Hippocampal and medial prefrontal cortices encode structural task representations following progressive and interleaved training schedules

Abstract

Memory generalisations may be underpinned by either encoding- or retrieval-based mechanisms. We used a transitive inference task to investigate whether these generalisation mechanisms are influenced by progressive vs randomly interleaved training, and overnight consolidation. On consecutive days, participants learnt pairwise discriminations from two transitive hierarchies before being tested during fMRI. Inference performance was consistently better following progressive training, and for pairs further apart in the transitive hierarchy. BOLD pattern similarity correlated with hierarchical distances in the medial temporal lobe (MTL) and medial prefrontal cortex (MPFC). These results are consistent with the use of representations that directly encode structural relationships between different task features. Furthermore, BOLD patterns in MPFC were similar across the two independent hierarchies. We conclude that humans preferentially employ encoding-based mechanisms to store map-like relational codes that can be used for memory generalisation. While both MTL and MPFC support these representations, the MPFC encodes more abstract relational information.

Emergent neural dynamics and geometry for generalization in a transitive inference task

“…Despite the long history of TI as a cognitive task, investigation of its neural basis in the brain is relatively recent [52, 61, 62, 63, 64, 65]. Prior work implies that an approach seeking to identify biologically accurate neural implementations would benefit from three criteria:…”