Balint's syndrome in Alzheimer's disease: visuospatial functions.

A subgroup of patients with Alzheimer's disease (AD) developed Balint's syndrome, an uncommon and incompletely understood disorder of visuospatial processing. We characterized the visuospatial features of three AD patients with Balint's syndrome and compared them to three comparably demented AD patients without this syndrome. On visuospatial tasks, the Balint patients were unable to integrate visual stimuli over space. On contrast sensitivity testing, the Balint patients had significantly decreased contrast sensitivities for low spatial frequency gratings (0.5, 1.0 and 2.0 cpd) alternated at 7.5 Hz. Furthermore, the Balint patients had left visual field attentional deficits and normal hemifield P100 visual evoked potentials. In AD, Balint's syndrome involved decreased sensitivity to low spatial frequencies necessary for global visuospatial analysis, a disturbance suggesting damage to the magnocellular visual system in the occipitoparietal association cortex and, possibly, in the optic nerves.