Mesoscale connectivity of the human hippocampus and fimbria revealed by ex vivo diffusion MRI.

Motivation: To investigate the connectome of the human hippocampus. Goal(s): To elucidate intra-hippocampal connectivity, especially along the anterior-posterior axis. Approach: To use mesoscale resolution (250 um isotropic) diffusion MR images to segment with high accuracy hippocampal substructures for tractography. Results: Intra-hippocampal connectivity between subregions (head, body, tail) and subfields (CA1-3, dentate gyrus) was visualized and quantitated. Additionally, fibers from the fimbria were mapped onto the hippocampal substructures to provide a unique view of how intra- and extra-hippocampal networks interact. Impact: Improving our conceptualization of intra- and extra-hippocampal connectivity is essential to further understanding of the structure-function relationship of hippocampal networks and how these are impacted by neurological and psychiatric conditions.