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

Driving research on successful aging and neuroprotection in Latin America: Insights from the inaugural symposium on brain resilience and healthy longevity

INTRODUCTION

Global life expectancy has steadily increased in recent decades, resulting in a significant rise in the number of individuals aged 80 years and older. This trend is also evident in Latin America, where life expectancy is improving, though at varying rates across countries and regions.

METHODS

Partnering with the Neurosciences Group of Antioquia (GNA), we launched a Colombian study on resilience in families with autosomal dominant Alzheimer's disease and the oldest-old population. Over the past 2 years, the project has expanded to include participants from Peru, Chile, and Costa Rica.

RESULTS

This research led to the first symposium on Brain Resilience and Healthy Longevity, held in Medellín, Colombia, in August 2024.

DISCUSSION

The article summarizes key discussions from the symposium, highlighting the most promising opportunities for brain resilience and prevention research in the region and offering recommendations for future research to promote healthy aging and dementia-free communities.

HIGHLIGHTS

Uncovering the genetic and physiological drivers of cognitive resilience, neurodegeneration resistance, and healthy longevity is essential for maintaining brain function as we age. "Superagers" and cognitively resilient individuals from Latin American families with Alzheimer's disease offer valuable insights into brain protection mechanisms. Studying the interplay of socio-environmental and genetic factors in the oldest-old is key to understanding healthy longevity and improving dementia prevention. The inaugural Brain Resilience and Healthy Longevity Symposium highlights the need for global collaboration to uncover factors that drive cognitive resilience and healthy aging in Latin America, advancing dementia prevention.

A Novel Method to Disentangle Tightly Linked Risk and Resilience Genes for Brain Disorders: Application to Alzheimer's Disease

Background

Genetic risk factors for psychiatric and neurodegenerative disorders are well documented. However, some individuals with high genetic risk remain unaffected, and the mechanisms underlying such resilience remain poorly understood. The presence of protective resilience factors that mitigate risk could help explain the disconnect between predicted risk and reality, particularly for brain disorders, where genetic contributions are substantial but incompletely understood. Identifying and studying resilience factors could improve our understanding of pathology, enhance risk prediction, and inform preventive measures or treatment strategies. However, such efforts are complicated by the difficulty of identifying resilience that is separable from low risk.

Methods

We developed a novel adversarial multi-task neural network model to detect genetic resilience markers. The model learns to separate high-risk unaffected individuals from affected individuals at similar risk while "unlearning" patterns found in low-risk groups using adversarial learning. In simulated and existing Alzheimer's disease (AD) datasets, we identified markers of resilience with a feature-importance-based approach that prioritized specificity, generated resilience scores, and analyzed associations with polygenic risk scores (PRS).

Results

In simulations, our model had high specificity and moderate sensitivity in identifying resilience markers, outperforming traditional approaches. Applied to AD data, the model generated genetic resilience scores protective against AD and independent of PRS. We identified five resilience-associated SNPs, including known AD-associated variants, underscoring their potential involvement in risk/resilience interactions.

Conclusions

Our methods of modeling and evaluation of feature-importance successfully identified resilience markers that were obscured in previous work. The high specificity of our model provides high confidence that these markers reflect resilience and not simply low risk. Our findings support the utility of resilience scores in modifying risk predictions, particularly for high-risk groups. Expanding this method could aid in understanding resilience mechanisms, potentially improving diagnosis, prevention, and treatment strategies for AD and other complex brain disorders.

Age-invariant approaches to cognitive reserve

Cognitive reserve (CR) and its measurement by proxies have gained interest in cognitive aging research. While CR proxies seem valuable for predicting cognitive function, their measures are often conflated with age effects. The current study aims to address this by introducing an age-invariant approach of CR. We included 380 participants (age = 18-79) from the Advanced Brain Imaging on aging and Memory (ABRIM) study who completed the Cognitive Reserve Index questionnaire (CRIq), a measure to estimate verbal IQ, and several neuropsychological tasks in the domains of memory, executive function and attention/speed. With various regression models and structural equation modeling, we assessed age effects on the CRIq subscales and their predictive value on cognitive function. Results showed a significant non-linear age effect on the Education and Occupation subscale of the CRIq and a linear age effect on the Leisure subscale. New age-corrections derived from these effects were more accurate than age-corrections from the original norm scores. Moreover, the three cognitive domains were significantly predicted in the expected direction by the new age-corrected CRIq scores, and not by the raw scores or original age-corrected scores. However, compared to verbal IQ, the predictive value of these CRIq scores was still low. Associations between the CRIq and cognitive function seemed to vary across the lifespan, but were not consistently stronger for older adults. These findings illustrate the importance of age adjustments in CR research. Most importantly, appropriate age-adjustments may be sample specific and non-linear effects to properly correct for age must be considered.

