Optogenetic activation of the ventral tegmental area-hippocampal pathway facilitates rapid adaptation to changes in spatial goals.

Animal adaptation to environmental goals to pursue rewards is modulated by dopamine. However, the role of dopamine in the hippocampus, involved in spatial navigation, remains unclear. Here, we studied dopaminergic inputs from the ventral tegmental area (VTA) to the hippocampus, focusing on spatial goal persistence and adaptation. Mice with VTA dopaminergic lesions struggled to locate and update learned reward locations in a circular maze with dynamic reward locations, emphasizing the importance of VTA dopaminergic neurons in the persistence and adaptation of spatial memory. Further, these deficits were accompanied by motor impairments or motivational loss even when dopamine receptors in the dorsal hippocampus were selectively blocked. Stimulation of VTA dopaminergic axons within the dorsal hippocampus enhanced the mice's ability to adapt to changing reward locations. These findings provide insights into the contribution of dopaminergic inputs within the hippocampus to spatial goal adaptation.

The neural representation of time distributed across multiple brain regions differs between implicit and explicit time demands.

Animals appear to possess an internal timer during action, based on the passage of time. However, the neural underpinnings of the perception of time, ranging from seconds to minutes, remain unclear. Herein, we considered the neural representation of time based on mounting evidence on the neural correlates of time perception. The passage of time in the brain is represented by two types of neural encoding as follows: (i) the modulation of firing rates in single neurons and (ii) the sequential activity in neural ensembles. Time-dependent neural activity reflects the relative time rather than the absolute time, similar to a clock. They emerge in multiple regions, including the hippocampus, medial and lateral entorhinal cortices, medial prefrontal cortex, and dorsal striatum. Moreover, they involve different brain regions, depending on an implicit or explicit event duration. Thus, the two types of internal timers distributed across multiple brain regions simultaneously engage in time perception, in response to implicit or explicit time demands.

Utilizing a Reconfigurable Maze System to Enhance the Reproducibility of Spatial Navigation Tests in Rodents.

Several maze shapes are used to test spatial navigation performance and behavioral phenotypes. Traditionally, each experiment requires a unique maze shape, thus requiring several separate mazes in different configurations. The maze geometry cannot be reconfigured in a single environment to accommodate scalability and reproducibility. The reconfigurable maze is a unique approach to address the limitations, allowing quick and flexible configurations of maze pathways in a repeatable manner. It consists of interlocking pathways and includes feeders, treadmills, movable walls, and shut-off sensors. The current protocol describes how the reconfigurable maze can replicate existing mazes, including the T-shaped, plus-shaped, W-shaped, and figure-eight mazes. Initially, the T-shaped maze was constructed inside a single experimental room, followed by modifications. The rapid and scalable protocol outlined herein demonstrates the flexibility of the reconfigurable maze, achieved through the addition of components and behavioral training phases in a stepwise manner. The reconfigurable maze systematically and precisely assesses the performance of multiple aspects of spatial navigation behavior.