Working memory (WM) provides temporary information storage for performance of cognitive tasks. Neural signals in hippocampus-prefrontal cortex (HPC-PFC) circuit interact and construct a network. The question raised here is how the neural signals connect and transfer in the HPC-PFC network to perform a WM task? In this study, 32-channel local field potentials (LFPs) were recorded with two electrode arrays respectively implanted in HPC and PFC during a rat Y-maze working memory task. The principle frequency band of LFPs during the task was theta, determined via short-time Fourier transform. Functional connectivity strength was further calculated quantitatively and a causal network was defined by directed transfer function (DTF). The information transfer in the network was described by information flow. The results show that (1)the DTF curve peaked before the choice point. (2) The information flow in working memory was from HPC to PFC. These findings suggest that the functional connectivity strengthens at WM state and HPC is the WM information source in the HPC- PFC network.
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