Precision Estimates of Longitudinal Brain Aging Capture Unexpected Individual Differences in One Year

Individual differences in human brain aging are difficult to estimate over short intervals because of measurement error. Using a cluster scanning approach that reduces error by densely repeating rapid structural scans, we measured brain aging in individuals in one year. Expected differences between young and older individuals were evident, as were differences between cognitively unimpaired and impaired individuals. Each person's brain change trajectory was compared to modeled expectations from a large cohort of age-matched UK Biobank participants. Cognitively unimpaired older individuals variably revealed relative brain maintenance, unexpectedly rapid change, and asymmetrical change. These atypical brain aging trajectories were found across structures and verified in independent within-individual test and retest data. Precision estimates of brain change are possible over short intervals and reveal marked variability including among cognitively unimpaired individuals.

Investigating Modifiable Factors Associated with Cognitive Decline: Insights from the UK Biobank

Objectives: Given the escalating global prevalence of age-related cognitive impairments, identifying modifiable factors is crucial for developing targeted interventions. Methods: After excluding participants with dementia and substantial missing data, 453,950 individuals from UK Biobank (UKB) were included. Cognitive decline was assessed across four cognitive domains. The top 10% exhibiting the greatest decline were categorized as the "Cognitively At-Risk Population". Eighty-three potential factors from three categories were analyzed. Univariate and multivariate Cox proportional hazards models were employed to assess the independent and joint effects of these factors on cognitive decline. Population Attributable Fractions (PAFs) were calculated to estimate the potential impact of eliminating each risk category. Results: Our findings revealed a significant impact of unfavorable medical and psychiatric histories on processing speed and visual episodic memory decline (Hazard Ratio (HR) = 1.34, 95% CI: 1.20-1.51, p = 6.06 × 10⁻7; HR = 1.50, 95% CI: 1.22-1.86, p = 1.62 × 10⁻4, respectively). Furthermore, PAF analysis indicated that physiological and biochemical markers were the most critical risk category for preventing processing speed decline (PAF = 7.03%), while social and behavioral factors exerted the greatest influence on preventing visual episodic memory decline (PAF = 9.68%). Higher education, socioeconomic status, and handgrip strength emerged as protective factors, whereas high body mass index (BMI), hypertension, and depression were detrimental. Conclusions: By identifying this high-risk group and quantifying the impact of modifiable factors, this study provides valuable insights for developing targeted interventions to delay cognitive decline and improve public health outcomes in middle-aged and older adults.

Neuroimaging Predictors of Cognitive Resilience against Alzheimer's Disease Pathology

OBJECTIVE

Some individuals demonstrate greater cognitive resilience-the ability to maintain cognitive performance despite adverse brain-related changes-through as yet unknown mechanisms. We examined whether cortical thickness in several brain regions confers resilience against cognitive decline in amyloid-positive adults by moderating the effects of thinner cortex in Alzheimer's disease (AD)-related brain regions and of higher levels of tau.

METHODS

Amyloid-positive participants from the Alzheimer's Disease Neuroimaging Initiative with relevant imaging data were included (n = 160, observations = 473). Risk factors included an AD brain signature and cerebrospinal fluid phosphorylated tau. Cognitive measures were episodic memory and executive function composites. Mixed effects models tested whether region-specific cortical thickness moderated relationships between markers of AD risk and memory or executive function.

RESULTS

Cross-sectionally, thicker cortex in 8 regions minimized the negative impact of thinner cortex/smaller volume in AD signature regions on executive function. Longitudinally, higher baseline thickness in a composite of these 8 regions predicted less memory decline (p = 0.007) and weakened negative effects of phosphorylated tau on memory decline (p = 0.014), independent of baseline cognition and risk markers.

INTERPRETATION

We identified 8 cortical regions that appear to confer cognitive resilience cross-sectionally and longitudinally in the face of established indicators of AD pathology. Brain regions fostering executive function may enable compensation in later memory performance and confer cognitive resilience against effects of phosphorylated tau and AD-related cortical changes. These "resilience" regions suggest the value of focusing on brain regions beyond only those determined to be AD-related and may partially explain variability in AD-related cognitive trajectories. ANN NEUROL 2025.

