It's not a mystery how both hunger and a full stomach can make noticeable changes to human behavior. To take this a step further, scientists from Max Planck Institute of Neurobiology have conducted a new study, which explains how hunger could lessen the individual's ability to make decisions and affect the perception of risk.

The scientists used fruit flies (Drosophila) for the study, and demonstrated how this theory works well in animals too.

Unlike humans, animals are constantly faced with hurdles and decision-making troubles to help them decide their course of action and survive. The extent to which an animal is willing to take risks could determine whether the animal would be hungry or full, the researchers explain.

To elaborate on this, the researchers explained how the fruit fly needs to change its behavior to obtain food.

Drosophila usually perceives low carbon dioxide levels to a sign of danger, and opts to take a flight. However, rotting fruits and plants, which form the basic diet of the drosophila, also emit carbon dioxide.

To detect how the drosophila brain manages to detect the source of carbon dioxide as its food or a danger, neurobiologists at the institute have worked on a number of small experiments.

In these experiments, the drosophilas were subjected to a mixture of carbon dioxide gases and the smell of their food. They noticed that the drosophilas that were hungry, overcame the fear of being faced by a danger, and readily came to feed, as opposed to the drosophilas that were full.

"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 (a part of the brain) 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," Ilona Grunwald-Kadow, lead author of the study, explained.

"If the fly is hungry, it will no longer rely on the 'direct line' but will use brain centers to gauge internal and external signals and reach a balanced decision. It is fascinating to see the extent to which metabolic processes and hunger affect the processing systems in the brain," she added.