Communication from Learned to Innate Olfactory Processing Centers Is Required for Memory Retrieval in Drosophila

The behavioral response to a sensory stimulus may depend on both learned and innate neuronal representations. How these circuits interact to produce appropriate behavior is unknown. In Drosophila, the lateral horn (LH) and mushroom body (MB) are thought to mediate innate and learned olfactory behavior, respectively, although LH function has not been tested directly. Here we identify two LH cell types (PD2a1 and PD2b1) that receive input from an MB output neuron required for recall of aversive olfactory memories. These neurons are required for aversive memory retrieval and modulated by training. Connectomics data demonstrate that PD2a1 and PD2b1 neurons also receive direct input from food odor-encoding neurons. Consistent with this, PD2a1 and PD2b1 are also necessary for unlearned attraction to some odors, indicating that these neurons have a dual behavioral role. This provides a circuit mechanism by which learned and innate olfactory information can interact in identified neurons to produce appropriate behavior. [Display omitted] •Specific Drosophila lateral horn neurons mediate innate attraction to food odors•The same neurons receive plastic odor information from the mushroom body•Recall after associative learning depends on reduced drive to lateral horn neurons•Connectomics circuit for integration of learned and innate odor representations Sensory stimuli can engage both learned and innate behaviors. Dolan et al. identify neurons in Drosophila that directly integrate unlearned and plastic odor representations; they are required for innate approach to food odors but also learned aversive recall.