Visual Mechanisms of Spatial Disorientation in Alzheimer's Disease

Abstract

Impaired optic flow perception may contribute to the visuospatial disorientation of Alzheimer's disease (AD). We find that 36% of AD patients have elevated perceptual thresholds for left/right outward radial optic flow discrimination. This impairment is related to independent visual motion processing deficits affecting the perception of left/right motion-defined boundaries and in/out radial motion. Elevated optic flow thresholds in AD are correlated with greater difficulty in the Road Map test of visuospatial function (r = -0.5) and in on-the-road driving tests (r = -0.83). When local motion cues are removed from optic flow, subjects must rely on the global pattern of motion. This reveals global pattern perceptual deficits that affect most AD patients (85%) and some normal elderly subjects (21%). This deficit might combine with impaired local motion processing to undermine the alternative perceptual strategies for visuospatial orientation. The greater prevalence of global pattern deficits suggests that it might precede local motion processing impairments, possibly relating to the sequence of early hippocampal and later posterior cortical damage that is typical of AD.

Spatial Navigation Impairment in Healthy Aging and Alzheimer’s Disease

“…In contrast, there was no significant correlation between the MMSE score and spatial navigation score and adding MMSE scores to optic flow threshold in a regression model did not explain more variance in the spatial navigation scores. Another study found significant correlation of the optic flow thresholds also with a score in the table-top left-right orientation Money Road Map test and the ability to respect lane boundaries during sustained driving in On-the-Road Driving test (O'Brien et al, 2001). Rather convincing evidence of the importance of visual perception deficit in spatial disorientation in AD was recently provided in a study by Kavcic et al (2006).…”

Spatial navigation deficit in amnestic mild cognitive impairment

“…such as disorientation in a hospital lobby (14), a score in the Money Road Map (MRM) test and the ability to respect lane boundaries during sustained driving in an on-the-road driving test (25). Further studies described results consistent with this theory, such as poor incidental landmark learning instead of proper recognition of landmarks mentioned during the walk (12), or a lack of relationship between disorientation with memory tests and a failure to use spatial architectural information (13).…”

Enkephalin Elevations Contribute to Neuronal and Behavioral Impairments in a Transgenic Mouse Model of Alzheimer's Disease

“…␤-FNA may also have affected other brain regions and behavioral domains. Although hAPP FAD mice have normal visual acuity, they have difficulty associating a visual cue with escape from water (deIpolyi et al, 2008), an impairment that might relate to visual processing deficits (O'Brien et al, 2001;Kergoat et al, 2002;Mapstone et al, 2003) or topographic agnosia (Kiyosawa et al, 1989;Mendez and Cherrier, 2003) in AD. Although the precise neural substrates of these behavioral deficits are unknown, aberrant activation of -opioid receptors might be involved.…”