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Hunger Linked to Risky Decisions, Study

Update Date: Jun 25, 2013 05:58 PM EDT

Are you easily irritated when your stomach is grumbling? A new study reveals that being "hangry" is perfectly normal and can also cause people to make more risky decisions.

Scientists found that having a good meal can affect more than our mood, it can also influence our willingness to take risks.  What's more, this phenomenon is also seen in a variety of species in the animal kingdom.

Researchers found not hunger not only changes behavior, but also modifies pathways in the brain of fruit flies.

Researchers said that animal behavior is significantly affected by the availability and amount of food.  Numerous studies found that the willingness of many animals to take risks increases or declines depending on whether the animal is hungry of full.  For instance, studies have shown that predators only hunt more dangerous prey when they are close to starvation.

This phenomenon has even been documented in humans.  Previous research found that hungry people took significantly more financial risks than their full counterparts.

In the latest study researcher found that fruit flies change their behavior depending on its nutritional state. The insects usually perceive even low quantities of carbon dioxide to be a sign of danger and opt to take flight.  However, rotting fruit and plants -- the flies' main sources of food -- also release carbon dioxide.

In the latest experiment on fruit flies, neurobiologists have discovered how the brain deals with this constant conflict in deciding between a hazardous substance and a potential food source.

In the study, investigators presented flies with environments containing carbon dioxide or a mix of carbon dioxide and the smell of food.  They found that hungry flies overcame their aversion to carbon dioxide significantly faster than fed flies if there was a smell of food in the environment at the same time.

Researchers explain that hungry animals are significantly more willing to take risks than their fed counterparts when there is the prospect of food.

In another experiment, researchers temporarily disabled nerve cells linked to learning and behavior patterns in the brains of flies.  Researchers explain that because aversion to carbon dioxide is an innate behavior, and should therefore be generated outside the mushroom body in the fly's brain.  Nerve cells in the mushroom body were linked only with earning and behavior patterns that are based on learned associations. The findings revealed that hungry flies with temporarily disabled nerve cells no longer showed any reaction to carbon dioxide.  However, the behavior of fed flies remained the same and they still avoided the carbon dioxide.

Further analysis revealed that a projection neuron is responsible for transporting the carbon dioxide information to the mushroom body. Researchers explain that this nerve cell is crucial in triggering a flight response in hungry, but not in fed animals.

"In fed flies, nerve cells outside the mushroom body are enough for flies to flee from the carbon dioxide. In hungry animals, however, the nerve cells are in the mushroom body and the projection neuron, which carries the carbon dioxide information there, is essential for the flight response. If mushroom body or projection neuron activity is blocked, only hungry flies are no longer concerned about the carbon dioxide," lead researcher Ilona Grunwald-Kadow said in a news release.

Researchers said the findings suggest that the innate flight response to carbon dioxide in fruit flies is controlled by two parallel neural circuits, depending on how hungry the animals are.

"If the fly is hungry, it will no longer rely on the 'direct line' but will use brain centres to gauge internal and external signals and reach a balanced decision," explained Grunwald-Kadow.

The findings are published in the journal Current Biology.

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