Dissociating behavioral disorders in early dementia—An FDG-PET study

Behavioral impairments occur frequently in dementia. Studies with magnetic resonance imaging, measuring atrophy, have systematically investigated their neural correlates. Such a systematic approach has not yet been applied to imaging with [18F] fluorodeoxyglucose positron emission tomography (FDG-PET), although regional hypometabolism may precede and exceed atrophy in dementia. The present study related all behavioral disorders as assessed with the Neuropsychiatric Inventory to reductions in brain glucose utilization as measured by FDG-PET with Statistical Parametric Mapping (SPM5). It included 54 subjects mainly with early Alzheimer's disease, frontotemporal lobar degeneration, and subjective cognitive impairment. Apathy, disinhibition and eating disorders – most frequent in frontotemporal lobar degeneration – correlated significantly with regional brain hypometabolism. Whereas a single regressor analysis and conjunction analysis revealed largely overlapping frontomedian regions that were associated with all three behavioral domains, a disjunction analysis identified three specific neural networks for each behavioral disorder, independent of dementia severity. Apathy was related to the ventral tegmental area, a component of the motivational dopaminergic network; disinhibition to both anterior temporal lobes including the anterior hippocampi and left amygdala, caudate head, orbitofrontal cortex and insulae; and eating disorders to the right lateral (orbito) frontal cortex/insula. Our study contributes to the understanding of behavioral deficits in early dementia and suggests specific diagnostic and therapeutic approaches.