Aging-related magnification of genetic effects on cognitive and brain integrity

The influence of hippocampal dopamine D2 receptor losses on episodic-memory decline across 5 years is moderated by BDNF and KIBRA polymorphisms

Losses in dopamine (DA) functioning may contribute to aging-related decline in cognition. Hippocampal DA is necessary for successful episodic memory formation. Previously, we reported that higher DA D2 receptor (D2DR) availability in hippocampus is beneficial for episodic memory only in older carriers of more advantageous genotypes of well-established plasticity-related genetic variations, the brain-derived neurotrophic factor (BDNF, rs6265) and the kidney and brain expressed protein (KIBRA, rs17070145) polymorphisms. Extending our observations to the longitudinal level, the current data show that individuals with one or no beneficial BDNF and KIBRA genotype (n = 80) decline more in episodic memory across five years, without any contribution of losses in hippocampal D2DR availability to memory decline. Although carriers of two beneficial genotypes (n = 39) did not decline overall in episodic memory, losses of hippocampal D2DR availability were predictive of episodic-memory decline among these individuals. Our findings have implications for interventions targeting DA modulation to enhance episodic memory in aging, which may not benefit all older individuals.

The lifestyle for brain health index, the cluster of differentiation 33 (CD33) gene, and cognitive function among rural Chinese older adults: A population-based study

BACKGROUND

We sought to examine the associations of the Lifestyle for Brain Health (LIBRA) index with cognitive function among rural Chinese older adults and to explore the potential role of cluster of differentiation 33 gene (CD33) in the associations.

METHODS

This population-based cross-sectional study included 4914 dementia-free participants (age ≥60 years; 56.43 % women) in the 2018 baseline examination of MIND-China. The LIBRA index was generated from 11 factors. We used a neuropsychological test battery to assess episodic memory, verbal fluency, attention, executive function, and global cognition. The CD33(rs3865444) polymorphism was detected using multiple-polymerase chain reaction amplification. Data were analyzed using the general linear regression models.

RESULTS

A higher LIBRA index was associated with multivariable-adjusted β-coefficient (95 %CI) of -0.011(-0.020- -0.001) for global cognitive z-score, -0.020(-0.033- -0.006) for episodic memory, and -0.016(-0.029- -0.004) for verbal fluency. The CD33(rs3865444) was associated with a lower global cognitive z-score in the additive (CA vs. CC: β-coefficient=0.042; 95 %CI=0.008-0.077), the dominant (CA+AA vs. CC: 0.040; 0.007-0.073), and the over-dominant (CA vs. CC+AA: 0.043; 0.009-0.077) models. Similar results were obtained for verbal fluency and attention. The CD33 gene showed statistical interactions with LIBRA index on cognitive function (Pinteraction<0.05) such that a higher LIBRA index was significantly associated with lower z-scores of global cognition and attention only among CD33 CC carriers (P < 0.05).

CONCLUSIONS

This population-based study reveals for the first time that a higher LIBRA index is associated with worse cognitive performance in rural Chinese older adults and that CD33 gene could modify the association.

A Subtype Perspective on Cognitive Trajectories in Healthy Aging

Cognitive aging is a complex and dynamic process characterized by changes due to genetics and environmental factors, including lifestyle choices and environmental exposure, which contribute to the heterogeneity observed in cognitive outcomes. This heterogeneity is particularly pronounced among older adults, with some individuals maintaining stable cognitive function while others experience complex, non-linear changes, making it difficult to identify meaningful decline accurately. Current research methods range from population-level modeling to individual-specific assessments. In this work, we review these methodologies and propose that population subtyping should be considered as a viable alternative. This approach relies on early individual-specific detection methods that can lead to an improved understanding of changes in individual cognitive trajectories. The improved understanding of cognitive trajectories through population subtyping can lead to the identification of meaningful changes and the determination of timely, effective interventions. This approach can aid in informing policy decisions and in developing targeted interventions that promote cognitive health, ultimately contributing to a more personalized understanding of the aging process within society and reducing the burden on healthcare systems.

Remember This: Age Moderation of Genetic and Environmental Contributions to Verbal Episodic Memory from Midlife through Late Adulthood

It is well documented that memory is heritable and that older adults tend to have poorer memory performance than younger adults. However, whether the magnitudes of genetic and environmental contributions to late-life verbal episodic memory ability differ from those at earlier ages remains unresolved. Twins from 12 studies participating in the Interplay of Genes and Environment in Multiple Studies (IGEMS) consortium constituted the analytic sample. Verbal episodic memory was assessed with immediate word list recall (N = 35,204 individuals; 21,792 twin pairs) and prose recall (N = 3,805 individuals; 2,028 twin pairs), with scores harmonized across studies. Average test performance was lower in successively older age groups for both measures. Twin models found significant age moderation for both measures, with total inter-individual variance increasing significantly with age, although it was not possible definitively to attribute the increase specifically to either genetic or environmental sources. Pooled results across all 12 studies were compared to results where we successively dropped each study (leave-one-out) to assure results were not due to an outlier. We conclude the models indicated an overall increase in variance for verbal episodic memory that was driven by a combination of increases in the genetic and nonshared environmental parameters that were not independently statistically significant. In contrast to reported results for other cognitive domains, differences in environmental exposures are comparatively important for verbal episodic memory, especially word list learning.

