Conceptual and measurement challenges in research on cognitive reserve

Cognitive reserve, broadly conceived, encompasses aspects of brain structure and function that optimize individual performance in the presence of injury or pathology. Reserve is defined as a feature of brain structure and/or function that modifies the relationship between injury or pathology and performance on neuropsychological tasks or clinical outcomes. Reserve is challenging to study for two reasons. The first is: reserve is a hypothetical construct, and direct measures of reserve are not available. Proxy variables and latent variable models are used to attempt to operationalize reserve. The second is: in vivo measures of neuronal pathology are not widely available. It is challenging to develop and test models involving a risk factor (injury or pathology), a moderator (reserve) and an outcome (performance or clinical status) when neither the risk factor nor the moderator are measured directly. We discuss approaches for quantifying reserve with latent variable models, with emphasis on their application in the analysis of data from observational studies. Increasingly latent variable models are used to generate composites of cognitive reserve based on multiple proxies. We review the theoretical and ontological status of latent variable modeling approaches to cognitive reserve, and suggest research strategies for advancing the field.

The cognitive reserve hypothesis: a longitudinal examination of age-associated declines in reasoning and processing speed

The term cognitive reserve is frequently used to refer to the ubiquitous finding that, during later life, those higher in experiential resources (e.g., education, knowledge) exhibit higher levels of cognitive function. This observation may be the result of either experiential resources playing protective roles with respect to the cognitive declines associated with aging or the persistence of differences in functioning that have existed since earlier adulthood. These possibilities were examined by applying accelerated longitudinal structural equation (growth curve) models to 5-year reasoning and speed data from the no-contact control group (N = 690; age 65-89 years at baseline) of the Advanced Cognitive Training for Independent and Vital Elderly study. Vocabulary knowledge and years of education, as markers of cognitive reserve, were related to levels of cognitive functioning but unrelated to rates of cognitive change, both before and after the (negative) relations between levels and rates were controlled for. These results suggest that cognitive reserve reflects the persistence of earlier differences in cognitive functioning rather than differential rates of age-associated cognitive declines.

Cognitive reserve in multiple sclerosis

Cognitive impairment is common among persons with multiple sclerosis (MS), but some patients are able to withstand considerable disease burden (e.g. white matter lesions, cerebral atrophy) without cognitive impairment (cognitive inefficiency, memory decline). What protects these patients from cognitive impairment? We review the literature on cognitive reserve in MS, which shows that heritable (larger maximal lifetime brain growth) and environmental (greater intellectual enrichment) factors attenuate the negative effect of disease burden on cognitive status. That is, persons with larger maximal lifetime brain growth, greater vocabulary knowledge, and/or greater early life participation in cognitive leisure activities (e.g. reading, hobbies) are better able to cope with MS disease without cognitive impairment. We review evidence that benefits of intellectual enrichment on cognitive status may stem from more efficient patterns of brain function. We discuss clinical implications and highlight important unanswered questions for future research on reserve against cognitive impairment in MS.

The impact of bilingualism on brain reserve and metabolic connectivity in Alzheimer's dementia

Cognitive reserve (CR) prevents cognitive decline and delays neurodegeneration. Recent epidemiological evidence suggests that lifelong bilingualism may act as CR delaying the onset of dementia by ∼4.5 y. Much controversy surrounds the issue of bilingualism and its putative neuroprotective effects. We studied brain metabolism, a direct index of synaptic function and density, and neural connectivity to shed light on the effects of bilingualism in vivo in Alzheimer's dementia (AD). Eighty-five patients with probable AD and matched for disease duration (45 German-Italian bilingual speakers and 40 monolingual speakers) were included. Notably, bilingual individuals were on average 5 y older than their monolingual peers. In agreement with our predictions and with models of CR, cerebral hypometabolism was more severe in the group of bilingual individuals with AD. The metabolic connectivity analyses crucially supported the neuroprotective effect of bilingualism by showing an increased connectivity in the executive control and the default mode networks in the bilingual, compared with the monolingual, AD patients. Furthermore, the degree of lifelong bilingualism (i.e., high, moderate, or low use) was significantly correlated to functional modulations in crucial neural networks, suggesting both neural reserve and compensatory mechanisms. These findings indicate that lifelong bilingualism acts as a powerful CR proxy in dementia and exerts neuroprotective effects against neurodegeneration. Delaying the onset of dementia is a top priority of modern societies, and the present in vivo neurobiological evidence should stimulate social programs and interventions to support bilingual or multilingual education and the maintenance of the second language among senior citizens.

