Acquiring new memories is a multistage process. Numerous studies have convincingly demonstrated that initially acquired memories are labile and are stabilized only by later consolidation processes. These multiple phases of memory formation are known to involve modification of both cellular excitability and synaptic connectivity, which in turn change neuronal activity at both the single neuron and ensemble levels. However, the specific mapping between the known phases of memory and the changes in neuronal activity at different organizational levels-the single-neuron, population representations, and ensemblestate dynamics-remains unknown. Here we address this issue in the context of conditioned taste aversion learning by continuously tracking gustatory cortex neuronal taste responses in alert male and female rats during the 24 h following a taste-malaise pairing. We found that the progression of activity changes depends on the neuronal organizational level: whereas the population response changed continuously, the population mean response amplitude and the number of taste-responsive neurons only increased during the acquisition and consolidation phases. In addition, the known quickening of the ensemble-state dynamics associated with the faster rejection of harmful foods appeared only after consolidation. Overall, these results demonstrate how complex dynamics in the different representational levels of cortical activity underlie the formation and stabilization of memory within the cortex.
Acquiring new memories is a multi-stage process. Ample of studies have convincingly demonstrated that initially acquired memories are labile, and only stabilized by later consolidation processes. These multiple phases of memory formation are known to involve modification of both cellular excitability and synaptic connectivity, which in turn change neuronal activity at both the single neuron and ensemble levels. However, the specific mapping between the known phases of memory and the observed changes in neuronal activity remains unknown. Here we address this unknown in the context of conditioned taste aversion learning by continuously tracking gustatory cortex (GC) neuronal taste responses from alert rats in the 24 hours following a taste-malaise pairing. We found that the progression of neuronal activity changes in the GC depend on the neuronal organizational level. The population response changed continuously; these changes, however, were only reflected in the population mean amplitude during the acquisition and consolidation phases, and in the known quickening of the ensemble state dynamics after the time of consolidation. Together our results demonstrate how complex dynamics in different representational level of cortical activity underlie the formation and stabilization of memory within the cortex.
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