Brain reserve capacity on symptom onset after brain injury: A formulation and review of evidence for threshold theory.

Decline in cognitive functioning and onset of cognitive impairment are potentially important predictors of elderly persons needing informal assistance and formal health care. This article describes the measures of cognitive functioning that were developed for the Asset and Health Dynamics Among the Oldest Old (AHEAD) study of some 6,500 Americans aged 70 years and older. The study was designed to investigate the impact of health on disbursement of family and economic resources. Evaluation of the cognitive measures in terms of psychometric properties and missing data, telephone administration, and formation of an aggregate index is encouraging. Their construct validity is evidenced by their correlations with sociodemographic characteristics and health indicators that replicate existing findings as well as by their prediction of IADL and ADL functioning that are consistent with theory.

Measures of Cognitive Functioning in the AHEAD Study

We used path analysis on data from the British 1946 birth cohort to model lifetime antecedents of cognitive reserve, represented by the NART at 53 years, and compared this model for verbal memory and psychomotor function at this age, cognitive outcomes that are sensitive to age-associated decline. We showed independent paths from childhood cognition, educational attainment and adult occupation to cognitive reserve, with that from childhood cognition the strongest, and that from adult occupation the weakest. A similar pattern was found for the verbal memory and psychomotor outcomes, although the pathways were weaker than those to the NART. The pattern was also mirrored by the paths from paternal occupation to childhood cognition, educational attainment and adult occupation, with that to childhood cognition the strongest, and that to adult occupation the weakest. The direct influence of paternal occupation on cognitive reserve was negligible, and almost entirely mediated by childhood cognitive ability and educational attainment.

Lifetime Antecedents of Cognitive Reserve

There is an urgent need to identify lifestyle activities that reduce functional decline and dementia associated with population aging. The goals of this article are to review critically the evidence on the benefits associated with formal volunteering among older adults, propose a theoretical model of how volunteering may reduce functional limitations and dementia risk, and offer recommendations for future research. Database searches identified 113 papers on volunteering benefits in older adults, of which 73 were included. Data from descriptive, cross-sectional, and prospective cohort studies, along with 1 randomized controlled trial, most consistently reveal that volunteering is associated with reduced symptoms of depression, better self-reported health, fewer functional limitations, and lower mortality. The extant evidence provides the basis for a model proposing that volunteering increases social, physical, and cognitive activity (to varying degrees depending on characteristics of the volunteer placement) which, through biological and psychological mechanisms, leads to improved functioning; we further propose that these volunteering-related functional improvements should be associated with reduced dementia risk. Recommendations for future research are that studies (a) include more objective measures of psychosocial, physical, and cognitive functioning; (b) integrate qualitative and quantitative methods in prospective study designs; (c) explore further individual differences in the benefits associated with volunteering; (d) include occupational analyses of volunteers' specific jobs in order to identify their social, physical, and cognitive complexity; (e) investigate the independent versus interactive health benefits associated with volunteering relative to engagement in other forms of activity; and (f) examine the relationship between volunteering and dementia risk.

The benefits associated with volunteering among seniors: : A critical review and recommendations for future research

The Mini-Mental State Examination (MMSE) measures global cognitive performance and is often used as a screening test for dementia. This paper presents a 5-year longitudinal study of the MMSE score in a sample of 2,537 non-demented French community residents aged 65 years and older who were participants in the Paquid Study in 1988-1992. Subjects were evaluated at the baseline visit (T0) and 1 year (T1), 3 years (T3), and 5 years (T5) later. Analyses performed with a random effects linear model showed that the score rose between T0 and T1 (by 0.60 points for subjects aged 65 years at T0 to 0.83 points for subjects aged 85 years at T0), then it decreased very slightly between T1 and T5 (by 0.02 points for subjects aged 65 years to 0.57 points for subjects aged 85 years). The improvement during the first year, which was larger for less educated subjects, may be explained by the stress due to the test situation at T0 or by a learning effect at T1. The decline during the last 4 years was more pronounced for older and less well educated subjects. The cross-sectional measure of age effect was larger than the longitudinal measure of time effect. This difference may be explained by a cohort effect or by a practice effect induced by repetition of the test. The authors conclude that the MMSE score declines very slightly in non-demented subjects, thus suggesting that the cognitive processes involved are spared by the aging process. These results may have implications for dementia screening.

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A 5-Year Longitudinal Study of the Mini-Mental State Examination in Normal Aging

The purpose of the present study was to examine the relation between principal lifetime occupation and cognitive performance with the initial data collected (1988-1989) in a cohort of 3,777 community residents of the area of Bordeaux, France, aged 65 years and older. Subjects were considered as cognitively impaired if they scored under 24 on the French version of the mini-mental state examination. Cognitive impairment was found to vary significantly across the different occupational categories. Results of the logistic regression show that age, sex, and educational level are significantly related to cognitive impairment. Moreover, after controlling for these and other covariates, farmworkers (odds ratio (OR) = 6.1, 95% confidence interval (CI) 3.3-11.4), farm managers (OR = 2.9, 95% CI 1.6-5.1), domestic service employees (OR = 2.8, 95% CI 1.5-5.1), and blue-collar workers (OR = 2.5, 95% CI 1.4-4.4) had a higher risk of cognitive impairment than did subjects who had an intellectual occupation. Follow-up of the cohort will permit precise determination of the role of principal lifetime occupation in subsequent cognitive deterioration. Occupational status should be taken into consideration when studying brain aging.

Magali Evaldre

Papers

Principal Lifetime Occupation and Cognitive Impairment in a French Elderly Cohort (Paquid)