Cognitive reserve and lifestyle: moving towards preclinical Alzheimer's disease

The large majority of neuroimaging studies in Alzheimer’s disease (AD) patients have supported the idea that lifestyle factors may protect against the clinical manifestations of AD rather than influence AD neuropathological processes (the cognitive reserve hypothesis). This evidence argues in favor of the hypothesis that lifestyle factors act as moderators between AD pathology and cognition, i.e., through indirect compensatory mechanisms. In this review, we identify emerging evidence in cognitively normal older adults that relate lifestyle factors to established AD neuroimaging biomarkers. While some of these investigations are in agreement with the compensatory view of cognitive reserve, other studies have revealed new clues on the neural mechanisms underlying beneficial effects of lifestyle factors on the brain. Specifically, they provide novel evidence suggesting direct effects of lifestyle factors on AD neuropathological processes. We propose a tentative theoretical model where lifestyle factors may act via direct neuroprotective and/or indirect compensatory mechanisms. Importantly, we suggest that neuroprotective mechanisms may have a major role during early stages and compensatory mechanisms in later stages of the disease. In the absence of an effective treatment for AD and considering the potential of lifestyle factors in AD prevention, understanding the neural mechanisms underlying lifestyle effects on the brain seems crucial. We hope to provide an integrative view that may help to better understand the complex effects of lifestyle factors on AD neuropathological processes, starting from the preclinical stage.

Hippocampal volume varies with educational attainment across the life-span

Socioeconomic disparities—and particularly differences in educational attainment—are associated with remarkable differences in cognition and behavior across the life-span. Decreased educational attainment has been linked to increased exposure to life stressors, which in turn have been associated with structural differences in the hippocampus and the amygdala. However, the degree to which educational attainment is directly associated with anatomical differences in these structures remains unclear. Recent studies in children have found socioeconomic differences in regional brain volume in the hippocampus and amygdala across childhood and adolescence. Here we expand on this work, by investigating whether disparities in hippocampal and amygdala volume persist across the life-span. In a sample of 275 individuals from the BRAINnet Foundation database ranging in age from 17 to 87, we found that socioeconomic status (SES), as operationalized by years of educational attainment, moderates the effect of age on hippocampal volume. Specifically, hippocampal volume tended to markedly decrease with age among less educated individuals, whereas age-related reductions in hippocampal volume were less pronounced among more highly educated individuals. No such effects were found for amygdala volume. Possible mechanisms by which education may buffer age-related effects on hippocampal volume are discussed.

Gender differences in healthy aging and Alzheimer's Dementia: A 18 F-FDG-PET study of brain and cognitive reserve

Cognitive reserve (CR) and brain reserve (BR) are protective factors against age-associated cognitive decline and neurodegenerative disorders. Very limited evidence exists about gender effects on brain aging and on the effect of CR on brain modulation in healthy aging and Alzheimer's Dementia (AD). We investigated gender differences in brain metabolic activity and resting-state network connectivity, as measured by ¹⁸ F-FDG-PET, in healthy aging and AD, also considering the effects of education and occupation. The clinical and imaging data were retrieved from large datasets of healthy elderly subjects (HE) (225) and AD patients (282). In HE, males showed more extended age-related reduction of brain metabolism than females in frontal medial cortex. We also found differences in brain modulation as metabolic increases induced by education and occupation, namely in posterior associative cortices in HE males and in the anterior limbic-affective and executive networks in HE females. In AD patients, the correlations between education and occupation levels and brain hypometabolism showed gender differences, namely a posterior temporo-parietal association in males and a frontal and limbic association in females, indicating the involvement of different networks. Finally, the metabolic connectivity in both HE and AD aligned with these results, suggesting greater efficiency in the posterior default mode network for males, and in the anterior frontal executive network for females. The basis of these brain gender differences in both aging and AD, obtained exploring cerebral metabolism, metabolic connectivity and the effects of education and occupation, is likely at the intersection between biological and sociodemographic factors. Hum Brain Mapp 38:4212-4227, 2017. © 2017 Wiley Periodicals, Inc.

