Hippocampal and nonhippocampal contributions to place learning in rats.

Brain structures thought to be critical for learning and memory were lesioned, and the effects on rats' ability to locate food on a radial maze in situations that provided different types of information was used to suggest general principles of information processing by hypothesized neural systems that include each of the lesioned structures. When animals were confined to food-containing and empty arms on different training trials, the learned discrimination between the arms was amygdala based. More training trials were required for ambiguous (adjacent arms) than for unambiguous (widely separated arms) discriminations. When rats moved around and entered both food and no-food arms on the same trial, the unambiguous discrimination was learned by both dorsal striatum- and hippocampus-based systems; however, the ambiguous discrimination was learned only by the hippocampus system.