After age 50, the brain starts to shrink, and mental function declines. But the severity and rate varies greatly from person to person. Here are the different stages of brain aging:
AGE-ASSOCIATED MEMORY IMPAIRMENT
Occasional forgetfulness, primarily of new information, such as names of people you recently met. Considered a normal response to aging.
MILD COGNITIVE IMPAIRMENT
Severe or frequent memory lapses, such as repeatedly missing appointments, but no other mental impairment. About 40% of people diagnosed with MCI develop Alzheimer's within three years.
Severe cognitive decline, marked by large memory deficits. Dementia is a not a disease but a symptom of a number of diseases, including stroke, substance abuse, head trauma, and Alzheimer's.
A progressive brain disease that initially causes mild memory loss and eventually destroys all cognitive functions, leading to death. Alzheimer's is responsible for about 50% of all dementia cases.