Egocentric conditional associative learning: effects of restricted lesions to the hippocampo-mammillo-thalamic pathway.

Rats with lesions of the hippocampus, the mammillary region, the anterior thalamic nuclei, and normal control animals were trained on a conditional associative learning task in which they had to learn to make one of two motor responses (i.e., turn left or right), depending on which one of two visual cues was presented. Damage to the hippocampus severely impaired performance of this task. By contrast, rats with lesions of the mammillary region or the anterior thalamic nuclei were able to acquire the task at a rate comparable to that of the normal animals. These findings demonstrate that hippocampal lesions impair the ability to form arbitrary associations between visual cues and kinesthetic responses (body turns) and, furthermore, suggest that the hippocampus does not rely on input from its major subcortical targets for learning such visual-kinesthetic associations. 2004 Wiley-Liss, Inc.