Static and Dynamic Cognitive Reserve Proxy Measures: Interactions with Alzheimer's Disease Neuropathology and Cognition

The role of cognitive reserve and depression on executive function in older adults: A 10-year study from the Wisconsin Registry for Alzheimer's Prevention

Objective: The current study examined the longitudinal relationship between cognitive reserve (CR), depression, and executive function (EF) in a cohort of older adults. Methods: 416 participants were selected from the Wisconsin Registry for Alzheimer's Prevention. They were native English speakers, aged ≥50+, and cognitively unimpaired at baseline, with no history of neurological or other psychiatric disorders aside from depression. Depression was assessed with the 20-item Center for Epidemiologic Studies Depression Scale (CES-D). A composite score, based on the premorbid IQ (WRAT-3 Reading subtest) and years of education was used to estimate CR. Another composite score from four cognitive tests was used to estimate EF. A moderation analysis was performed to evaluate the effects of CR and Depression on EF at follow-up after controlling for age, gender, and APOE risk score. Moreover, a multinomial logistic regression was used to predict conversion to Mild Cognitive Impairment (MCI) from the healthy baseline. Results: The negative relationship between depression and EF was stronger in individuals with higher CR levels, suggesting a possible floor effect at lower CR levels. In the multinomial regression, the interaction between CR and depression predicted conversion to MCI status, indicating that lower CR paired with more severe depression at baseline was associated with a higher risk of subsequent impairment. Conclusions: This study sheds light on the intricate relationship between depression and EF over time, suggesting that the association may be influenced by varying levels of CR. Further studies may replicate these findings in clinical populations.

Vocabulary knowledge as a reliable proxy of cognitive reserve in multiple sclerosis: a validation study

INTRODUCTION

The present study aimed to explore the suitability of the vocabulary knowledge (VOC) test as an accurate and reliable proxy of cognitive reserve (CR) by evaluating its psychometric properties and discrimination accuracy compared with other CR measures in multiple sclerosis (MS).

METHODS

Sixty-eight consecutive people with multiple sclerosis (pwMS), followed at our MS outpatient clinic, completed a clinical evaluation and neuropsychological assessment including: VOC, Brief Repeatable Battery of Neuropsychological Tests (BRB-N), Cognitive Reserve Index Questionnaire (CRIq), Beck Depression Inventory-II, and State-Trait Anxiety Inventory. Reliability, convergent and divergent validity, and discrimination accuracy of the VOC were assessed using educational level as reference standard. The possible effects of sociodemographic and clinical factors on VOC and their role in predicting global cognitive status were also explored.

RESULTS

VOC demonstrated good internal consistency (Cronbach's α = 0.894) and adequate construct validity. It showed an acceptable level of discrimination between pwMS with high and low CR, comparable to the CRIq score. Education strongly affected VOC scores, which in turn were independent of MS features. VOC emerged as an independent predictor of global cognitive status together with MS-related disability.

CONCLUSION

We demonstrated the validity of VOC as a reliable CR measure in pwMS. Thus, CR may also be estimated using fixed objective measures, independent of brain pathology and clinical features. Early CR estimation may help clinicians identify pwMS at a higher risk of cognitive decline and plan strict neuropsychological monitoring and cognitive interventions.

Identifying longitudinal cognitive resilience from cross-sectional amyloid, tau, and neurodegeneration

BACKGROUND

Leveraging Alzheimer's disease (AD) imaging biomarkers and longitudinal cognitive data may allow us to establish evidence of cognitive resilience (CR) to AD pathology in-vivo. Here, we applied latent class mixture modeling, adjusting for sex, baseline age, and neuroimaging biomarkers of amyloid, tau and neurodegeneration, to a sample of cognitively unimpaired older adults to identify longitudinal trajectories of CR.

