Requirement of the combination of mushroom body γ lobe and α/β lobes for the retrieval of both aversive and appetitive early memories in Drosophila.

Extensive studies of Drosophila mushroom body in formation and retrieval of olfactory memories allow us to delineate the functional logic for memory storage and retrieval. Currently, there is a questionable disassociation of circuits for memory storage and retrieval during Drosophila olfactory memory processing. Formation of the initial aversive olfactory memory involves mushroom body γ lobe, whereas α/β lobes are reported to be necessary for the retrieval of such memory. In contrast, formation and retrieval of the short-term appetitive olfactory memory appears to involve γ lobe. With the help of newly identified Gal4 lines and of focusing on 3-h memory for both aversive and appetitive conditionings, our reexamination of the retrieval of aversive and appetitive olfactory memories suggests a new view. Blocking γ lobe output led to severe deficiency of aversive early memory retrieval and partial impairment of appetitive early memory retrieval. Interrupting α/β lobe output impaired the retrieval of both aversive and appetitive early memories. The contribution of the γ lobe and α/β lobes appeared to be additive for the retrieval of appetitive early memory. Thus, these results suggest that the retrieval of aversive and appetitive olfactory early memories requires the synaptic outputs from both γ lobe and α/β lobe neurons. This discovery may help us to rethink how aversive and appetitive memories are processed from memory formation to memory retrieval.