Information about Alzheimer's, Dementia, and Memory

Alzheimer's disease, which is named for the German physician who first identified it in 1906, is the most common form of dementia, accounting for 60 to 70 percent of cases. It is a progressive disorder of the brain and is characterized by a gradual deterioration of mental faculties caused by a loss of nerve cells and the connections between them. The disease is often accompanied by changes in behavior and personality.

Its course is relentless and relatively predictable, but the rate of mental decline varies from person to person. A recent study of people identified during a community study found that only half of people with Alzheimer's survive more than three years after the initial diagnosis, but earlier studies of people diagnosed in doctors’ offices and clinics reported survival times of five to nine years. But some individuals can live for 20 years or more after diagnosis.

Alzheimer's Disease & Degenerative Changes in the Brain

In Alzheimer's disease, nerve cells (neurons) stop functioning, lose connections with each other, and ultimately die. The death of many neurons in key parts of the brain causes those areas to atrophy (shrink) and results in abnormalities in memory, thinking, and behavior.

Early in the disease, destruction of neurons is particularly widespread in parts of the brain that control memory, especially the hippocampus. This explains why memory impairment is often the first sign of Alzheimer's disease. As nerve cells in the hippocampus break down, memory of recent events begins to fail, and the ability to do familiar tasks begins to decline as well.

The other part of the brain that sustains major damage is the cerebral cortex, particularly the areas responsible for language, reasoning, perception, and judgment (the temporal, frontal, and parietal lobes). As a result, unwarranted emotional outbursts (referred to as catastrophic reactions), disturbing behaviors (such as wandering), and episodes of extreme agitation occur and become more frequent as the disease progresses.

As additional areas of the brain are affected, the person with Alzheimer's disease becomes bedridden, incontinent, totally helpless, and unresponsive to the outside world.

Causes of Alzheimer's Disease

Despite tremendous advances in the understanding of Alzheimer's disease, scientists have yet to pinpoint a true cause of the disorder. The leading theory is that Alzheimer's disease is caused by an accumulation of insoluble fragments of beta-amyloid in the brain. Because these fragments are not dissolved, researchers suspect that this form of beta-amyloid more readily builds up and forms plaques.

Publication Review By: Peter V. Rabins, M.D., M.P.H.

Published: 09 Mar 2011

Last Modified: 28 Aug 2015