An estimated 44 million people 65 years and older worldwide have Alzheimer's, the most common cause of dementia. Alzheimer's is a degenerative brain disorder that causes memory loss, and impairs thinking, judgment and problem solving. So far, scientists have not found a drug that can stop the disease. But a research program in the United States is trying to prevent it by targeting the earliest changes in the brain while memory and thinking skills are still intact. VOA's Deborah Block has more.