Heritability of cognitive abilities and regional brain structures in middle-aged to elderly East Asians

This study examined the single-nucleotide polymorphism heritability and genetic correlations of cognitive abilities and brain structural measures (regional subcortical volume and cortical thickness) in middle-aged and elderly East Asians (Korean) from the Gwangju Alzheimer's and Related Dementias cohort study. Significant heritability was found in memory function, caudate volume, thickness of the entorhinal cortices, pars opercularis, superior frontal gyri, and transverse temporal gyri. There were 3 significant genetic correlations between (i) the caudate volume and the thickness of the entorhinal cortices, (ii) the thickness of the superior frontal gyri and pars opercularis, and (iii) the thickness of the superior frontal and transverse temporal gyri. This is the first study to describe the heritability and genetic correlations of cognitive and neuroanatomical traits in middle-aged to elderly East Asians. Our results support the previous findings showing that genetic factors play a substantial role in the cognitive and neuroanatomical traits in middle to advanced age. Moreover, by demonstrating shared genetic effects on different brain regions, it gives us a genetic insight into understanding cognitive and brain changes with age, such as aging-related cognitive decline, cortical atrophy, and neural compensation.

Thalamic gray matter volume mediates the association between KIBRA polymorphism and olfactory function among older adults: a population-based study

The kidney and brain expressed protein (KIBRA) rs17070145 polymorphism is associated with both structure and activation of the olfactory cortex. However, no studies have thus far examined whether KIBRA can be linked with olfactory function and whether brain structure plays any role in the association. We addressed these questions in a population-based cross-sectional study among rural-dwelling older adults. This study included 1087 participants derived from the Multidomain Interventions to Delay Dementia and Disability in Rural China, who underwent the brain MRI scans in August 2018 to October 2020; of these, 1016 took the 16-item Sniffin' Sticks identification test and 634 (62.40%) were defined with olfactory impairment (OI). Data were analyzed using the voxel-based morphometry analysis and general linear, logistic, and structural equation models. The KIBRA rs17070145 C-allele (CC or CT vs. TT genotype) was significantly associated with greater gray matter volume (GMV) mainly in the bilateral orbitofrontal cortex and left thalamus (P < 0.05) and with the multi-adjusted odds ratio of 0.73 (95% confidence interval 0.56-0.95) for OI. The left thalamic GMV could mediate 8.08% of the KIBRA-olfaction association (P < 0.05). These data suggest that the KIBRA rs17070145 C-allele is associated with a reduced likelihood of OI among older adults, partly mediated through left thalamic GMV.

DyNAMiC: A prospective longitudinal study of dopamine and brain connectomes: A new window into cognitive aging

Concomitant exploration of structural, functional, and neurochemical brain mechanisms underlying age‐related cognitive decline is crucial in promoting healthy aging. Here, we present the DopamiNe, Age, connectoMe, and Cognition (DyNAMiC) project, a multimodal, prospective 5‐year longitudinal study spanning the adult human lifespan. DyNAMiC examines age‐related changes in the brain’s structural and functional connectome in relation to changes in dopamine D1 receptor availability (D1DR), and their associations to cognitive decline. Critically, due to the complete lack of longitudinal D1DR data, the true trajectory of one of the most age‐sensitive dopamine systems remains unknown. The first DyNAMiC wave included 180 healthy participants (20–80 years). Brain imaging included magnetic resonance imaging assessing brain structure (white matter, gray matter, iron), perfusion, and function (during rest and task), and positron emission tomography (PET) with the [¹¹C]SCH23390 radioligand. A subsample (n = 20, >65 years) was additionally scanned with [¹¹C]raclopride PET measuring D2DR. Age‐related variation was evident for multiple modalities, such as D1DR; D2DR, and performance across the domains of episodic memory, working memory, and perceptual speed. Initial analyses demonstrated an inverted u‐shaped association between D1DR and resting‐state functional connectivity across cortical network nodes, such that regions with intermediate D1DR levels showed the highest levels of nodal strength. Evident within each age group, this is the first observation of such an association across the adult lifespan, suggesting that emergent functional architecture depends on underlying D1DR systems. Taken together, DyNAMiC is the largest D1DR study worldwide, and will enable a comprehensive examination of brain mechanisms underlying age‐related cognitive decline.

