Circuit mechanisms underlying memory encoding and retrieval in the long axis of the hippocampal formation

Circuits within the hippocampal formation are active during memory processi ng. Here we used functional magnetic resonance imaging (fMRI) to examine mu ltiple sites across the long axis of the hippocampal formation while subjec ts performed different phases of an associative memory task, learning to as sociate faces with names. Viewing faces and hearing names in isolation resu lted in separate hippocampal activation patterns. Pairing faces with names resulted a spatially redistributed activation pattern, rather than a simple summation of the activation patterns resulting from viewing faces and hear ing names in isolation. Recalling names when cued with faces reactivated a pattern similar to that found during paired training. Finally, the activati on patterns representing faces and names were found to be experience depend ent, emerging with repeated exposure. Interpreted in the context of hippoca mpal anatomy and physiology, these findings reveal hippocampal circuit mech anisms that underlie memory encoding and retrieval.