Nucleus reuniens transiently synchronizes memory networks at beta frequencies

• Published in: Nature communications 2023-07, Vol.14 (1), p.4326-4326, Article 4326
• Main Authors: Jayachandran, Maanasa, Viena, Tatiana D., Garcia, Andy, Veliz, Abdiel Vasallo, Leyva, Sofia, Roldan, Valentina, Vertes, Robert P., Allen, Timothy A.
• Format: Article
• Language: English
• Subjects: 631/378/1595; 631/378/3920; Animals; Coherence; Decision making; Hippocampus; Hippocampus - physiology; Humanities and Social Sciences; Memory tasks; Mental task performance; Midline Thalamic Nuclei - physiology; multidisciplinary; Neural Pathways - physiology; Oscillations; Prefrontal cortex; Prefrontal Cortex - physiology; Rats; Science; Science (multidisciplinary); Thalamic Nuclei; Thalamus
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-40044-z

Episodic memory-based decision-making requires top-down medial prefrontal cortex and hippocampal interactions. This integrated prefrontal-hippocampal memory state is thought to be organized by synchronized network oscillations and mediated by connectivity with the thalamic nucleus reuniens (RE). Whether and how the RE synchronizes prefrontal-hippocampal networks in memory, however, remains unknown. Here, we recorded local field potentials from the prefrontal-RE-hippocampal network while rats engaged in a nonspatial sequence memory task, thereby isolating memory-related activity from running-related oscillations. We found that synchronous prefrontal-hippocampal beta bursts (15–30 Hz) dominated during memory trials, whereas synchronous theta activity (6–12 Hz) dominated during non-memory–related running. Moreover, RE beta activity appeared first, followed by prefrontal and hippocampal synchronized beta, suggesting that prefrontal-hippocampal beta could be driven by the RE. To test whether the RE is capable of driving prefrontal-hippocampal beta synchrony, we used an optogenetic approach (retroAAV-ChR2). RE activation induced prefrontal-hippocampal beta coherence and reduced theta coherence, matching the observed memory-driven network state in the sequence task. These findings are the first to demonstrate that the RE contributes to memory by driving transient synchronized beta in the prefrontal-hippocampal system, thereby facilitating interactions that underlie memory-based decision-making. The prefrontal cortex interacts with the hippocampus to guide memory, but the mechanisms driving functional connectivity are unknown. Here, the authors demonstrate that the nucleus reuniens elicits synchronizations at beta (15–30 Hz) rhythms during retrieval.