Verbal intelligence is a more robust cross-sectional measure of cognitive reserve than level of education in healthy older adults

The Advanced BRain Imaging on ageing and Memory (ABRIM) data collection: Study design, data processing, and rationale

To understand the neurocognitive mechanisms that underlie heterogeneity in cognitive ageing, recent scientific efforts have led to a growing public availability of imaging cohort data. The Advanced BRain Imaging on ageing and Memory (ABRIM) project aims to add to these existing datasets by taking an adult lifespan approach to provide a cross-sectional, normative database with a particular focus on connectivity, myelinization and iron content of the brain in concurrence with cognitive functioning, mechanisms of reserve, and sleep-wake rhythms. ABRIM freely shares MRI and behavioural data from 295 participants between 18-80 years, stratified by age decade and sex (median age 52, IQR 36-66, 53.20% females). The ABRIM MRI collection consists of both the raw and pre-processed structural and functional MRI data to facilitate data usage among both expert and non-expert users. The ABRIM behavioural collection includes measures of cognitive functioning (i.e., global cognition, processing speed, executive functions, and memory), proxy measures of cognitive reserve (e.g., educational attainment, verbal intelligence, and occupational complexity), and various self-reported questionnaires (e.g., on depressive symptoms, pain, and the use of memory strategies in daily life and during a memory task). In a sub-sample (n = 120), we recorded sleep-wake rhythms using an actigraphy device (Actiwatch 2, Philips Respironics) for a period of 7 consecutive days. Here, we provide an in-depth description of our study protocol, pre-processing pipelines, and data availability. ABRIM provides a cross-sectional database on healthy participants throughout the adult lifespan, including numerous parameters relevant to improve our understanding of cognitive ageing. Therefore, ABRIM enables researchers to model the advanced imaging parameters and cognitive topologies as a function of age, identify the normal range of values of such parameters, and to further investigate the diverse mechanisms of reserve and resilience.

Influence of cognitive reserve on cognitive and motor function in α-synucleinopathies: A systematic review and multilevel meta-analysis

Cognitive reserve has shown promise as a justification for neuropathologically unexplainable clinical outcomes in Alzheimer's disease. Recent evidence suggests this effect may be replicated in conditions like Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. However, the relationships between cognitive reserve and different cognitive abilities, as well as motor outcomes, are still poorly understood in these conditions. Additionally, it is unclear whether the reported effects are confounded by medication. This review analysed studies investigating the relationship between cognitive reserve and clinical outcomes in these α-synucleinopathy cohorts, identified from MEDLINE, Scopus, psycINFO, CINAHL, and Web of Science. 85 records, containing 176 cognition and 31 motor function effect sizes, were pooled using multilevel meta-analysis. There was a significant, positive association between higher cognitive reserve and both better cognition and motor function. Cognition effect sizes differed by disease subtype, cognitive reserve measure, and outcome type; however, no moderators significantly impacted motor function. Review findings highlight the clinical implications of cognitive reserve and importance of engaging in reserve-building behaviours.

Instruments to Assess Cognitive Reserve Among Older Adults: a Systematic Review of Measurement Properties

Cognitive reserve explains the differences in the susceptibility to cognitive impairment related to brain aging, pathology, or insult. Given that cognitive reserve has important implications for the cognitive health of typically and pathologically aging older adults, research needs to identify valid and reliable instruments for measuring cognitive reserve. However, the measurement properties of current cognitive reserve instruments used in older adults have not been evaluated according to the most up-to-date COnsensus-based Standards for the selection of health status Measurement INstruments (COSMIN). This systematic review aimed to critically appraise, compare, and summarize the quality of the measurement properties of all existing cognitive reserve instruments for older adults. A systematic literature search was performed to identify relevant studies published up to December 2021, which was conducted by three of four researchers using 13 electronic databases and snowballing method. The COSMIN was used to assess the methodological quality of the studies and the quality of measurement properties. Out of the 11,338 retrieved studies, only seven studies that concerned five instruments were eventually included. The methodological quality of one-fourth of the included studies was doubtful and three-seventh was very good, while only four measurement properties from two instruments were supported by high-quality evidence. Overall, current studies and evidence for selecting cognitive reserve instruments suitable for older adults were insufficient. All included instruments have the potential to be recommended, while none of the identified cognitive reserve instruments for older adults appears to be generally superior to the others. Therefore, further studies are recommended to validate the measurement properties of existing cognitive reserve instruments for older adults, especially the content validity as guided by COSMIN.Systematic Review Registration numbers: CRD42022309399 (PROSPERO).

