EVOLUTION OF HIPPOCAMPAL PLACE REPRESENTATIONS DURING FEW-SHOT EPISODIC LEARNING

In rodents, the location of the animal in physical space can be accurately decoded from hippocampal place cells, which are thought to form a framework for the spatial organization of mnemonic information. But place coding is often studied in the context of repetitive navigation tasks that require tens to hundreds of trials for the animal to learn, whereas episodic memories are formed one-shot and form a durable memory trace that can be recalled over long timescales.
We designed a novel visual VR task that allowed us to examine both place coding during spatial exploration and neural plasticity during episodic learning. In mice trained to run through linear VR hallways, we introduce a cued "Trap" in the environment, which locks the running wheel and prevents the animal from moving for several seconds. On the very next trials mice rapidly adapt their behavior to avoid the Trap, by waiting outside of the cued location until the Trap cue disappears. Chemogenetic inactivation of dorsal CA1 reduced the speed of learning in the memory task
Using 2-photon calcium imaging, we recorded populations of CA1 neurons during behavior and found that novel place fields spontaneously formed around the Trap zone within the first few trials, which orthogonalized the neural representation after the moment the cue appears.
We are now connecting these dynamics to rapid plasticity mechanisms in CA1, and studying its generalization to novel sensory environments. Overall, our work links rapid memory formation and adaptive behavior to concrete and rapid plasticity in hippocampal neural codes.