Dynamics of the Hippocampus During Encoding and Retrieval of Face-Name Pairs

TLDR

The medial temporal lobe is essential for new memory formation, yet the specific roles of its subregions during encoding and retrieval remain unclear. The study aimed to identify mnemonic properties of hippocampal subregions while participants learned face‑name associations. This was accomplished using novel high‑resolution fMRI acquisition and analysis techniques. CA2/3 and dentate gyrus activity rose during encoding and fell as associations were learned, whereas subiculum activity declined mainly during retrieval, indicating distinct contributions of hippocampal subdivisions to memory formation.

Abstract

The medial temporal lobe (MTL) is critical in forming new memories, but how subregions within the MTL carry out encoding and retrieval processes in humans is unknown. Using new high-resolution functional magnetic resonance imaging (fMRI) acquisition and analysis methods, we identified mnemonic properties of different subregions within the hippocampal circuitry as human subjects learned to associate names with faces. The cornu ammonis (CA) fields 2 and 3 and the dentate gyrus were active relative to baseline only during encoding, and this activity decreased as associations were learned. Activity in the subiculum showed the same temporal decline, but primarily during retrieval. Our results demonstrate that subdivisions within the hippocampus make distinct contributions to new memory formation.