Estimating Gender Differences in the Association between Cognitive Resilience and Mild Cognitive Impairment Incidence

INTRODUCTION

Recent evidence suggests that the influence of verbal intelligence and education on the onset of subjective cognitive decline may be modulated by gender, where education contributes less to cognitive resilience (CR) in women than in men. This study aimed to examine gender differences in the association between CR and mild cognitive impairment (MCI) incidence in an Australian population-based cohort.

METHODS

We included 1,806 participants who had completed at least the first two waves and up to four waves of assessments in the Personality and Total Health (PATH) Through Life study (baseline: 49% female, male = 62.5, SD = 1.5, age range = 60-66 years). CR proxies included measures of educational attainment, occupation skill, verbal intelligence, and leisure activity. Discrete-time survival analyses were conducted to examine gender differences in the association between CR proxies and MCI risk, adjusting for age and apolipoprotein E4 status.

RESULTS

Gender differences were only found in the association between occupation and MCI risk, where lower occupation skill was more strongly associated with higher risk in men than in women (odds ratio [OR] = 1.30, 95% confidence interval [CI] [1.07, 1.57]). In both genders, after adjusting for education and occupation, one SD increase in leisure activity was associated with lower MCI risk by 32% (OR = 0.76, 95% CI [0.65, 0.89]). Higher scores in verbal intelligence assessment were associated with reduced risk of MCI by 28% (OR = 0.78, 95% CI [0.69, 0.89]).

CONCLUSION

Occupational experience may contribute to CR differently between genders. Life course cognitive engagement and verbal intelligence may be more protective against MCI than education and occupation for both men and women.

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.

The effects of CNS atrophy and ICVD on tests of executive function and functional status are mediated by intelligence

Background

Impairments in executive function (EF) are often attributed to ischemic cerebrovascular disease (ICVD) and frontal circuit pathology. However, EF can be distinguished from general intelligence and the latter is likely to manifest in "executive" measures. We aimed to distinguish the effects of imaging biomarkers on these constructs.

Methods

We tested neuroimaging biomarkers as independent predictors of observed 12 month-prospective cognitive performance by a Multiple Indicators Multiple Causes (MIMIC) model in the Alzheimer's Disease Neuroimaging Initiative (ADNI) (N ≅ 1750).

Results

ICVD was associated with ''Organization" (ORG) and "Planning" (PLAN) domain scores from the test of Every Day Cognition. Left anterior cingulate (LAC) atrophy was independently associated with Trail-Making part B and Animal Naming. The MIMIC model had excellent fit and tests additional latent variables i.e., EF and dEF (a latent δ homolog derived from Spearman's general intelligence factor, g). Only dEF was associated with instrumental activities of daily living (IADL). ICVD and LAC were both associated with observed executive measures through dEF. ICVD was independently associated with those same measures through EF.

Conclusions

Observed EF is independently determined by multiple factors. The effects of EF-associated MRI biomarkers can be related to disability and dementia only via their effects on g. Because g /δ are unlikely to be located within the frontal lobes, the dementia-specific variance in executive measures may have little to do with either frontal structure or function. Conversely, domain-specific variance in EF may have little to do with either IADL-impairment or dementia.

