rats on a previously trained radial arm maze, but rats can gradually improve to the level of the controls as a function of experience. Lesions to this area also cause deficits on delayed nonmatching-to-positions tasks and impairments in the acquisition of spatial memory tasks during training trials. Retrosplenial cortex The retrosplenial cortex is involved in the processing of allocentric memory and geometric properties in the environment. Inactivation of this region accounts for impaired navigation in the dark and it may be involved in the process of path integration. Lesions to the retrosplenial cortex consistently impair tests of allocentric memory, while sparing egocentric memory. Animals with lesions to the caudal retrosplenial cortex show impaired performance on a radial arm maze only when the maze is rotated to remove their reliance on intramaze cues. In humans, damage to the retrosplenial cortex results in topographical disorientation. Most cases involve damage to the right retrosplenial cortex and include Brodmann area 30. Patients are often impaired at learning new routes and at navigating through familiar environments. However, most patients usually recover within 8 weeks. The retrosplenial cortex preferentially processes spatial information in the right hemisphere. Perirhinal cortex The perirhinal cortex is associated with both spatial reference and spatial working memory. It processes relational information of environmental cues and locations. Lesions in the perirhinal cortex account for deficits in reference memory and working memory, and increase the rate of forgetting of information during training trials of the Morris water maze. This accounts for the impairment in the initial acquisition of the task. Lesions also cause impairment on an object location task and reduce habituation to a novel environment. Neuroplasticity Spatial memories are formed after an animal gathers and processes sensory information about its surroundings (especially vision and proprioception). In general, mammals require a functioning hippocampus (particularly area CA1) in order to form and process memories about space. There is some evidence that human spatial memory is strongly tied to the right hemisphere of the brain. Spatial learning requires both NMDA and AMPA receptors, consolidation requires NMDA receptors, and the retrieval of spatial memories requires AMPA receptors. In rodents, spatial memory has been shown to covary with the size of a part of the hippocampal mossy fiber projection. The function of NMDA receptors varies according to the subregion of the hippocampus. NMDA receptors are required in the CA3 of the hippocampus when spatial information needs to be