Alzheimer's disease (AD) is a progressive disease of the brain that is characterized by impairment of memory and a disturbance in at least one other thinking function (for example, language or perception of reality). Many scientists believe that AD results from an increase in the production or accumulation of a specific protein (beta-amyloid protein) that leads to nerve cell death. Loss of nerve cells in strategic brain areas, in turn, causes deficits in the neurotransmitters, which are the brain's chemical messengers.

Alzheimer's disease is not a normal part of aging and is not something that inevitably happens in later life. Rather, it is one of the dementing disorders, which are a group of brain diseases that result in the loss of mental and physical functions.