A young woman who lost the sensation of hunger after a stroke may help us explain how we regulate food intake, and improve our understanding of one of the most mysterious areas of the brain.
The unique case study of what has happened to her might even help us develop new treatments for obesity.
The 28-year-old Canadian woman was hospitalised after feeling weak on one side of her body and having trouble speaking. Brain imaging showed that she had experienced a stroke in a brain area called the insular cortex.
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Soon after having the stroke, the woman noticed a strange aftertaste of iron whenever she ate anything. This resolved after a few weeks, but then she noticed that she never felt hungry any more, even when she hadn’t eaten for a long time.
Because she wasn’t hungry, the woman often forgot to eat and lost more than 10 kilograms in weight. “She had no way of knowing when it was time to eat and had to create a meal schedule,” says Benjamin Hébert-Seropian at the University of Quebec in Montreal, Canada, who wrote her case report.
The woman could still taste, smell and sense the texture of food, but found she only tended to eat about half as much as usual because she no longer enjoyed eating. Even chocolate, her favourite food, gave her no pleasure.
The woman’s hunger finally came back about 15 months after the stroke.
Her case adds to emerging clues that the insular cortex – also known as the insula – is involved in the brain circuits that motivate us to eat, says Hébert-Seropian.
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.
HĂ©bert-Seropian and his colleagues have recently found that people who have their insulas removed to treat severe epilepsy can also have reduced appetite, which strengthens the idea that the insula is involved in appetite regulation.
Together, these findings could pave the way for new weight-loss treatments for obesity, says HĂ©bert-Seropian.
For example, it may be possible to use psychological techniques to improve people’s understanding of their bodily signals and know when they are full, or to send electric currents to the insula to prevent overeating, he says.
Livneh agrees this is a possibility but says it will be important not to affect other behaviours that the insula helps to motivate. “You might want to reduce motivation for eating food, but you don’t want to reduce motivation for other aspects of life because you risk turning people into listless zombies,” he says.
Neurocase
