Despite the clinical significance of topographical disorientation in Alzheimer's disease, it is not clear which cognitive spatial processes are primarily impaired. Here, we argue that a deficit in " mental frame syncing" between egocentric and allocentric spatial representations causes early manifestations of topographical disorientation in AD. Specifically, patients show impairment in translating from an allocentric hippocampal representation to an egocentric parietal one for the purpose of effective spatial orientation and navigation. We suggest that a break in " mental frame syncing" , underpinned by damage to the hippocampus and retrosplenial cortex, may be a crucial cognitive marker both for early and differential diagnosis of AD. Identification of these spatial deficits could facilitate the development of early cognitive rehabilitation interventions and the possibility of identifying individuals most at risk for progression to AD during the preclinical stages.
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