Dementia is a group of symptoms caused by disorders that affect the brain, rather than a single disease. It is characterized by impaired brain functions including problems with memory, language, thinking, and behavior. The main types of dementia are cortical, which affects the brain's cortex; subcortical, which affects areas below the cortex; and progressive forms that get worse over time. Dementia can be caused by neurological diseases like Alzheimer's and strokes, as well as head injuries, infections, and other illnesses. Symptoms include memory loss, confusion, impaired problem-solving, and personality changes. A diagnosis involves medical history, exam, and tests to determine if the dementia is reversible or requires management of symptoms.