Neural Similarity Between Encoding and Retrieval is Related to Memory Via Hippocampal Interactions

TLDR

Memory depends on the similarity between encoding and retrieval, with cortical traces stored and the hippocampus reactivating them during recall. The study aimed to test whether item‑level encoding–retrieval similarity predicts memory performance. Researchers applied multivariate representational similarity analysis to fMRI data collected while participants encoded and retrieved emotional and neutral scenes, comparing similarity patterns across conditions. Encoding–retrieval similarity in frontal and posterior cortices tracked memory success, with increased similarity in posterior regions during correct recognition, hippocampal mediation of the cortical similarity–memory link, and enhanced similarity for emotionally arousing scenes, supporting the utility of pattern similarity for probing hippocampal‑cortical interactions.

Abstract

A fundamental principle in memory research is that memory is a function of the similarity between encoding and retrieval operations. Consistent with this principle, many neurobiological models of declarative memory assume that memory traces are stored in cortical regions, and the hippocampus facilitates the reactivation of these traces during retrieval. The present investigation tested the novel prediction that encoding–retrieval similarity can be observed and related to memory at the level of individual items. Multivariate representational similarity analysis was applied to functional magnetic resonance imaging data collected during encoding and retrieval of emotional and neutral scenes. Memory success tracked fluctuations in encoding–retrieval similarity across frontal and posterior cortices. Importantly, memory effects in posterior regions reflected increased similarity between item-specific representations during successful recognition. Mediation analyses revealed that the hippocampus mediated the link between cortical similarity and memory success, providing crucial evidence for hippocampal–cortical interactions during retrieval. Finally, because emotional arousal is known to modulate both perceptual and memory processes, similarity effects were compared for emotional and neutral scenes. Emotional arousal was associated with enhanced similarity between encoding and retrieval patterns. These findings speak to the promise of pattern similarity measures for evaluating memory representations and hippocampal–cortical interactions.