Relationship between lifestyle proxies of cognitive reserve and cortical regions in older adults

Introduction

With the rapid increase in the population over 65 years old, research on healthy aging has become one of the priorities in the research community, looking for a cost-effective method to prevent or delay symptoms of mild cognitive disorder or dementia. Studies indicate that cognitive reserve theory could be beneficial in this regard. The aim of this study was to investigate the potential relationship between lifestyle socio-behavioral proxies of cognitive reserve and cortical regions in adults with no subjective cognitive decline.

Methods

Overall, 58 participants, aged 65-85 years, were included in the data analysis (M = 71.83, SD = 5.02, 20.7% male). Cognitive reserve proxies were measured using the Cognitive Reserve Index questionnaire, while cortical volumes were obtained with the Siemens 1.5 T Avanto MRI scanner and further mapped using the Desikan-Killiany-Tourville (DKT) Atlas. Estimated intracranial volume and age were used as covariates.

Results

The results indicated that higher occupational complexity was associated with larger cortical volume in the left middle temporal gyrus, the left and right inferior temporal gyrus, and the left inferior parietal lobule, while a combined proxy (the total CRI score) showed a positive relationship with the volume of left middle temporal gyrus and inferior parietal lobule, and pars orbitalis in the right hemisphere.

Discussion

These results might indicate that more complex occupational activities and overall more intellectually and socially active life-style could contribute to better brain health, especially in regions known to be more vulnerable to Alzheimer's disease.

Association of primary lifetime occupational cognitive complexity and cognitive decline in a diverse cohort: Results from the KHANDLE study

INTRODUCTION

Higher occupational complexity has been linked to favorable cognitive outcomes, but rarely examined in racially and ethnically diverse populations.

METHODS

In a diverse cohort (n = 1536), linear mixed-effects models estimated associations between main lifetime occupational complexity and domain-specific cognitive decline (z-standardized). Occupational complexity with data, people, and things were classified using the Dictionary of Occupational Titles.

RESULTS

For occupational complexity with data, highest tertile (vs. lowest) was associated with higher baseline executive function (β = 0.11; 95% confidence interval [CI] 0.00-0.22) and slower annual rate of decline (β = 0.03; 95% CI 0.01-0.06), and higher baseline semantic memory (β = 0.14; 95% CI 0.04-0.25). Highest tertile of occupational complexity with people was associated with higher baseline executive function (β = 0.29; 95% CI 0.18-0.40), verbal episodic memory (β = 0.12; 95% CI 0.00-0.24), and semantic memory (β = 0.23; 95% CI 0.12-0.34).

DISCUSSION

In a diverse cohort, higher occupational complexity is associated with better cognition. Findings should be verified in larger cohorts.

HIGHLIGHT

Few studies have examined associations of occupational complexity with cognition in diverse populations. Racial and ethnic minorities are disproportionately exposed to lower occupational complexity. Occupational complexity with data and people are associated with better cognition.

Social enrichment on the job: Complex work with people improves episodic memory, promotes brain reserve, and reduces the risk of dementia

Individuals with more complex jobs experience better cognitive function in old age and a lower risk of dementia, yet complexity has multiple dimensions. Drawing on the Social Networks in Alzheimer Disease study, we examine the association between occupational complexity and cognition in a sample of older adults (N = 355). A standard deviation (SD) increase in complex work with people is associated with a 9% to 12% reduction in the probability of mild cognitive impairment or dementia, a 0.14-0.19 SD increase in episodic memory, and a 0.18-0.25 SD increase in brain reserve, defined as the gap (residual) between global cognitive function and magnetic resonance imaging (MRI) indicators of brain atrophy. In contrast, complexity with data or things is rarely associated with cognitive outcomes. We discuss the clinical and methodological implications of these findings, including the need to complement data-centered activities (e.g., Sudoku puzzles) with person-centered interventions that increase social complexity.

Occupational complexity and cognition in the FINGER multidomain intervention trial

INTRODUCTION

Lifetime exposure to occupational complexity is linked to late-life cognition, and may affect benefits of preventive interventions.

METHODS

In the 2-year multidomain Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER), we investigated, through post hoc analyses (N = 1026), the association of occupational complexity with cognition. Occupational complexity with data, people, and substantive complexity were classified through the Dictionary of Occupational Titles.

RESULTS

Higher levels of occupational complexity were associated with better baseline cognition. Measures of occupational complexity had no association with intervention effects on cognition, except for occupational complexity with data, which was associated with the degree of intervention-related gains for executive function.

DISCUSSION

In older adults at increased risk for dementia, higher occupational complexity is associated with better cognition. The cognitive benefit of the FINGER intervention did not vary significantly among participants with different levels of occupational complexity. These exploratory findings require further testing in larger studies.

The relationship between cognitive engagement and better memory in midlife

INTRODUCTION

Engagement in cognitively stimulating work and activities may slow cognitive decline and dementia. We examined the individual and combined associations of four cognitive engagement indices (educational attainment, occupational complexity, social engagement, and cognitively stimulating leisure activities) with objective and subjective cognition.

METHODS

Middle-aged adults (n = 1864) enrolled in the Healthy Brain Project completed the Cogstate Brief Battery, the Cognitive Function Instrument, and self-report questionnaires of cognitive engagement.

