According to the National Institute of Health, “dementia is the loss of cognitive functioning — thinking, remembering, and reasoning — to such an extent that it interferes with a person’s daily life and activities.”

Some people with dementia have difficulty controlling their emotions. And their personalities may change.

Dementia ranges in severity from the mildest stage, when it is just beginning to affect a person’s functioning, to the most severe stage, when the person must depend completely on others for basic activities of living.

The cause of dementia is unknown in many cases. Research is ongoing to better understand what causes dementia. However, the underlying mechanism is thought to be related to a build-up of proteins in the brain that interferes with how the brain functions or works.

Neurodegenerative diseases, like frontotemporal dementia, lead to abnormal protein build-ups in the brain. Different protein build-ups are seen in different types of dementia. For example, proteins called beta-amyloid and tau are associated with Alzheimer’s disease. While the protein alpha-synuclein is associated with Lewy body dementia. Changes in the blood vessels in the brain may result in vascular dementia. In a minority of cases, a reversible cause of a person’s dementia can be identified and treated. Screening for these reversible causes is part of the diagnostic evaluation for anyone with changes in memory or thinking.