Phylogeny of Cortical-Hippocampal Projections Reveals Selective Elimination of Input From Sensory Regions

The study of cross-species differences in the organization of the cerebral cortex received significant attention during the past century. However, the evolutionary principles governing changes in brain connectivity and their impact on cognition remain poorly understood. In the current study, we analyzed differences in anatomical input from the cerebral cortex to the hippocampal region across six species spanning more than 100 million years of mammalian evolution-the tenrec, rat, cat, marmoset, macaque and human. Our results demonstrate that, unlike direct transmodal cortical input, direct unimodal cortical input to the hippocampal region was selectively eliminated with the increase in brain size. Additionally, input from primary sensory regions was eliminated prior to input from non-primary sensory regions. Our findings suggest that hippocampus-related processes in different species operate on fundamentally different types of information, potentially underpinning cross-species differences in hippocampus-dependent cognition. Furthermore, our findings outline the evolutionary trajectory of the anatomical circuitry associating the human hippocampal region with the neocortex.