Dementia refers to a loss of cognitive function (an intellectual process resulting in an understanding, perception, or awareness of one's thoughts and ideas). Dementia can be caused by changes in the brain such as those associated with disease or trauma. The changes may occur gradually or quickly.
Cognition is the act or process of thinking, perceiving, and learning. Cognitive functions that may be affected by dementia include decision making, judgment, memory, spatial orientation, thinking, reasoning, and verbal communication. Dementia may also result in behavioral and personality changes, depending on the area(s) of the brain affected.
Dementia is actually a word for a group of symptoms caused by disorders that affect the brain. It is not a specific disease. Individuals with dementia may not be able to think well enough to do normal activities, such as getting dressed or eating. They may lose the ability to solve problems or control emotions and their personalities may change. These individuals may become agitated or hallucinate.
Dementia usually results from a widespread destruction of, or interference with, brain cells. Consequently, there is a loss of mental functions previously controlled by those cells.
Many different diseases can cause dementia, including Alzheimer's disease, Huntington's disease (an inherited movement disorder), and stroke (neurological damage due to a lack of oxygen to the brain). Drugs are available to treat some of these diseases. While these drugs cannot cure dementia or repair brain damage, they may improve symptoms or slow down the disease.
Dementia can be progressive, such as with Alzheimer's disease, or occur for a short period of time, perhaps as the result of a head injury.
Progressive dementia is most common among the elderly. These individuals are usually termed "senile." However, dementia should not be considered a part of the normal aging process. Most individuals who reach their elderly years do not develop dementia.
Some dementia is reversible and can be cured partially or completely with a doctor's treatment. The degree of reversibility often depends on how quickly the underlying cause is treated. Irreversible dementia is caused by an incurable condition (such as in Alzheimer's disease and Huntington's disease). Individuals with irreversible dementia are eventually unable to care for themselves and may require constant care.
Some types of dementia, such as Alzheimer's disease and Huntington's disease, have been linked to genetics. However, most cases of dementia are thought to involve multiple factors besides heredity, such as age, gender, and lifestyle choices.
An estimated two million people in the United States suffer from severe dementia and another one to five million people experience mild to moderate dementia. Approximately five to eight percent of individuals over the age of 65 have some form of dementia; the number doubles every five years over age 65.

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