Egocentric and Allocentric Spatial Cognition in Amnestic Mild Cognitive Impairment and Early Alzheimer's Disease.

ABSTRACT

BACKGROUND: Topographical disorientation is one of the early symptoms of Alzheimer's disease (AD). The nature of this symptom, however, remains unclear. OBJECTIVE: The aim of the study was to investigate egocentric and allocentric spatial cognition in patients with amnestic mild cognitive impairment (aMCI) and early AD. PARTICIPANTS AND METHODS: The participants consisted of normal healthy volunteers (n = 23), patients with aMCI (n = 26), and patients with early AD (n = 22). We administered the card placing test (CPT), in which a subject was required to recreate an array of 3 cards, each of which was randomly placed on 8 grids around the individual, before (part A) and after (part B) the individual's rotation. With this design, the CPT can reveal an individual's ability to represent spatial information either egocentrically (CPT-A) or allocentrically (CPT-B). A qualitative analysis of errors in performing the CPT was also conducted. RESULTS: Compared with the controls, the aMCI patients showed significantly poorer CPT-B performance, while there was no significant difference in CPT-A performance between these 2 groups. In contrast, the AD patients demonstrated significantly poorer performance on both the CPT-A and CPT-B than the controls and aMCI patients. There was no significant difference in the profile of errors on the CPT-B between the controls and aMCI patients, whereas there was a notable difference in those on the CPT-A between the controls and AD patients and the aMCI and AD patients. CONCLUSION: Allocentric spatial cognition is selectively impaired in aMCI patients, while an egocentric spatial cognition is additionally impaired in AD patients.