The topography of three-dimensional exploration: a new quantification of vertical and horizontal exploration, postural support, and exploratory bouts in the cylinder test.

The study of exploratory behavior in confined spaces can provide insights into both the spatial and the motor behavior of animals. In the present study, the behavior of rats placed inside of a cylinder (the cylinder test) for 5 min was examined to uncover: (1) the overall organization of exploratory behavior, (2) pattern of movement on the horizontal surface, (3) pattern of movement on the vertical surface, and (4) supporting and stepping movements. The results show that exploratory behavior is organized into a number of bouts of lateral and vertical scans with each bout ending by movement arrest and face washing. Within bouts, activity consists of alternating horizontal and vertical progressions that vary systematically over the course of a bout. Horizontal progressions consist of head scans, turning, and stepping, and decrease in amplitude across a bout. Vertical progressions consist of rears, head scans, and descent with an amplitude expressed by an inverted-U across bouts. Each horizontal and vertical progression is directed toward a different portion of the cylinder and the direction of lateral movements alternate within progressions and between progressions. For each rat, bouts tended to end in the same location suggesting the establishment of a home base. Eshkol-Wachmann movement analysis indicates that during progressions, the forepaws are mainly used for postural support and follow forequarter movements, while upward, downward, and sideward shifts in body weight are generated from the hind limbs. These findings illustrate that in even brief exploratory tests the three-dimensional exploratory behavior of rats is organized. The results are discussed in relation to the use of the cylinder test for analyzing a number of behaviors including exploration, locomotion, and supporting reactions.