Spatial Learning Based on Boundaries in Rats Is Hippocampus-Dependent and Prone to Overshadowing

In three experiments, rats were required to find a submerged platform by referring to the boundaries of a circular swimming pool. In the first experiment, rats with lesions of the hippocampus were impaired at finding the hidden platform, lending support for the proposal that learning to find a goal that is a certain direction and distance from a boundary is dependent upon the hippocampus. Experiments 2 and 3 offered preliminary tests to see if such boundary learning occurred incidentally, irrespective of the presence of a reliable landmark. In contrast to this proposal, a landmark hanging above the platform successfully restricted learning about the location of the platform with respect to the boundary of the arena. The discussion explores the capacity of the hippocampus to encode boundary information, as well as interprets the behavioral results on the basis of an associative learning framework.