Dementia refers to the loss of cognitive functions (thinking, reasoning, the ability to remember) that is severe enough to interfere with a person’s daily functioning. This group of symptoms may accompany certain diseases or conditions. Alzheimer’s disease is the most common form (and cause) of dementia. It is a progressive, degenerative disease of the brain, characterized by loss of function and death of nerve cells in several brain areas. This leads to loss of recent memories and new learning first, and eventually old memories, too.