Aging, brain disease, and reserve: implications for delirium

Cognitive and brain reserve are well studied in the context of age-associated cognitive impairment and dementia. However, there is a paucity of research that examines the role of cognitive or brain reserve in delirium. Indicators (or proxy measures) of cognitive or brain reserve (such as brain size, education, and activities) pose challenges in the context of the long prodromal phase of Alzheimer disease but are diminished in the context of delirium, which is of acute onset. This article provides a review of original articles on cognitive and brain reserve across many conditions affecting the central nervous system, with a focus on delirium. The authors review current definitions of reserve. The authors identify indicators for reserve used in earlier studies and discuss these indicators in the context of delirium. The authors highlight future research directions to move the field ahead. Reserve may be a potentially modifiable characteristic. Studying the role of reserve in delirium can advance prevention strategies for delirium and may advance knowledge of reserve and its role in aging and neuropsychiatric disease generally.

The functional connectome of cognitive reserve

Cognitive Reserve (CR) designates the brain's capacity to actively cope with insults through a more efficient use of its resources/networks. It was proposed in order to explain the discrepancies between the observed cognitive ability and the expected capacity for an individual. Typical proxies of CR include education and Intelligence Quotient but none totally account for the variability of CR and no study has shown if the brain's greater efficiency associated with CR can be measured. We used a validated model to estimate CR from the residual variance in memory and general executive functioning, accounting for both brain anatomical (i.e., gray matter and white matter signal abnormalities volume) and demographic variables (i.e., years of formal education and sex). Functional connectivity (FC) networks and topological properties were explored for associations with CR. Demographic characteristics, mainly accounted by years of formal education, were associated with higher FC, clustering, local efficiency and strength in parietal and occipital regions and greater network transitivity. Higher CR was associated with a greater FC, local efficiency and clustering of occipital regions, strength and centrality of the inferior temporal gyrus and higher global efficiency. Altogether, these findings suggest that education may facilitate the brain's ability to form segregated functional groups, reinforcing the view that higher education level triggers more specialized use of neural processing. Additionally, this study demonstrated for the first time that CR is associated with more efficient processing of information in the human brain and reinforces the existence of a fine balance between segregation and integration. Hum Brain Mapp 37:3310–3322, 2016.. © 2016 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.

Cognitive Reserve in Healthy Aging and Alzheimer's Disease: A Meta-Analysis of fMRI Studies

Cognitive reserve (CR) has been defined as the ability to optimize or maximize performance through differential recruitment of brain networks. In the present study, we aimed at providing evidence for a consistent brain network underpinning CR in healthy and pathological aging. To pursue this aim, we performed a coordinate-based meta-analysis of 17 functional magnetic resonance imaging studies on CR proxies in healthy aging, Alzheimer's disease (AD), and mild cognitive impairment (MCI). We found that different brain areas were associated with CR proxies in healthy and pathological aging. A wide network of areas, including medial and lateral frontal areas, that is, anterior cingulate cortex and dorsolateral prefrontal cortex, as well as precuneus, was associated with proxies of CR in healthy elderly patients. The CR proxies in patients with AD and amnesic-MCI were associated with activation in the anterior cingulate cortex. These results were discussed hypothesizing the existence of possible compensatory mechanisms in healthy and pathological aging.

Translational research on reserve against neurodegenerative disease: consensus report of the International Conference on Cognitive Reserve in the Dementias and the Alzheimer's Association Reserve, Resilience and Protective Factors Professional Interest Area working groups

BACKGROUND

The concept of reserve was established to account for the observation that a given degree of neurodegenerative pathology may result in varying degrees of symptoms in different individuals. There is a large amount of evidence on epidemiological risk and protective factors for neurodegenerative diseases and dementia, yet the biological mechanisms that underpin the protective effects of certain lifestyle and physiological variables remain poorly understood, limiting the development of more effective preventive and treatment strategies. Additionally, different definitions and concepts of reserve exist, which hampers the coordination of research and comparison of results across studies.

