FUNCTION AND CIRCUITRY OF NUCLEUS REUNIENS IN TEMPORAL MEMORY AND BEHAVIOR

This dissertation examined the intricate neurocircuitry and associated behavioral roles of the nucleus reuniens (RE), situating it within the broader context of temporal context memory (TCM) and behavior. Utilizing a combination of anatomical fluorescent retrograde tracing, advanced neuroimaging techniques, and behavioral recordings, this dissertation provides a comprehensive understanding of the functional dynamics and intricate connectivity patterns of RE. A key focus was the long-range neural connections, especially those bridging the hippocampus (HC) and the medial prefrontal cortex (mPFC), and their implications for cognitive functionality. The research was structured around two primary, expansive aims. First, we explored the mPFC-HC interaction and the role of RE, using dual fluorescent retrograde tracing to reveal distinct neural pathways connecting these regions with the ventral midline thalamus (vmThal) and entorhinal cortices (EC), critical for memory functions. Second, this dissertation explored the functional role of RE in TCM, specifically interval timing. Through various experimental paradigms, I elucidated RE contribution to the temporal organization of memories and its impact on behavioral outcomes, particularly in tasks requiring precise temporal judgments. The first chapter set the foundation by examining temporal memory and the overall role of RE. The subsequent second chapter focused on detailing the neuroanatomical connections between the mPFC and HC, with an emphasis on the role of RE. The third chapter encompassed a comprehensive review of the neurobiological basis of temporal memory, specifically focusing on interval timing. The final fourth experimental chapter examined the behavioral changes in rats upon the inactivation of RE with muscimol, providing insights into its role in modulating temporal memory. A significant finding from this research was RE crucial function within the mPFC-HC network, a key area for spatial memory processing. The RE serves as both an anatomical and functional intermediary, actively modulating communication between these important brain regions. Its strategic position facilitates the integration of memory functions based in the medial temporal lobe system with executive processes centered in the mPFC. This research highlights the critical role of RE in memory retrieval and its connections with related systems, laying the groundwork for future studies on the implications of RE dysfunction in cognitive disorders. This work not only underscores potential avenues for therapeutic interventions but also emphasizes the importance of understanding its role within the larger network.

Major Professor: Dr. Timothy A. Allen