Intelligence, cognition, and major neurocognitive disorders: From constructs to measures

The study of intelligence's role in development of major neurocognitive disorders (MND) is influenced by the approaches used to conceptualize and measure these constructs. In the field of cognitive impairment, the use of single 'intelligence' tests is a common approach to estimate intelligence. Despite being a practical compromise between feasibility and constructs, variance of these tests is only partially explained by general intelligence, and some tools (e.g., lexical tasks for premorbid intelligence) presented inherent limitations. Alternatively, factorial models allow an actual measure of intelligence as a latent factor superintending all mental abilities. Royall and colleagues used structural equation modeling to decompose the Spearman's general intelligence factor g in δ (shared variance across cognitive and functional measures) and g' (shared variance across cognitive measures only). Authors defined δ as the 'cognitive correlates of functional status', and thus a 'phenotype for all cause dementia'. Compared to g', δ explained a little rate of cognitive measures' variance, but it demonstrated a higher accuracy in dementia case-finding. From the methodological perspective, given g 'indifference' to its indicators, further studies are needed to identify the minimal set of tools necessary to extract g, and to test also non-cognitive variables as measures of δ. From the clinical perspective, general intelligence seems to influence MND presence and severity more than domain specific cognitive abilities. Giving δ 'blindness' to etiology, its association with biomarkers and contribution to differential diagnosis might be limited. Classical neuropsychological approaches based on patterns of performances at cognitive tests remained fundamental for differential diagnosis.

Determinants of cognitive and brain resilience to tau pathology: a longitudinal analysis

Mechanisms of resilience against tau pathology in individuals across the Alzheimer's disease spectrum are insufficiently understood. Longitudinal data are necessary to reveal which factors relate to preserved cognition (i.e. cognitive resilience) and brain structure (i.e. brain resilience) despite abundant tau pathology, and to clarify whether these associations are cross-sectional or longitudinal. We used a longitudinal study design to investigate the role of several demographic, biological and brain structural factors in yielding cognitive and brain resilience to tau pathology as measured with PET. In this multicentre study, we included 366 amyloid-β-positive individuals with mild cognitive impairment or Alzheimer's disease dementia with baseline 18F-flortaucipir-PET and longitudinal cognitive assessments. A subset (n = 200) additionally underwent longitudinal structural MRI. We used linear mixed-effects models with global cognition and cortical thickness as dependent variables to investigate determinants of cognitive resilience and brain resilience, respectively. Models assessed whether age, sex, years of education, APOE-ε4 status, intracranial volume (and cortical thickness for cognitive resilience models) modified the association of tau pathology with cognitive decline or cortical thinning. We found that the association between higher baseline tau-PET levels (quantified in a temporal meta-region of interest) and rate of cognitive decline (measured with repeated Mini-Mental State Examination) was adversely modified by older age (Stβinteraction = -0.062, P = 0.032), higher education level (Stβinteraction = -0.072, P = 0.011) and higher intracranial volume (Stβinteraction = -0.07, P = 0.016). Younger age, higher education and greater cortical thickness were associated with better cognitive performance at baseline. Greater cortical thickness was furthermore associated with slower cognitive decline independent of tau burden. Higher education also modified the negative impact of tau-PET on cortical thinning, while older age was associated with higher baseline cortical thickness and slower rate of cortical thinning independent of tau. Our analyses revealed no (cross-sectional or longitudinal) associations for sex and APOE-ε4 status on cognition and cortical thickness. In this longitudinal study of clinically impaired individuals with underlying Alzheimer's disease neuropathological changes, we identified education as the most robust determinant of both cognitive and brain resilience against tau pathology. The observed interaction with tau burden on cognitive decline suggests that education may be protective against cognitive decline and brain atrophy at lower levels of tau pathology, with a potential depletion of resilience resources with advancing pathology. Finally, we did not find major contributions of sex to brain nor cognitive resilience, suggesting that previous links between sex and resilience might be mainly driven by cross-sectional differences.

Prevalence and modifiable risk factors for dementia in persons with intellectual disabilities

BACKGROUND

People with intellectual disability (ID) without Down syndrome (DS) are presumed to be at higher risk of developing dementia due to their lower baseline cognitive reserve. We aimed to determine the prevalence of dementia in people with ID without DS and to identify risk factors of dementia.

