Locus coeruleus-hippocampal pathway activation promotes spatial memory updating during reversal learning

Spatial navigation relies on animals merging real-time environmental cues with their existing spatial memories. The locus coeruleus (LC), a brain region, sends signals to the hippocampus, but it's uncertain if this communication aids general spatial learning or specifically enhances the updating of prior information. In this study, researchers selectively triggered LC projections to the dorsal hippocampus while mice participated in two tasks: object-location recognition and an appetitive radial-maze challenge that combined initial spatial learning with a later reversal.

The researchers discovered that activating LC projections improved mice's ability to remember object locations and reduced mistakes in both types of memory tasks. However, the pathway did not impact the initial acquisition and retention of spatial references. To examine navigation patterns beyond standard performance metrics, the team created a graph-based analysis, comparing each mouse's path to trajectories generated from random, regular, small-world, and goal-directed network models.

The radial-maze routes exhibited a blend of goal-directed-like and regular/serial-like behaviors that changed over time. Importantly, alignment with the goal-directed model correlated with fewer errors and closer approach to the reward arm. In summary, the findings suggest that LC inputs to the hippocampus specifically enhance spatial memory updating rather than uniformly boosting spatial learning capabilities. This work also proposes a novel method for assessing the structure of radial-maze trajectories.