Mohammed T. Abou-Saleh

Principles and Practice of Geriatric Psychiatry.Editors: Professor John R. M. Copeland, Dr Mohammed T. Abou-Saleh and Professor Dan G. BlazerCopyright & 2002 John Wiley & Sons LtdPrint ISBN 0-471-98197-4 Online ISBN 0-470-84641-055bBenign Senescent Forgetfulness,Age-associated Memory Impairment, andAge-related Cognitive DeclineKathleen A. Welsh-Bohmer and David J. MaddenDuke University Medical Center, Durham, NC, USAChanges in cognitive functioning are prevalent in aging. Thesechanges are perhaps best considered as falling along a continuum,with normal aging at one end of the scale and brain diseasesproducing bona fide dementias at the other end. It is not clear thatthe continuum of cognitive changes in aging and disease is entirelylinear. There may be periods of plateaux in cognitive declines oreven improvements in cognition as a function of adaptive brainchanges. The relationship of cognitive change in normal aging andbrain disease, such as Alzheimer’s disease (AD) is an area of activeinvestigation, benefiting from the advances in behavioral methodsand imaging technologies 1,2 .Normal aging is now recognized as a complex mosaic ofcognitive changes in which there is decline in some areas and asubstantial degree of either stability or improvement in others 3 .Ithas been frequently observed, for example, that fluid abilities,those relying primarily on the efficiency of current processing (e.g.measures of spatial and reasoning abilities), exhibit pronouncedand approximately linear age-related decline, whereas crystallizedabilities, those relying more on accumulated knowledge andexpertise (e.g. vocabulary measures) exhibit greater stability as afunction of age. A prominent feature of normal age-relatedcognitive change is a decline in the speed of informationprocessing, a decline that is more critical to the functioning offluid abilities than to the functioning of crystallized abilities.Salthouse 4 has developed a general theory of age-related changesin fluid cognition. The theory contains two central components: alimited time mechanism and a simultaneity mechanism. Accordingto Salthouse, changes in these mechanisms, at an elementarylevel, lead to changes that are observed in a variety of cognitivetasks. For example, the time available to perform higher-ordercognitive operations would be limited by an increase in theproportion of the available time occupied by initial processingstages. Similarly, if initial processing is slowed, then the productsof this processing may not be available simultaneously, asrequired by later operations.Between the two boundaries of normal aging and genuinecognitive impairment is a broad transition state comprisinggradations of cognitive change attributable to any of a host ofetiologies, including benign effects of aging to early-stage AD.Over the last three decades, a variety of nomenclatures haveemerged to describe the observed transitional memory stateattributed to aging. The most commonly recognized terms include‘‘benign senescent forgetfulness’’, ‘‘age-associated memoryimpairment’’ and, more recently, ‘‘mile cognitive impairment’’.These terms vary in subtle ways from one another. However,regardless of which terminology is used, all of these categorizationschemas basically describe the same phenomenon, an admixtureof mild memory problems that exceeds the range of normalcognition but falls short of being classified as dementia.The term ‘‘benign senescent forgetfulness’’ (BSF) was originallycoined by Kral 5 in the early 1960s to describe a form of mildmemory impairment that occurred in the context of aging and didnot appear to progress to dementia. In cohorts of elderly nursinghome residents followed over 4 years, Kral et al. 6 observed thatapproximately 18% demonstrated a form of mild memory lossdescribed as ‘‘subjective complaints of memory loss’’ and‘‘difficulty in retrieving stored recent or remote information’’,such as names or other proper nouns. Frequently, theseindividuals were able to retrieve the ‘‘forgotten’’ information ata later time and they had well-maintained mental facultiesotherwise. Compared to this group, another subgroup emergedwith a more significant memory impairment, characterized by aprominent inability to retain recent information over even briefperiods of time. These individuals typically had limited awarenessof their difficulties and had tendencies to confabulate. This lattergroup, designated as ‘‘malignant memory loss’’, was associatedwith progression in symptoms to dementia, shorter survival timesand increased mortality rates 6 . Kral believed that BSF wasassociated with physiological aging, whereas the more malignantform of memory decline was related to either vascular ordegenerative disease.The construct of BSF, although useful in succinctly describingthe boundary conditions of aging, fell out of favor in later years,primarily due to a lack of standardization in the diagnosticcriteria and the absence of clinical validation within representativeelderly populations. The samples used in Kral’s early work werecriticized because of the inclusion of a very large proportion ofchronic conditions, such as neurodegenerative diseases, cerebrovascularconditions and neuropsychiatric disorders. In morerecent years, interest in aging and AD led to a re-emergence ofattention on transitional memory states. In 1986, a workgroupconvened under the auspices of the National Institute of MentalHealth (NIMH) proposed the construct ‘‘age-associated memoryimpairment’’ (AAMI) to replace BSF. The new terminology had afirmer theoretical basis than its predecessor, with clinical andanatomical data to support its validity. The new nomenclaturealso improved upon BSF in that it included well-delineatedstandardized diagnostic criteria. The latter feature rendered thePrinciples and Practice of Geriatric Psychiatry, 2nd edn. Edited by J. R. M. Copeland, M. T. Abou-Saleh and D. G. Blazer&2002 John Wiley & Sons, Ltd