Dementia is a an illness that usually occurs slowly over time, and usually includes a progressive state of deterioration. The earliest signs of dementia are usually memory problems, confusion, and changes in the way a person behaves and communicates.
Dementia is the loss of cognitive functioning, which means the loss of the ability to think, remember, or reason, as well as behavioral abilities, to such an extent that it interferes with a person’s daily life and activities.
Signs and symptoms of dementia occur when healthy neurons (nerve cells) in the brain stop working, lose connections with other brain cells, or die.
Everyone loses some neurons as they age, but people with dementia experience far greater loss in neurons and brain cells.
Scientists have some theories about mechanisms that may lead to different forms of dementias, but more research is needed to better understand if and how these mechanisms contribute to the development of dementia.
Dementia is more common with advanced age, as many as half of all people age 85 or older may have some type of dementia,
it is not a normal part of aging.
Memory loss is not the only sign of dementia. For a person to be considered to have dementia, he or she must meet the following criteria:
- Two or more core mental functions must be impaired. These functions include memory, language skills, visual perception, and the ability to focus and pay attention. These also include cognitive skills such as the ability to reason and solve problems.
- The loss of brain function is severe enough that a person cannot do normal, everyday tasks.
Some people with dementia cannot control their emotions. Their personalities may change. They can have delusions, which are strong beliefs without proof, such as the idea that someone is stealing from them.
Source
http://www.ninds.nih.gov/disorders/dementias/detail_dementia.htm
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