Trial-by-Trial Hippocampal Encoding Activation Predicts the Fidelity of Cortical Reinstatement During Subsequent Retrieval.

According to current models of episodic memory, the hippocampus binds together the neural representation of an experience during encoding such that it can be reinstated in cortex during subsequent retrieval. However, direct evidence linking hippocampal engagement during encoding with subsequent cortical reinstatement during retrieval is lacking. In this study, we aim to directly test the relationship between hippocampal activation during encoding and cortical reinstatement during retrieval. During a scanned encoding session, human participants studied Noun-Sound and Noun-Picture pairs. One day later, during a scanned retrieval session, participants retrieved the sounds and pictures when given the nouns as cues. First, we found that trial-by-trial hippocampal encoding activation was related to trial-by-trial reactivation during retrieval as measured by the univariate BOLD response in several modality-specific cortical regions. Second, using multivariate measures, we found a correlation between encoding-retrieval pattern similarity computed for each trial and hippocampal encoding activation on the corresponding encoding event, suggesting that the magnitude of hippocampal activation during an experience is related to the fidelity of subsequent reinstatement of cortical activity patterns during retrieval. Consistent with current theories of episodic memory, our findings demonstrate a critical link between initial hippocampal activation during an experience and subsequent cortical reinstatement.