The reuniens nucleus of the thalamus facilitates hippocampo-cortical dialogue during sleep

Memory consolidation during sleep depends on the interregional coupling of slow waves, spindles, and sharp wave-ripples (SWRs), across the cortex, thalamus, and hippocampus. The reuniens nucleus of the thalamus, linking the medial prefrontal cortex (mPFC) and the hippocampus, may facilitate interregional coupling during sleep. To test this, electrophysiological recordings were obtained in vivo from the cat reuniens nucleus, prefrontal cortex and hippocampus. Interregional synchrony was measured using phase-amplitude coupling and interregional time delays between SWRs, spindles and slow waves together with reuniens spiking and local field potential (LFP) activity. Electrical stimulation of the reuniens evoked intracellular mPFC responses, consistent with bidirectional functional connectivity between mPFC-reuniens and hippocampus. Cortical slow waves preceded reuniens slow waves and hippocampal SWRs. Hippocampal SWRs and REM sleep theta modulated reuniens activities and reuniens spindles preceded cortical spindles. The neural mass model of this network demonstrates that the strength of bidirectional hippocampo-thalamic connections determines the coupling of oscillations, suggesting a mechanistic link between synaptic weights and the propensity for interregional synchrony.The nucleus reuniens of the thalamus play a central role in synchronizing the mPFC-hippocampal network during sleep and integrates converging activity from hippocampal and mPFC oscillations.