DISCUSSION

This paper represents the consensus of a multidisciplinary group of experts from different areas of research related to reserve, including clinical, epidemiological and basic sciences. The consensus was developed during meetings of the working groups of the first International Conference on Cognitive Reserve in the Dementias (24-25 November 2017, Munich, Germany) and the Alzheimer's Association Reserve and Resilience Professional Interest Area (25 July 2018, Chicago, USA). The main objective of the present paper is to develop a translational perspective on putative mechanisms underlying reserve against neurodegenerative disease, combining evidence from epidemiological and clinical studies with knowledge from animal and basic research. The potential brain functional and structural basis of reserve in Alzheimer's disease and other brain disorders are discussed, as well as relevant lifestyle and genetic factors assessed in both humans and animal models.

CONCLUSION

There is an urgent need to advance our concept of reserve from a hypothetical model to a more concrete approach that can be used to improve the development of effective interventions aimed at preventing dementia. Our group recommends agreement on a common dictionary of terms referring to different aspects of reserve, the improvement of opportunities for data sharing across individual cohorts, harmonising research approaches across laboratories and groups to reduce heterogeneity associated with human data, global coordination of clinical trials to more effectively explore whether reducing epidemiological risk factors leads to a reduced burden of neurodegenerative diseases in the population, and an increase in our understanding of the appropriateness of animal models for reserve research.

The Neuroprotective Effects of Experience on Cognitive Functions: Evidence from Animal Studies on the Neurobiological Bases of Brain Reserve

Brain plasticity is the ability of the nervous system to change structurally and functionally in response to experience. By shaping brain structure and function, experience leads to the creation of a protective reserve that accounts for differences among individuals in susceptibility to age-related brain modifications and pathology. This review is aimed to address the biological bases of the experience-dependent "brain reserve" by describing the results of animal studies that focused on the neuroanatomical and molecular effects of environmental enrichment. More specifically, the effects at the cellular level are considered in terms of changes in neurogenesis, gliogenesis, angiogenesis, and synaptogenesis. Moreover, the effects at the molecular level are described, highlighting gene- and protein-level changes in neurotransmitter and neurotrophin expression. The experimental evidence for the basic biological consequences of environmental enrichment is described for healthy animals. Subsequently, by discussing the findings for animal models that mimic age-related diseases, the involvement of such plastic changes in supporting an organism as it copes with normal and pathological age-related cognitive decline is considered. On the whole, studies of the structural and molecular effects of environmental enrichment strongly support the neuroprotective action of a particularly stimulating lifestyle on cognitive functions. Our current level of understanding of these effects and mechanisms is such that additional and novel studies, systematic reviews, and meta-analyses are necessary to investigate the specific effects of the different components of environmental enrichment in both healthy and pathological models. Only in this way can comprehensive recommendations for proper life habits be developed.

The Contribution of Physical Exercise to Brain Resilience

Increasing attention has been given to understanding resilience to brain diseases, often described as brain or cognitive reserve. Among the protective factors for the development of resilience, physical activity/exercise has been considered to play an important role. Exercise is known to induce many positive effects on the brain. As such, exercise represents an important tool to influence neurodevelopment and shape the adult brain to react to life's challenges. Among many beneficial effects, exercise intervention has been associated with cognitive improvement and stress resilience in humans and animal models. Thus, a growing number of studies have demonstrated that exercise not only recovers or minimizes cognitive deficits by inducing better neuroplasticity and cognitive reserve but also counteracts brain pathology. This is evidenced before disease onset or after it has been established. In this review, we aimed to present encouraging data from current clinical and pre-clinical neuroscience research and discuss the possible biological mechanisms underlying the beneficial effects of physical exercise on resilience. We consider the implication of physical exercise for resilience from brain development to aging and for some neurological diseases. Overall, the literature indicates that brain/cognitive reserve built up by regular exercise in several stages of life, prepares the brain to be more resilient to cognitive impairment and consequently to brain pathology.

The positive impacts of early-life education on cognition, leisure activity, and brain structure in healthy aging

Education in people's early lives are positively related to their cognitive function, but its modulating effects on detailed cognition domains, its interaction with leisure activities and the associated brain changes have yet to be investigated. This report used data from 659 cognitively normal community dwelling elderly who completed neuropsychological tests, leisure activities measurement, and 78 of them underwent structural and diffusion MRI scans. We found that: (i) the highly educated elderly had a better cognitive functioning in multi-domains, higher frequencies of participation in knowledge-related leisure activities, and slower age-related reductions of executive function; (ii) the intellectual and social types of leisure activities mediated the association between education and multiple cognitive domains, including memory, language, attention and executive function; (iii) there was a significant age by education interaction on the gray matter volume of the anterior brain regions and white matter integrity; and (iv) the interaction between age and education affected cognition indirectly through white matter integrity analyzed using structural equation model. Overall, our results revealed that high education in early life served as a protective factor in aging that may help to postpone cognitive and brain reserve decline in cognitively normal aging.