Cognitive Reserve? Cognitive Capacity!

The concept of cognitive reserve (CR) has been a cornerstone in cognitive aging research, offering a framework to explain how life experiences like education, occupation, bilingualism, and physical exercise may buffer individuals from cognitive decline in the face of aging or neurological disease. However, this paper argues that the CR model, while influential, may have outlived its usefulness due to inherent limitations that constrain future research directions and unintentionally encourage "magical thinking". Specifically, CR's definition, which relies on cognitive performance being "better than expected" based on known measures of brain structure and function, makes the concept temporally bound to current scientific understanding, potentially stifling novel insights into cognition. In contrast, we propose a shift to a cognitive capacity (CC) framework, which views cognitive performance as being always determined by the brain's structural and functional capacities, without needing to invoke expectations based on incomplete knowledge. The CC framework is broader, encompassing factors that either promote or demote cognitive performance by directly modifying brain structure and function. This reconceptualization opens avenues for investigating cognitive enhancement not only in the context of aging or disease but also in young, healthy individuals. By emphasizing causal pathways between brain changes and cognitive outcomes, this perspective provides a more flexible and testable approach to understanding the mechanisms behind cognitive performance and its modulation across the lifespan.

Examining resilience to Alzheimer's disease through the lens of monoaminergic neuromodulator systems

The monoaminergic nuclei are thought to be some of the earliest sites of Alzheimer's disease (AD) pathology in the brain, with tau-containing pretangles appearing in these nuclei decades before the onset of clinical impairments. It has increasingly been recognized that monoamine systems represent a critical target of investigation towards understanding the progression of AD and designing early detection and treatment approaches. This review synthesizes evidence across animal studies, human neuropathology, and state-of-the-art neuroimaging and daily life assessment methods in humans, which demonstrate robust relationships between monoamine systems and AD pathophysiology and behavior. Further, the review highlights the promise of multimethod, multisystem approaches to studying monoaminergic mechanisms of resilience to AD pathology.

Brain reserve in midlife is associated with executive function changes across 12 years

We examined how brain reserve in midlife, measured by brain-predicted age difference scores (Brain-PADs), predicted executive function concurrently and longitudinally into early old age, and whether these associations were moderated by young adult cognitive reserve or APOE genotype. 508 men in the Vietnam Era Twin Study of Aging (VETSA) completed neuroimaging assessments at mean age 56 and six executive function tasks at mean ages 56, 62, and 68 years. Results indicated that greater brain reserve at age 56 was associated with better concurrent executive function (r=.10, p=.040) and less decline in executive function over 12 years (r=.34, p=.001). These associations were not moderated by cognitive reserve or APOE genotype. Twin analysis suggested associations with executive function slopes were driven by genetic influences. Our findings suggest that greater brain reserve allowed for better cognitive maintenance from middle- to old age, driven by a genetic association. The results are consistent with differential preservation of executive function based on brain reserve that is independent of young adult cognitive reserve or APOE genotype.

Mid- and late-life lifestyle activities as main drivers of general and domain-specific cognitive reserve in individuals with Parkinson's disease: cross-sectional and longitudinal evidence from the LANDSCAPE study

BACKGROUND

Cognitive reserve (CR) is considered a protective factor for cognitive function and may explain interindividual differences of cognitive performance given similar levels of neurodegeneration, e.g., in Alzheimer´s disease. Recent evidence suggests that CR is also relevant in Parkinson's disease (PD).

OBJECTIVE

We aimed to explore the role of life-stage specific CR for overall cognition and specific cognitive domains cross-sectionally and longitudinally in PD.

METHODS

The cross-sectional analysis with data from the DEMPARK/LANDSCAPE study included 81 individuals without cognitive impairment (PD-N) and 87 individuals with mild cognitive impairment (PD-MCI). Longitudinal data covered 4 years with over 500 observations. CR was operationalized with the Lifetime of Experiences Questionnaire (LEQ), capturing the complexity of lifestyle activities across distinct life-stages. Cognition was assessed using a comprehensive neuropsychological test battery.

