Water and standard rodent chow were provided ad libitum. Male Wistar rats ( n = 16 age 3 months weight 300–400 g) were housed in groups of 3–4 individuals in metal cages (60 cm × 40 cm × 25 cm) with sawdust bedding, in a temperature-controlled room (21 ☌) under 12/12 dark/light cycle (lights on: 7 p.m.). In light of the above studies, the aim of the present study was to determine whether round and square arenas differentially shape the paths of spontaneous travel in the arena. It was also suggested that there are ‘border cells’, neurons that are sensitive to the periphery of the arena, and that these cells could be instrumental in planning trajectories and anchoring place fields to a geometric reference frame. Accordingly, it was suggested that place cells are sensitive to the surface orientation of the arena walls. It was found that for rats tested in a square arena, place fields were round, whereas for rats tested in a round arena, place fields had a crescent shape. Specifically, there are special neurons, termed place cells, which fire when the animal is in a specific area of the environment that is termed ‘place field’,. Moreover, the global geometry also has an impact on how the environment is encoded in the brain. The lack of information on the effect of arena shape on the trajectories of travel paths is surprising, considering that the global geometry of the environment has been suggested as comprising the key for orientation and navigation, ,, see however. Accordingly, findings regarding a similar level of activity in round and square arenas do not contribute in determining spatial patterns, which may be similar or different in a square versus round arena.

However, spatial locomotor behavior is multi-dimensional, and thus needs to be studied using at least two independent dimensions: (i) the amount of activity and (ii) the spatial patterns. Similarly, in reviewing the literature on open-field behavior, it was suggested that there are no data available on the impact of open-field geometry on path shape. Previous studies that compared behavior in square versus round arenas have suggested that, in terms of the amount of activity, arena shape does not seem to be a crucial parameter, and that animals can be equally tested using either square or round arenas.

In a square open-field, rats and mice tend to spend extended periods at the corners, ,, ,, ,, and therefore, the round open-field arena has been preferred by many experimenters due to the absence of corners, ,,. This latter variation of a round opposed to a square open-field was employed in the present study, which was aimed at determining whether the different geometries of the apparatus influence the shape of the paths of spontaneous travel. There are numerous versions of the open-field: for example, with or without walls, with or without objects inside it and, most commonly, a round or square open-field. The above processes have been revealed in various experimental environments, and one such environment is the open-field. This environment representation enables path-planning, based on identifying origin, destination, directions, and distances. For this, they rely on external and internal cues that are integrated into a spatial representation, ,,. Instead, travelers may veer toward salient landmarks, follow the boundaries of the area, ,, ,, , or focus on security, on gathering information, or on visiting memorized locations. When humans and other animals travel from one place to another, or when traveling in a certain direction, the shortest path is not necessarily taken. We suggest that the shapes of these paths are exploited for the same spatial task: returning back to a familiar location in the unsighted environment. Indeed, when the rats abandoned the arena walls to crosscut through the center of the arena, their center paths were circuitous in the round arena and relatively straight in the square arena. A similar impact of arena geometry was observed for travel away from the arena walls. When traveling along the perimeter, path shape basically followed the arena walls, with perimeter paths curving along the walls of the round arena, while being straight along the walls of the square arena. We found that while the level of the rats’ activity did not seem to differ between both arenas, path shape differed significantly. Testing was in a total darkness, since in the absence of visual information the geometry is not perceived immediately and the extraction of environment shape is slower. One group of rats ( n = 8) was tested in a square arena (2 m × 2 m), and the other group ( n = 8) in a round arena (2 m diameter). To examine this, individual rats were introduced into an unfamiliar arena. We show here that the global geometry of the environment affects the shape of the paths of travel in rats.

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