The Neuroanatomy of Spatial Memory: the Roles of the Hippocampus, Entorhinal Cortex, Amygdala and Fimbria-fornix in a Spatial Discrimination on the Radial Maze

The role of the dorsal hippocampus, entorhinal cortex, amygdala and fimbria fornix in spatial discrimination was investigated using temporary inactivation and lesioning methods. Spatial learning was tested in a conditioned cue preference (CCP) paradigm on an eight-arm radial maze. Only when given unreinforced pre-exposure trials did rats discriminate between two adjacent arms on the maze. Rats with muscimol induced inactivation of the dorsal hippocampus during unreinforced pre-exposure discriminated between the arms, whereas rats with hippocampal inactivation during training or testing did not. Inactivation of the entorhinal cortex resulted in impairment when done during any phase of the paradigm and during pre-exposure when combined with fimbria-fornix lesions. The effects of dorsal hippocampus inactivation were reversed in rats with combined amygdala lesions. These results revealed that spatial learning may rely on the interactions between the hippocampus, entorhinal cortex, amygdala,and fimbria fornix and that the dogma that the hippocampus mediates all forms of spatial learning requires revision.