RESULTS

Higher LEQ scores, particularly from mid- and late-life, were observed in PD-N compared to PD-MCI [F(1,153) = 4.609, p = .033, ηp2 = 0.029]. They were significantly associated with better cognitive performance (0.200 ≤ β ≤ 0.292). Longitudinally, linear mixed effect models (0.236 ≤ marginal R2 ≤ 0.441) revealed that LEQ scores were positively related to cognitive performance independent of time. However, the decline in overall cognition and memory over time was slightly more pronounced with higher LEQ scores.

CONCLUSIONS

This study emphasizes the association between complex lifestyle activities and cognition in PD. Data indicate that while CR might be related to a delay of cognitive decline, individuals with high CR may experience a more pronounced drop in overall cognition and memory. Future studies will have to replicate these findings, particularly regarding domain-specific effects and considering reverse causal mechanisms.

Reserve, resilience and maintenance of episodic memory and other cognitive functions in aging

We tested if cognitive and brain reserve and maintenance explain individual differences in episodic memory and other cognitive domains from late middle to early older adulthood. We used The Vietnam Era Twin Study of Aging data (n=1604 men) with episodic memory measured at mean ages of 56, 62 and 68 years, and magnetic resonance imaging data for a subsample of participants (n=321). Cognitive reserve -young adult general cognitive ability at a mean age of 20 years and, to a lesser degree, educational attainment- was positively related to episodic memory performance at each assessment, but not to memory change. We found no evidence for the associations of brain reserve or brain maintenance on memory change. Results were highly similar when looking at processing speed, executive function and verbal fluency. In conclusion, higher young adult cognitive reserve was related to better episodic memory in midlife and older adulthood, but it did not confer better cognitive maintenance with respect to memory. This supports the importance of early cognitive development in dementia prevention.

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.

Understanding the Temporal Dynamics of Accelerated Brain Aging and Resilient Brain Aging: Insights from Discriminative Event-Based Analysis of UK Biobank Data

The intricate dynamics of brain aging, especially the neurodegenerative mechanisms driving accelerated (ABA) and resilient brain aging (RBA), are pivotal in neuroscience. Understanding the temporal dynamics of these phenotypes is crucial for identifying vulnerabilities to cognitive decline and neurodegenerative diseases. Currently, there is a lack of comprehensive understanding of the temporal dynamics and neuroimaging biomarkers linked to ABA and RBA. This study addressed this gap by utilizing a large-scale UK Biobank (UKB) cohort, with the aim to elucidate brain aging heterogeneity and establish the foundation for targeted interventions. Employing Lasso regression on multimodal neuroimaging data, structural MRI (sMRI), diffusion MRI (dMRI), and resting-state functional MRI (rsfMRI), we predicted the brain age and classified individuals into ABA and RBA cohorts. Our findings identified 1949 subjects (6.2%) as representative of the ABA subpopulation and 3203 subjects (10.1%) as representative of the RBA subpopulation. Additionally, the Discriminative Event-Based Model (DEBM) was applied to estimate the sequence of biomarker changes across aging trajectories. Our analysis unveiled distinct central ordering patterns between the ABA and RBA cohorts, with profound implications for understanding cognitive decline and vulnerability to neurodegenerative disorders. Specifically, the ABA cohort exhibited early degeneration in four functional networks and two cognitive domains, with cortical thinning initially observed in the right hemisphere, followed by the temporal lobe. In contrast, the RBA cohort demonstrated initial degeneration in the three functional networks, with cortical thinning predominantly in the left hemisphere and white matter microstructural degeneration occurring at more advanced stages. The detailed aging progression timeline constructed through our DEBM analysis positioned subjects according to their estimated stage of aging, offering a nuanced view of the aging brain's alterations. This study holds promise for the development of targeted interventions aimed at mitigating age-related cognitive decline.

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.

Associations of plasma neurofilament light chain with cognition and neuroimaging measures in community-dwelling early old age men

BACKGROUND

Plasma neurofilament light chain (NfL) is a promising biomarker of neurodegeneration with potential clinical utility in monitoring the progression of neurodegenerative diseases. However, the cross-sectional associations of plasma NfL with measures of cognition and brain have been inconsistent in community-dwelling populations.

METHODS

We examined these associations in a large community-dwelling sample of early old age men (N = 969, mean age = 67.57 years, range = 61-73 years), who are either cognitively unimpaired (CU) or with mild cognitive impairment (MCI). Specifically, we investigated five cognitive domains (executive function, episodic memory, verbal fluency, processing speed, visual-spatial ability), as well as neuroimaging measures of gray and white matter.

