Distinct brain dysfunctions underlying visuo-constructive deficit in DLB and AD.

Visuo-constructive abilities are a multicomponential process that can be impaired in several neurodegenerative dementias. Among visuo-constructive tasks, the Rey-Osterrieth Complex Figure-copy (ROCF-c) is the most commonly used and it seems influenced by different skills mediated by specific brain regions. This task complexity allows exploring differential mechanisms of impairment in different neurodegenerative disorders. In this study we examined the neuroanatomical substrates of ROCF-c performance in patients with Dementia with Lewy Bodies (DLB) and patients with Alzheimer's disease (AD). We included forty-five patients with probable DLB, and thirty-four patients with probable typical-AD. To identify the ROCF-c scores neural correlates we performed a regression analysis with brain hypometabolism using the ROCF-c scores as independent variable. Then we evaluated the correlation between regional hypometabolism and ROCF-c scores in each group separately, throughout offline Pearson correlation analysis. The DLB and AD groups differed only in visuo-constructive and memory performances. DLB patients performed worse at the visuo-constructive test, while typical-AD patients performed worse at the verbal memory task. In DLB, worse performance at ROCF-c scores (more severe visuo-constructive impairment) correlated with occipital and temporo-parietal hypometabolism. In AD, worse performance at ROCF-c score was associated with brain hypometabolism in the temporo-parietal regions. The inability to correctly perform the ROCF-c derives from distinct brain dysfunctions in DLB and AD. The present results suggest alterations in visuoperceptual processes due to the severe occipital hypometabolism in DLB, and in visuospatial processes related to temporo-parietal hypometabolism in AD.