METHODS

This was a cross-sectional survey and multicenter study in Japan. Adults with ID without DS residing in the facilities were included. Caregivers of all participants were interviewed by medical specialists, and participants suspected of having cognitive decline were examined directly. ICD-10 criteria for dementia, DC-LD criteria for dementia, and DSM-5 criteria for neurocognitive disorders were used to diagnose dementia. The severity of ID, educational history, and comorbidities were compared by dividing the groups into those with and without dementia.

RESULTS

A total of 1831 participants were included; 118/1831 (6.44%) were diagnosed with dementia. The prevalence of dementia for each age group was 8.8%, 60-64 years; 9.0%, 65-69 years; 19.6%, 70-74 years; and 19.4%, 75-79 years. Age, severity of ID, duration of education, hypertension, depression, stroke, and traumatic brain injury were significantly associated with the presence of dementia.

CONCLUSIONS

Although the prevalence of dementia in people with ID without DS was found to be higher at a younger age than in the general population, the results of this study suggested that adequate education, prevention of head trauma and stroke, and treatments of hypertension and depression may reduce the risk of dementia. These may be potentially important modifiable risk factors for the prevention of dementia in these people.

The Role of Brain Integrity in the Association between Occupational Complexity and Cognitive Performance in Subjects with Increased Risk of Dementia

INTRODUCTION

Mechanisms underlying the positive association between occupational mental demands and late-life cognition are poorly understood. The objective of this study was to assess whether the association between occupational complexity and cognition is related to and moderated by brain integrity in individuals at risk for dementia. Brain integrity was appraised throughout structural measures (magnetic resonance imaging, MRI) and amyloid accumulation (Pittsburgh compound B (PiB)-positron emission tomography, PiB-PET).

METHODS

Participants from the Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER) neuroimaging sample - MRI (N = 126), PiB-PET (N = 41) - were included in a post hoc cross-sectional analysis. Neuroimaging parameters comprised the Alzheimer's disease signature (ADS) cortical thickness (FreeSurfer 5.3), medial temporal atrophy (MTA), and amyloid accumulation (PiB-PET). Cognition was assessed using the neuropsychological test battery. Occupational complexity with data, people, and substantive complexity were classified through the Dictionary of Occupational Titles. Linear regression models included cognition as dependent variable, and occupational complexity, measures of brain integrity, and their interaction terms as predictors.

RESULTS

Occupational complexity with data and substantive complexity were associated with better cognition (overall cognition, executive function) when adjusting for ADS and MTA (independent association). Significant interaction effects between occupational complexity and brain integrity were also found, indicating that, for some indicators of brain integrity and cognition (e.g., overall cognition, processing speed), the positive association between occupational complexity and cognition occurred only among persons with higher brain integrity (moderated association).

CONCLUSIONS

Among individuals at risk for dementia, occupational complexity does not seem to contribute toward resilience against neuropathology. These exploratory findings require validation in larger populations.

Moderating effects of cognitive reserve on the relationship between brain structure and cognitive abilities in middle-aged and older adults

The cognitive reserve (CR) hypothesis is reinforced by negative moderating effects, suggesting that those with higher CR are less reliant on brain structure for cognitive function. Previous research on CR's moderating effects yielded inconsistent results, motivating our 3 studies using UK Biobank data. Study I examined five CR proxies' moderating effects on global, lobar, and regional brain-cognition models; study II extended study I by using a larger sample size; and study III investigated age-related moderating effects on the hippocampal regions. In study I, most moderating effects were negative and none survived the multiple comparison correction, but study II identified 13 global-level models with significant negative moderating effects that survived correction. Study III showed age influenced CR proxies' moderating effects in hippocampal regions. Our findings suggest that the effects of CR proxies on brain integrity and cognition varied depending on the proxy used, brain integrity indicators, cognitive domain, and age group. This study offers significant insights regarding the importance of CR for brain integrity and cognitive outcomes.

