Tracking and decoding individual memories across the brain from creation to long-term storing
How can we vividly remember so many episodes of our life that, by definition, only happened once? During wakefulness, the hippocampus – a brain structure critical for episodic memory – encodes ‘memory traces’ of our experience. During sleep, it “replays” the very same sequences of neurons that were originally activated during the awake episode. Such reactivations are essential for memory consolidation. Over the years, a growing body of studies have unveiled “on-site” reactivations within the hippocampus, sometimes with a neocortical or subcortical “partner” structure, but the overall activity in the brain during these events remains largely unknown. It is unclear whether brain regions replay memory traces all at once or separately. This is a major knowledge gap because numerous cortical and subcortical structures strongly influence memory. In this project, we propose a unique combination of recording and analysis techniques to reveal the whole-brain correlates of hippocampal replay. To achieve this, we will use functional ultrasound, a newly emerging technology which monitors subtle changes in cerebral blood flow over the whole brain at a resolution up to tens of milliseconds, in combination with high-density electrophysiology, the actual gold-standard to record neuronal activity. With the help of a dedicated behavioral task, we will first establish ‘brain maps’ associated with hippocampal replay and then learn how to decode a specific memory trace from these maps. In a second time, we will investigate how emotional valence affects these maps, and in particular how replay patterns are modified over the course of learning. This project has the potential to track across the brain an individual memory trace from its creation to storage, all along consolidation processes. This project will considerably enhance our understanding of memory networks and potentially provide new regions of interest for the study of neurodegenerative disorders.