Stopping behavior: constraints on exploration in rats (Rattus norvegicus).

In the absence of an obvious reference place, rat locomotor behavior in a novel environment appears haphazard. In previous work, one or two places termed home bases, were shown to stand out from all the other places in the environment in terms of the behaviors performed in them and in terms of their behavioral stability. We use home base location as a reference place for rat movement in locale space, by defining an excursion as a trip starting at a home base and ending at the next stop at a home base. We then establish the uniform distribution as an appropriate model for the number of stops per excursion. This way we show that there is an intrinsic upper bound on the number of times a rat stops during an excursion. As a rat leaves the home base, home base attraction increases with every additional stop performed by it, first slowly and then fast. This cumulative process of attraction may be concluded after each stop, as long as the number of stops does not exceed an intrinsic upper bound; once the upper bound is reached, the rat concludes that excursion and returns to base. The session's upper bound does not increase with the size of the explored area.