Why do we sometimes keep eating even when we’re full, and other times turn down food completely? Why do we crave salty things at certain times and sweets at others? New neuroscience research from the University of Delaware may hold the answers, revealing insights from an unexpected source: the tiny brain of a fruit fly.
Lisha Shao, an assistant professor in the Department of Biological Sciences at the University of Delaware, has uncovered a neural network in fruit flies that represents an early step in how the brain decides—minute by minute—whether a specific food is worth eating. This groundbreaking work was published in the journal 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 explained. This discovery sheds light on the previously murky connection between taste and the brain systems that determine which foods we pursue, learn, and remember.
Tiny Brains, Big Insights
Fruit flies, despite their minuscule brains, use many of the same chemical messengers and basic building blocks found in mammals and humans. This makes them a valuable model for understanding the general rules the human brain uses to process rewards. As behavior is determined by our brains, understanding the neurological circuits involved in the reward system’s early stages can help scientists map the entire system and identify where unhealthy behaviors, such as eating disorders, may originate.
“Reward drives almost everything we do,” Shao noted. “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.”
Unraveling the Taste-Reward Connection
Scientists have long understood how the body decides whether a food is sweet, salty, bitter, or umami. Neurons in the taste buds detect these flavors, and the brain assigns them default meanings. However, taste is only part of the story. The challenge has been explaining how the brain interprets the meaning of a taste—how the same food can feel rewarding one moment and not the next, depending on context.
From an evolutionary perspective, sweetness usually signals that a food is nutritionally important for survival. Yet, we don’t always eat sweet things, even when they’re readily available. “If you just ate breakfast and you’re full, you’ll say no to a donut,” Shao said. “But that doesn’t mean donuts aren’t rewarding. It means the brain is integrating context, internal state, and past experience.”
Like humans, fruit flies exhibit sophisticated food behaviors. They won’t eat when they’re full. Shao’s team discovered that activating a pair of neurons—dubbed Fox neurons because of their fox-ear shape—in the flies’ brains prompted them to consume significantly more food, even after they had just eaten.
From Flies to Safer Treatments for Humans
Understanding the neural connections that assign values to experiences in humans can illuminate what happens when the reward processing system malfunctions, leading to disorders like addiction, anorexia, or binge eating. “Behavior starts with value,” Shao emphasized. “If we understand how value is built, we can better understand why we do what we do, and why sometimes it goes wrong.”
In today’s fast-paced, technology-driven world, our brains are constantly bombarded with new experiences, complicating the assignment of correct values. “Our brains evolved to process natural rewards like food and reproduction,” Shao said. “But now we’re surrounded by artificial rewards—endless short videos, processed foods—that the brain was never designed to handle.”
Implications for Treatment
Many current treatments for psychiatric and neurological disorders focus on brain chemical messengers, such as dopamine and serotonin, which regulate mood and bodily functions. Imbalances can lead to mental health issues, and medications aim to restore chemical balance. However, as Shao pointed out, this approach treats the brain like a “chemical soup.” “If dopamine is too high, we try to lower it everywhere. If serotonin is too low, we raise it everywhere,” she explained.
This broad approach can result in significant side effects and inconsistent outcomes. Shao’s research opens doors to understanding the full scope of the reward processing system and developing more targeted and safer treatments. “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.”
The implications of this research extend beyond fruit flies, offering a promising avenue for addressing complex human behaviors and disorders. As scientists continue to explore these neural circuits, the potential for breakthroughs in treatment and understanding grows ever closer.
