Hippocampal-thalamo-cortical coupling in spatial learning and memory consolidation

Spatial memory consolidation is supported by the coupling of hippocampus (HPC) and medial prefrontal cortex (mPFC) activities during sleep. The thalamic nucleus reuniens (NR), reciprocally connected to the HPC and the mPFC, is thought to play a key role in this process. In order to characterize the interactions of these structures during memory consolidation, we developed a new experimental protocol. On an automated maze, animals learn a daily trajectory to a reward and are tested for performance in subsequent sleep. During this protocol, we conduct high-density recording of the HPC, NR and mPFC with silicon probes.Current analyses are focused on determining how oscillations, such as ripples/delta spindles and gamma oscillations, get synchronized between the HPC and mPFC during sleep and how NR neuronal discharge influences such coupling. Moreover, given the prevailing hypothesis that information is encoded via cell assemblies, we aim to analyze the activity of these cells within the HPC-NR-mPFC network during learning and memory consolidation. Our preliminary results show that animals’ performance is improved after sleep. Therefore, we hypothesize that during sleep consolidation, the synchronization of HPC-mPFC oscillations will increase. We expect that the NR will facilitate this process in increasing his neuronal discharge right before the synchronization. Furthermore, we expect to observe more stable and reliable cell assemblies across the recorded brain regions, accompanied by augmented coordination among these cell assemblies.