Nucleus reuniens gates selective hippocampal-prefrontal interactions during NREM sleep

Memory consolidation requires functional synchrony between the hippocampus (HC) and the medial prefrontal cortex (mPFC). The nucleus reuniens (RE) is a structural and functional hub between HC and mPFC. Here, we used in vivo electrophysiology to monitor the hippocampal-thalamic-prefrontal network in rats during non-rapid eye movement (NREM) sleep. We identified ripple-like activity in the RE (120 Hz peak frequency, 45 ms oscillatory duration) that occurred most frequently during NREM sleep and was associated with robust recruitment of thalamic neural spiking. RE ripple activity was phase-locked to both hippocampal sharp wave-ripples (SWR) and mPFC ripples. Although ripples were independently detected in all three structures, we found that coupling between HC and mPFC ripples mainly involved co-occurring RE ripples. These results suggest RE ripples help organize when hippocampal activity engages prefrontal circuits during sleep, with potential implications for network mechanisms of memory consolidation.