“You’re not yourself when you’re hungry” isn’t just a memorable Snickers ad slogan, it also happens to be true. Our brains process information slightly differently depending on our internal state, whether we’re hungry, thirsty, in pain, etc. Of course, the same is true of other animals, even those with relatively simple brains like fruit flies. Now, a new study published in Current Biology finds that hunger may be involved with triggering cravings for alcohol (at least in the aforementioned fruit flies).
Why study fruit flies to understand human brains?
For starters, there’s a much broader toolkit available (including a map of the entire fly brain and a slew of genetic tools). It also helps to start with less complex neural circuitry. “If we can understand at a smaller level how an organism like a fly can remember alcohol, that is a step forward to understanding how humans associate cues with alcohol and can provide hints at how we can prevent relapse and treat addiction,” study author Lewis Sherer of Brown University explained in a statement.
Read more: “Do Calorie‑Restricted Diets Work?”
When humans are hungry, we produce the fight-or-flight neurotransmitter norepinephrine, and fruit flies have their own version of it called octopamine. Sherer and his fellow neuroscientists wanted to investigate what role octopamine plays in memory and sensory processing related to alcohol, so they trained fruit flies to associate a specific odor with ethanol. Food-deprived flies learned to associate the odor with ethanol much more quickly, which the team traced to a single octopamine-producing neuron: VUMa3(mx). Genetically silencing this neuron was enough to erase the effect.
Here’s how it works: When flies are satiated, preference for ethanol is governed by an entirely different set of neurons. When flies are hungry, the neuron VUMa3(mx) joins the party, acting on alcohol memory pathways. In other words, hunger can rewire the neural circuitry of the brain in a way that makes flies more susceptible to alcohol cravings.
According to the team, these findings could have implications for understanding addiction in humans, specifically how we respond to environmental cues. “For example, perhaps you usually pass by a bar you like on your way home from work every day,” study author Karla Kaun of Brown University explained. “But maybe today you’re hungry after skipping lunch. You’re more likely to notice that cute sign and feel like stopping to have a drink. The cute sign, which didn’t entice you when you weren’t hungry, can trigger your craving for alcohol.”
That makes the sidewalk bar signs advertising beer soup as the “soup of the day” doubly pernicious. 
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Lead Image: Nanzeeba / Shutterstock