Alzheimer disease (AD) is a widely known type of dementia. It is an irreversible brain disease that slowly affects memory, thinking, and behavior. In the brain, brain cells talk to each other with special signals, helping people control their minds and bodies. People with AD have lower amounts of these signals. One possible reason for this is that people with AD also have a buildup of a specific protein called amyloid-β that prevents their brain cells from communicating with each other. When this happens, a person begins to act and think differently. They may start to show strange behavior or experience delusions. The person may also start showing mood symptoms like aggression, depression, or anxiety. Together, mood symptoms are also called neuropsychiatric symptoms (NPS). In addition, people with AD gradually lose cognitive function. Loss of cognitive abilities are separate from NPS. They include things like troubles with reasoning, memory, problem solving, or mathematical or verbal skills.