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Brain Advance Access published online on February 3, 2006
Brain, doi:10.1093/brain/awh727
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© The Author (2006). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Received September 23, 2005
Revised November 18, 2005
Accepted November 25, 2005

Article

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

Voyko Kavcic 1, Roberto Fernandez 1, David Logan 1, and Charles J. Duffy 1 *

1 Department of Neurology, the Center for Visual Science, The University of Rochester Medical Center, Rochester, NY, USA; Department of Brain and Cognitive Sciences, the Center for Visual Science, The University of Rochester Medical Center, Rochester, NY, USA; Department of Neurobiology, the Center for Visual Science, The University of Rochester Medical Center, Rochester, NY, USA; Department of Anatomy, the Center for Visual Science, The University of Rochester Medical Center, Rochester, NY, USA; Department of Ophthalmology, the Center for Visual Science, The University of Rochester Medical Center, Rochester, NY, USA

* To whom correspondence should be addressed.
Charles J. Duffy, E-mail: cjd{at}cvs.rochester.edu


  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.

Keywords: Alzheimer's disease; evoked potentials; optic flow; spatial disorientation; navigational impairment.
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