METHODS

We identified 200 Harvard Aging Brain Study (HABS) participants (mean age = 71.89 years, SD = 9.41 years, 59% women) who were cognitively unimpaired at baseline with 2 or more timepoints of cognitive assessment following a single amyloid-PET, tau-PET and structural MRI. We examined latent class mixture models with longitudinal cognition as the dependent variable and time from baseline, baseline age, sex, neocortical Aβ, entorhinal tau, and adjusted hippocampal volume as independent variables. We then examined group differences in CR-related factors across the identified subgroups from a favored model. Finally, we applied our favored model to a dataset from the Alzheimer's Disease Neuroimaging Initiative (ADNI; n = 160, mean age = 73.9 years, SD = 7.6 years, 60% women).

RESULTS

The favored model identified 3 latent subgroups, which we labelled as Normal (71% of HABS sample), Resilient (22.5%) and Declining (6.5%) subgroups. The Resilient subgroup exhibited higher baseline cognitive performance and a stable cognitive slope. They were differentiated from other groups by higher levels of verbal intelligence and past cognitive activity. In ADNI, this model identified a larger Normal subgroup (88.1%), a smaller Resilient subgroup (6.3%) and a Declining group (5.6%) with a lower cognitive baseline.

CONCLUSION

These findings demonstrate the value of data-driven approaches to identify longitudinal CR groups in preclinical AD. With such an approach, we identified a CR subgroup who reflected expected characteristics based on previous literature, higher levels of verbal intelligence and past cognitive activity.

Interaction between catechol-O-methyltransferase Val/Met polymorphism and cognitive reserve for negative symptoms in schizophrenia

BACKGROUND

Cognitive reserve (CR) and the catechol-O-methyltransferase (COMT) Val/Met polymorphism are reportedly linked to negative symptoms in schizophrenia. However, the regulatory effect of the COMT genotype on the relationship between CR and negative symptoms is still unexamined.

AIM

To investigate whether the relationship between CR and negative symptoms could be regulated by the COMT Val/Met polymorphism.

METHODS

In a cross-sectional study, 54 clinically stable patients with schizophrenia underwent assessments for the COMT genotype, CR, and negative symptoms. CR was estimated using scores in the information and similarities subtests of a short form of the Chinese version of the Wechsler Adult Intelligence Scale.

RESULTS

COMT Met-carriers exhibited fewer negative symptoms than Val homozygotes. In the total sample, significant negative correlations were found between negative symptoms and information, similarities. Associations between information, similarities and negative symptoms were observed in Val homozygotes only, with information and similarities showing interaction effects with the COMT genotype in relation to negative symptoms (information, β = -0.282, 95%CI: -0.552 to -0.011, P = 0.042; similarities, β = -0.250, 95%CI: -0.495 to -0.004, P = 0.046).

CONCLUSION

This study provides initial evidence that the association between negative symptoms and CR is under the regulation of the COMT genotype in schizophrenia.

Intersectional Effects of Race and Educational Attainment on Memory Function of Middle-Aged and Older Adults With Alzheimer's Disease

BACKGROUND

High educational attainment may protect individuals, particularly middle-aged and older adults, against a wide range of health risks, including memory decline with age; however, this protection is less clear in patients with Alzheimer's disease (AD). In addition, this effect may differ across racial groups. According to the Marginalized-Related Diminished Return (MDR) theory, for example, the protective effect of high educational attainment on mental and physical health shows a weaker protective effect for racial minority groups, particularly Black people compared to White individuals.

OBJECTIVES

This longitudinal study used data of middle-aged and older adults with AD with two aims: first, to test the association between educational attainment and memory, and second, to explore racial differences in this association in the USA.

METHODS

Data came from the Alzheimer's Disease Neuroimaging Initiative (ADNI) study. The total sample was 1673 American middle-aged and older adults. The independent variable was educational attainment measured as years of education. The main outcome was memory operationalized as Rey Auditory Verbal Learning Test (RAVLT) Verbal Forgetting percentage (VF%). Age, gender, and follow-up duration were covariates. Race was the effect modifier. Linear regression model was utilized to analyze the data.

RESULTS

Of all participants, 68 (4.1%) were Black, and the remaining were White, with a mean age of 75 years old. In the pooled sample, educational attainment did not show a significant association with memory, independent of confounders. Educational attainment showed a significant interaction with race on memory, with higher educational attainment having a different effect on memory in White patients compared to Black patients.

