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 dis-tances between state-space locations, consistent with cognitive mapping and relational memory space the-ories of episodic memory. Prefrontal modulation of hippocampal activity may guide choices by directing memory representations toward appropriate state-space goal locations.

Automated summary

This article investigates how the hippocampus and prefrontal cortex describe events using spatial structures in the execution of memory tasks. The study found that ensembles in both brain regions can distinguish task features by the distances between state-space locations, and prefrontal modulation of hippocampal activity may guide decision-making.