RESULTS

After adjusting for age, health status, and young adult general cognitive ability, plasma NfL level was only significantly associated with processing speed and white matter hyperintensity (WMH) volume, but not with other cognitive or neuroimaging measures. The association with processing speed was driven by individuals with MCI, as it was not detected in CU individuals.

CONCLUSIONS

These results suggest that in early old age men without dementia, plasma NfL does not appear to be sensitive to cross-sectional individual differences in most domains of cognition or neuroimaging measures of gray and white matter. The revealed plasma NfL associations were limited to WMH for all participants and processing speed only within the MCI cohort. Importantly, considering cognitive status in community-based samples will better inform the interpretation of the relationships of plasma NfL with cognition and brain and may help resolve mixed findings in the literature.

A lifetime perspective on risk factors for cognitive decline with a special focus on early events

Both Alzheimer's disease and vascular dementia are the result of disease processes that typically develop over several decades. Population studies have estimated that more than half of the risk for dementia is preventable or at least modifiable through behavioral adaptations. The association between these lifestyle factors and the risk of dementia is most evident for exposure in midlife. However, habits formed in middle age often reflect a lifetime of behavior patterns and living conditions. Therefore, individuals who, for example, are able to maintain healthy diets and regular exercise during their middle years are likely to benefit from these cognition-protective habits they have practiced throughout their lives. For numerous adult diseases, significant risks can often be traced back to early childhood. Suboptimal conditions during the perinatal period, childhood and adolescence can increase the risk of adult diseases, including stroke, heart disease, insulin resistance, hypertension and dementia. This review aims at summarizing some of the evidence for dementia risks from a life-time perspective with the goal of raising awareness for early dementia prevention and successful aging.

Childhood Disadvantage Moderates Late Midlife Default Mode Network Cortical Microstructure and Visual Memory Association

BACKGROUND

Childhood disadvantage is a prominent risk factor for cognitive and brain aging. Childhood disadvantage is associated with poorer episodic memory in late midlife and functional and structural brain abnormalities in the default mode network (DMN). Although age-related changes in DMN are associated with episodic memory declines in older adults, it remains unclear if childhood disadvantage has an enduring impact on this later-life brain-cognition relationship earlier in the aging process. Here, within the DMN, we examined whether its cortical microstructural integrity-an early marker of structural vulnerability that increases the risk for future cognitive decline and neurodegeneration-is associated with episodic memory in adults at ages 56-66, and whether childhood disadvantage moderates this association.

METHODS

Cortical mean diffusivity (MD) obtained from diffusion magnetic resonance imaging was used to measure microstructural integrity in 350 community-dwelling men. We examined both visual and verbal episodic memory in relation to DMN MD and divided participants into disadvantaged and nondisadvantaged groups based on parental education and occupation.

RESULTS

Higher DMN MD was associated with poorer visual memory but not verbal memory (β = -0.11, p = .040 vs β = -0.04, p = .535). This association was moderated by childhood disadvantage and was significant only in the disadvantaged group (β = -0.26, p = .002 vs β = -0.00, p = .957).

CONCLUSIONS

Lower DMN cortical microstructural integrity may reflect visual memory vulnerability in cognitively normal adults earlier in the aging process. Individuals who experienced childhood disadvantage manifested greater vulnerability to cortical microstructure-related visual memory dysfunction than their nondisadvantaged counterparts who exhibited resilience in the face of low cortical microstructural integrity.

A bidirectional relationship between cognitive reserve and cognition among older adults in a rural Chinese community: a cross-lagged design

Background

The concept of cognitive reserve (CR) plays a crucial role in understanding cognitive aging and resilience. Accumulating evidence revealed the influence of CR proxy on cognitive function, but it remains unknown whether a reverse association or reciprocal effect exists.

Objective

The aim of this study is to observe the bidirectional relationship between cognitive reserve proxies and cognitive function among older adults in rural Chinese communities, providing a better understanding of the underlying mechanisms and potential moderating factors involved.

Method

This longitudinal study analyzed 792 older adults (70.23 ± 5.87 years; 59.8%female) aged 60 years and older from the health status of rural older adults (HSRO) study over a 3-year period. Cognition was assessed by the Mini-Mental State Examination (MMSE). Cross-lagged panel modeling was utilized to analyze the interrelationship between cognitive reserve proxies and cognitive performance. Additionally, latent profile analysis was employed to identify different subtypes of neuropathic load within the study population.

