How do animals navigate in their environment?

Animals use a number of strategies to navigate their environments, and it still needs to be determined how they choose these strategies based on the nature and familiarity of the environment. The new study provides a valuable behavioral tool for differentiating how animals orient themselves. 

An automated Barnes Maze variant was developed to address this issue, which allowed researchers to randomize the start and goal positions without interfering with the experiment. Similarly to the Barnes maze, mice navigate through an open arena to reach a goal through 24 doors evenly spaced along the edge.

The Barnes maze, which involves rodents exploring a circular arena until they reach an escape box. In addition, the authors argue that Barnes mazes mice maintain the same strategy from trial to trial, making it unclear whether they accurately capture mice’s full range of navigational strategies.

Co-lead author Ju-Young Lee, a Ph.D. student at the Brain Science Institute, Korea Institute of Science and Technology (KIST), Seoul, Republic of Korea, said, “Typical Barnes mazes work under the assumption that the same strategy is maintained across a whole trial, so it is unclear whether they accurately capture the full range of navigational strategies used by mice.” 

Three navigational tactics were taken into consideration by the group: random, spatial, and serial search. They performed simulations using models to determine which search method was responsible for the patterns of vestibules visited by the mice. In one of the models, mice first chose a strategy at the start of the trial. Then they repeated it every time they finished a specific amount of segments. This paradigm best explains how mice use bright objects to gather spatial information.

Co-lead author Dahee Jung, Postdoc at the Brain Science Institute, KIST, said, “The difference with ours is that it features two luminous objects inside the arena as orienting cues, and the mice start at the edge instead of the center.”

The researchers tracked the progress of 10 male and ten female mice through the maze over the course of 15 days, with ten trials each day during the acquisition phase. During the acquisition phase, mice visited fewer vestibules and moved faster to the goal vestibule. The researchers looked at the proportion of visits to each vestibule. During the acquisition phase, they discovered a preference for vestibules near the goal site. 

The scientists discovered that the mice’s learning rates and spatial strategies were equivalent to those reported in the conventional Barnes maze despite the variations in the labyrinth’s design. Mice visited progressively fewer vestibules throughout the acquisition phase and traveled there more quickly. The researchers assessed the percentage of visits to each vestibule to ascertain if they relied on visual clues to locate the goal. This supported the idea that the mice employed the bright markers to gather spatial information by showing a preference for vestibules close to the objective location throughout the acquisition phase.

Senior author Sébastien Royer, a Principal Investigator at the Brain Science Institute, KIST, concludes, “Our study provides a novel version of the Barnes maze and analytical tools that have allowed us to track the repertoire of mouse navigation strategies over time. These tools could be combined with optogenetic and pharmacogenetic approaches to investigate the neural mechanisms underlying strategy selection in a given environment.”

The researchers investigated differences in strategy development between individual mice by tracking strategy changes over time and analyzing the population average.

Journal Reference:

1. Ju-Young Lee, Dahee Jung ,Sébastien Royer, et al. Stochastic characterization of navigation strategies in an automated variant of the Barnes maze. eLife. DOI: 10.7554/eLife.88648.1