The effects of item familiarity on the neural correlates of successful relational memory encoding

Relational memory is resource demanding in that participants are required not only to learn individual items, but also the specific relationships between individual items. Previous research has shown that prior study of individual items aids in relational memory for pairs composed of those same items compared to pairs of items that were not pre-learned (Kilb & Naveh-Benjamin, 2011). The current study sought to elucidate the neural correlates mediating this memory facilitation. After being trained on, or familiarized with individual faces and scenes, participants were scanned while encoding face-scene pairs composed of items from the pre-trained phase (familiarized-item pairs) and pairs whose items had not previously been learned (unfamiliarized-item pairs). Overall subsequent recollection showed engagement of bilateral parahippocampal gyrus (PHG) and hippocampus when compared to subsequent familiarity - a finding consistent with previous literature. However, a comparison between familiarized and unfamiliarized-item pairs showed that subsequently recollected unfamiliarized-item pairs were associated with increased activity across the encoding network including bilateral PHG, hippocampus and right medial prefrontal cortex (PFC); whereas no region exhibited greater activity for encoding of familiarized-item pairs. Results suggest simultaneous encoding of both items and the relationship between items leads to increased recruitment of encoding resources in the PHG and PFC, whereas familiarized-item pairs may utilize the preexisting trace of individual items when encoding pairs of items. These results highlight the demands of relational memory on medial temporal lobe processing and suggest a means by which such demands can be alleviated with prior exposure to individual items.