From allo- to egocentric spatial ability in early Alzheimer's disease: a study with virtual reality spatial tasks.

The ability to orient in space constitutes a main sign of cognitive impairment in Alzheimer's disease (AD). Presently, a peculiar aspect of topographical disorientation in AD linked with spatial reference frame congruence appears to have been only minimally investigated. We aim to study whether there is a decline in performing the allo- to egocentric translation of spatial knowledge during different types of wayfinding in AD patients. We introduced two virtual reality tasks, the VR-Maze and VR-Road Map tasks, in which we compared 26 AD and 26 healthy, elderly subjects. The results emphasize that there is a specific reduction in performing allo- to egocentric spatial tasks in AD, whereas this reduction is not as evident in equivalent allocentric spatial tasks. The data are consistent with the neurological results regarding the early degeneration of the hippocampus and retrosplenial cortex in AD, which underlies the ability to translate between these two reference frames.