Neural correlates of executive function in mild cognitive impairment and Alzheimer's disease–an FDG-PET study

Executive dysfunction in Alzheimer’s disease (AD) is associated with delusions, agitation and disinhibition, rapid progression and care dependency. We correlated resting cerebral glucose metabolism in Alzheimer’s disease (AD) and mild cognitive impairment (MCI) with scores on the Trail Making Test (TMT) as a measure of executive function. Methods: Ten patients with AD, 10 patients with mild cognitive impairment (MCI) and 14 controls were included. We compared cerebral glucose metabolism in patients with that in controls and correlated TMT scores with cerebral glucose metabolism. Neuropsychological correlates of the TMT were also investigated. Results: Patients had reduced frontotemporoparietal and posterior cingulate metabolism compared to controls. TMT-A correlated with left middle frontal, TMT-B and TMT-Q with right middle frontal and TMT-B with right precentral glucose metabolism. TMT-A and TMT-B scores correlated with word fluency and recall subtests of the CERAD neuropsychological test battery, TMT-Q with delayed constructional praxis scores. Conclusions: PET and neuropsychological correlates indicate that executive function is frontal lobe mediated and demands working memory. The neuropsychological correlates of the tasks confirm the complexity of the task.