Educational attainment, structural brain reserve and Alzheimer's disease: a Mendelian randomization analysis

Higher educational attainment is observationally associated with lower risk of Alzheimer's disease. However, the biological mechanisms underpinning this association remain unclear. The protective effect of education on Alzheimer's disease may be mediated via increased brain reserve. We used two-sample Mendelian randomization to explore putative causal relationships between educational attainment, structural brain reserve as proxied by MRI phenotypes and Alzheimer's disease. Summary statistics were obtained from genome-wide association studies of educational attainment (n = 1 131 881), late-onset Alzheimer's disease (35 274 cases, 59 163 controls) and 15 measures of grey or white matter macro- or micro-structure derived from structural or diffusion MRI (nmax = 33 211). We conducted univariable Mendelian randomization analyses to investigate bidirectional associations between (i) educational attainment and Alzheimer's disease; (ii) educational attainment and imaging-derived phenotypes; and (iii) imaging-derived phenotypes and Alzheimer's disease. Multivariable Mendelian randomization was used to assess whether brain structure phenotypes mediated the effect of education on Alzheimer's disease risk. Genetically proxied educational attainment was inversely associated with Alzheimer's disease (odds ratio per standard deviation increase in genetically predicted years of schooling = 0.70, 95% confidence interval 0.60, 0.80). There were positive associations between genetically predicted educational attainment and four cortical metrics (standard deviation units change in imaging phenotype per one standard deviation increase in genetically predicted years of schooling): surface area 0.30 (95% confidence interval 0.20, 0.40); volume 0.29 (95% confidence interval 0.20, 0.37); intrinsic curvature 0.18 (95% confidence interval 0.11, 0.25); local gyrification index 0.21 (95% confidence interval 0.11, 0.31)]; and inverse associations with cortical intracellular volume fraction [-0.09 (95% confidence interval -0.15, -0.03)] and white matter hyperintensities volume [-0.14 (95% confidence interval -0.23, -0.05)]. Genetically proxied levels of surface area, cortical volume and intrinsic curvature were positively associated with educational attainment [standard deviation units change in years of schooling per one standard deviation increase in respective genetically predicted imaging phenotype: 0.13 (95% confidence interval 0.10, 0.16); 0.15 (95% confidence interval 0.11, 0.19) and 0.12 (95% confidence interval 0.04, 0.19)]. We found no evidence of associations between genetically predicted imaging-derived phenotypes and Alzheimer's disease. The inverse association of genetically predicted educational attainment with Alzheimer's disease did not attenuate after adjusting for imaging-derived phenotypes in multivariable analyses. Our results provide support for a protective causal effect of educational attainment on Alzheimer's disease risk, as well as potential bidirectional causal relationships between education and brain macro- and micro-structure. However, we did not find evidence that these structural markers affect risk of Alzheimer's disease. The protective effect of education on Alzheimer's disease may be mediated via other measures of brain reserve not included in the present study, or by alternative mechanisms.

Cognitive control, cognitive reserve, and memory in the aging bilingual brain

In recent years bilingualism has been linked to both advantages in executive control and positive impacts on aging. Such positive cognitive effects of bilingualism have been attributed to the increased need for language control during bilingual processing and increased cognitive reserve, respectively. However, a mechanistic explanation of how bilingual experience contributes to cognitive reserve is still lacking. The current paper proposes a new focus on bilingual memory as an avenue to explore the relationship between executive control and cognitive reserve. We argue that this focus will enhance our understanding of the functional and structural neural mechanisms underlying bilingualism-induced cognitive effects. With this perspective we discuss and integrate recent cognitive and neuroimaging work on bilingual advantage, and suggest an account that links cognitive control, cognitive reserve, and brain reserve in bilingual aging and memory.

