Differential representations of spatial environments in mPFC and hippocampus underpinning flexible navigation.

Studies on spatial schemas have primarily derived from rodent literature examining the development of task representations in the animal's brain. However, traditional models of schema in humans have largely (although not exclusively) been non-navigation-based, with theoretical frameworks not always aligning with data from rodent studies using navigational contexts. Both literatures support that schemas accelerate learning of novel associations when prior associations already exist. However, theories vary in how adversarial hippocampus and ventromedial prefrontal cortex (vmPFC) functions are for schema memory (despite intimate anatomical connections). Critically, cognitive maps, as a simple form of schema, are used for planning and decision-making, not just learning. Extant literature suggests there may be different stages of goal-directed navigation that are more demanding on hippocampal mechanisms than others (since planning and online decisions may differentially tax inference from what has previously been learned about this and "similar" environments) and demands may differ further depending on how closely-aligned routes are with prior navigational experiences in the environment. Such alignment may also influence how dissociable hippocampal mechanisms are from mPFC correlates of performance. Using desktop virtual reality, fMRI, and targeted region of interest analyses, findings from 19 healthy young adults demonstrate 1) functional differences between anterior and posterior subdivisions of vmPFC (which have been previously tied to schema processing and navigation), with significant differences between these subregions in how they process navigation stages and explain individual differences in navigation behavior. 2) Representational analyses demonstrate broad agreement in coding between the hippocampus and posterior mPFC, while anterior mPFC may support navigation through more generalized levels of processing.