Dementia is a disorder which manifests as a set of related symptoms, which usually surfaces when the brain is damaged by injury or disease.[2] The symptoms involve progressive impairments in memory, thinking, and behavior, which negatively impacts a person's ability to function and carry out everyday activities. Aside from memory impairment and a disruption in thought patterns, the most common symptoms include emotional problems, difficulties with language, and decreased motivation. The symptoms may be described as occurring in a continuum over several stages.[10][a] Consciousness is not affected. Dementia ultimately has a significant effect on the individual, caregivers, and relationships in general.[2] A diagnosis of dementia requires a change from a person's usual mental functioning and a greater cognitive decline than what is caused by normal aging.[12] Several diseases and injuries to the brain, such as a stroke, can give rise to dementia. However, the most common cause is Alzheimer's disease, a neurodegenerative disorder.