Cognitive reserve as a moderator of outcomes in five clusters of first episode psychosis patients: a 10-year follow-up study of the PAFIP cohort

BACKGROUND

Cognitive reserve (CR) has been associated with the development and prognosis of psychosis. Different proxies have been used to estimate CR among individuals. A composite score of these proxies could elucidate the role of CR at illness onset on the variability of clinical and neurocognitive outcomes.

METHODS

Premorbid intelligence quotient (IQ), years of education and premorbid adjustment were explored as proxies of CR in a large sample (N = 424) of first-episode psychosis (FEP) non-affective patients. Clusters of patients were identified and compared based on premorbid, clinical and neurocognitive variables at baseline. Additionally, the clusters were compared at 3-year (N = 362) and 10-year (N = 150) follow-ups.

RESULTS

The FEP patients were grouped into five CR clusters: C1 (low premorbid IQ, low education and poor premorbid) 14%; C2 (low premorbid IQ, low education and good premorbid adjustment) 29%; C3 (normal premorbid IQ, low education and poor premorbid adjustment) 17%; C4 (normal premorbid IQ, medium education and good premorbid adjustment) 25%; and C5 (normal premorbid IQ, higher education and good premorbid adjustment) 15%. In general, positive and negative symptoms were more severe in the FEP patients with the lowest CR at baseline and follow-up assessments, while those with high CR presented and maintained higher levels of cognitive functioning.

CONCLUSIONS

CR could be considered a key factor at illness onset and a moderator of outcomes in FEP patients. A high CR could function as a protective factor against cognitive impairment and severe symptomatology. Clinical interventions focused on increasing CR and documenting long-term benefits are interesting and desirable.

Influence of cognitive reserve on cognitive and motor function in α-synucleinopathies: A systematic review protocol

Cognitive reserve has been used to justify neuropathologically unexplainable mismatches in Alzheimer's disease outcomes. Recent evidence has suggested this effect may be replicable across other conditions. However, it is still unclear whether cognitive reserve applies to α-synucleinopathies or to motor outcomes, or if medication confounds effects. This review protocol follows PRISMA-P guidelines and aims to investigate whether cognitive reserve can predict both cognitive and motor outcomes for α-synucleinopathy patients. MEDLINE (via PubMed), Scopus, psycINFO (via Ovid), CINAHL (via EBSCO), and Web of Science have been searched. Cross-sectional, cohort, case-control, and longitudinal studies investigating the association between cognitive reserve and cognitive and/or motor outcomes for Parkinson's disease, dementia with Lewy bodies, or multiple system atrophy will be included. Reviewers will independently perform screening, while also extracting data, assessing the risk of bias (using a version of the Quality in Prognostic Studies tool), and rating evidence quality (using GRADE). If possible, random-effects meta-analyses will be conducted for each unique outcome variable and α-synucleinopathy; otherwise, a narrative synthesis will be performed. Depending on the number of studies, exploratory analyses may involve meta-regression to assess potential confounding effects. Understanding the broader protective effect of cognitive reserve has significant implications for preventive interventions in the wider population.

Connectome-based predictive modelling of cognitive reserve using task-based functional connectivity

Cognitive reserve supports cognitive function in the presence of pathology or atrophy. Functional neuroimaging may enable direct and accurate measurement of cognitive reserve which could have considerable clinical potential. The present study aimed to develop and validate a measure of cognitive reserve using task-based fMRI data that could then be applied to independent resting-state data. Connectome-based predictive modelling with leave-one-out cross-validation was applied to predict a residual measure of cognitive reserve using task-based functional connectivity from the Cognitive Reserve/Reference Ability Neural Network studies (n = 220, mean age = 51.91 years, SD = 17.04 years). This model generated summary measures of connectivity strength that accurately predicted a residual measure of cognitive reserve in unseen participants. The theoretical validity of these measures was established via a positive correlation with a socio-behavioural proxy of cognitive reserve (verbal intelligence) and a positive correlation with global cognition, independent of brain structure. This fitted model was then applied to external test data: resting-state functional connectivity data from The Irish Longitudinal Study on Ageing (TILDA, n = 294, mean age = 68.3 years, SD = 7.18 years). The network-strength predicted measures were not positively associated with a residual measure of cognitive reserve nor with measures of verbal intelligence and global cognition. The present study demonstrated that task-based functional connectivity data can be used to generate theoretically valid measures of cognitive reserve. Further work is needed to establish if, and how, measures of cognitive reserve derived from task-based functional connectivity can be applied to independent resting-state data.

