One Olfactory Neuron Can Drive Two Distinct Behaviors in Fruit Flies

Recent research from Yale scientists has uncovered a fascinating aspect of neural functioning in fruit flies. Contrary to the long-held belief that each neuron has a single purpose, new findings show that a single olfactory neuron can trigger multiple behaviors. Specifically, the study reveals that one neuron can send different electrical signals to two downstream neurons, leading to distinct responses to the same smell.

The research focused on how fruit flies respond to odors associated with rotting fruit, a vital cue for finding food. When a fruit fly detects this smell, a receptor neuron in its antenna transmits a message to a projection neuron, which then passes signals to various third-order neurons in the brain. The scientists examined two such neurons, LHN1 and LHN2, discovering that although they received the same signal, their electrical activity differed—LHN1 maintained a steady response, while LHN2 exhibited a brief spike.

To determine the behavioral significance of these differences, the team genetically modified flies to disable either LHN1 or LHN2. Flies without functional LHN2 failed to speed up in response to higher concentrations of the smell, indicating that LHN2 is involved in speeding movement toward the odor source. Conversely, flies lacking LHN1 still approached the smell but stopped if the concentration dropped. This suggests that these parallel pathways allow the fly to both approach and stay close to a scent source efficiently.

The findings imply that even when the initial sensory input is the same, the neural circuitry can produce multiple behavioral outcomes by diverging downstream signals. This discovery not only enhances our understanding of neural complexity in simple organisms but also hints at broader principles applicable across animals, including humans. Future investigations aim to identify structural markers that predict how neurons transmit signals, potentially leading to new insights into the neural basis of behavior.

Overall, this study exemplifies how multifunctional neurons contribute to flexible responses in the animal brain, adding a new layer of understanding to sensory processing and behavior generation.

Source: https://medicalxpress.com/news/2025-07-olfactory-neuron-triggers-behaviors-fruit.html