COMPLEX REUNIENS-HIPPOCAMPUS INTERACTIONS ACCOMPANY SPATIAL LEARNING AND DECISION-MAKING IN THE RAT

Emerging evidence suggests that the midline thalamic nucleus reuniens (RE) is a critical node within the hippocampal-prefrontal network supporting spatial recall and goal-directed navigation. Anatomically, RE is directly connected to the hippocampus (HC) and prefrontal cortex (PFC), but the functional connectivity within the extended cortical-subcortical network supporting spatial cognition remains insufficiently understood. To explore the local and cross-regional contributions to spatial behavior, we used local field potentials (LFP, 1-300Hz) from HC, PFC, and RE that were simultaneously recorded in rats undergoing a spatial navigation task in a complex maze. We used a novel unsupervised signal analysis method, iterated masking EMD, to decompose LFPs into distinct, region-specific frequency components; notably, most of the ranges corresponded to conventional frequency bands. We found that the strength of cross-regional interactions increased with navigational accuracy and efficiency: RE and PFC showed an increase in cross-regional phase-phase coherence across a broad range of signal components (5-200Hz); in addition, HC and RE showed significantly increased "theta" (8Hz) coherence and "theta/beta" (8Hz/20Hz) phase-amplitude coupling. We further explored the relationship between the time-frequency-resolved signals and within-trial behavior. We observed a transient reduction in HC-RE beta coherence associated with navigation errors and "vicarious trial-and-error" (VTE), a behavioral marker of indecision or consideration of options. Collectively, our findings support the role of HC-RE-PFC synchronization in successful navigation and decision-making.