Verbal intelligence and leisure activities are associated with cognitive performance and resting-state electroencephalogram

Cognitive reserve (CR) is the adaptability of cognitive processes that helps to explain differences in the susceptibility of cognitive or daily functions to resist the onslaught of brain-related injury or the normal aging process. The underlying brain mechanisms of CR studied through electroencephalogram (EEG) are scarcely reported. To our knowledge, few studies have considered a combination of exclusively dynamic proxy measures of CR. We evaluated the association of CR with cognition and resting-state EEG in older adults using three of the most frequently used dynamic proxy measures of CR: verbal intelligence, leisure activities, and physical activities. Multiple linear regression analyses with the CR proxies as independent variables and cognitive performance and the absolute power (AP) on six resting-state EEG components (beta, alpha1, alpha2, gamma, theta, and delta) as outcomes were performed. Eighty-eight healthy older adults aged 60–77 (58 female) were selected from previous study data. Verbal intelligence was a significant positive predictor of perceptual organization, working memory, processing speed, executive functions, and central delta power. Leisure activities were a significant positive predictor of posterior alpha2 power. The dynamic proxy variables of CR are differently associated with cognitive performance and resting-state EEG. Implementing leisure activities and tasks to increase vocabulary may promote better cognitive performance through compensation or neural efficiency mechanisms.

Alpha3/alpha2 power ratios relate to performance on a virtual reality shopping task in ageing adults

Background

Aspects of cognitive function decline with age. This phenomenon is referred to as age-related cognitive decline (ARCD). Improving the understanding of these changes that occur as part of the ageing process can serve to enhance the detection of the more incapacitating neurodegenerative disorders such as Alzheimer’s disease (AD). In this study, we employ novel methods to assess ARCD by exploring the utility of the alpha3/alpha2 electroencephalogram (EEG) power ratio – a marker of AD, and a novel virtual reality (VR) functional cognition task – VStore, in discriminating between young and ageing healthy adults.

Materials and methods

Twenty young individuals aged 20–30, and 20 older adults aged 60–70 took part in the study. Participants underwent resting-state EEG and completed VStore and the Cogstate Computerised Cognitive Battery. The difference in alpha3/alpha2 power ratios between the age groups was tested using t-test. In addition, the discriminatory accuracy of VStore and Cogstate were compared using logistic regression and overlying receiver operating characteristic (ROC) curves. Youden’s J statistic was used to establish the optimal threshold for sensitivity and specificity and model performance was evaluated with the DeLong’s test. Finally, alpha3/alpha2 power ratios were correlated with VStote and Cogstate performance.

Results

The difference in alpha3/alpha2 power ratios between age cohorts was not statistically significant. On the other hand, VStore discriminated between age groups with high sensitivity (94%) and specificity (95%) The Cogstate Pre-clinical Alzheimer’s Battery achieved a sensitivity of 89% and specificity of 60%, and Cogstate Composite Score achieved a sensitivity of 83% and specificity of 85%. The differences between the discriminatory accuracy of VStore and Cogstate models were statistically significant. Finally, high alpha3/alpha2 power ratios correlated strongly with VStore (r = 0.73), the Cogstate Pre-clinical Alzheimer’s Battery (r = -0.67), and Cogstate Composite Score (r = -0.76).

