Dorsal and ventral stream visuoperceptual processing deficits in Lewy body disease.

INTRODUCTION: Hypometabolism of visual-processing cortices is the hallmark of dementia in Lewy body diseases (LBD) yet visuoperceptual impairments remain under-researched compared to other cognitive domains. METHODS: Novel, sensitive measures of dorsal- and ventral-stream visual processing were developed and administered to n=53 LBD patients, spanning cognitively asymptomatic to dementia, and compared to n=29 Alzheimer's disease (AD) patients. Further analyses stratified LBD for visual hallucination status and contrasted visuoperceptual performance to measures of attention/executive function. RESULTS: Visuoperceptual impairments were more prominent in LBD than AD, being detectable even in some that were cognitively asymptomatic. LBD demonstrated comparable ventral and dorsal impairments, whereas ventral visuoperceptual performance was relatively preserved compared to dorsal in AD. In LBD, visuoperceptual impairments were strongly associated with visual hallucination and explained a significant amount of performance on visually presented executive function/attention measures. The effect sizes of impairment in demented LBD were substantially larger on the novel visuoperceptual tests compared to standard non-visually presented tests of attention (Digit Span) and executive function (phonemic fluency). DISCUSSION: Early dorsal and ventral stream impairments are a hallmark of dementia in LBD, differing quantitatively and qualitatively from AD. These deficits in LBD were more pronounced than those of attention and executive function.