Cerebral metabolism, cognition, and functional abilities in Alzheimer disease

Patients with Alzheimer disease (AD) exhibit profound difficulties in completing instrumental activities of daily living (IADLs), such as managing finances, organizing medications, and food preparation. It is unclear which brain areas underlie IADL deficits in AD. To address this question, we used voxel-based analysis to correlate the performance of IADLs with resting cerebral metabolism as measured during [(18)F] fluorodeoxyglucose-positron emission tomography (FDG-PET) imaging in 44 patients with AD. Poorer ability to complete IADLs was associated with hypometabolism in right-sided cortical regions, including the parietal lobe, posterior temporal cortex, dorsolateral prefrontal cortex, and frontal pole. Follow-up path analyses examining anatomically defined regions of interest (ROI) demonstrated that the association between metabolism and IADLs was mediated by global cognition in frontal ROIs, and partially mediated by global cognition in the parietal ROI. Findings suggest that hypometabolism of right sided brain regions involved in executive functioning, visuospatial processing, attention, and working memory underlie functional impairments in patients with AD.