1. Dementia is defined by multiple cognitive deficits such as memory loss, language problems, and impaired executive function, leading to functional decline. The most common causes are Alzheimer's disease, vascular dementia, and Lewy body disease.
2. Alzheimer's disease accounts for over 50% of dementia cases. Its prevalence doubles every 5 years after age 60. The clinical features include loss of cognition and daily functioning as well as abnormal behaviors.
3. In Alzheimer's disease, there is cholinergic dysfunction and neurodegeneration in the brain, likely caused by beta-amyloid plaques and neurofibrillary tangles due to genetic and environmental risk factors.