A common polymorphism in the dopamine transporter gene predicts working memory performance and in vivo dopamine integrity in aging

Dopamine (DA) integrity is suggested as a potential cause of individual differences in working memory (WM) performance among older adults. Still, the principal dopaminergic mechanisms giving rise to WM differences remain unspecified. Here, 61 single-nucleotide polymorphisms, located in or adjacent to various dopamine-related genes, were assessed for their links to WM performance in a sample of 1313 adults aged 61-80 years from the Berlin Aging Study II. Least Absolute Shrinkage and Selection Operator (LASSO) regression was conducted to estimate associations between polymorphisms and WM. Rs40184 in the DA transporter gene, SLC6A3, showed allelic group differences in WM, with T-carriers performing better than C homozygotes (p<0.01). This finding was replicated in an independent sample from the Cognition, Brain, and Aging study (COBRA; baseline: n = 181, ages: 64-68 years; 5-year follow up: n = 129). In COBRA, in vivo DA integrity was measured with ¹¹C-raclopride and positron emission tomography. Notably, WM as well as in vivo DA integrity was higher for rs40184 T-carriers at baseline (p<0.05 for WM and caudate and hippocampal D2-receptor availability) and at the 5-year follow-up (p<0.05 for WM and hippocampal D2 availability). Our findings indicate that individual differences in DA transporter function contribute to differences in WM performance in old age, presumably by regulating DA availability.

Contributions of HFE polymorphisms to brain and blood iron load, and their links to cognitive and motor function in healthy adults

Background

Brain iron overload is linked to brain deterioration, and cognitive and motor impairment in neurodegenerative disorders and normal aging. Mutations in the HFE gene are associated with iron dyshomeostasis and are risk factors for peripheral iron overload. However, links to brain iron load and cognition are less consistent and data are scarce.

Aims and methods

Using quantitative susceptibility mapping with magnetic resonance imaging, we investigated whether C282Y and H63D contributed to aging‐related increases in brain iron load and lower cognitive and motor performance in 208 healthy individuals aged 20‐79 years. We also assessed the modulatory effects of HFE mutations on associations between performance and brain iron load, as well as peripheral iron metabolism.

Results

Independent of age, carriers of either C282Y and/or H63D (HFE‐pos group, n = 66) showed a higher load of iron in putamen than non‐carriers (HFE‐neg group, n = 142), as well as higher transferrin saturation and lower transferrin and transferrin receptors in blood. In the HFE‐neg group, higher putaminal iron was associated with lower working memory. In the HFE‐pos group, higher putaminal iron was instead linked to higher executive function, and lower plasma transferrin was related to higher episodic memory. Iron‐performance associations were modest albeit reliable.

Conclusion

Our findings suggest that HFE status is characterized by higher regional brain iron load across adulthood, and support the presence of a modulatory effect of HFE status on the relationships between iron load and cognition. Future studies in healthy individuals are needed to confirm the reported patterns.

This study investigated the contribution of genetic polymorphisms in the HFE gene (C282Y and H63D) on blood and brain iron load, and their relationships with cognition, in a healthy sample of adults. The findings indicated that carriers of C282Y and/or H63D displayed higher iron load in putamen and higher transferrin saturation in blood. Results further suggested that in carriers, higher iron load may be beneficial for cognitive performance, independent of age.

Tract Specificity of Age Effects on Diffusion Tensor Imaging Measures of White Matter Health

Well-established literature indicates that older adults have poorer cerebral white matter integrity, as measured through diffusion tensor imaging (DTI). Age differences in DTI have been observed widely across white matter, although some tracts appear more sensitive to the effects of aging than others. Factors like APOE ε4 status and sex may contribute to individual differences in white matter integrity that also selectively impact certain tracts, and could influence DTI changes in aging. The present study explored the degree to which age, APOE ε4, and sex exerted global vs. tract specific effects on DTI metrics in cognitively healthy late middle-aged to older adults. Data from 49 older adults (ages 54–92) at two time-points separated by approximately 2.7 years were collected. DTI metrics, including fractional anisotropy (FA) and mean diffusivity (MD), were extracted from nine white matter tracts and global white matter. Results showed that across timepoints, FA and MD increased globally, with no tract-specific changes observed. Baseline age had a global influence on both measures, with increasing age associated with lower FA and higher MD. After controlling for global white matter FA, age additionally predicted FA for the genu, callosum body, inferior fronto-occipital fasciculus (IFOF), and both anterior and posterior cingulum. Females exhibited lower global FA on average compared to males. In contrast, MD was selectively elevated in the anterior cingulum and superior longitudinal fasciculus (SLF), for females compared to males. APOE ε4 status was not predictive of either measure. In summary, these results indicate that age and sex are associated with both global and tract-specific alterations to DTI metrics among a healthy older adult cohort. Older women have poorer white matter integrity compared to older men, perhaps related to menopause-induced metabolic changes. While age-related alterations to white matter integrity are global, there is substantial variation in the degree to which tracts are impacted, possibly as a consequence of tract anatomical variability. The present study highlights the importance of accounting for global sources of variation in DTI metrics when attempting to investigate individual differences (due to age, sex, or other factors) in specific white matter tracts.

