Phylogeny of neocortical-hippocampal projections provides insight in the nature of human memory

Throughout mammalian evolution, the hippocampal region, unlike the neocortex, largely preserved its cytoarchitectural organization and its role in mnemonic functions. This contrast raises the possibility that the hippocampal region receives different types of cortical input across species, which may be reflected in species-specific memory-related differences. To test this hypothesis, we examined differences in unimodal and transmodal cortical input to the hippocampal region in the rat, marmoset, macaque and human. Our results demonstrate that unlike unimodal cortical input, transmodal cortical input to the hippocampal region was selectively preserved during mammalian evolution. These findings suggest that memory-related processes in different species likely operate on different types of sensory information. Our observations provide a comparative anatomical framework elucidating the process of dimensionality reduction underlying the formation of human memory.