The interaction of relational encoding and unitization: Effects on medial temporal lobe processing during retrieval

In retrieval of typical episodic memories, recollection leads to retrieval of context details whereas familiarity is only diagnostic for item memory. Unitization is an encoding strategy that allows context details to be processed as item features and therefore increases the involvement of familiarity-based recognition in retrieval of these context details. Relational encoding is a hippocampally-dependent process that stores items and contexts independently. Our previous study Tu and Diana [1] concluded that mixing unitized and non-unitized context details in the same episode reduced the contribution of familiarity to retrieval of any one detail. In the current study, we modified the paradigm by removing visual cues to the context details and the condition-specific blocking during test. Surprisingly, the behavioral data diverged from our 2016 study and indicated that the two manipulated context details in the modified paradigm were processed independently of one another. Neuroimaging data further revealed anterior hippocampal activation was associated with unitization of source information as compared to relational encoding. We also found the predicted increase in bilateral perirhinal cortex activation and decrease in parahippocampal cortex activation during retrieval of unitized color information when compared to relationally-encoded color information. We did not find that same predicted pattern of differences due to unitization of size information.