Voles scale locomotion to the size of the open-field by adjusting the distance between stops: a possible link to path integration

In this study we show that social voles (Microtus socialis guentheri) preserve the same level of activity and spatio-temporal organization of behavior whether exploring a small (1 x 1 in) or a large (2 x 2 in) open field. In each open field, a vole established a home base from which it set on to round-trips of exploration; taking fewer but longer trips in the large open field, compared with more frequent but shorter trips in the small open field. Each trip comprised bouts of progression (locomotion) interrupted by stops. The number of stops per trip was the same for both large open field (longer trips) and small open field (shorter trips), and achieved by scaling the distance between stops according to the size of the open field. Voles traveled more along the walls in the large compared with the small open field. These adjustments in locomotor behavior to open field size were observed immediately after the voles were introduced into the arena, indicating that the perceived distances available for locomotion were identified by the voles immediately at the beginning of exploration. It is suggested that these properties of spontaneous exploration are an expression of navigation using visual landmarks and path integration. (C) 2002 Elsevier Science B.V. All rights reserved.