CONCLUSION

The effect of higher educational attainment on memory differs for Black patients with AD compared to White patients. To prevent cognitive disparities by race, we need to go beyond racial inequality in access to resources (e.g., education) and minimize diminished returns of educational attainment for racial minorities. To tackle health inequalities, social policies should not be limited to equalizing socioeconomic status but also help minority groups leverage their available resources, such as educational attainment, and secure tangible outcomes.

The role of cognitive reserve in traumatic brain injury: a systematic review of observational studies

OBJECTIVE

Evaluate the role of cognitive reserve (CR) on cognitive and physical sequelae in traumatic brain injury (TBI).

METHODS

A comprehensive search strategy was conducted in four databases in English and Spanish in the last 12 years (2011-2023). Inclusion criteria: original cross-sectional and longitudinal studies whose main or secondary objective was to evaluate the effect of CR in adult patients with TBI. PRISMA guidelines were used to report the search and selection method and STROBE checklist was used to evaluate the quality of studies.

RESULTS

Eighteen observational studies were included in this review. Multiple sources of variability were observed: number of patients, time of evolution, severity of the TBI, type of CR proxy, cognitive assessment instrument, etc. However, the most commonly used indicators of CR were premorbid IQ and educational attainment. A positive and consistent association between CR and performance on cognitive tests after injury was found.

CONCLUSIONS

CR has a consistent positive effect on cognition and on some other aspects of recovery in traumatic brain injury. In future studies, it will be necessary to promote the use of CR indices based on various indicators and explore the effects of CR on other aspects related to the recovery of brain trauma.

Effect of cognitive reserve on the association between slow wave sleep and cognition in community-dwelling older adults

Sleep, especially slow wave sleep (SWS), is essential for cognitive functioning and is reduced in aging. The impact of sleep quality on cognition is variable, especially in aging. Cognitive reserve (CR) may be an important modulator of these effects. We aimed at investigating this question to better identify individuals in whom sleep disturbances might have greater behavioral consequences. Polysomnography and neuropsychological assessments were performed in 135 cognitively intact older adults (mean age ± SD: 69.4 ± 3.8y) from the Age-Well randomized controlled trial (baseline data). Two measures of cognitive engagement throughout life were used as CR proxies. Linear regression analyses were performed between the proportion of SWS, and executive function and episodic memory composite scores. Then, interaction analyses between SWS and CR proxies on cognition were conducted to assess the possible impact of CR on these links. SWS was positively associated with episodic memory, but not with executive function. CR proxies modulated the associations between SWS and both executive and episodic memory performance. Specifically, individuals with higher CR were able to maintain cognitive performance despite low amounts of SWS. This study provides the first evidence that CR may protect against the deleterious effects of age-related sleep changes on cognition.

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.

Midlife occupational cognitive requirements protect cognitive function in old age by increasing cognitive reserve

Introduction

Several lifestyle factors promote protection against Alzheimer's disease (AD) throughout a person's lifespan. Although such protective effects have been described for occupational cognitive requirements (OCR) in midlife, it is currently unknown whether they are conveyed by brain maintenance (BM), brain reserve (BR), or cognitive reserve (CR) or a combination of them.

Methods

We systematically derived hypotheses for these resilience concepts and tested them in the population-based AgeCoDe cohort and memory clinic-based AD high-risk DELCODE study. The OCR score (OCRS) was measured using job activities based on the O*NET occupational classification system. Four sets of analyses were conducted: (1) the interaction of OCR and APOE-ε4 with regard to cognitive decline (N = 2,369, AgeCoDe), (2) association with differentially shaped retrospective trajectories before the onset of dementia of the Alzheimer's type (DAT; N = 474, AgeCoDe), (3) cross-sectional interaction of the OCR and cerebrospinal fluid (CSF) AD biomarkers and brain structural measures regarding memory function (N = 873, DELCODE), and (4) cross-sectional and longitudinal association of OCR with CSF AD biomarkers and brain structural measures (N = 873, DELCODE).

