Dementia is a loss of mental ability severe enough to interfere with normal activities of daily living, lasting more than six months, not present since birth, and not associated with a loss or alteration of consciousness. Dementia is a group of symptoms caused by gradual death of brain cells. Dementia is usually caused by degeneration in the cerebral cortex, the part of the brain responsible for thoughts, memories, actions and personality. Death of brain cells in this region leads to the cognitive impairment which characterizes dementia.

The loss of cognitive abilities that occurs with dementia leads to impairments in memory, reasoning, planning, and personality. While the overwhelming number of people with dementia are elderly, it is not an inevitable part of aging. Instead, dementia is caused by specific brain diseases. Alzheimer's disease is the most common cause, accounting for three quarters of all cases, followed by vascular or...