b'AGING IN THE 21ST CENTURYCHAPTER 2 | THE AGING BRAINThe human brain is a remarkable organ, but it too experiences aging. Most cognitive abilities begin declining early in adulthood. For most people its 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 Alzheimers disease (AD) is likely to grow from5.1 million in the US now to 13.8 million in 2050 (Alzheimers 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 agingof dementia known as the Aging, Demographics,Assessing Dementiabrain, the HRS has included measures ofand Memory Study (ADAMS). Initially fielded inin the Populationcognition since it began in 1992. With2001 as a supplement to the HRS, and therefore many years of data on cognitive functioninglinked to the rich information available in theChallengesacross multiple birth cohorts, researchers are nowmain survey, ADAMS enables researchers toDementia is challenging to study for several reporting on changes in cognitive functioningidentify risk factors and outcomes of AD andreasons. Foremost is the fact that the typical with age and time. Extensive information ondementia subtypes such as medical, economiccognitive decline of dementia is gradual and takes social and medical factors in the HRS enablesand social costs. A new supplemental study,place over a number of years, making it hard the tracking of new trendssuch as changesthe Healthy Cognitive Aging Project (HCAP),to determine when a threshold for diagnosis of in family structure or growth in the prevalenceis underway to continue collecting high-valueillness is reached. Similarly, it can be difficult to of obesitythat may also affect cognition.data on cognition and dementia. Taken together,differentiate between mild levels of cognitive de-To facilitate even more in-depth research, thethese data resources provide unprecedentedcline that are typical of normal aging as opposed HRS conducted an in-home clinical interviewopportunities for studying the aging brain andto the more significant and pathological changes study designed to produce estimates of thefor providing critical information to plan for theof AD or dementia. Diagnostic criteria for demen-incidence and prevalence of AD and other formsneeds of the aging population. tia and the pre-dementia stage of mild cognitive 36'