Layer-specific reorganization of mnemonic representations in primate retrosplenial cortex during learning

Rapid learning of associations between co-occurring stimuli is essential for episodic memory formation. The retrosplenial cortex (RSC) is strongly interconnected with the hippocampus, and in rodents, the RSC has been shown to support spatial navigation and fear conditioning. Although lesion and neuroimaging studies in humans and macaques have further implicated the RSC in episodic memory, it is unclear how memory representations form and evolve in the RSC. Here we show that representations of memorized contexts in primate RSC form within minutes. These initial representations reorganize as the memory matures, with a shift in the weight of neuronal contributions from superficial to deep RSC layers across an hour and increased local connectivity between deep layer neurons. Because RSC superficial and deep layers represent input and output layers respectively, it suggests that hippocampal inputs provide context information to superficial layers during early learning, and this context information consolidates in deep RSC layers.