Neurophysiological and perceptual correlates of navigational impairment in Alzheimer's disease

Abstract

We assessed visual processing related to navigational impairment in Alzheimer's disease hypothesizing that visual motion evoked responses to optic flow simulating observer self-movement would be linked to navigational performance. Mild Alzheimer's disease and older adult control subjects underwent open-field navigational testing, visual motion perceptual threshold determination and a battery of neuropsychological examinations. We recorded visual motion evoked potentials (EPs) at occipital and parietal sites during centred visual fixation. Randomly moving or stationary pattern pre-stimuli preceded horizontal motion and radial optic flow stimuli to separate motion N200s from pattern onset responses. Radial optic flow evoked N200 responses comparable with those obtained with uniform horizontal motion, despite the variety of motion directions in radial optic flow. Alzheimer's disease patients showed smaller radial optic flow N200s than older adult subjects, and these were greatly diminished when preceded by stationary dots. Combining N200 amplitudes with optic flow perceptual thresholds and contrast sensitivities yielded a strong correlation with navigational impairment in Alzheimer's disease (R2 = 0.95). We conclude that navigational impairment in Alzheimer's disease is linked to a disorder of extrastriate visual cortical motion processing reflected in specific perceptual and neurophysiological measures.

Topographical short‐term memory differentiates Alzheimer's disease from frontotemporal lobar degeneration

“…3). It has also been suggested that impaired perception of radial optic flow underlies the poor navigation of a-MCI and AD patients (Mapstone et al, 2003;Kavcic et al, 2006). Although optic flow may well be important for real-world navigation, our results, using static pictures, show that other aspects of topographical processing are impaired in AD, consistent with a deficit in topographical representation.…”

Spatial Navigation Impairment in Healthy Aging and Alzheimer’s Disease

“…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). The authors required elderly and AD subjects to attend to a 300 m path through a hospital lobby being pushed on a wheelchair, retrace it and complete a set of tests.…”

Visual evoked potentials to pattern, motion and cognitive stimuli in Alzheimer’s disease

“…In contrast, it was described that critical flicker fusion thresholds (also testing function of the motion detecting system) were normal relative to age-matched healthy subjects [9]. To our knowledge, there are so far only two studies using VEPs for evaluation of motion perception processing in patients with AD [8,10]. The first one reports a decline of relevant N200 peak amplitude in motion-onset VEPs to both horizontal (translational) and radial optic flow stimuli in patients with AD when compared with healthy controls, and this finding correlated well with results of psychophysical tests directed to estimation of navigational abilities.…”

“…A particularly prominent feature among these symptoms seems to be a deficit in motion perception and target tracing [1]. According to some psychophysical studies, the patients with AD exhibit significantly higher thresholds for detecting direction of motion [2], they have significantly greater thresholds for perceiving shapes defined by motion cues [3] and display impaired optic flow perception associated with poor performance on the spatial navigation test [4][5][6][7][8]. In contrast, it was described that critical flicker fusion thresholds (also testing function of the motion detecting system) were normal relative to age-matched healthy subjects [9].…”