Drosophila Dorsal Paired Medial Neurons Provide a General Mechanism for Memory Consolidation

Memories are formed, stabilized in a time-dependent manner, and stored in neural networks. In Drosophila, retrieval of punitive and rewarded odor memories depends on output from mushroom body (MB) neurons, consistent with the idea that both types of memory are represented there. Dorsal Paired Medial (DPM) neurons innervate the mushroom bodies, and DPM neuron output is required for the stability of punished odor memory. Here we show that stable reward-odor memory is also DPM neuron dependent. DPM neuron expression of amnesiac (amn) in amn mutant flies restores wild-type memory. In addition, disrupting DPM neurotransmission between training and testing abolishes reward-odor memory, just as it does with punished memory. We further examined DPM-MB connectivity by overexpressing a DScam variant that reduces DPM neuron projections to the MB alpha, beta, and gamma lobes. DPM neurons that primarily project to MB alpha' and beta' lobes are capable of stabilizing punitive- and reward-odor memory, implying that both forms of memory have similar circuit requirements. Therefore, our results suggest that the fly employs the local DPM-MB circuit to stabilize punitive- and reward-odor memories and that stable aspects of both forms of memory may reside in mushroom body alpha' and beta' lobe neurons.