Creating true and false memories from forgotten information in Drosophila

Recovering forgotten memories is a double-edged sword. While regaining access to forgotten information can be advantageous, targeted memory recovery carries the risk of generating false memories. The neuronal processes governing true memory recovery and false memory formation remain poorly understood. Here we show in Drosophila that reminder cues recover forgotten aversive memories. Forgotten memories persist as silent memory traces in behaviorally neutral mushroom body output neurons. From this silent state, reminders recover memory expression by reinstating the original memory trace in mushroom body output neurons that guide behavior. However, manipulating reminders can distort recovery, leading to false memory formation. The effectiveness of this distortion depends on whether misleading reminder cues were present during the original training event. Both true memory recovery and false memory formation are context-dependent processes gated by separable dopaminergic pathways. Together, these findings suggest that forgotten memories can re-emerge through a reconstructive process that flexibly integrates stored information and recent experiences.