Constraints and the emergence of 'free' exploratory behavior in rat ontogeny

The present study attempts to combine the study of spatial learning with the study of open field behavior. We examine rat moment-to-moment behavior in the wide context of i) a large testing environment, ii) repeated exposures, and iii) development. Previous studies have shown that in adult rats, exploratory behavior of a novel environment is organized around a reference place termed the rat's home base. In this study we show that the appearance of a homebase is a singular stage in ontogeny, marking the transition from a low to a high scatter of movement in the environment. The increase in scatter is characterized by the appearance of several additional reference places. We suggest that the rat connects these reference places gradually and in a regular fashion. To do so we employ statistical filters which extract the principal places visited by the rat, and use measures of diversity which estimate the scatter of movement around these places. The presented data are the first derived from unconstrained behavior, supporting the hypothesis that the rat's cognitive space is represented in terms of local charts eventually combined into a global map.