CHARM

In CHARM, we will characterize the role of the thalamic reuniens and rhomboid nuclei (ReRh) in systems consolidation of a spatial memory by establishing 1) When, during the consolidation period, ReRh are involved, 2) How ReRh regulate the reorganization of the memory trace between the hippocampus (HPC) and the medial prefrontal cortex (mPFC), and 3) Which pathways within the HPC-ReRh-mPFC circuit are specifically recruited. The system consolidation of episodic memories is a dynamical process that requires a dialogue between the HPC and the mPFC, mostly during sleep. Although the HPC establishes direct anatomical contacts with the mPFC, there is no direct return pathway. Thus, other brain regions appear necessary for the HPC-mPFC dialogue to occur. The ReRh are ideally placed to enable such a dialogue since these nuclei are an anatomical hub reciprocally connected to the HPC and mPFC, and their lesion/inactivation prevents memory persistence. However, when and how ReRh enable the transfer of information is not yet known. We will address these questions using a combination of behavioural, viral vector-mediated disconnections, pharmacogenetics, and state-of-the-art in vivo electrophysiological approaches in rats. We will reach three objectives: 1) Establish when the hippocampal-cortical dialogue comes into play in order to consolidate a memory at the systems level, and the temporal window during which the ReRh intervene using pharmacogenetics. 2) Evaluate how ReRh regulate the hippocampal-cortical dialogue through the synchronization of oscillations and the recruitment of neuronal assemblies using in vivo recordings. 3) Determine which pathway(s )in the hippocampal-thalamo-cortical network is (are) involved in the consolidation process with selective disconnections. CHARM is designed to elucidate how the ReRh enable the consolidation of episodic memory supported by a hippocampal-cortical dialogue. This information will be instrumental for the study of episodic memory deficits, which are common to most, if not all, neurological disorders, as well as during normal aging.