Sex-Specific Protective Effects of APOE ε2 on Cognitive Performance

Apolipoprotein E (APOE) has an important role in the multiple trajectories of cognitive aging. However, environmental variables and other genes mediate the impact of APOE on cognition. Our main objective was to analyze the effect of APOE genotype on cognition and its interactions and relationships with sex, age, lipid profile, C-reactive protein, and Brain-derived neurotrophic factor (BDNF) genotype in a sample of 648 healthy participants over 50 years of age with a comprehensive neuropsychological assessment. Our results showed that APOE ε2 carriers performed better in the Verbal Memory (p = .002) and Fluency Domains (p = .001). When we studied the effect of sex, we observed that the beneficial effect of APOE ε2 on the normalized values of these cognitive domains occurred only in females (β = 0.735; 95% confidence interval, 0.396-1.074; p = 3.167·10-5 and β = 0.568; 95% confidence interval, 0.276-0.861; p = 1.853·10-4, respectively). Similarly, the sex-specific effects of APOE ε2 were further observed on lipidic and inflammation biomarkers. In the whole sample, APOE ε2 carriers showed significantly lower levels of total cholesterol, low-density lipoprotein cholesterol, and C-reactive protein. These differences were found only among females. Furthermore, total cholesterol and low-density lipoprotein cholesterol mediated the protective effect of APOE ε2 on cognition in the whole sample and total cholesterol in females, providing candidate physiological mechanisms for the observed genetic effects. Our results show that the neuroprotective role of APOE ε2 in cognition varies with sex and that the lipidic profile partially mediates this protection. Age-related cognitive and functional decline is a continuous biological process with different cognitive trajectories (1). Complex interactions between heritability, environmental influence, and cognitive functions in aging have been highlighted (2). In particular, genetic differences explain around 15%-25% of the variance in life expectancy (3). Therefore, the identification of susceptibility genes and their biological effects on cognitive aging is required to establish interindividual differences in this process and promote early personalized interventions to delay cognitive decline and minimize the financial burden of aging in the health care system.

Cortical thickness mediates the relationship between DRD2 C957T polymorphism and executive function across the adult lifespan

Dopamine (DA) signaling is critical for optimal cognitive performance. Aging is accompanied by a change in the strength of this signaling, with a loss of striatal and extrastriatal D2 binding potential. The reduction in dopamine modulation with age negatively influences various aspects of cognition. DRD2 C957T (rs6277) impacts DA D2 receptor density and availability, with C homozygotes linked to lower striatal DA availability and reduced executive functioning (EF), but also high extrastriatal binding potential. Here, we investigated in 176 participants aged 20-94 years whether: (1) DRD2 C carriers differ from T carriers in cortical thickness or subcortical volume in areas of high concentrations of D2 receptors that receive projections from mesocortical or nigrostriatal dopaminergic pathways; (2) whether the DRD2*COMT relationship has any synergistic effects on cortical thickness; (3) whether the effect of DRD2 on brain structure depends upon age; and (4) whether DRD2-related regional thinning affects executive function performance. We show that DRD2 impacts cortical thickness in the superior parietal lobule, precuneus, and anterior cingulate (marginal after FDR correction), while statistically controlling sex, age, and COMT genotype. Specifically, C homozygotes demonstrated thinner cortices than both heterozygotes and/or T homozygotes in an age-invariant manner. Additionally, DRD2 predicted executive function performance via cortical thickness. The results highlight that genetic influences on dopamine availability impact cognitive performance via the contribution of brain structure in cortical regions influenced by DRD2.

Assessing the Effect of Training on the Cognition and Brain of Older Adults: Protocol for a Three-Arm Randomized Double-Blind Controlled Trial (ACTOP)

BACKGROUND

To prevent age-related cognitive impairment, many intervention programs offer exercises targeting different central cognitive processes. However, the effects of different process-based training programs are rarely compared within equivalent experimental designs.

OBJECTIVE

Using a randomized double-blind controlled trial, this project aims to examine and compare the impact of 2 process-based interventions, inhibition and updating, on the cognition and brain of older adults.

METHODS

A total of 90 healthy older adults were randomly assigned to 1 of 3 training conditions: (1) inhibition (Stroop-like exercises), (2) updating (N-back-type exercises), and (3) control active (quiz game exercise). Training was provided in 12 half-hour sessions over 4 weeks. First, the performance gain observed will be measured on the trained tasks. We will then determine the extent of transfer of gain on (1) untrained tasks that rely on the same cognitive process, (2) complex working memory (WM) measurements hypothesized to involve 1 of the 2 trained processes, and (3) virtual reality tasks that were designed to mimic real-life situations that require WM. We will assess whether training increases cortical volume given that the volume of the cortex is determined by cortical area and thickness in regions known to be involved in WM or changes task-related brain activation patterns measured with functional magnetic resonance imaging. Dose effects will be examined by measuring outcomes at different time points during training. We will also determine whether individual characteristics moderate the effect of training on cognitive and cerebral outcomes. Finally, we will evaluate whether training reduces the age-related deficit on transfer and brain outcomes, by comparing study participants to a group of 30 younger adults.

RESULTS

The project was funded in January 2017; enrollment began in October 2017 and data collection was completed in April 2019. Data analysis has begun in June 2020 and the first results should be published by the end of 2020 or early 2021.

CONCLUSIONS

The results of this study will help understand the relative efficacy of 2 attentional control interventions on the cognition and the brain of older adults, as well as the moderating role of individual characteristics on training efficiency and transfer.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03532113; https://clinicaltrials.gov/ct2/show/NCT03532113.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/20430.

