Positron emission tomography (PET) of Alzheimer's disease (AD) patients with delusional misidentification syndromes identified reduced glucose metabolism in orbitofrontal, anterior cingulate, and temporal brain structures compared to matched AD patients and controls. Delusion formation was independent of cognitive abnormalities. Compared with controls, elderly patients with late- onset depression without cognitive impairment and without "secondary depression," were found by PET to have globally increased brain glucose metabolism compared with controls, but no regional increase compared with the global value. Neuropsychiatric rating scales were introduced to quantify behavioral abnormalities in aging and dementia, and to relate these to regional changes in brain metabolism as measured with PET. Behavioral changes are a major cause of institutionalization of AD patients.