscientists from Bochum 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 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.
The study was published in the journal Behavioural Brain Research.