Neuropsychological test performance and cognitive reserve in healthy aging and the Alzheimer's disease spectrum: a theoretically driven factor analysis

Accurate measurement of cognitive function is critical for understanding the disease course of Alzheimer's disease (AD). Detecting cognitive change over time can be confounded by level of premorbid intellectual function or cognitive reserve and lead to under- or over-diagnosis of cognitive impairment and AD. Statistical models of cognitive performance that include cognitive reserve can improve sensitivity to change and clinical efficacy. We used confirmatory factor analysis to test a four-factor model composed of memory/language, processing speed/executive function, attention, and cognitive reserve factors in a group of cognitively healthy older adults and a group of participants along the spectrum of amnestic mild cognitive impairment to AD (aMCI-AD). The model showed excellent fit for the control group (χ(2) = 100; df = 78; CFI = .962; RMSEA = .049) and adequate fit for the aMCI-AD group (χ(2) = 1750; df = 78; CFI = .932; RMSEA = .085). Although strict invariance criteria were not met, invariance testing to determine if factor structures are similar across groups yielded acceptable absolute model fits and provide evidence in support of configural, metric, and scalar invariance. These results provide further support for the construct validity of cognitive reserve in healthy and memory impaired older adults.

Newly Generated and Non-Newly Generated "Immature" Neurons in the Mammalian Brain: A Possible Reservoir of Young Cells to Prevent Brain Aging and Disease?

Brain plasticity is important for translational purposes since most neurological disorders and brain aging problems remain substantially incurable. In the mammalian nervous system, neurons are mostly not renewed throughout life and cannot be replaced. In humans, the increasing life expectancy explains the increase in brain health problems, also producing heavy social and economic burden. An exception to the “static” brain is represented by stem cell niches leading to the production of new neurons. Such adult neurogenesis is dramatically reduced from fish to mammals, and in large-brained mammals with respect to rodents. Some examples of neurogenesis occurring outside the neurogenic niches have been reported, yet these new neurons actually do not integrate in the mature nervous tissue. Non-newly generated, “immature” neurons (nng-INs) are also present: Prenatally generated cells continuing to express molecules of immaturity (mostly shared with the newly born neurons). Of interest, nng-INs seem to show an inverse phylogenetic trend across mammals, being abundant in higher-order brain regions not served by neurogenesis and providing structural plasticity in rather stable areas. Both newly generated and nng-INs represent a potential reservoir of young cells (a “brain reserve”) that might be exploited for preventing the damage of aging and/or delay the onset/reduce the impact of neurological disorders.

CRJ, Knopman DS, Vemuri P. Relationship Between Risk Factors and Brain Reserve in Late Middle Age: Implications for Cognitive Aging

Background

Brain reserve can be defined as the individual variation in the brain structural characteristics that later in life are likely to modulate cognitive performance. Late midlife represents a point in aging where some structural brain imaging changes have become manifest but the effects of cognitive aging are minimal, and thus may represent an ideal opportunity to determine the relationship between risk factors and brain imaging biomarkers of reserve.

Objective

We aimed to assess neuroimaging measures from multiple modalities to broaden our understanding of brain reserve, and the late midlife risk factors that may make the brain vulnerable to age related cognitive disorders.

Methods

We examined multimodal [structural and diffusion Magnetic Resonance Imaging (MRI), FDG PET] neuroimaging measures in 50-65 year olds to examine the associations between risk factors (Intellectual/Physical Activity: education-occupation composite, physical, and cognitive-based activity engagement; General Health Factors: presence of cardiovascular and metabolic conditions (CMC), body mass index, hemoglobin A1c, smoking status (ever/never), CAGE Alcohol Questionnaire (>2, yes/no), Beck Depression Inventory score), brain reserve measures [Dynamic: genu corpus callosum fractional anisotropy (FA), posterior cingulate cortex FDG uptake, superior parietal cortex thickness, AD signature cortical thickness; Static: intracranial volume], and cognition (global, memory, attention, language, visuospatial) from a population-based sample. We quantified dynamic proxies of brain reserve (cortical thickness, glucose metabolism, microstructural integrity) and investigated various protective/risk factors.

Results

Education-occupation was associated with cognition and total intracranial volume (static measure of brain reserve), but was not associated with any of the dynamic neuroimaging biomarkers. In contrast, many general health factors were associated with the dynamic neuroimaging proxies of brain reserve, while most were not associated with cognition in this late middle aged group.

