Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24 Page 25 Page 26 Page 27 Page 28 Page 29 Page 30 Page 31 Page 32 Page 33 Page 34 Page 35 Page 36 Page 37 Page 38 Page 39 Page 40 Page 41 Page 42 Page 43 Page 44 Page 45 Page 46 Page 47 Page 48 Page 49 Page 50 Page 51 Page 52 Page 53 Page 54 Page 55 Page 56 Page 57 Page 58 Page 59 Page 60 Page 61 Page 62 Page 63 Page 64 Page 65 Page 66 Page 67 Page 68 Page 69 Page 70 Page 71 Page 72 Page 73 Page 74 Page 75 Page 76 Page 77 Page 78 Page 79 Page 80 Page 81 Page 82 Page 83 Page 84 Page 85 Page 86 Page 87 Page 88 Page 89 Page 90 Page 91 Page 92 Page 93 Page 94 Page 95 Page 96 Page 97 Page 98 Page 99 Page 100 Page 101 Page 102 Page 103 Page 104 Page 105 Page 106 Page 107 Page 108AGING IN THE 21S T CENTURY 36 CHAPTER 2 | THE AGING BRAIN The human brain is a remarkable organ, but it too experiences aging. Most cognitive abilities begin declining early in adulthood. For most people it’s only at relatively advanced ages that cognitive decline begins to create significant impairment, and there is great diversity in when or if significant impairment occurs. The rapid growth in the size of the elderly population as the Baby Boom generation reaches retirement translates to a significant rise in the size of the population with dementia and other cognitive problems, despite some favorable evidence that age-specific dementia rates may be declining. The number of individuals over age 65 with Alzheimer’s disease (AD) is likely to grow from 5.1 million in the US now to 13.8 million in 2050 (Alzheimer’s Association 2015). These statistics demonstrate a vital need for reliable information on the size of the problem, as well as the causes, consequences, and the economic and societal impact of dementia. T o meet the need for data on the aging brain, the HRS has included measures of cognition since it began in 1992. With many years of data on cognitive functioning across multiple birth cohorts, researchers are now reporting on changes in cognitive functioning with age and time. Extensive information on social and medical factors in the HRS enables the tracking of new trends — such as changes in family structure or growth in the prevalence of obesity — that may also affect cognition. To facilitate even more in-depth research, the HRS conducted an in-home clinical interview study designed to produce estimates of the incidence and prevalence of AD and other forms of dementia known as the Aging, Demographics, and Memory Study (ADAMS). Initially fielded in 2001 as a supplement to the HRS, and therefore linked to the rich information available in the main survey, ADAMS enables researchers to identify risk factors and outcomes of AD and dementia subtypes such as medical, economic and social costs. A new supplemental study, the Healthy Cognitive Aging Project (HCAP), is underway to continue collecting high-value data on cognition and dementia. Taken together, these data resources provide unprecedented opportunities for studying the aging brain and for providing critical information to plan for the needs of the aging population. Assessing Dementia in the Population Challenges Dementia is challenging to study for several reasons. Foremost is the fact that the typical cognitive decline of dementia is gradual and takes place over a number of years, making it hard to determine when a threshold for diagnosis of illness is reached. Similarly, it can be difficult to differentiate between mild levels of cognitive de- cline that are typical of normal aging as opposed to the more significant and pathological changes of AD or dementia. Diagnostic criteria for demen- tia and the pre-dementia stage of mild cognitive