RESULTS

Educational attainment and leisure activity engagement were individually associated with memory performance. Participants were classified based on whether they rated highly in zero to four cognitive engagement indices. Compared to participants with no indices, participants with two or more indices performed moderately better on memory.

DISCUSSION

Results suggest that greater variety of cognitive engagement across different areas of life is related to better memory in midlife. Possible explanation for this relationship may be increased opportunity for enhancing cognitive reserve, but further investigations are required.

Education, Occupational Complexity, and Incident Dementia: A COSMIC Collaborative Cohort Study

BACKGROUND

Education and occupational complexity are main sources of mental engagement during early life and adulthood respectively, but research findings are not conclusive regarding protective effects of these factors against late-life dementia.

OBJECTIVE

This project aimed to examine the unique contributions of education and occupational complexity to incident dementia, and to assess the mediating effects of occupational complexity on the association between education and dementia across diverse cohorts.

METHOD

We used data from 10,195 participants (median baseline age = 74.1, range = 58∼103), representing 9 international datasets from 6 countries over 4 continents. Using a coordinated analysis approach, the accelerated failure time model was applied to each dataset, followed by meta-analysis. In addition, causal mediation analyses were performed.

RESULT

The meta-analytic results indicated that both education and occupational complexity were independently associated with increased dementia-free survival time, with 28%of the effect of education mediated by occupational complexity. There was evidence of threshold effects for education, with increased dementia-free survival time associated with 'high school completion' or 'above high school' compared to 'middle school completion or below'.

CONCLUSION

Using datasets from a wide range of geographical regions, we found that both early life education and adulthood occupational complexity were independently predictive of dementia. Education and occupational experiences occur during early life and adulthood respectively, and dementia prevention efforts could thus be made at different stages of the life course.

Impact of occupational complexity on cognitive decline in the oldest-old

OBJECTIVES

The theory of "Cognitive Reserve" assumes that premorbid factors such as high educational and occupational attainment may enable a better way of coping with brain damage. It has been suggested that more stimulating lifestyles, including more complex work environments, may provide a buffer against cognitive decline in later life. This study aimed to investigate the association between occupational history and cognitive decline in a large cohort of Italian oldest-old.

METHODS

392 individuals (266 women/126 men, mean age 93 ± 3 years) enrolled in the "Mugello study" provided information about their work history. Jobs were classified in nine categories, according to the level of expertise required to perform them, as suggested by the Italian National Institute for Statistics (ISTAT). In addition, socio-demographic characteristics, comorbidities, level of independence, depression, and cognitive status were assessed. The presence of dementia was established based on cognitive status and independence in performing four selected instrumental activities of daily living (ability to manage telephone, transportation, medications, and budget).

RESULTS

Neither work complexity (p = 0.995) nor work duration (p = 0.701) showed a significant effect on the likelihood of presenting a lower cognitive profile or developing dementia (p = 0.385 and p = 0.096, for work complexity and work duration, respectively).

CONCLUSION

In the observed sample of oldest-old individuals, cognitive decline did not seem to be influenced by cognitive reserve as assessed through the evaluation of cognitive status and level of independence. It is conceivable that in this population, the decline of the brain reserve has a preponderant role in the definition of the cognitive profile.

Complexity of Primary Lifetime Occupation and Cognitive Processing

Today, there are a lack of studies focusing on the relationship between occupational complexity and executive functioning. This is noteworthy since executive functions are core aspects of cognitive processing. The present study was aimed to investigate if three occupational complexity factors (with data, people, and things) of main lifetime occupation were related to performance in executive tasks (inhibition, switching, updating). We analyzed cross-sectional data that were available for 225 participants aged 50-75 years. Results from structural equation models showed that higher complexity levels of working with data were related to lower error rates in the updating component of cognitive control. In addition, higher rates of complexity working with people was associated with lower error rates in task-switching, which also persisted after adjustment of fluid intelligence. Complexity with things, however, was not related to performance in the executive tasks. Future studies would benefit from a longitudinal design to investigate if the results from this study also hold in the long term and to further investigate the directionality between factors.

Influence of young adult cognitive ability and additional education on later-life cognition

How and when education improves cognitive capacity is an issue of profound societal importance. Education and later-life education-related factors, such as occupational complexity and engagement in cognitive-intellectual activities, are frequently considered indices of cognitive reserve, but whether their effects are truly causal remains unclear. In this study, after accounting for general cognitive ability (GCA) at an average age of 20 y, additional education, occupational complexity, or engagement in cognitive-intellectual activities accounted for little variance in late midlife cognitive functioning in men age 56-66 (n = 1009). Age 20 GCA accounted for 40% of variance in the same measure in late midlife and approximately 10% of variance in each of seven cognitive domains. The other factors each accounted for <1% of the variance in cognitive outcomes. The impact of these other factors likely reflects reverse causation-namely, downstream effects of early adult GCA. Supporting that idea, age 20 GCA, but not education, was associated with late midlife cortical surface area (n = 367). In our view, the most parsimonious explanation of our results, a meta-analysis of the impact of education, and epidemiologic studies of the Flynn effect is that intellectual capacity gains due to education plateau in late adolescence/early adulthood. Longitudinal studies with multiple cognitive assessments before completion of education would be needed to confirm this speculation. If cognitive gains reach an asymptote by early adulthood, then strengthening cognitive reserve and reducing later-life cognitive decline and dementia risk may really begin with improving educational quality and access in childhood and adolescence.