Conclusion

Brain reserve, as exemplified by the four dynamic neuroimaging features studied here, is itself at least partly influenced by general health status in midlife, but may be largely independent of education and occupation.

Education modulates brain maintenance in presymptomatic frontotemporal dementia

OBJECTIVE

Cognitively engaging lifestyles have been associated with reduced risk of conversion to dementia. Multiple mechanisms have been advocated, including increased brain volumes (ie, brain reserve) and reduced disease progression (ie, brain maintenance). In cross-sectional studies of presymptomatic frontotemporal dementia (FTD), higher education has been related to increased grey matter volume. Here, we examine the effect of education on grey matter loss over time.

METHODS

Two-hundred twenty-nine subjects at-risk of carrying a pathogenic mutation leading to FTD underwent longitudinal cognitive assessment and T1-weighted MRI at baseline and at 1 year follow-up. The first principal component score of the graph-Laplacian Principal Component Analysis on 112 grey matter region-of-interest volumes was used to summarise the grey matter volume (GMV). The effects of education on cognitive performances and GMV at baseline and on the change between 1 year follow-up and baseline (slope) were tested by Structural Equation Modelling.

RESULTS

Highly educated at-risk subjects had better cognition and higher grey matter volume at baseline; moreover, higher educational attainment was associated with slower loss of grey matter over time in mutation carriers.

CONCLUSIONS

This longitudinal study demonstrates that even in presence of ongoing pathological processes, education may facilitate both brain reserve and brain maintenance in the presymptomatic phase of genetic FTD.

Are Brain and Cognitive Reserve Shaped by Early Life Circumstances?

When growing older, many people are faced with cognitive deterioration, which may even amount to a form of dementia at some point in time. Although neuropathological signs of dementia disorders can often be demonstrated in brains of patients, the degree to which clinical symptoms are present does mostly not accurately reflect the amount of neuropathology that is present. Sometimes existent pathology even goes without any obvious clinical presentation. An explanation for this phenomenon may be found in the concept of reserve capacity. Reserve capacity refers to the ability of the brain to effectively buffer changes that are associated with normal aging processes and to cope with pathological damage. A larger reserve capacity has been suggested to increase resilience against age-associated cognitive deterioration and dementia disorders. Traditionally, a division has been made between brain reserve, which is based on morphological characteristics of the brain, and cognitive reserve, which is based on functional characteristics of the brain. The present review discusses the premises that brain and cognitive reserve capacity are shaped by prenatal and early postnatal factors. Evidence is accumulating that circumstances during the first 1,000 days of life are of the utmost importance for the lifelong health of an individual. Cognitive deterioration and dementia disorders may also have their origin in early life and a potentially important pathway by which the early environment affects the risk for neurodegenerative diseases is by developmental programming of the reserve capacity of the brain. The basic idea behind developmental programming of brain and cognitive reserve is explained and an overview of studies that support this idea is presented. The review is concluded by a discussion of potential mechanisms, synthesis of the evidence and relevance and future directions in the field of developmental origins of reserve capacity.

Motivational processes in mild cognitive impairment and Alzheimer's disease: results from the Motivational Reserve in Alzheimer's (MoReA) study

BACKGROUND

Brain reserve, i.e., the ability of the brain to tolerate age- and disease-related changes in a way that cognitive function is still maintained, is assumed to be based on the lifelong training of various abilities. The Motivational Reserve in Alzheimer's (MoReA) is a longitudinal study that aims to examine motivational processes as a protective factor in mild Alzheimer's dementia (AD) and mild cognitive impairment (MCI). This paper presents the results of motivational variables, frequency of diagnoses, and prediction of global cognition as well as depression in a one-year longitudinal study.

METHODS

The sample consists of 64 subjects with MCI and 47 subjects with mild AD at baseline. At baseline, the physical/neurological examinations, standard clinical assessment, neuropsychological testing, and assessment of motivational variables were performed. At follow-up (FU) one year later, neuropsychological testing including cognition, functional abilities, behavioral and affective symptoms, and global clinical assessments of severity have been repeated.

