Poster Presentation

Poster C in Poster Session C: Wednesday, August 5, 9:30 – 11:15 am, Kimmel Center, Shorin & Rosenthal Rooms

Complementary learning dynamics within neocortex and hippocampus

Zoya Khan¹, Ivan Voitov¹, Abhishek Shah¹, Attila Losonczy¹, Stefano Fusi¹; ¹Columbia University

Presenter: Zoya Khan

Efficient learning requires the brain to rapidly encode new experiences while leveraging shared structure across related episodes. Although both area CA1 of the hippocampus and the posterior parietal area of the neocortex (PPC) have been implicated in spatial memory, it remains unclear how their specialized computations jointly support learning. Here, we used two-photon calcium imaging to record population activity in CA1 and PPC as mice navigated three sequential virtual reality corridors: one familiar environment followed by two novel environments. Each corridor contained a unique cue configuration and a single hidden reward location that the mice rapidly learned following each corridor change, consistent with a meta-learning rule for flexible navigation. PPC neurons exhibited spatial tuning comparable to CA1, but were preferentially anchored to salient cue transitions, whereas CA1 neurons more consistently organized relative to reward location across environments. Next, to capture learning-related changes in population structure within each environment, we developed a representational-geometry metric to quantify how population similarity among positions within each corridor changed with experience, and uncovered both local and distal restructuring of the population code. We find that while CA1 and PPC both rapidly reorganize during learning, they do so at different stages: CA1 strongly modifies its position encodings and decorrelates distal positions during exposure to a familiar environment, whereas PPC encodings most strongly decorrelate upon exposure to novelty. Both regions lack this modification upon exposure to a second novel environment, suggesting a physiological limit to such rapid network reorganization. Together, our findings demonstrate that CA1 and PPC both update their representations over experience, but with distinct population-level signatures, suggesting that learning is supported by different modes of plasticity across the hippocampus and neocortex.

Topic Area: Memory, Learning & Knowledge Structures