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What do we, humans, have in common with other animals, including fruit flies? A lot more than we'd probably like to think, it turns out. Though the fruit fly's organism is tiny and far less complex than the human body, it possesses the ability to do some pretty advanced stuff, including detecting carbon dioxide levels.
The rotting produce fruit flies consume emits some carbon dioxide, but higher levels of carbon dioxide usually indicate that a breathing — and therefore potentially dangerous — life form is somewhere nearby. When well-fed, fruit flies steer well clear of environments with higher carbon dioxide levels.
It's a different story when they're hungry, though! A study discovered a specific neuron, something that biologically programs fruit flies to ignore carbon dioxide as danger sign when they're hungry.
Though not through the same mechanism, that exact phenomenon can be observed pretty much throughout the animal world. Hungry predators are far more bold and dangerous than their well-fed counterparts, because they are more willing to take risks. Why? That's hardly a difficult question to answer — food is the stuff of life, and when its supply is in danger, it begins taking priority over all else, on a very primal, biological level.
What does that mean for humans, though? Arranged in complex societies and possessing more advanced decision-making skills than any other animal, you'd think that we'd be slightly different to, say, fruit flies. To attain long-term survival and well-being, humans need so much more than food and water alone, after all! Hunger also comes in rather many different levels, ranging from famine-level starvation to the kind of stomach rumbling you may experience when you are on a calorie-restricted weight loss diet. Hunger can be chronic, or occasional. How does it affect our decision-making skills?
New Study Confirms: Hunger Leads To Poor Decisions
So, fruit flies have pinpointed neurons in their tiny bodies that biologically over-ride risk aversion when they are hungry. Just as avoiding high-carbon dioxide environments makes sense for fruit flies, delayed gratification is an essential quality in humans and some other animals. This ability means that we know that simply acting on impulse by doing what our brain tells us to do right now is a bad idea.
Some people, of course, are better at delaying gratification than others, and impulsivity is associated with a range of mental disorders, including ADHD, alcohol abuse disorder, and obsessive compulsive disorder. Where does food come into the picture? Since previous studies (more about that later) already suggested that there was a link between hunger and impulsivity, researchers from the Sahlgrenska Academy of the University of Gothenburg in Sweden wanted to find out more.
The catch is that their experiments involved rats rather than humans, but rats also have ghrelin.
In the experiment, rats were first trained to get rewards for either pressing a lever or not doing so. The reward was food, of course. The rats would get more food if they waited a while than if they collected their reward right away. Researchers then injected ghrelin directly into the lab rats' brains to simulate the condition of being hungry.