Abstract
In humans and all other animals tested, memory consolidation occurs through multiple temporal phases and usually involves more than one neuroanatomical brain region. Genetic dissection of Pavlovian olfactory learning in Drosophila also has revealed multiple memory phases. While emerging studies suggest roles for antennal lobes (ALs) and dorsal paired medial (DPM) neurons, the predominant view holds that the long-term memory (LTM) is consolidated only in the mushroom body (MB) neurons. In this study, I demonstrate an acute requirement of NMDARs for LTM consolidation outside the MB. Knocking down, with RNAi, dNR1 or dNR2 in cholinergic large-field neurons, the R4m subtype, of the ellipsoid body (EB) specifically disrupts LTM. Knockdown of NMDARs in MB disrupts the middle term memory while leaving LTM intact. These results strongly suggest an anatomical site outside of MB involved in LTM consolidation, for the first time, therefore imply the existence of distributed regions for olfactory memory formation in Drosophila brains. My results also mean that functionally independent memory traces exist at different anatomical sites during memory consolidation. Such evidences for a system-level memory consolidation in an invertebrate imply that the transfer of memory from one brain location to another during memory consolidation may be evolutionarily conserved, in spite of huge anatomical (circuit) differences between flies and mammals.