From a pool of 198 patients with dementia initially seen at the University of California Los Angeles (UCLA) Alzheimer's Disease Center, 20 outpatients who met all clinical criteria described below, comparable across demographic and behavioral domains and divided equally into those with and without agitation/aggression, were studied. All patients had acquired persistent decline involving at least 3 of the following domains: language, memory, visuospatial skills, cognition (ie, calculation, abstraction, judgment, and others), and emotion or personality.42 All patients with AD met National Institute of Neurological and Communicative Disorders and Stroke–Alzheimer's Disease and Related Disorders Association criteria for probable or possible AD.43 All patients with vascular dementia met National Institute of Neurological Disorders and Stroke–Alzheimer's Disease and Related Disorders Association International Workshop criteria for probable or possible vascular dementia44; patients with large cortical strokes were excluded from the study. All patients with dementia who had Lewy bodies met the Consortium for Dementia with Lewy Bodies criteria for probable dementia with Lewy bodies.45 Diagnostic evaluation for all patients included complete medical history, physical and neurological examination, magnetic resonance imaging or computed tomographic imaging, technetium Tc 99m–labeled hexamethylpropylene amineoxime–SPECT imaging of the brain, and electroencephalography, and routine blood tests (including thyrotropin level, vitamin B12 level, and serological test for syphilis), and had caregivers who were willing to be interviewed. Exclusion criteria for all patients were delirium, history of alcohol or other substance abuse, history of head trauma with loss of consciousness, and history of psychiatric disorder preceding the onset of symptoms of dementia. Patients were physically well without pain or other identifiable precipitants of behavioral disturbances. Cognitive assessment included the Mini-Mental State Examination,46 the Consortium to Establish a Registry for Alzheimer's Disease47 10-word memory test, the modified 15-item Boston Naming Test,48 the Consortium to Establish a Registry for Alzheimer's Disease visuospatial task (copying a circle, diamond, overlapping rectangles, and cube), and a verbal fluency task (animal name generation in 1 minute). The 20 patients chosen were representative of the 198 patient pool having a similar sex, age, Mini-Mental State Examination score, and educational level of the larger group; the pool was assembled from all patients seen in the UCLA Alzheimer's Disease Center who had cognitive, behavioral, laboratory, structural, and functional (SPECT) imaging.