It is a chronic and irreversible disease in which brain cells are irreversibly damaged leading to impaired function and loss of memory. It is the most common form of dementia which results in disorientation, impaired thinking, mood swings, and behavioral changes. The disease causes clumps or aggregations near the brain cells that destroy brain connective tissue. It usually occurs in older individuals as a sequel to lowered metabolic rates and gradually destroys their ability to process information into actions.