As the population ages, cognitive impairment, including Alzheimer_s disease and other forms of dementia as well as lesser declines associated with aging, has become one of the greatest health threats. The total number of new cases of dementia each year worldwide is nearly 7.7 million, and the total number worldwide isprojected to nearly double every 20 yr, to 65.7 million in 2030 and 115.4 million in 2050 (36).