Female-specific effects of the catechol-O-methyl transferase Val158Met gene polymorphism on working memory-related brain function

The catechol-O-methyltransferase (COMT) Val¹⁵⁸Met polymorphism has been associated with working memory (WM) in many studies, but the results have not been consistent. One plausible explanation is sex-specific effects of this polymorphism as reported in several studies. The current study aimed to explore the sex-specific effects of the COMT Val¹⁵⁸Met polymorphism on WM-related brain function in an elderly sample. We found that Val homozygotes outperformed Met allele carriers on the backward digit span subtest for both males and females. The triangular part of the left inferior frontal gyrus and the left inferior temporal gyrus exhibited higher activation in Met allele carriers compared with Val homozygotes during the n-back task, while the background functional connectivity (bFC) between the left angular gyrus (ANG) and the right ANG was enhanced in Val homozygotes as compared to Met allele carriers. Finally, the associations between brain activation, bFC (among various regions), and WM performance were identified only in specific genotype groups of the female participants. These findings provide new insights into the role of COMT Val¹⁵⁸Met gene polymorphism in brain function, particularly its female-specific nature.

Genetic risk for Alzheimer disease predicts hippocampal volume through the human lifespan

Objective

To test the hypothesis that genetic risk for Alzheimer disease (AD) may represent a stable influence on the brain from early in life, rather than being primarily age dependent, we investigated in a lifespan sample of 1,181 persons with a total of 2,690 brain scans, whether higher polygenic risk score (PGS) for AD and presence of APOE ε4 was associated with lower hippocampal volumes to begin with, as an offset effect, or possibly faster decline in older age.

Methods

Using general additive mixed models, we assessed the relations of PGS for AD, including variants in APOE with hippocampal volume and its change in a cognitively healthy longitudinal lifespan sample (age range: 4–95 years, mean visit age 39.7 years, SD 26.9 years), followed for up to 11 years.

Results

AD-PGS and APOE ε4 in isolation showed a significant negative effect on hippocampal volume. The effect of a 1 sample SD increase in AD-PGS on hippocampal volume was estimated to –36.4 mm³ (confidence interval [CI]: –71.8, –1.04) and the effect of carrying ε4 allele(s) –107.0 mm³ (CI: –182.0, –31.5). Offset effects of AD-PGS and APOE ε4 were present in hippocampal development, and interactions between age and genetic risk on volume change were not consistently observed.

Conclusions

Endophenotypic manifestation of polygenic risk for AD may be seen across the lifespan in cognitively healthy persons, not being confined to clinical populations or older age. This emphasizes that a broader population and age range may be relevant targets for attempts to prevent AD.

Impact of dopamine-related genetic variants on physical activity in old age - a cohort study

OBJECTIVES

The beneficial effects of a physically active lifestyle in aging are well documented. Understanding the factors of importance for physical activity in older adults are therefore essential. Informed by animal and human data linking the dopamine system to motivation and reward processes, we investigated the associations between variations in dopamine genes and objectively measured physical activity and sedentary behaviour. Further, we aimed to verify whether higher age may exacerbate the impact of dopamine genes on physical activity.

METHODS

We analyzed data from 504 older adults, 66-87 years, from the population-based Swedish National study on Aging and Care in Kungsholmen (SNAC-K). Physical activity was measured with activPAL accelerometers and DNA was extracted from blood samples for genotyping. We assessed the effects of three dopamine relevant genetic variations (DRD1, DRD2, and DRD3) on daily time in sedentary behavior, light-intensity physical activity and moderate-to-vigorous physical activity using analyses of covariance, adjusting for sex, age and physical function.

RESULTS

Higher dopamine receptor efficacy was related to moderate-to-vigorous physical activity, but not to light-intensity physical activity or sedentary time. DRD1 explained 2.7% of variance in moderate-to-vigorous physical activity, with more pronounced effect in people aged ≥80 years, about 10% of explained variance.

CONCLUSION

Stronger genetic effects in older adults are in line with the well-established nonlinear effects of dopamine signaling on performance, expected to be exacerbated with aging. Individuals over 80 years, genetically predisposed to lower dopamine receptor efficacy, engaged on average 100 min/week in moderate-to-high physical activity, below the recommended levels beneficial for healthy aging. Our findings highlight that some individuals might need extra support to maintain a physically active lifestyle.

Lifestyle mediates the role of nutrient-sensing pathways in cognitive aging: cellular and epidemiological evidence

Aging induces cellular and molecular changes including modification of stem cell pools. In particular, alterations in aging neural stem cells (NSCs) are linked to age-related cognitive decline which can be modulated by lifestyle. Nutrient-sensing pathways provide a molecular basis for the link between lifestyle and cognitive decline. Adopting a back-translation strategy using stem cell biology to inform epidemiological analyses, here we show associations between cellular readouts of NSC maintenance and expression levels of nutrient-sensing genes following NSC exposure to aging human serum as well as morphological and gene expression alterations following repeated passaging. Epidemiological analyses on the identified genes showed associations between polymorphisms in SIRT1 and ABTB1 and cognitive performance as well as interactions between SIRT1 genotype and physical activity and between GRB10 genotype and adherence to a Mediterranean diet. Our study contributes to the understanding of neural stem cell molecular mechanisms underlying human cognitive aging and hints at lifestyle modifiable factors.

