The influence of the precuneus on the hippocampus determines the subjective quality of memory during the retrieval of naturalistic episodes

Abstract Memory retrieval entails dynamic interactions between the medial temporal lobe and areas in the parietal and frontal cortices. Here, we targeted changes of connectivity associated with the subjective quality of remembering objects together with information about their rich spatio-temporal encoding context. During a 45 min encoding session, the participants actively explored a virtual town and were presented with pictures of objects that where later tested during retrieval. The following day, under fMRI, participants were presented with images of objects and had to report whether: they recognized the object and could remember the place/time of encoding, the object was familiar only, or the object was new. The hippocampus, the precuneus and the ventro-medial prefrontal cortex activated when the participants successfully recognized objects they had seen in the virtual town, and reported that they could remember the place/time of that event. Analyses of effective connectivity showed that the influence exerted by the precuneus on the hippocampus mediates this effect of episodic recollection, and indicated also a contribution of the connectivity between the hippocampus and the medial prefrontal cortex. We conclude that the causal influences between the nodes of the medial memory system underlie the subjective experience of remembering contextually-rich episodes.