Drosophila larval Odd neurons process innate and learned information to regulate chemotaxis behavior

Adaptive decision-making emerges from the integration of innate preferences and learned experiences to guide behavior. Using Drosophila larvae as a model, we investigated the neural circuitry underlying olfactory processing, focusing on Odd neurons--a distinct neuronal population that receives innate valence signals from Kenyon cells (KCs) rather than lateral horn inputs. Through larval connectomics, trans-tango labeling, and detailed anatomical analyses, we found that Odd neurons integrate innate valence through dendro-dendritic connections with KCs and learned valence via inhibitory inputs from mushroom body output neurons (MBON-g1 and MBON-g2). Optogenetic silencing of Odd neurons disrupted larval chemotaxis and associative memory by selectively impairing memory retrieval, while sparing memory formation, and by altering the turn rate during navigation. These results suggest that Odd neurons serve as an integrative hub, converging innate olfactory cues with learned reinforcement signals to fine-tune navigational choices. This study illuminates how distinct neural pathways converge in the larval brain to shape behavior, offering novel insights into decision-making circuitry that may extend to more complex nervous systems.