Remote spatial and autobiographical memory in cases of episodic amnesia and topographical disorientation

A number of theories have postulated that there is a strong relationship between episodic memory and spatial processes mediated by the hippocampus. Evidence for episodic amnesia following damage to the medial temporal lobes is extensive, but less is known about the types of spatial memory affected by damage to these regions. In this study, we compared episodic memory with detailed scene memory, landmark recognition and schematic (map-based) spatial memory in a group of individuals with amnesia related to damage to the medial temporal lobes (MTL) including the hippocampus. We compared their performance to matched controls, and to an individual with topographical disorientation, a selective spatial memory deficit relating to more posterior temporal and occipital lobe damage. For individuals with MTL lesions, impairments to scene memory were comparable to those in episodic memory. Landmark recognition was impaired only for less familiar landmarks, and schematic spatial memory was not impaired compared to controls. Despite the absence of hippocampal damage, the individual with topographical disorientation, like the MTL amnesic patients, demonstrated impairments to scene memory and recognition of less familiar landmarks, and intact schematic spatial memory, but with less severe episodic memory loss. These results highlight the similarities between detailed scene memory and episodic memory, including their reliance on the medial temporal lobe, and suggest that more schematic forms of spatial memory may be unaffected by medial temporal damage. In addition, the results suggest that damage to more posterior temporal or occipital regions that leads to spatial memory deficits may entail some impairment to episodic memory even if the hippocampus is spared.