Using hippocampal amnesia to understand the neural basis of diencephalic amnesia

A review of recent neuropsychological and anatomical findings makes it possible to reconsider the neural basis of diencephalic amnesia in the light of the inputs to this region from the hippocampal formation. Not only is the fornix necessary for normal episodic memory but also its component pathways only serve two diencephalic structures implicated by repeated clinical evidence in anterograde amnesia, the mammillary bodies and the anterior thalamic nuclei. While damage to other medial diencephalic sites might contribute the cognitive loss in diencephalic amnesia, these two structures appear preeminent if it is assumed that diencephalic and medial temporal lobe amnesia share a common cause, that is, there are dysfunctions in some of the same functional pathways. Data from both animal and human studies are reviewed and found to support this parsimonious view of anterograde amnesia. At the same time, new anatomical findings provide much more detailed information about the likely, relative importance of other medial temporal lobe areas to medial diencephalic interactions