Prior knowledge influences on hippocampus and medial prefrontal cortex interactions in subsequent memory

Prior knowledge is known to influence the encoding of new events. Specifically, recent theoretical frameworks suggest that positively correlated hippocampus (HC)-medial prefrontal cortex (mPFC) activity is involved in creating enduring traces of events inconsistent with our prior knowledge. Events that are consistent with our schemas are suggested to be encoded via mPFC-cortical interactions. Previous studies examined differences in functional connectivity between subsequently remembered and forgotten items, but the source of these differences was not addressed. Therefore, the involvement of the inter-regions functional connectivity in subsequent remembering or subsequent forgetting of events is unknown. In this study, in addition to probing for a remembered-forgotten difference in functional connectivity, we also examined how connectivity differed from baseline in each of the memory conditions. At encoding, the participants were presented with pairs of semantically related (schema-consistent) and semantically unrelated (schema-inconsistent) words. A surprise recognition test was administered, and a subsequent memory analysis evaluating potential interactions with the HC and mPFC was conducted. Consistent with the suggested frameworks, subsequent memory modulated HC-mPFC connectivity only in schema-inconsistent events. Importantly, the HC and mPFC were positively correlated with respect to subsequently remembered schema-inconsistent items, whereas the subsequently forgotten schema-inconsistent events did not differ from baseline. We also found that positively correlated activity of the mPFC with visual and parietal regions mediated subsequent memory of schema-inconsistent items. Therefore, inconsistent events may be encoded by a network of cortical and medial temporal lobe regions.