Selective visual attention and simultanagnosia

The parietal lobe is an important key station in the network for selective attention. We found that spontaneous shift of visual attention, depending on task requirement, was impaired by parietal lobe lesions and confirmed the relationship between parietal lobes and visual attention with cortical electric stimulation. Patient 1. A 52-year-old, right-handed carpenter with a diagnosis of 'visual form' of Alzheimer disease showed marked kanji (logogram) agraphia and constructional impairment. Cerebral atrophy and hypoperfusion were observed in bilateral parietal lobes. He showed preserved form and color perception and an ability to describe spatial relationship among several items. In contrast, he could not copy or match them. He seemed to look at only the site he was drawing. Patient 2. A 77-year-old man with cerebral infarction in bilateral parietal lobes and right frontotemporal areas, demonstrated simultanagnosia and visuomotor ataxia. He readily named an object but could not describe a scene. Furthermore he noticed a line between sentences when they were written in English, but could not notice a line when sentences were written in Japanese. Cortical electric mapping, in two patients with subdural electrodes on the left or right parietal lobe, revealed circumscribed regions related to global/local attention shift or line bisection tasks.