Reversible hippocampal inactivation partially dissociates how and where to search in the water maze

To assess the interaction between spatial and procedural memory systems, the authors developed a learning protocol in the water maze using a rising "Atlantis" platform that requires rats to learn to swim to a specific location and, once there, to learn a "dwelling" response to raise the platform. In this protocol, the effects of temporal inactivation of the dorsal hippocampus with the AMPA/kainate receptor antagonist LY326325 on different memory phases were investigated. Hippocampal inactivation impaired acquisition of the searching task, mainly because of disruption of procedural learning. Inactivation also impeded consolidation and retrieval of spatial information, while leaving expression of dwelling responses intact. These findings challenge the idea of a sharp demarcation between spatial and procedural learning with respect to hippocampal involvement.