Impaired Translation of Spatial Representation in Young Onset Alzheimer's Disease Patients

Background: Many early-stage Alzheimer's disease (AD) patients suffer from spatial navigational impairment even in familiar environments. Growing evidence shows that the retrosplenial cortex (RSC) is more damaged in youngonset AD patients (YOAD, onset age before 65) than in late-onset AD (LOAD) in the early-stage of AD. Impaired translation between egocentric and allocentric representations of the environment, as a cause for spatial navigational impairment, usually occurs in people with lesions in the RSC. Objective: To test translational ability between spatial representations in early-stage YOAD and LOAD patients. Methods Tests deemed sensitive to translation of spatial representations were used to evaluate 29 AD (14 YOAD, 15 LOAD) and 27 cognitively healthy controls (14 younger NC and 13 older NC). Results: Younger NC outperformed YOAD in the tests of translation of spatial representations in spite of their equal basic visuoperceptual abilities and distance estimation. No such difference existed between LOAD and older NC. Conclusion: The translation of egocentric-allocentric representation ability, as a principal function of RSC, does not deteriorate equally in early-stage AD patients of different onset age. That early-stage YOAD show more deviations in translation of their spatial representation ability deserves our attention because it may endanger their daily activities.