Pattern visual evoked potential mapping in Alzheimer's disease correlations with visuospatial impairment

We evaluated pattern visual evoked potentials (PVEPs) in patients with Alzheimer's disease (AD) and correlated the neurophysiological results with visuospatial performances in order to understand better the underlying causes of visual disturbances. Latencies and topographical distribution of PVEP components were evaluated in 20 AD patients who underwent an extensive battery of neuropsychological tests. Mean latencies of N70 and P100 were normal in AD patients, while mean latencies of N140 and P200 were significantly increased in comparison with age-matched healthy controls. The topographical distribution of PVEP components did not show any significant difference between the two groups. Visuospatial impairment was detected in 8 patients (40%). Statistically significant positive correlations were observed between P200 amplitude (posterior right hemisphere mean z score) and performance in visuospatial tests. Our data are consistent with a sparing of foveal retinocortical pathways and with the selective dysfunction of either corticocortical connections between the striate cortex and the visual associative structures or of right temporo-parieto-occipital visual analyzers.