Scientists have discovered that the brains of anorexics respond differently to certain tastes than the brains of control subjects, possibly explaining why sufferers eschew tasty foods.
Writing in this month's Neuropsychopharmacology, University of Pittsburgh researcher Walter Kaye, Angela Wagner and their colleagues brain scanned sixteen recovered anorexics as they were fed a sweet drink containing 10% sucrose, or just plain water, and compared their patterns neural activity with those detected in sixteen healthy women. Amongst the normal subjects, whenever the sugary stimulus was presented, a region of the brain's grey matter known as the insula cortex lit up. The increase in activity in this region also tallied with the subjects' reports of how pleasant they found the sweet liquid to be. But amongst the recovered anorexics the levels of activity detected in the insula were much lower in response to both the plain water and sugar solutions.
The finding fits in with previous studies on this part of the brain which have shown that the insula seems to be involved in processing how the "value" of certain foods might affect the body. For instance animals with damage to this brain region lose the ability to avoid foods that have previously made them sick, and fail to stop eating high-calorie foods when they are full. This suggests that the insula may help to translate the experience of eating foods into pleasurable sensations, but this function seems to be abnormal amonst people with anorexia, possibly explaining why they avoid "pleasurable" foods, fail to respond appropriately to hunger and lose so much weight.
"We know that the insula and the connected regions are thought to play an important role in interoceptive information, which determines how the individual senses the condition of the entire body," says Kaye.