Distinct goal location beta frequency dynamics in hippocampus and prefrontal cortex across learning

Neural activity at goal locations contributes to learning by providing feedback on the success of preceding actions. This period engages neocortical and hippocampal networks, which serve distinct functions in processing reward and forming associations with experience that lead to reward. A neocortical network signature for reward feedback processing is beta oscillations (15-30Hz). Beta oscillations are thought to coordinate distributed neural processes across brain regions. However, it is unknown whether beta oscillations coordinate hippocampal-neocortical networks during the goal period, or how their dynamics relate to learning. Here, we show that beta oscillations occur in both hippocampal CA1 and the prefrontal cortex (PFC) when rats reach goal locations in spatial navigation tasks. Despite the presence of beta oscillations in both regions after goal entry, beta activity in each region differed in spectral and temporal properties. These differences suggest that the hippocampus and PFC are not strongly coupled at the beta frequency. We found the strengths of PFC and CA1 beta oscillations across learning were inversely related: PFC beta activity increasing in strength and CA1 beta activity decreasing in strength. Beta burst properties in PFC also had an inverse relationship to those of hippocampal sharp wave-ripples (SWRs), a prominent hippocampal process required for learning. We found a subset of PFC neurons modulated by both beta and hippocampal SWRs, which had distinct task-related firing patterns. Our results suggest that during outcome processing at goal locations, the neocortex and hippocampus are independently modulated by beta oscillations before becoming coordinated for memory-related processes during SWRs.