Results

Our cross-lagged analyses revealed significant associations between CR at T0 and MMSE scores at T1 (β = 0.81), as well as between MMSE scores at T0 and CR at T1 (β = 0.04). However, when conducting stratified analyses, we found no significant lagged relationships among individuals with high neuropathic load or those at an advanced age (p > 0.05). Furthermore, our longitudinal comparisons indicated changes in the contribution of CR proxy factors over time.

Conclusion

The findings suggested a bidirectional relationship between cognitive reserve and cognitive performance in older adults. These results emphasized the importance of implementing timely public health measures to enhance cognitive reserve and cognitive performance ultimately promoting healthier aging among older adults.

Machine learning analyses identify multi-modal frailty factors that selectively discriminate four cohorts in the Alzheimer's disease spectrum: a COMPASS-ND study

BACKGROUND

Frailty indicators can operate in dynamic amalgamations of disease conditions, clinical symptoms, biomarkers, medical signals, cognitive characteristics, and even health beliefs and practices. This study is the first to evaluate which, among these multiple frailty-related indicators, are important and differential predictors of clinical cohorts that represent progression along an Alzheimer's disease (AD) spectrum. We applied machine-learning technology to such indicators in order to identify the leading predictors of three AD spectrum cohorts; viz., subjective cognitive impairment (SCI), mild cognitive impairment (MCI), and AD. The common benchmark was a cohort of cognitively unimpaired (CU) older adults.

METHODS

The four cohorts were from the cross-sectional Comprehensive Assessment of Neurodegeneration and Dementia dataset. We used random forest analysis (Python 3.7) to simultaneously test the relative importance of 83 multi-modal frailty indicators in discriminating the cohorts. We performed an explainable artificial intelligence method (Tree Shapley Additive exPlanation values) for deep interpretation of prediction effects.

RESULTS

We observed strong concurrent prediction results, with clusters varying across cohorts. The SCI model demonstrated excellent prediction accuracy (AUC = 0.89). Three leading predictors were poorer quality of life ([QoL]; memory), abnormal lymphocyte count, and abnormal neutrophil count. The MCI model demonstrated a similarly high AUC (0.88). Five leading predictors were poorer QoL (memory, leisure), male sex, abnormal lymphocyte count, and poorer self-rated eyesight. The AD model demonstrated outstanding prediction accuracy (AUC = 0.98). Ten leading predictors were poorer QoL (memory), reduced olfaction, male sex, increased dependence in activities of daily living (n = 6), and poorer visual contrast.

CONCLUSIONS

Both convergent and cohort-specific frailty factors discriminated the AD spectrum cohorts. Convergence was observed as all cohorts were marked by lower quality of life (memory), supporting recent research and clinical attention to subjective experiences of memory aging and their potentially broad ramifications. Diversity was displayed in that, of the 14 leading predictors extracted across models, 11 were selectively sensitive to one cohort. A morbidity intensity trend was indicated by an increasing number and diversity of predictors corresponding to clinical severity, especially in AD. Knowledge of differential deficit predictors across AD clinical cohorts may promote precision interventions.

Higher cortical thickness/volume in Alzheimer's-related regions: protective factor or risk factor?

Some evidence suggests a biphasic pattern of changes in cortical thickness wherein higher, rather than lower, thickness is associated with very early Alzheimer's disease (AD) pathology. We examined whether integrating information from AD brain signatures based on mean diffusivity (MD) can aid in the interpretation of cortical thickness/volume as a risk factor for future AD-related changes. Participants were 572 men in the Vietnam Era Twin Study of Aging who were cognitively unimpaired at baseline (mean age = 56 years; range = 51-60). Individuals with both high thickness/volume signatures and high MD signatures at baseline had lower cortical thickness/volume in AD signature regions and lower episodic memory performance 12 years later compared to those with high thickness/volume and low MD signatures at baseline. Groups did not differ in level of young adult cognitive reserve. Our findings are in line with a biphasic model in which increased cortical thickness may precede future decline and establish the value of examining cortical MD alongside cortical thickness to identify subgroups with differential risk for poorer brain and cognitive outcomes.

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.

