Concurrent interactions between prefrontal cortex and hippocampus during a spatial working memory task.

Spatial working memory (SWM) refers to a short-term system for temporary manipulation of spatial information and requires the cooperation of multiple brain regions. Despite evidence that the hippocampus (HPC) and prefrontal cortex (PFC) are involved in SWM, how the PFC and HPC interact during SWM remains puzzling. In this study, local field potentials (LFPs) were recorded simultaneously from rat ventral HPC and medial PFC during SWM tasks firstly. A cross-frequency coupling algorithm was used to test for functional connectivity in the PFC and HPC. Granger causality (GC) algorithm was used to test for effective connectivity in the PFC and HPC. Finally, concurrent interactions across two brain regions were analyzed based on functional connectivity and effective connectivity. Experimental results show that the LFPs power in the PFC and HPC decreased during the learning period and peaked before the rats' behavioral selection during SWM. Moreover, the LFPs power mainly distributed in theta and gamma that are related to SWM. In relation to the functional connectivity, the effect of activity transmission during SWM in the PFC and HPC is the same; the phase-amplitude coupling (PAC) between gamma in the PFC and theta in the HPC is correlated with the formation of SWM and supports concurrent interactions between the PFC and HPC. In relation to the effective connectivity, the directed activity transmission in the HPC is greater than that in the PFC during SWM, indicating flow of activity from the HPC to the PFC.