The differential requirement of mushroom body α/β subdivisions in long-term memory retrieval in Drosophila

The mushroom body(MB),a bilateral brain structure pos-sessing about 2000-2500 neurons per hemisphere,plays a central role in olfactory learning and memory in Dros-ophila melanogaster.Extensive studies have demonstrat-ed that three major types of MB neurons(α/β,α’/β’andγ)exhibit distinct functions in memory processing,including the critical role of approximately 1000 MBα/βneurons in retrieving long-term memory.Inspired by recent fi ndings that MBα/βneurons can be further divided into three subdivisions(surface,posterior and core)and wherein theα/βcore neurons play an permissive role in long-term memory consolidation,we examined the functional differ-ences of all the three morphological subdivisions of MBα/βby temporally precise manipulation of their synaptic outputs during long-term memory retrieval.We found the normal neurotransmission from a combination of MBα/βsurface and posterior neurons is necessary for retrieving both aversive and appetitive long-term memory,whereas output from MBα/βposterior or core subdivision alone is dispensable.These results imply a specifi c requirement of about 500 MBα/βneurons in supporting long-term memory retrieval and a further functional partitioning for memory processing within the MBα/βregion.