Cognitive reserve moderates the association between cerebral blood flow and language performance in older adults with mild cognitive impairment

Higher cognitive reserve (CR) may offer protection from cognitive changes associated with reduced cerebral blood flow (CBF). We investigated CR as a moderator of the effect of CBF on cognition in older adults with mild cognitive impairment (MCI; N = 46) and those who are cognitively unimpaired (CU; N = 101). Participants underwent arterial spin labeling MRI, which was used to quantify CBF in 4 a priori regions. Estimated verbal intelligence quotient (VIQ) served as a proxy for CR. Multiple linear regressions examined whether VIQ moderated associations between CBF and cognition and whether this differed by cognitive status. Outcomes included memory and language performance. There were 3-way interactions (CBF*VIQ*cognitive status) on category fluency when examining hippocampal, superior frontal, and inferior frontal CBF. Follow-up analyses revealed that, within the MCI but not CU group, there were CBF*VIQ interactions on fluency in all a priori regions examined, where there were stronger, positive associations between CBF and fluency at higher VIQ. Conclusion: In MCI, higher CR plays a role in strengthening CBF-fluency associations.

Associations among executive function Abilities, free Water, and white matter microstructure in early old age

BACKGROUND

Studies have investigated white matter microstructure in relation to late-life cognitive impairments, with fractional anisotropy (FA) and mean diffusivity (MD) measures thought to capture demyelination and axonal degradation. However, new post-processing methods allow isolation of free water (FW), which captures extracellular fluid contributions such as atrophy and neuroinflammation, from tissue components. FW also appears to be highly relevant to late-life cognitive impairment. Here, we evaluated whether executive functions are associated with FW, and FA and MD corrected for FW (FAFWcorr and MDFWcorr).

METHOD

We examined 489 non-demented men in the Vietnam Era Twin Study of Aging (VETSA) at mean age 68. Two latent factors capturing 'common executive function' and 'working-memory specific' processes were estimated based on 6 tasks. Analyses focused on 11 cortical white matter tracts across three metrics: FW, FAFWcorr, and MDFWcorr.

RESULTS

Better 'common executive function' was associated with lower FW across 9 of the 11 tracts. There were no significant associations with intracellular metrics after false discovery rate correction. Effects also appeared driven by individuals with MCI (13.7% of the sample). Working memory-specific tasks showed some associations with FAFWcorr, including the triangularis portion of the inferior frontal gyrus. There was no evidence that cognitive reserve (i.e., general cognitive ability assessed in early adulthood) moderated these associations between executive function and FW or FA.

DISCUSSION

Executive function abilities in early old age are associated primarily with extracellular fluid (FW) as opposed to white matter (FAFWcorr or MDFWcorr). Moderation analyses suggested cognitive reserve does not play a strong role in these associations, at least in this sample of non-demented men.

Issues and recommendations for the residual approach to quantifying cognitive resilience and reserve

BACKGROUND

Cognitive reserve and resilience are terms used to explain interindividual variability in maintenance of cognitive health in response to adverse factors, such as brain pathology in the context of aging or neurodegenerative disorders. There is substantial interest in identifying tractable substrates of resilience to potentially leverage this phenomenon into intervention strategies. One way of operationalizing cognitive resilience that has gained popularity is the residual method: regressing cognition on an adverse factor and using the residual as a measure of resilience. This method is attractive because it provides a statistical approach that is an intuitive match to the reserve/resilience conceptual framework. However, due to statistical properties of the regression equation, the residual approach has qualities that complicate its interpretation as an index of resilience and make it statistically inappropriate in certain circumstances.

METHODS AND RESULTS

We describe statistical properties of the regression equation to illustrate why the residual is highly correlated with the cognitive score from which it was derived. Using both simulations and real data, we model common applications of the approach by creating a residual score (global cognition residualized for hippocampal volume) in individuals along the AD spectrum. We demonstrate that in most real-life scenarios, the residual measure of cognitive resilience is highly correlated with cognition, and the degree of this correlation depends on the initial relationship between the adverse factor and cognition. Subsequently, any association between this resilience metric and an external variable may actually be driven by cognition, rather than by an operationalized measure of resilience. We then assess several strategies proposed as potential solutions to this problem, such as including both the residual and original cognitive measure in a model. However, we conclude these solutions may be insufficient, and we instead recommend against "pre-regression" strategies altogether in favor of using statistical moderation (e.g., interactions) to quantify resilience.

CONCLUSIONS

Caution should be taken in the use and interpretation of the residual-based method of cognitive resilience. Rather than identifying resilient individuals, we encourage building more complete models of cognition to better identify the specific adverse and protective factors that influence cognitive decline.