Putting Humpty together and pulling him apart: accessing and unbinding the hippocampal item-context engram

A remarkable act of memory entails binding different forms of information. We focus on the timeless question of how the bound engram is accessed such that its component features-item and context-are extracted. To shed light on this question, we investigate the dynamics between brain structures that together mediate the binding and extraction of item and context. Converging evidence has implicated the Parahippocampal cortex (PHc) in contextual processing, the Perirhinal cortex (PRc) in item processing, and the hippocampus in item-context binding. Effective connectivity analysis was conducted on fMRI data gathered during retrieval on tests that differ with regard to the to-be-extracted information. Results revealed that recall is initiated by context-related PHc activity, followed by hippocampal item-context engram activation, and completed with retrieval of the study-item by the PRc. The reverse path was found for recognition. We thus provide novel evidence for dissociative patterns of item-context unbinding during retrieval.