Impairments in the Acquisition, Retention and Selection of Spatial Navigation Strategies After Medial Caudate-putamen Lesions in Rats

Using the Morris swimming pool test of spatial navigation, medial caudate-putamen lesions in rats produce impairments in the acquisition and retention of both place and cue tasks, and impair the selection of normal navigation strategies. Also described are some novel features of spatial navigation behaviour displayed by control animals in cue and place tasks that provide insights into the performance of the caudate-putamen rats. Analyses of the swim patterns on postacquisition probe trials, in which the target platform was removed or relocated, showed that the strategy used by the caudate-putamen lesioned rats was dependent upon the task that they were required to solve. Control rats used a place strategy and distal visual cues to identify the location of the start points, the routes from the start points to the platform, and the location of the platform on both the cue and place tasks. The caudate-putamen lesioned rats used distal visual cues and a place strategy only to acquire the place task. They solved the cue task using a taxon strategy consisting of a combination of proximal and position response cues. The results suggest that when necessary, medial caudate-putamen lesioned rats, like normal rats, can use place strategies for spatial navigation, but if an alternate, perhaps simpler, taxon solution is available they seemingly ignore place information and navigate using the simpler strategy. The deficit, which has features of a neglect rather than a loss of ability per se, suggests that medial caudate-putamen neural systems are involved in the selection of alternative strategies in spatial navigation tasks.