Conclusion

While we did not find evidence that the alpha3/alpha2 power ratio is elevated in healthy ageing individuals compared to young individuals, we demonstrated that VStore can classify age cohorts with high accuracy, supporting its utility in the assessment of ARCD. In addition, we found preliminary evidence that elevated alpha3/alpha2 power ratio may be linked to lower cognitive performance.

Moderating Role of Cognitive Reserve Markers Between Childhood Cognition and Cognitive Aging: Evidence From the 1946 British Birth Cohort

BACKGROUND AND OBJECTIVES

As the population ages, differences in cognitive abilities become more evident. We investigated key genetic and life course influences on cognitive state at age 69 years, building on previous work using the longitudinal Medical Research Council National Survey of Health and Development (the British 1946 birth cohort).

METHODS

Multivariable regressions investigated the association between 4 factors: (1) childhood cognition at age 8 years; (2) a Cognitive Reserve Index (CRI) composed of 3 markers: (i) educational attainment by age 26 years, (ii) engagement in leisure activities at age 43 years, and (iii) occupation up to age 53 years; (3) reading ability assessed by the National Adult Reading Test (NART) at age 53 years; and (4) APOE genotype in relation to cognitive state measured at age 69 years with Addenbrooke's Cognitive Examination, third edition (ACE-III). We then investigated the modifying role of the CRI, NART, and APOE in the association between childhood cognition and the ACE-III.

RESULTS

The analytical sample comprised 1,184 participants. Higher scores in childhood cognition, CRI, and NART were associated with higher scores in the ACE-III. We found that the CRI and NART modified the association between childhood cognition and the ACE-III: for 30 additional points in the CRI or 20 additional points in the NART, the simple slope of childhood cognition decreased by approximately 0.10 points (CRI = 70: marginal effects (MEs) 0.22, 95% CI 0.12-0.32, p < 0.001 vs CRI = 100: MEs 0.12, 95% CI 0.06-0.17, p < 0.001; NART = 15: MEs 0.22, 95% CI 0.09-0.35, p = 0.001, vs NART = 35: MEs 0.11, 95% CI 0.05-0.17, p < 0.001). The association between childhood cognition and the ACE-III was nonsignificant at high levels of the CRI or NART. Furthermore, the e4 allele of the APOE gene was associated with lower scores in the ACE-III (β = -0.71, 95% CI -1.36 to -0.06, p = 0.03) but did not modify the association between childhood cognition and cognitive state in later life.

DISCUSSION

The CRI and NART are independent measures of cognitive reserve because both modify the association between childhood cognition and cognitive state.

Cognitive Reserve and Related Constructs: A Unified Framework Across Cognitive and Brain Dimensions of Aging

Cognitive reserve and related constructs are valuable for aging-related research, but consistency and clarification of terms is needed as there is still no universally agreed upon nomenclature. We propose a new set of definitions for the concepts of reserve, maintenance, and resilience, and we invoke parallel concepts for each that are applicable to cognition and to brain. Our definitions of reserve and resilience correspond reasonably well to dictionary definitions of these terms. We demonstrate logical/methodological problems that arise from incongruence between commonly used conceptual and operational definitions. In our view, cognitive reserve should be defined conceptually as one's total cognitive resources at a given point in time. IQ and education are examples of common operational definitions (often referred to as proxies) of cognitive reserve. Many researchers define cognitive reserve conceptually as a property that allows for performing better than expected cognitively in the face of aging or pathology. Performing better than expected is demonstrated statistically by interactions in which the moderator is typically IQ or education. The result is an irreconcilable situation in which cognitive reserve is both the moderator and the moderation effect itself. Our proposed nomenclature resolves this logical inconsistency by defining performing better than expected as cognitive resilience. Thus, in our usage, we would test the hypothesis that high cognitive reserve confers greater cognitive resilience. Operational definitions (so-called proxies) should not conflate factors that may influence reserve-such as occupational complexity or engagement in cognitive activities-with cognitive reserve itself. Because resources may be depleted with aging or pathology, one's level of cognitive reserve may change over time and will be dependent on when assessment takes place. Therefore, in addition to cognitive reserve and cognitive resilience, we introduce maintenance of cognitive reserve as a parallel to brain maintenance. If, however, education is the measure of reserve in older adults, it precludes assessing change or maintenance of reserve. Finally, we discuss consideration of resistance as a subcategory of resilience, reverse causation, use of residual scores to assess performing better than expected given some adverse factor, and what constitutes high vs. low cognitive reserve across different studies.

