Dysfunction of visual cortex contributes to disturbed processing of visual information in Alzheimer's disease

The relation between visual impairment and regional cerebral metabolic rate of glucose (rCMRGl) was studied in 31 patients with probable Alzheimer's disease (AD) by using positron emission tomography with 18F-2-fluoro-2-deoxy-D-glucose. To exclude any precortical cause of visual dysfunction only patients were included who had amplitudes and latencies of visually evoked potentials (flash and pattern reversal) within the normal range. Visual information processing was evaluated psychometrically by a fragmented picture test (FPT), which is a combined perception (identification score) and memory (reidentification score) task and refers to Gollin's incomplete pictures. The identification and reidentification scores were significantly worse than in normals. Reductions of the rCMRGl in the primary visual fields, and in the secondary visual fields were found. A significant partial correlation with adjustment for age between the reidentification score of the FPT and the rCMRGl of the secondary visual fields (r = -.39, p < .05) in AD patients was found, indicating involvement of the secondary visual cortex in the pathological changes in AD.