Hippocampal and medial prefrontal ensemble spiking represents episodes and rules in similar task spaces

Episodic memory requires the hippocampus and prefrontal cortex to guide decisions by representing events in spatial, temporal, and personal contexts. Both brain regions have been described by cognitive theories that represent events in context as locations in maps or memory spaces. We query whether ensemble spiking in these regions described spatial structures as rats performed memory tasks. From each ensemble, we construct a state-space with each point defined by the coordinated spiking of single and pairs of units in 125-ms bins and investigate how state-space locations discriminate task features. Trajectories through state-spaces correspond with behavioral episodes framed by spatial, temporal, and internal contexts. Both hippocampal and prefrontal ensembles distinguish maze locations, task intervals, and goals by distances between state-space locations, consistent with cognitive mapping and relational memory space theories of episodic memory. Prefrontal modulation of hippocampal activity may guide choices by directing memory representations toward appropriate state-space goal locations. [Display omitted] •Neural activity associated with learning and memory is described by multidimensional maps•Activity spaces represent environmental features to associate goals and behavioral variables•HPC and mPFC activity spaces interact with each other to support goal-directed behavior The HPC and PFC help people and other animals adapt to current circumstances by recalling previous relevant experiences. We show the mechanisms by which memories are organized so appropriate information is readily accessible in cognitive maps, instantiated by multidimensional neural activity spaces. These spaces represent salient environmental features that help associate goals with behavior.