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 0-470-84641-012Normal Ageing—A Problematical ConceptD. B. BromleyDepartment of Psychology, University of Liverpool, UKINTRODUCTIONThe word ‘‘normal’’ is used to refer to what is statistically normal,that is within the average range. The range can vary somewhat,say from the middle 50% of a normal distribution to perhaps themiddle 80%, depending upon one’s purpose. The word is alsoused to refer to prototypical members of a category, memberswith characteristics that best exemplify the category as a whole.The word is used to refer to what is socially prescribed andexpected, such as the usual forms of appearance and behaviourfor a given occasion in a community. Another usage refers to astandard pattern or sequence of events that have a highprobability of occurrence, such as impairment of vision andhearing in later life.NORMAL AND PATHOLOGICAL AGEINGWith regard to human ageing, the word ‘‘normal’’ is used in allthe above senses, depending upon the context. In professionalgerontology, however, the phrase ‘‘normal ageing’’ usually impliesthe existence of a contrasting condition or process, viz.‘‘pathological ageing’’. Difficulties arise because normal ageingand pathological ageing are conceptually interdependent. Themain historical landmark in attempts to distinguish between themwas the publication of Korenchevsky’s Physiological and PathologicalAgeing 1 . Korenchevsky drew attention to the fact thatsome physiological functions in some elderly human subjects wereequal to or superior to those of chronologically younger subjects.Psychological research into sensorimotor and cognitive performanceoften reveals that some elderly subjects perform as well asor better than the average younger subject.On the basis of evidence that some individuals show relativelylittle physiological impairment with age, at least until late life,Korenchevsky inferred the existence of primary (non-pathological)ageing. On the basis of evidence that other individuals showsubstantially greater than average impairment earlier in adult life,he inferred the existence of secondary (pathological) ageing.These two inferences, however, are simply two versions of thesame argument, namely, that ageing is characterized by widedifferences between individuals. If we plot the distributions ofscores on physiological or psychological functions for several agegroups in a cross-sectional study, we often find considerableoverlap between even widely spaced age groups. If the distributionsof performance scores for the same respondents at differentages in a longitudinal study are compared, we usually find thatindividuals tend to retain their position (rank order) relative toother respondents. A minority, however, show decline relative totheir position at earlier ages. These are the people who appear toexhibit pathological ageing. Thus, individual differences in normalageing tend to be maintained, even though there is a decline withage, on average, over the period studied. These differences arebrought about by various causes, including genetic characteristics,life-history events, life styles and environmental conditions.Even among the community-dwelling elderly, there are widevariations in physical and mental health and wide variations insuch things as living conditions, social support, stress and copingstrategies and health. In a multicultural society, the range ofdifferences between individuals at later ages is likely to be verywide. The process of normal ageing is a social as well as abiological process. That is to say, society prescribes or normalizesvarious stages in the life cycle, so that there are typical ages for thecompletion of full-time education, marriage (or sexual partnership),parenthood, occupational status and retirement. Sucharrangements may change from one generation to the next.This, together with secular changes in health, longevity, life stylesand so on, make the concept of ‘‘normal ageing’’ a moving target.Flynn has reported substantial secular (cohort) effects onmeasures of intelligence 2 . Consider how the contraceptive pilland hormone replacement therapy have changed the life styles ofwomen. Consider also how drugs, AIDS, migration and economicfactors may affect ageing in sections of the population. These aretechnical issues for demography and epidemiology.It is possible to demonstrate general age trends and effects. Forexample, the sex difference in longevity is well established; there isa differential decline in fluid and crystallized psychologicalabilities; anatomical and physiological functions have theircharacteristic normal patterns of change with age. There aresome similarities between the normal (common) effects of ageingand the effects of pathologies such as Alzheimer’s disease, asshown by neurological and psychological tests. These trends andeffects are compatible with the view that ageing is the result of amultiplicity of causes. They are not proof that there are two sortsof ageing: pathological and normal (non-pathological) 3 . On theother hand, there is the question of whether senile dementia of theAlzheimer type or multi-infarct dementia are the end-results of anormal intrinsic ageing process that would affect anyone wholived long enough, or whether they are abnormal conditionsinduced by genetic faults, life-history factors or specific extrinsiccauses, such as infection or exposure to noxious substances.Genetic mutations increase with advancing age, and may affectperformance before the obvious signs and symptoms of disease.The argument in favour of the notion that there are two sorts ofageing—normal and pathological—is supported by evidence thatpeople suffering from identifiable pathologies, such as cancer,heart disease or diabetes, have reduced life expectations and arePrinciples 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