To assess the role of hippocampal NMDA receptors in spatial memory, Bannerman et al. tested mice lacking NR1 selectively in the hippocampal CA1 and dentate gyrus. The mice had memory impairments in the radial maze task but performed similar to controls in the spatial reference memory water maze task. However, further investigation using the water maze revealed that, although spatial memory regarding the platform location and decoy marker was intact, the mice were unable to use this knowledge to make the correct choice. This suggests that NMDA receptors on hippocampal principal cells are not necessary for spatial memory per se but are required for spatial discrimination.