Dementia is a broad category of brain diseases that cause a long-term and often gradual decrease in the ability to think and remember that is great enough to affect a person's daily functioning.
Other common symptoms include emotional problems, difficulties with language, and a decrease in motivation. A person's consciousness is usually not affected.
A dementia diagnosis requires a change from a person's usual mental functioning and a greater decline than one would expect due to aging. These diseases also have a significant effect on a person's caregivers.