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

Many animals are surface-bounded, traveling mostly in two-dimensional (2D) environments. However, those that inhabit structured habitats might also require wayfinding in three-dimensional (3D) environments. Here we forced rodents to ascend or descend when traveling. We tested three species: laboratory rats (a common experimental subject); fat sand rats, which forage while climbing shrubs (representing those used to 3D travel); and Tristram's jirds, which forage in plains (not used to climbing). We examined differences between individuals initially placed on top of the apparatus compared with those placed on its bottom, assuming that this, in addition to the above difference in habitats and motor habits, would influence their spatial behavior. Exploratory activity of top-starting rats and sand rats, but not jirds, differed from bottom starters. Nevertheless, despite the need to continuously ascend or descend, both top- and bottom-starters of the three species displayed the spatio-temporal structure of open-field exploration as previously revealed in a horizontal arena. Specifically, exploration constituted a set of round-trips to a home-base. It is suggested that the preservation of a regular structure of spatial behavior was due to the ability of the tested rodents to mostly maintain a horizontal posture of their head when ascending and descending.