ANTERIOR OLFACTORY NUCLEUS ACTIVITY DYNAMICS IN CONTEXT-DEPENDENT ODOR MEMORY

The anterior olfactory nucleus (AON) is a central component of early olfactory processing. It modulates odor-guided behaviours by integrating bottom-up olfactory bulb (OB) inputs with top-down hippocampal (HPC) inputs. We previously demonstrated the necessity of HPC-AON circuits for episodic odor memory, highlighting the AON as a repository for odor-context engrams. However, it remains unknown how odor memory processes are represented in spatiotemporal dynamics of AON activity. In this study, we coupled in vivo fiber photometry and optogenetics with an olfactory go/no-go paradigm to assess how AON activity reflects the development and expression of odor memories. We found that distinct AON subregions showed distinct temporal dynamics of activity depending on task complexity: dorsal AON exhibits pre-odor activation in two-chamber but not in single- chamber go/no-go tasks, and this pre-odor activity is strongest when context- dependent odor memory is required. Optogenetic inhibition of this pre-odor AON activity impairs context-dependent odor memory encoding and short-term retrieval, but spares context-independent odor memory. These findings support our hypothesis that the AON stores odor-context memories. To further characterize how AON activity encodes odor memories, we coupled one-photon calcium imaging with passive odor exposure assays. Preliminary analyses suggest that AON activity contains structured information about odor identity through correlated response patterns. This study provides novel insight into the crucial role of AON circuits in odor-context memory, which deepens our understanding of how the brain processes sensory elements of episodic memory.