Apolipoprotein ε4 modifies obesity-related atrophy in the hippocampal formation of cognitively healthy adults

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Age-related inverted U-shaped curve of hippocampal myelin/neurite packing.

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Reduced hippocampal myelin/neurite packing and size/complexity in obesity.

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APOE modifies the effects of obesity on hippocampal size/complexity.

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Age-related slowing of spatial navigation but no risk effects on cognition.

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CA/DG predict episodic memory and subiculum predicts spatial navigation performance.

Characterizing age- and risk-related hippocampal vulnerabilities may inform about the neural underpinnings of cognitive decline. We studied the impact of three risk-factors, Apolipoprotein (APOE)-ε4, a family history of dementia, and central obesity, on the CA1, CA2/3, dentate gyrus and subiculum of 158 cognitively healthy adults (38-71 years). Subfields were labelled with the Automatic Segmentation of Hippocampal Subfields and FreeSurfer (version 6) protocols. Volumetric and microstructural measurements from quantitative magnetization transfer and Neurite Orientation Density and Dispersion Imaging were extracted for each subfield and reduced to three principal components capturing apparent myelin/neurite packing, size/complexity, and metabolism. Aging was associated with an inverse U-shaped curve on myelin/neurite packing and affected all subfields. Obesity led to reductions in myelin/neurite packing and size/complexity regardless of APOE and family history of dementia status. However, amongst individuals with a healthy Waist-Hip-Ratio, APOE ε4 carriers showed lower size/complexity than non-carriers. Segmentation protocol type did not affect this risk pattern. These findings reveal interactive effects between APOE and central obesity on the hippocampal formation of cognitively healthy adults.

Cognitive Reserve and Related Constructs: A Unified Framework Across Cognitive and Brain Dimensions of Aging

Cognitive reserve and related constructs are valuable for aging-related research, but consistency and clarification of terms is needed as there is still no universally agreed upon nomenclature. We propose a new set of definitions for the concepts of reserve, maintenance, and resilience, and we invoke parallel concepts for each that are applicable to cognition and to brain. Our definitions of reserve and resilience correspond reasonably well to dictionary definitions of these terms. We demonstrate logical/methodological problems that arise from incongruence between commonly used conceptual and operational definitions. In our view, cognitive reserve should be defined conceptually as one's total cognitive resources at a given point in time. IQ and education are examples of common operational definitions (often referred to as proxies) of cognitive reserve. Many researchers define cognitive reserve conceptually as a property that allows for performing better than expected cognitively in the face of aging or pathology. Performing better than expected is demonstrated statistically by interactions in which the moderator is typically IQ or education. The result is an irreconcilable situation in which cognitive reserve is both the moderator and the moderation effect itself. Our proposed nomenclature resolves this logical inconsistency by defining performing better than expected as cognitive resilience. Thus, in our usage, we would test the hypothesis that high cognitive reserve confers greater cognitive resilience. Operational definitions (so-called proxies) should not conflate factors that may influence reserve-such as occupational complexity or engagement in cognitive activities-with cognitive reserve itself. Because resources may be depleted with aging or pathology, one's level of cognitive reserve may change over time and will be dependent on when assessment takes place. Therefore, in addition to cognitive reserve and cognitive resilience, we introduce maintenance of cognitive reserve as a parallel to brain maintenance. If, however, education is the measure of reserve in older adults, it precludes assessing change or maintenance of reserve. Finally, we discuss consideration of resistance as a subcategory of resilience, reverse causation, use of residual scores to assess performing better than expected given some adverse factor, and what constitutes high vs. low cognitive reserve across different studies.