The role of cortico-hippocampal interaction in memory consolidation

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System memory consolidation is a brain-wide process that transforms recently encodedliable memories into more stable and long-term memories. The 'two-stage' theory ofmemory process posits that memory consolidation engages bi-directional dialogueduring offline state between the hippocampus, where memory traces are initiallyformed, and the neocortex, where memory traces are eventually stored for long-termretention. During active exploration of a spatial context, sub-populations of neurons inboth CA1 region of hippocampus (HPC) and primary visual cortex (V1) develop spatialsensitivity with experience such that those spatially-modulated neurons would beactivated sequentially along animal's running trajectory. Strikingly, during offline period,the neuronal sequences observed in both regions during active spatial experience can bereplayed in a spatiotemporally coordinated fashion. Disruption of such replay inhippocampus would impair spatial memory performance. These observations led to thepossibility that interaction between the hippocampus and the neocortex around thetime of coherent replay may be instrumental to memory consolidation. However, as oftoday, we are unclear about the nature and direction of cortico-hippocampalinformation flow around the time of replay. Previous evidence suggested that change inneocortical activity can precede replay events. Nevertheless, it is unknown if the V1activity patterns prior to a replay event can selectively influence the memory content toreplay in both hippocampus and V1. Furthermore, we do not know whetherimprovement in coherence of hippocampal-cortical interaction during post-trainingreplay predict the memory performance and fidelity of the learned spatial informationin the V1.To address these research questions, we aim to record from V1 and CA1 of HPC whilemice learn to discriminate two novel linear tracks in virtual reality (VR). Two VR lineartracks with visually-identical landmarks in two positions will be used to trackdevelopment of spatial modulation in V1 over time. We will also train the animal to lickfor a reward when reaching a designated reward zone for each linear track, whichencourages animals to actively discriminate between two linear tracks. By recording V1and CA1 neural activities during multiple learning sessions and post-learning restsessions over the course of several weeks, we would like to examine how replaydynamics and cortico-hippocampal interactions during replay change as thediscriminatory memory performance improves over time.