Harnessing brain and cognitive reserve for the prevention of dementia

The concepts of brain and cognitive reserve capture several elements of common wisdom - that we all differ in the neural resources we are endowed at birth, that experience and especially complex mental activities then modify how these neural resources are organized and cultivated, and that after any form of brain injury there is significant individual variation in the degree to which clinical deficits may manifest. Transforming these insights into a formal and refutable working definition, however, has been more challenging. Depending on the scale of analysis, brain and cognitive reserve have been defined from neurocentric, neuropsychological, computational, and behavioral perspectives. In our research, we have focused on the behavioral definition, whereby an individual's lifetime exposure to complex mental activities is used for prediction of longitudinal cognitive and neurological change. This approach also benefits from a wealth of epidemiological studies linking heightened complex mental activity with reduced dementia risk. Research in the field of cognitive training is also beginning to indicate that incident cognitive decline can be attenuated, with recent clinical trials addressing the major challenges of transfer of gain and durability of effect. High quality randomized clinical trials are therefore the most urgent priority in this area so that the promise of brain and cognitive reserve can be harnessed for the purpose of the primary prevention of dementia.

Decreased cognition in children with risk factors for Alzheimer's disease

BACKGROUND

The epsilon4 allele of the apolipoprotein E gene (APOE-epsilon4) and a family history (+FH) of Alzheimer's disease (AD) are both risk factors for the development of AD. Although studies to identify a preclinical phase of AD have led to evidence of APOE-epsilon4- and +FH-related differences in brain and cognitive functioning in healthy adults, the relative influence of these factors in children is unknown.

METHODS

To investigate this issue, school-age children (n = 109) received standardized achievement tests, the Rey-Osterrieth Complex Figure Test (Copy Condition; RCFT-CC), assessment of family medical history, and buccal swab testing to determine their APOE genotype.

RESULTS

Analyses revealed that, relative to children without these risk factors, children who possess both an APOE-epsilon4 allele and a +FH of AD and/or significant memory problems (MP) obtained lower scores on nearly every cognitive test administered.

CONCLUSIONS

Findings suggest that when both AD risk factors are present, cognition may be adversely affected as early as childhood. Thus, risk factors for a disorder of pathological aging (i.e., AD) may have implications for the etiology of certain types of learning difficulties in children.

Contribution of education, occupation and cognitively stimulating activities to the formation of cognitive reserve

The cognitive reserve (CR) concept posits that there is individual variability in processing task demands and coping with neurodegenerative diseases. This variability can be attributed to the protective effects derived from continuous cognitive stimulation throughout life, including formal education, engagement in cognitively stimulating activities and occupation. These can result in protection against age-related cognitive decline and reduce the risk of developing Alzheimer’s disease. The aim of this review is to summarize the main features of CR formation and to discuss the challenges in carrying out CR research in developing countries.

The response-signal method reveals age-related changes in object working memory

Sixteen healthy young adults (ages 18-32) and 16 healthy older adults (ages 67-81) completed a delayed response task in which they saw the following visual sequence: memory stimuli (2 abstract shapes; 3,000 ms), a blank delay (5,000 ms), a probe stimulus of variable duration (one abstract shape; 125, 250, 500, 1,000, or 2,000 ms), and a mask (500 ms). Subjects decided whether the probe stimulus matched either of the memory stimuli; they were instructed to respond during the mask, placing greater emphasis on speed than accuracy. The authors used D. L. Hintzman & T. Curran's (1994) 3-parameter compound bounded exponential model of speed-accuracy tradeoff to describe changes in discriminability associated with total processing time. Group-level analysis revealed a higher rate parameter and a higher asymptote parameter for the young adult group, but no difference across groups in x-intercept. Proxy measures of cognitive reserve (Y. Stern et al., 2005) predicted the rate parameter value, particularly in older adults. Results suggest that in working memory, aging impairs both the maximum capacity for discriminability and the rate of information accumulation, but not the temporal threshold for discriminability.

The heritability of abstract reasoning in Caribbean Latinos with familial Alzheimer disease

BACKGROUND

Alzheimer disease (AD) is under substantial genetic influence. To better understand the genetic influence on component phenotypes of AD, we estimated the heritability (h(2)) of abstract reasoning and examined its relation with apolipoprotein epsilon 4 (APOE-epsilon 4).

METHODS

We studied abstract reasoning in 1,116 individuals from 210 Caribbean Hispanic families with late onset AD, using the similarities subtest scores from the Wechsler Adult Intelligence Scale. We computed h(2), then performed analysis of variance to examine the effect of APOE-epsilon 4.

RESULTS

Abstract reasoning was highly heritable (h(2)(unadjusted) = 79.9%). After adjusting for covariates, the h(2) was reduced to 32.6%, with education accounting for 40.8% of the variance. The APOE-epsilon 4 allele had no effect.

CONCLUSION

Abstract reasoning was strongly influenced by genetic factors and education. Genes other than APOE contribute to the inheritance of abstract reasoning ability.

Education and rates of cognitive decline in incident Alzheimer's disease

BACKGROUND

Some (but not all) epidemiological studies have noted faster rates of progression in high education patients with Alzheimer's disease (AD), which has been attributed to harbouring/tolerating a higher pathological burden at the time of clinical dementia for subjects with higher education. We wanted to assess the relationship between education and rates of decline in AD.

METHODS

During the course of a community based multiethnic prospective cohort study of individuals aged > or = 65 years living in New York, 312 patients were diagnosed with incident AD and were followed overall for 5.6 (up to 13.3) years. The subjects received an average of 3.7 (up to 9) neuropsychological assessments consisting of 12 individual tests. With the aid of a normative sample, a standardised composite cognitive score as well as individual cognitive domain scores were calculated. Generalised estimating equation models were used to examine the association between education and rates of cognitive decline.

RESULTS

Composite cognitive performance declined by 9% of a standard deviation per year. Rates of decline before and after AD incidence were similar. For each additional year of education there was 0.3% standard deviation lower composite cognitive performance for each year of follow up. The association between higher education and faster decline was noted primarily in the executive speed (0.6%) and memory (0.5%) cognitive domains and was present over and above age, gender, ethnicity, differential baseline cognitive performance, depression, and vascular comorbidity.

CONCLUSIONS

We conclude that higher education AD patients experience faster cognitive decline.