Summary: For a fruit fly, a single bite can determine survival. New research overturns the idea that “sweet” and “bitter” taste signals travel entirely separate neural routes. Scientists have identified a compact decision-making hub—one pair of neurons—that integrates opposing taste cues to steer feeding behavior.
These neurons, called subesophageal LK neurons (SELKs), act like a biological scale, weighing caloric benefit against potential toxicity and choosing the appropriate behavioral response.
Key Facts
- SELK—The central decision cell: The subesophageal LK (SELK) neurons are the first identified cells that receive input from both sweet- and bitter-sensing pathways simultaneously.
- Asymmetric signal strength: Inputs from bitter-sensing neurons produce a stronger activation of SELKs than sweet inputs, biasing the system toward avoiding toxins over seeking calories.
- Two chemical messengers, two outcomes: SELKs use different communicators depending on input strength:
- Sweet-dominant input: Triggers release of a fast neurotransmitter that promotes feeding.
- Bitter-dominant input: Triggers release of the neuropeptide leucokinin (LK), which suppresses feeding immediately.
- Conserved strategy: Similar circuitry has been reported in mice, suggesting that this compact, cell-level decision architecture may exist across species.
- Genetic mapping tool: The trans-Tango toolkit, developed in the Barnea lab, made it possible to trace which sensory neurons connect to SELKs and revealed this unexpected integration.
Source: Brown University
Why taste matters for the fruit fly
Taste determines life or death for Drosophila. These flies have taste receptors not only on their mouthparts but also on their legs, wings and abdomen, allowing them to evaluate potential food the instant they land. Sweet signals indicate calories and encourage feeding; bitter signals warn of toxins and trigger avoidance.
Research from the lab of Brown University professor Gilad Barnea identified a pair of SELK neurons that perform this crucial computation. The findings, published in Nature Communications, explain how a single neural element can resolve opposing taste cues and decide whether the fly eats or retreats.
“A single wrong feeding decision can be fatal for a fly,” said Barnea, professor of neuroscience and director of the Center for the Neurobiology of Cells and Circuits at Brown’s Carney Institute for Brain Science. “This mechanism highlights the surprising computational power of individual neurons.”
Lead author Doruk Savaş, who began this work in Barnea’s lab and is now at Harvard University, noted that trans-Tango unexpectedly revealed neurons that received input from both sweet and bitter sensory populations. That observation prompted experiments to test how those inputs influence a single downstream neuron.
Electrophysiology and behavioral assays showed that bitter inputs produce stronger activation of SELKs than sweet inputs. Depending on the level of activation, SELKs release different chemical signals: a cholinergic neurotransmitter promotes feeding when activation is modest, whereas strong activation triggers LK neuropeptide release and immediate feeding suppression.
“There are many circuit-level strategies a brain can use to make choices,” Barnea said. “Finding that one pair of neurons can implement a reliable, flexible decision between eating and avoiding is an elegant, efficient solution.”
Funding: Supported by the National Institutes of Health (RO1DC020703, F31DC019540).
Key Questions Answered:
A: Taste receptors on the legs, wings and abdomen provide an immediate assessment of a surface when the fly lands. This early detection sends information to SELKs before the mouthparts engage, helping the fly avoid toxins or exploit a food source quickly.
A: Evolution favors safety: a missed meal costs energy, but ingesting toxins can cause death. Biasing the system so that bitter signals dominate reduces the risk of lethal mistakes.
A: Potentially. If human brains use a comparable single-neuron gatekeeper to weigh reward versus risk, understanding its mechanisms could point to new targets for treating overeating or altered taste sensitivity. Further research is required to confirm such parallels.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full.
- Additional explanatory context was added by staff editors.
About this neuroscience research news
Author: Corrie Pikul
Source: Brown University
Contact: Corrie Pikul – Brown University
Image credit: Neuroscience News
Original Research: Open access.
“Feeding decision-making by a single neuron via disparate neurotransmitters” by Doruk Savaş, Angel M. Okoro, Rareș A. Moșneanu, Anthony M. Crown, Zeyu Chang, Rebecca Siegel, Altar Sorkaç, Meet Zandawala & Gilad Barnea. Nature Communications.
DOI: 10.1038/s41467-026-69443-8
Abstract
Feeding decision-making by a single neuron via disparate neurotransmitters
Animals use taste information to decide whether to accept nutritious substances or avoid harmful ones. While some neurons in gustatory circuits respond to both attractive and aversive cues, the mechanism by which a single neuron resolves inputs with opposing valences has been unclear.
This study examines how the neuropeptide leucokinin (LK) in Drosophila melanogaster shapes gustatory processing and feeding behavior. The authors identify subesophageal LK neurons (SELKs) as direct synaptic partners of gustatory receptor neurons and demonstrate functional connectivity between these groups.
Experimental results show that SELKs influence bitter avoidance via LK release and drive feeding promotion through acetylcholine-dependent signaling. Strong activation of SELKs triggers LK release and feeding suppression; weaker activation favors acetylcholine signaling and promotes food intake.
Overall, the findings reveal that a single pair of SELK neurons can differentially control opposing feeding behaviors by switching between distinct neurotransmitters, providing a compact and efficient neural solution for balancing reward and risk.