Genetic influence on ageing-related changes in resting-state brain functional networks in healthy adults: A systematic review

This systematic review examines the genetic and epigenetic factors associated with resting-state functional connectivity (RSFC) in healthy human adult brains across the lifespan, with a focus on genes associated with Alzheimer's disease (AD). There were 58 studies included. The key findings are: (i) genetic factors have a low to moderate contribution; (ii) the apolipoprotein E ε2/3/4 polymorphism was the most studied genetic variant, with the APOE-ε4 allele most consistently associated with deficits of the default mode network, but there were insufficient studies to determine the relationships with other AD candidate risk genes; (iii) a single genome-wide association study identified several variants related to RSFC; (iv) two epigenetic independent studies showed a positive relationship between blood DNA methylation of the SLC6A4 promoter and RSFC measures. Thus, there is emerging evidence that genetic and epigenetic variation influence the brain's functional organisation and connectivity over the adult lifespan. However, more studies are required to elucidate the roles genetic and epigenetic factors play in RSFC measures across the adult lifespan.

Musculoskeletal Pain and Brain Morphology: Oxytocin's Potential as a Treatment for Chronic Pain in Aging

Chronic pain disproportionately affects older adults, severely impacting quality of life and independent living, with musculoskeletal pain most prevalent. Chronic musculoskeletal pain is associated with specific structural alterations in the brain and interindividual variability in brain structure is likely an important contributor to susceptibility for the development of chronic pain. However, understanding of age-related structural changes in the brain and their associations with chronic musculoskeletal pain is currently limited. Oxytocin (OT), a neuropeptide present in the periphery and central nervous system, has been implicated in pain attenuation. Variation of the endogenous OT system (e.g., OT receptor genotype, blood, saliva, and cerebrospinal fluid OT levels) is associated with morphology in brain regions involved in pain processing and modulation. Intranasal OT administration has been shown to attenuate pain. Yet, studies investigating the efficacy of OT for management of chronic musculoskeletal pain are lacking, including among older individuals who are particularly susceptible to the development of chronic musculoskeletal pain. The goal of this focused narrative review was to synthesize previously parallel lines of work on the relationships between chronic pain, brain morphology, and OT in the context of aging. Based on the existing evidence, we propose that research on the use of intranasal OT administration as an intervention for chronic pain in older adults is needed and constitutes a promising future direction for this field. The paper concludes with suggestions for future research in the emerging field, guided by our proposed Model of Oxytocin’s Anagelsic and Brain Structural Effects in Aging.

The relationship between cognitive decline and a genetic predictor of educational attainment

Genetic and environmental factors both make substantial contributions to the heterogeneity in individuals’ levels of cognitive ability. Many studies have examined the relationship between educational attainment and cognitive performance and its rate of change. Yet there remains a gap in knowledge regarding whether the effect of genetic predictors on individual differences in cognition becomes more or less prominent over the life course. In this analysis of over 5000 older adults from the Health and Retirement Study (HRS) in the U.S., we measured the change in performance on global cognition, episodic memory, attention & concentration, and mental status over 14 years. Growth curve models are used to evaluate the association between a polygenic risk score for education (education PGS) and cognitive change. Using the most recent education PGS, we find that individuals with higher scores perform better across all measures of cognition in later life. Education PGS is associated with a faster decline in episodic memory in old age. The relationships are robust even after controlling for phenotypic educational attainment, and are unlikely to be driven by mortality bias. Future research should consider genetic effects when examining non-genetic factors in cognitive decline. Our findings represent a need to understand the mechanisms between genetic endowment of educational attainment and cognitive decline from a biological angle.

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Older adults with higher scores perform better across all measures of cognition.

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The relationship is robust after controlling for phenotypic educational attainment.

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The genetic effect on episodic memory diminishes with age.

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Future research should consider genetic effects when examining cognitive decline.

Mapping the landscape of human dopamine D2/3 receptors with [11C]raclopride

The dopamine D2/3 system is fundamental for sensory, motor, emotional, and cognitive aspects of behavior. Small-scale human histopathological and animal studies show high density of D2/3 dopamine receptors (D2/3DR) in striatum, but also demonstrate the existence of such receptors across cortical and limbic regions. Assessment of D2/3DR BP_ND in the extrastriatal regions with [¹¹C]raclopride has long been considered unreliable due to the relatively low density of D2/3DR outside the striatum. We describe the distribution and interregional links of D2/3DR availability measured with PET and [¹¹C]raclopride across the human brain in a large sample (N = 176; age range 64–68 years). Structural equation modeling revealed that D2/3DR availability can be organized according to anatomical (nigrostriatal, mesolimbic, mesocortical) and functional (limbic, associative, sensorimotor) dopamine pathways. D2/3DR availability in corticolimbic functional subdivisions showed differential associations to corresponding striatal subdivisions, extending animal and pharmacological work. Our findings provide evidence on the dimensionality and organization of [¹¹C]raclopride D2/3DR availability in the living human brain that conforms to known dopaminergic pathways.

