Place learning in the Morris place navigation task is impaired by damage to the hippocampal formation even if the temporal demands are reduced

Abstract

Rats with hippocampal-formation damage display a persisting impairment of place learning in the Morris water task. In this paper, we evaluated the temporary memory buffer acount of hippocampal function (Rawlins, 1985, 1987) as an explanation for this place-learning impairment. The essence of this view is that the Morris task requires the animal to integrate information about its position and the relationships among the goal and distal cues over a long temporal interval. Animals with damage to the hippocampal formation are impaired because the temporal demands of the task exceed what can be bridged in the absence of an intact hippocampal formation. To evaluate this hypothesis, we reduced the temporal demands of the Morris task to a minimum by training animals to swim directly to a single, visible platform in a fixed location and subsequently probing them with trials using a hidden platform in the same location. In two experiments based on this general design, animals with colchicine-induced damage to the hippocampal formation were significantly impaired relative to control animals. Thus, our data provide no support for the temporary memory buffer account.