A 28-year-old Canadian woman had a stroke in a part of the brain known as the insular cortex—and after she recovered, she found she'd lost any sense of hunger.
She lost over 10 kilograms because she'd forget to eat. As this piece in Revyuh notes, when doctors examined her…
… they found that even with a lack of calories, the woman did not feel any physiological signals that it was time for her to eat, for example, a rumbling in her stomach. Despite the fact that the patient did not have problems with the sense of taste, smell and texture of food (only in the first two months she complained of a metallic aftertaste after eating any food), even her favorite foods and products, for example, chocolate.
There's a paper in Neurocase describing her experience, and a paywalled story in New Scientist notes that the brain region where her stroke occurred (sometimes just called "the insula") is still a mystery to science …
The insula is one of the least understood parts of the brain because it is tucked deep inside the folds of this organ. It appears to have a diverse set of functions, involved in consciousness, empathy and pain. But there is growing evidence that it also helps to process signals from different parts of the body in order to assess our internal bodily state – for example, whether we are hungry or full, warm or cold, or tired or rested.
If the insula senses that something is out of balance – our blood sugar levels are too low, say – it tries to amend this. For example, it may work with other parts of the brain to create a feeling of hunger that encourages eating, says Yoav Livneh at the Weizmann Institute of Science in Israel.
"In this woman's case, her brain would still have been receiving signals that she was missing calories, but because of the damage to her insula she wouldn't have been aware of them," he says.
As the scientists pondering this rare case note, it's possible — knowing now the role the insula has in sensations of hunger — that one could design a drug that targets its functioning and artificially reduces hunger, for weight loss. The problem is that because the insular seems involved in lots of other sensations and bodily self-regulation, you might cause new and weirder problems if you mucked with the insula's functioning.
More evidence of a what a crazy mystery the brain is.
(Public domain photo of fridge courtesy the US Department of Agriculture)