Transcriptomic changes in the prefrontal cortex of rats as a function of age and cognitive engagement

Although changes in cognitive functions including attention are well documented in aging, the neurobiological basis for such alterations is not fully understood. Increasing evidence points towards the contribution of genetic factors in age-related cognitive decline. However, genetic studies have remained inconsistent in characterizing specific genes that could predict functional decline in aging. Here we utilized next generation RNA sequencing (RNA-seq) to identify patterns of differentially expressed genes in the prefrontal cortex (PFC), a brain region implicated in attention, of young and aged animals that were either cognitively trained or had limited cognitive engagement. Consistent with previous investigations, aging alone was associated with increased expression of genes involved in multiple facets of innate and adaptive immune responses. On the contrary, the expression of immunity-related transcripts was reduced by cognitive engagement. In addition, transcripts across a wide range of cellular processes, including those associated with neuronal remodeling and plasticity, were upregulated by this behavioral manipulation. Surprisingly, aged subjects accounted for higher mean counts of upregulated transcripts and lower mean counts for downregulated transcripts as compared to the young subjects. Because aged rats exhibited lower attentional capacities, it is plausible that transcriptional changes associated with performance in these animals were reflective of compensatory changes that occurred to cope with the declining integrity of PFC functioning. Interestingly, the effects of both aging and cognitive engagement resulted in an upregulation of transcripts linked to extracellular exosomes, suggesting such extracellular vesicles may moderate a reciprocal gene by environment interaction in order to facilitate the reorganization of PFC circuitry and maintain functionality. Taken together, these findings provide novel insights into the capacities of both cognitive engagement as well as aging to alter gene expression in the PFC, and how the effects of such dynamic factors relate to variation in age-related cognitive abilities.

The Influence of Hippocampal Dopamine D2 Receptors on Episodic Memory Is Modulated by BDNF and KIBRA Polymorphisms

Episodic memory is a polygenic trait influenced by different molecular mechanisms. We used PET and a candidate gene approach to investigate how individual differences at the molecular level translate into between-person differences in episodic memory performance of elderly persons. Specifically, we examined the interactive effects between hippocampal dopamine D2 receptor (D2DR) availability and candidate genes relevant for hippocampus-related memory functioning. We show that the positive effects of high D2DR availability in the hippocampus on episodic memory are confined to carriers of advantageous genotypes of the brain-derived neurotrophic factor (BDNF, rs6265) and the kidney and brain expressed protein (KIBRA, rs17070145) polymorphisms. By contrast, these polymorphisms did not modulate the positive relationship between caudate D2DR availability and episodic memory.

Interactive effects of dopamine transporter genotype and aging on resting-state functional networks

Aging and dopamine modulation have both been independently shown to influence the functional connectivity of brain networks during rest. Dopamine modulation is known to decline during the course of aging. Previous evidence also shows that the dopamine transporter gene (DAT1) influences the re-uptake of dopamine and the anyA9 genotype of this gene is associated with higher striatal dopamine signaling. Expanding these two lines of prior research, we investigated potential interactive effects between aging and individual variations in the DAT1 gene on the modular organization of brain acvitiy during rest. The graph-theoretic metrics of modularity, betweenness centrality and participation coefficient were assessed in 41 younger (age 20–30 years) and 37 older (age 60–75 years) adults. Age differences were only observed in the participation coefficient in carriers of the anyA9 genotype of the DAT1 gene and this effect was most prominently observed in the default mode network. Furthermore, we found that individual differences in the values of the participation coefficient correlated with individual differences in fluid intelligence and a measure of executive control in the anyA9 carriers. The correlation between participation coefficient and fluid intelligence was mainly shared with age-related differences, whereas the correlation with executive control was independent of age. These findings suggest that DAT1 genotype moderates age differences in the functional integration of brain networks as well as the relation between network characteristics and cognitive abilities.

Polymorphisms of the DNA repair gene EXO1 modulate cognitive aging in old adults in a Taiwanese population

Evidence indicates that the age-related neuropathological mechanisms associated with DNA repair genes may contribute to cognitive aging and Alzheimer's disease. In this study, we hypothesize that single nucleotide polymorphisms (SNPs) within 155 DNA repair genes may be linked to cognitive aging independently and/or through complex interactions in an older Taiwanese population. A total of 3,730 Taiwanese subjects aged over 60 years from the Taiwan Biobank were analyzed. Mini-Mental State Examination (MMSE) was administered to all subjects, and MMSE scores were used to measure cognitive functions. Our data showed that out of 1,652 SNPs, the rs1776181 (P = 1.47 × 10^-5), rs1776177 (P = 8.42 × 10^-7), rs1635510 (P = 7.97 × 10^-6), and rs2526698 (P = 7.06 × 10^-6) SNPs in the EXO1 gene were associated with cognitive aging. The association with these SNP remained significant after performing Bonferroni correction. Additionally, we found that interactions between the EXO1 and RAD51C genes influenced cognitive aging (P = 0.002). Finally, we pinpointed the influence of interactions between EXO1 and physical activity (P < 0.001) as well as between DCLRE1C and physical activity (P < 0.001). Our study indicated that DNA repair genes may contribute to susceptibility in cognitive aging independently as well as through gene-gene and gene-physical interactions.

