Researchers at the University of Delaware have identified a neural network in fruit flies that plays a key role in how the brain determines whether to eat certain foods. The study, led by Lisha Shao, assistant professor in the Department of Biological Sciences, was published in Current Biology on January 29.
"Our goal is to understand how the brain assigns value - why sometimes eating something is rewarding and other times it's not," Shao said.
The research sheds light on an early stage of decision-making in the brain regarding food choices. While it has been known that taste buds detect flavors such as sweet, salty, bitter, or umami, less was understood about how the brain interprets these tastes based on context and internal state.
Shao's team discovered that activating a specific pair of neurons—called Fox neurons because of their shape—in fruit flies caused them to eat more food even when they were already full. Additionally, female flies needing protein for reproduction preferred protein-rich foods over sugar, while males and non-reproductive females maintained a balance between both types of food.
"Fox neurons are the earliest known place in flies where value computation for taste begins," Shao said. "Scientists are still debating where that very first step happens in mammals."
The findings suggest that fruit fly brains use similar chemical messengers and structures as those found in mammals and humans. This similarity provides insight into general principles behind reward processing in human brains. Understanding these mechanisms could help explain unhealthy behaviors like eating disorders.
"Reward drives almost everything we do," Shao said. "If the brain assigns the wrong value to something - too much or too little - behavior goes wrong. That's at the heart of many neurological and psychiatric disorders."
Current treatments for psychiatric conditions often target chemical messengers such as dopamine and serotonin throughout the entire brain, which can lead to side effects and inconsistent outcomes.
"If dopamine is thought to be too high, we try to lower it everywhere. If serotonin is thought to be too low, we raise it everywhere."
Shao emphasized that understanding decision-making at the circuit level could enable more targeted treatments for neurological and psychiatric disorders.
"If we understand how decisions are made at the circuit level," she said, "we're one step closer to understanding why they sometimes go wrong, and how to fix them. You can't fix what you don't understand."