Results

Regarding (1), higher OCRS was associated with a reduced association of APOE-ε4 with cognitive decline (mean follow-up = 6.03 years), consistent with CR and BR. Regarding (2), high OCRS was associated with a later onset but subsequently stronger cognitive decline in individuals converting to DAT, consistent with CR. Regarding (3), higher OCRS was associated with a weaker association of the CSF Aβ42/40 ratio and hippocampal volume with memory function, consistent with CR. Regarding (4), OCR was not associated with the levels or changes in CSF AD biomarkers (mean follow-up = 2.61 years). We found a cross-sectional, age-independent association of OCRS with some MRI markers, but no association with 1-year-change. OCR was not associated with the intracranial volume. These results are not completely consistent with those of BR or BM.

Discussion

Our results support the link between OCR and CR. Promoting and seeking complex and stimulating work conditions in midlife could therefore contribute to increased resistance to pathologies in old age and might complement prevention measures aimed at reducing pathology.

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.

The Assessment of Cognitive Reserve: A Systematic Review of the Most Used Quantitative Measurement Methods of Cognitive Reserve for Aging

The cognitive reserve (CR) is widely accepted as the active ability to cope with brain damage, using preexisting cognitive and compensatory processes. The common CR proxies used are the number of formal years of education, intelligence quotient (IQ) or premorbid functioning, occupation attainment, and participation in leisure activities. More recently, it has employed the level of literacy and engagement in high-level cognitive demand of professional activities. This study aims to identify and summarize published methodologies to assess the CR quantitatively. We searched for published studies on PubMed, ScienceDirect, and Web of Science between September 2018 and September 2021. We only included those studies that characterized the CR assessment methodology. The search strategy identified 1,285 publications, of which 25 were included. Most of the instruments targeted proxies individually. The lack of a gold standard tool that incorporates all proxies and cognitive tests highlights the need to develop a more holistic battery for the quantitative assessment of CR. Further studies should focus on a quantitative methodology that includes all these proxies supported by normative data to improve the use of CR as a valid measure in clinical contexts.

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

BACKGROUND

Cognitive reserve is most commonly measured using socio-behavioural proxy variables. These variables are easy to collect, have a straightforward interpretation, and are widely associated with reduced risk of dementia and cognitive decline in epidemiological studies. However, the specific proxies vary across studies and have rarely been assessed in complete models of cognitive reserve (i.e. alongside both a measure of cognitive outcome and a measure of brain structure). Complete models can test independent associations between proxies and cognitive function in addition to the moderation effect of proxies on the brain-cognition relationship. Consequently, there is insufficient empirical evidence guiding the choice of proxy measures of cognitive reserve and poor comparability across studies.

METHOD

In a cross-sectional study, we assessed the validity of 5 common proxies (education, occupational complexity, verbal intelligence, leisure activities, and exercise) and all possible combinations of these proxies in 2 separate community-dwelling older adult cohorts: The Irish Longitudinal Study on Ageing (TILDA; N = 313, mean age = 68.9 years, range = 54-88) and the Cognitive Reserve/Reference Ability Neural Network Study (CR/RANN; N = 234, mean age = 64.49 years, range = 50-80). Fifteen models were created with 3 brain structure variables (grey matter volume, hippocampal volume, and mean cortical thickness) and 5 cognitive variables (verbal fluency, processing speed, executive function, episodic memory, and global cognition).

RESULTS

No moderation effects were observed. There were robust positive associations with cognitive function, independent of brain structure, for 2 individual proxies (verbal intelligence and education) and 16 composites (i.e. combinations of proxies). Verbal intelligence was statistically significant in all models. Education was significant only in models with executive function as the cognitive outcome variable. Three robust composites were observed in more than two-thirds of brain-cognition models: the composites of (1) occupational complexity and verbal intelligence, (2) education and verbal intelligence, and (3) education, occupational complexity, and verbal intelligence. However, no composite had larger average effects nor was more robust than verbal intelligence alone.

CONCLUSION

These results support the use of verbal intelligence as a proxy measure of CR in cross-sectional studies of cognitively healthy older adults.

