How a specific memory is consolidated in the mushroom body output layer
Acquired associative memories are thought to transition between short and long-term phases. Due to the large amount of neurons and brain areas potentially involved in memory consolidation processes in vertebrates, analysis of how memory engrams persist and stabilize at defined sites, or get represented into network activity, has been largely confined to theoretical models. Drosophila with its reduced numerical neural complexity, genetic accessibility at single cellular precision, established in vivo imaging protocols and defined, well studied memory phases could help to overcome such boundaries. Our work has recently made significant contributions towards understanding the memory writing and reading logic at a third order olfactory neuropile, the mushroom bodies, in Drosophila. We discovered that the mushroom bodies are divided into individual reinforcement and readout ‘zones’ that could be attributed to distinct memories. However, our model does not inform us about how memories would get consolidated. Recent evidence suggests that zonally organized dopaminergic neurons exhibit ongoing basal activity that is crucial for memory consolidation while interacting with single zonally restricted mushroom body output neurons (MBONs). Protein synthesis in MBONs is required to stabilize memories and different MBONs are needed for the retrieval of various consolidated memories. Indeed, MBON to MBON connectivity studies have provided clues for information transfer and plastic adaptation at the network level within the mushroom bodies. We will here probe MBONs for activity requirements during the consolidation process for memories of aversive and appetitive nature. We aim at pinpointing time windows of increased neural activity to individual MBONs during the consolidation phase and test the hypothesis that memory consolidation depends on network activity across mushroom body zones. Finally, we aim at artificially changing activity profiles within MBONs during consolidation to boost or decrease memory performance or misguide a fly’s behavior. How memories are consolidated in a reduced complexity system will be informative for tackling questions in more complex vertebrate systems and from a theoretical perspective throughout this consortium.
Image Flies in vial (l) and magenta-stained mushroom body (r). Courtesy of Eric Reynolds