Cerebral asymmetries for radial-maze foraging in the rat

Abstract

Rats were trained to locate food rewards in a subset of maze arms over fifty trials in one of two radial mazes. One group was trained on this foraging task in a walled radial maze used by LaMendola & Bever (1997), and the other group was trained in a more conventional runway style radial maze. Experiment 1 demonstrated both quantitative and qualitative differences in foraging behavior amongst untreated control rats. Experiment 2 demonstrated different left-right asymmetries for learning in each maze. Asymmetries were elicited by locally anesthetizing the same side of a rat's whiskers throughout training. When rats were trained on the runway maze, they made fewer errors when their left whiskers were intact. When trained on the walled maze, rats made fewer errors when their right whiskers were intact. Qualitative differences in arm choice behavior accompanied the asymmetry in the walled maze only. Experiment 3 demonstrated that rats were affected in different ways to rotation of either intramaze or extramaze visual cues in either maze. Arm choice accuracy was adversely affected when the rewards were rotated with respect to the extramaze cues in the runway maze, and intramaze cues in the walled maze. Left-right differences amongst whisker treated rats emerged only in the walled maze. Cumulatively, the results suggest that rats use different foraging strategies to solve the same task in two different maze conditions. The strategy associated with each maze elicited unique contributions from each hemisphere. Left-right asymmetries emerged for the performance measures in the runway maze, and for both performance and arm choice measures in the walled maze. This suggested that the walled maze required more involvement of the cerebral hemispheres in the processing of the task. Each hemisphere solved the task in qualitatively different ways. The LH used an abstract or allocentric spatial strategy to represent the locations of rewards across trials, while the RH used an egocentric strategy to keep track of the rat's movement through the maze within a trial. No such specialization was found between hemispheres in the runway maze because of the dependence on the hippocampus for cognitive processing.