How do rodents explore a three-dimensional environment? Habitat-dependent and direction-dependent differences

Volumetric spatial behaviour in rats reveals the anisotropic organisation of navigation

“…Due to the much higher cost of vertical movements, rats may not exhibit the circuitous outbound and direct inbound paths described in flat mazes but instead choose to forage or explore homogeneously in both directions. Although this was not observed in a stepped maze (Gielman et al 2020), more consistent outbound and inbound trajectories were observed in mice climbing a vertical wall (Wexler et al 2018;their Fig. 2).…”

“…When rats climb across vertical (Casali et al 2019) or sloped surfaces (Knierim and McNaughton 2001;Jeffery et al 2006;Casali et al 2019), this activity is largely unchanged. Consistent with this, the behaviour of rats is also largely unchanged in sloped environments: Hagbi et al (2019) reported that in a pyramid maze composed of vertically stacked steps, rats formed multiple home bases on different levels, but their main home base was often on the bottom level; Gielman et al (2020) also found that in a maze composed of 16 steps arranged in linearly decreasing heights, rats tended to form home bases on the lowest step and made excursions from these bases which were longer in the outbound/ascending phase, much like in two-dimensional environments.…”

“…Importantly, rats' behaviour was unconstrained, and experimenters did not interfere other than to place them in or extract them from the mazes. However, the rats were mildly food deprived and very familiar with the environments, meaning that they were more likely to be engaged in foraging than in the novelty-induced exploration documented elsewhere (Fonio et al 2009;Wexler et al 2018;Hagbi et al 2019;Gielman et al 2020). Positions are relative to the maze centre.…”

“…Significance was determined using multiple two-sided one-sample t tests with Holm-Bonferroni correction (colour figure online) recognisable objects and visual cues (Hines and Whishaw 2005;Clark et al 2006;Whishaw et al 2006) or conspecifics (Loewen et al 2005). In tiered environments such as a pyramidal maze with stacked levels or a step maze with linearly varying heights, rats also tend to form a main home base in the lowest corners of the environment (Hagbi et al 2019;Gielman et al 2020). Consistent with these results, we found that rats formed home bases in the corners of the arenas, in the bottom corners of the aligned lattice and to a weaker degree along one edge of the tilted lattice.…”

“…We tracked the 3D position of rats foraging for randomly located food rewards in two-and three-dimensional environments (Grieves et al 2019(Grieves et al , 2020. Specifically, we investigated where animals chose to form their home bases (Eilam and Golani 1989), how they navigated through the environments with respect to gravity (Jovalekic et al 2011;Flores-Abreu et al 2014), if they navigated environments in excursions from their home bases (Wexler et al 2014;Gielman et al 2020) and if three-dimensional trajectories are solved equally quickly in all three dimensions (Jovalekic et al 2011). To evaluate how horizontal biases may affect these behaviours, we compared a maze where strong horizontal movement biases were reported previously (Grobéty and Schenk 1992;Jovalekic et al 2011) to a novel configuration where all maze axes were equally costly to traverse.…”