Hunger Changes Decision Making and Risk Perception

If you want to make a good deal, you'd better make sure that the person you're negotiating with is well fed. New research reveals that hunger not only affects decision making, but also affects risk perception.

Hunger affects the behavior of species all across the animal kingdom. Past studies have shown that animals are willing to take risks or not depending on whether or not they're full. For example, a predator only hunts more dangerous prey when it's close to starvation. In humans, increasingly hungry subjects took more financial risks than their full colleagues in a study.

In order to study this behavior a little more closely, the scientists turned to the fruit fly, Drosophila. These insects usually perceive even low quantities of carbon dioxide to be a sign of danger, which causes them to take flight. Yet this creature's main source of food, rotting fruit and plants, also releases carbon dioxide. Now, though, scientists have discovered how the brain of these insects deals with this constant conflict in deciding between a hazardous substance and a potential food source.

The researchers placed hungry and fed fruit flies in two different situations. In one scenario, the fruit flies were presented with carbon dioxide. In another, they were presented with a mix of carbon dioxide and the smell of food. The scientists found that the fruit flies that were hungry overcame their aversion to the gas far more quickly than the sated fruit flies if there was the smell of food in the environment.

But how does the brain decide between risk and hunger? Avoiding carbon dioxide is an innate behavior, which means that it should be generated outside the mushroom body in the fly's brain. Yet when the scientists temporarily disabled these nerve cells, hungry flies no longer showed any reaction whatsoever to carbon dioxide. The fed flies, in contrast, remained the same.

It turned out that a projection neuron which transports the carbon dioxide information to the mushroom body is crucial for triggering a flight response in hungry, but not in fed animals. The findings reveal that the innate flight response is controlled by two parallel neural circuits, depending on how sated the creatures are.

"It is fascinating to see the extent to which metabolic processes and hunger affect the processing systems in the brain," said Ilona Grunwald-Kadow, the researcher who headed the study, in a news release.

The findings are published in the journal Current Biology.