An abstract relational map emerges in the human medial prefrontal cortex with consolidation

Understanding the structure of a problem, such as the relationships between stimuli, supports fast learning and flexible reasoning. Rodent work has suggested that abstraction of structure away from sensory details occurs over the course of multiple days, in cortex. However, direct evidence of such explicit relational representations in humans is scarce, and it is unclear whether they emerge on similar timescales. Here, we combine a graph-learning paradigm with functional magnetic resonance imaging (fMRI) to look for such a relational map in the human brain. We first trained participants on two associative graphs with the same structure. We then scanned participants twice while they used this knowledge, with several days between scanning sessions. We found that the medial temporal lobe represented the specific associations between stimuli in each graph in both scanning sessions. In the medial prefrontal cortex (mPFC), on the other hand, fMRI repetition suppression and representational similarity analysis demonstrated the emergence of an abstract relational map over sessions. These results shed new light on how neural representations organising relational knowledge change with time.