Animals exhibit different behavioral responses to the same sensory cue depending on their state at a given moment in time. How and where in the brain are sensory inputs combined with internal state information to select an appropriate behavior? Here we investigate how food deprivation affects olfactory behavior in Drosophila larvae. We find that certain odors reliably repel well-fed animals but attract food-deprived animals. We show that feeding state flexibly alters neural processing in the first olfactory center, the antennal lobe. Food deprivation differentially modulates two separate output pathways that are required for opposing behavioral responses. Uniglomerular projection neurons mediate odor attraction and show elevated odor-evoked activity in the food-deprived state. A multiglomerular projection neuron mediates odor aversion and receives odor-evoked inhibition in the food-deprived state. The switch between these two pathways is regulated by the lone serotonergic neuron in the antennal lobe, CSD. Our findings demonstrate how flexible behaviors can arise from state-dependent circuit dynamics in an early sensory processing center. ### Competing Interest Statement The authors have declared no competing interest.

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