Education differentially contributes to cognitive reserve across racial/ethnic groups

INTRODUCTION

We examined whether educational attainment differentially contributes to cognitive reserve (CR) across race/ethnicity.

METHODS

A total of 1553 non-Hispanic Whites (Whites), non-Hispanic Blacks (Blacks), and Hispanics in the Washington Heights-Inwood Columbia Aging Project (WHICAP) completed structural magnetic resonance imaging. Mixture growth curve modeling was used to examine whether the effect of brain integrity indicators (hippocampal volume, cortical thickness, and white matter hyperintensity [WMH] volumes) on memory and language trajectories was modified by education across racial/ethnic groups.

RESULTS

Higher educational attainment attenuated the negative impact of WMH burden on memory (β = -0.03; 99% CI: -0.071, -0.002) and language decline (β = -0.024; 99% CI:- 0.044, -0.004), as well as the impact of cortical thinning on level of language performance for Whites, but not for Blacks or Hispanics.

DISCUSSION

Educational attainment does not contribute to CR similarly across racial/ethnic groups.

Education as a Moderator of the Relationship Between Episodic Memory and Amyloid Load in Normal Aging

The current study explored whether education, a proxy of cognitive reserve, modifies the association between episodic memory (EM) performance and βeta-amyloid load (Aβ), a biomarker of Alzheimer's disease, in a cohort of cognitively normal older adults. One hundred and four participants (mean age 73.3 years) evenly spread out in three bands of education were recruited. Participants underwent neuropsychological assessment, structural MRI as well as PET imaging to quantify Aβ load. Moderation analyses and the Johnson-Neyman technique were carried out to examine the interaction of education with Aβ load to predict EM performance. Linear regressions were then performed within each group of education to better illustrate the interaction effect (all analyses were controlled for age and sex). The interaction between education and Aβ load was significant (p < .05) for years of education, reaching a cutoff point of 13.5 years, above which the relationship between Aβ load and EM was no longer significant. Similarly, significant associations were found between Aβ and EM among participants with secondary (p < .01) and pre-university education (p < .01), but not with a university degree (p = .253). EM performance is associated with Aβ load in cognitively normal older individuals, and this relationship is moderated by educational attainment.

A Cognitive Reserve and Social Support-Focused Latent Class Analysis to Predict Self-Reported Confusion or Memory Loss among Middle-Aged World Trade Center Health Registry Enrollees

The World Trade Center Health Registry includes 9/11 survivors who have been surveyed about their health conditions over time. The prevalence of posttraumatic stress disorder (PTSD) remains high among the cohort and is a risk factor for cognitive impairment or dementia. We thus sought to examine the degree to which confusion or memory loss (CML)—potential symptoms of cognitive decline—are occurring among enrollees aged 35–64 years. Cognitive reserve theory suggests that higher levels of education and engaging in cognitively challenging activities can create stronger neural connections, offering protection against cognitive decline. We hypothesized that enrollees with less cognitive reserve would be more likely to report CML. In this study, we: (1) estimated the incidence of CML in our study sample; (2) identified indicators of cognitive reserve (e.g., indicators of educational attainment, social support); and (3) determined whether CML is associated with cognitive reserve level, stratified by PSTD status. First, we described demographics of the study sample (n = 14,574) and probable PTSD status, also stratifying by CML. Next, we conducted a latent class analysis on two groups: those with probable PTSD and those without probable PTSD, creating classes with varying cognitive reserve levels. Finally, using adjusted log binomial models, we predicted risk of CML based on cognitive reserve level. The probable PTSD group (n = 1213) and not probable PTSD group (n = 13,252) each had four latent classes: low, medium-low, medium-high, and high cognitive reserve. In the probable PTSD model, compared to the high cognitive reserve class, those with medium-low cognitive reserve were 35% more likely to report CML (relative risk (RR) = 1.4, 95% confidence interval (CI): 1.1, 1.7). Among the not probable PTSD group, those with low and medium levels of cognitive reserve were significantly more likely to report CML (RR = 1.8 and 1.4, respectively). Overall, those with less cognitive reserve were more likely to report CML regardless of PTSD status.