RESULTS

AD cases have lower motivational capacities as measured with a midlife motivation-related occupational score and informant-reported present motivational processes, but do not differ with regard to delay of gratification (DoG) and self-reported motivational processes. DoG and delay discounting (DD) were relatively stable during the measurement interval. However, 20 % of the MCI cases converted to mild AD at FU, and 17 % of the mild AD cases converted to moderate AD. The rate of depression of Alzheimer's disease was 9 at baseline and 21 % at FU, and the rate of apathy was 7 and 14 %, respectively. Global cognition at FU was mainly predicted by baseline global cognition but also by one of the motivational variables (scenario test). Depression at FU was predicted mainly by two motivational variables (self-reported and informant-reported motivational processes).

CONCLUSIONS

This research might inform motivation-related strategies for prevention and early intervention with older people or people at risk for AD.

Neural implementation of musical expertise and cognitive transfers: could they be promising in the framework of normal cognitive aging?

Brain plasticity allows the central nervous system of a given organism to cope with environmental demands. Therefore, the quality of mental processes relies partly on the interaction between the brain’s physiological maturation and individual daily experiences. In this review, we focus on the neural implementation of musical expertise at both an anatomical and a functional level. We then discuss how this neural implementation can explain transfers from musical learning to a broad range of non-musical cognitive functions, including language, especially during child development. Finally, given that brain plasticity is still present in aging, we gather arguments to propose that musical practice could be a good environmental enrichment to promote cerebral and cognitive reserves, thereby reducing the deleterious effect of aging on cognitive functions.

Effect of 5 Years of Exercise Intervention at Different Intensities on Brain Structure in Older Adults from the General Population: A Generation 100 Substudy

Purpose

The aim was to examine the effect of a 5-year exercise intervention at different intensities on brain structure in older adults from the general population partaking in the randomized controlled trial Generation 100 Study.

Participants and Methods

Generation 100 Study participants were invited to a longitudinal neuroimaging study before randomization. A total of 105 participants (52 women, 70–77 years) volunteered. Participants were randomized into supervised exercise twice a week performing high intensity interval training in 4×4 intervals at ~90% peak heart rate (HIIT, n = 33) or 50 minutes of moderate intensity continuous training at ~70% of peak heart rate (MICT, n = 24). The control group (n = 48) followed the national physical activity guidelines of ≥30 min physical activity daily. Brain MRI at 3T, clinical and cardiorespiratory fitness (CRF), measured as peak oxygen uptake, were collected at baseline, and after 1, 3, and 5 years of intervention. Brain volumes and cortical thickness were derived from T1 weighted 3D MRI data using FreeSurfer. The effect of HIIT or MICT on brain volumes over time was investigated with linear mixed models, while linear regressions examined the effect of baseline CRF on brain volumes at later time points.

Results

Adherence in each group was between 79 and 94% after 5 years. CRF increased significantly in all groups during the first year. Compared to controls, the HIIT group had significantly increased hippocampal atrophy located to CA1 and hippocampal body, though within normal range, and the MICT group greater thalamic atrophy. No other effects of intervention group were found. CRF across the intervention was not associated with brain structure, but CRF at baseline was positively associated with cortical volume at all later time points.

Conclusion

Higher baseline CRF reduced 5-year cortical atrophy rate in older adults, while following physical activity guidelines was associated with the lowest hippocampal and thalamic atrophy rates.

Association of cognition and brain reserve in aging and glymphatic function using diffusion tensor image-along the perivascular space (DTI-ALPS)

The glymphatic system is a fluid-clearance pathway that clears cerebral waste products, and its dysfunction has been associated with protein aggregation diseases such as Alzheimer's disease. To understand how the glymphatic system changes with aging, we enrolled 433 cognitive unimpaired participants (236 women and 197 men, 13 to 88 years) and evaluated the glymphatic function by calculating diffusion tensor imaging analysis along the perivascular space (ALPS) index and explored how the ALPS index is associated with cortical atrophy and cognitive decline in older people. We found a significant inverse correlation between ALPS index and age (ρ=-0.45, p<0.001), with a peak value in people in their thirties. A higher ALPS index indicated a better cortical reserve in regions coincided with the default mode network. Declines in mental manipulation and short-term memory performance in the older participants were associated with a lower ALPS index and cortical atrophy in the amygdala, anterior and posterior cingulate, thalamus and middle frontal regions. Our findings highlight that the ALPS index could be used to evaluate brain reserve and cognitive reserve in older people.