KIBRA polymorphism modulates gray matter volume to influence cognitive ability in the elderly

Genetic variation in the kidney and brain expressed protein (KIBRA) rs17070145 gene has been linked to episodic memory and cognitive aging; yet, the neural mechanism underlying this association remains to be fully understood. Using the magnetic resonance imaging (MRI) technique, this study investigated the effect of KIBRA polymorphism on gray matter volume in 37 healthy, Chinese adults from the older population. Voxel-based morphometry (VBM) analysis revealed that KIBRA gene selectivity influences the prefrontal cortex and the parahippocampal cortex. The gray matter volume (GMV) in these structures is significantly lower in KIBRA C-allele carriers than in TT carriers. Moreover, multi-voxel pattern correlation analysis revealed that decreased prefrontal GMV could in turn affect individual cognitive function in C-allele carriers; whereas, TT individuals utilized more integrated gray matter volume in whole-brain voxels to achieve relatively better cognitive function. Overall, the findings suggest that the KIBRA rs17070145 polymorphism modulates gray matter volume, which in turn further influences cognitive function in the elderly.

Frontoparietal cortical thickness mediates the effect of COMT Val158Met polymorphism on age-associated executive function

Proper dopamine (DA) signaling is likely necessary for maintaining optimal cognitive performance as we age, particularly in prefrontal-parietal networks and in fronto-striatal networks. Thus, reduced DA availability is a salient risk factor for accelerated cognitive aging. A common polymorphism that affects DA D1 receptor dopamine availability, COMT Val158Met (rs4680), influences enzymatic breakdown of DA, with COMT Val carriers having a 3- to 4-fold reduction in synaptic DA compared to COMT Met carriers. Furthermore, dopamine receptors and postsynaptic availability are drastically reduced with aging, as is executive function performance that ostensibly relies on these pathways. Here, we investigated in 176 individuals aged 20-94 years whether: (1) COMT Val carriers differ from their Met counterparts in thickness of regional cortices receiving D1 receptor pathways: prefrontal, parietal, cingulate cortices; (2) this gene-brain association differs across the adult lifespan; and (3) COMT-related regional thinning evidences cognitive consequences. We found that COMT Val carriers evidenced thinner cortex in prefrontal, parietal, and posterior cingulate cortices than COMT Met carriers and this effect was not age-dependent. Further, we demonstrate that thickness of these regions significantly mediates the effect of COMT genotype on an executive function composite measure. These results suggest that poorer executive function performance is due partly to thinner association cortex in dopaminergic-rich regions, and particularly so in individuals who are genetically predisposed to lower postsynaptic dopamine availability, regardless of age.

Alzheimer's Biomarkers From Multiple Modalities Selectively Discriminate Clinical Status: Relative Importance of Salivary Metabolomics Panels, Genetic, Lifestyle, Cognitive, Functional Health and Demographic Risk Markers

Background: Among the neurodegenerative diseases of aging, sporadic Alzheimer’s disease (AD) is the most prevalent and perhaps the most feared. With virtually no success at finding pharmaceutical therapeutics for altering progressive AD after diagnosis, research attention is increasingly directed at discovering biological and other markers that detect AD risk in the long asymptomatic phase. Both early detection and precision preclinical intervention require systematic investigation of multiple modalities and combinations of AD-related biomarkers and risk factors. We extend recent unbiased metabolomics research that produced a set of metabolite biomarker panels tailored to the discrimination of cognitively normal (CN), cognitively impaired and AD patients. Specifically, we compare the prediction importance of these panels with five other sets of modifiable and non-modifiable AD risk factors (genetic, lifestyle, cognitive, functional health and bio-demographic) in three clinical groups.

Method: The three groups were: CN (n = 35), mild cognitive impairment (MCI; n = 25), and AD (n = 22). In a series of three pairwise comparisons, we used machine learning technology random forest analysis (RFA) to test relative predictive importance of up to 19 risk biomarkers from the six AD risk domains.

Results: The three RFA multimodal prediction analyses produced significant discriminating risk factors. First, discriminating AD from CN was the AD metabolite panel and two cognitive markers. Second, discriminating AD from MCI was the AD/MCI metabolite panel and two cognitive markers. Third, discriminating MCI from CN was the MCI metabolite panel and seven markers from four other risk modalities: genetic, lifestyle, cognition and functional health.

Conclusions: Salivary metabolomics biomarker panels, supplemented by other risk markers, were robust predictors of: (1) clinical differences in impairment and dementia and even; (2) subtle differences between CN and MCI. For the latter, the metabolite panel was supplemented by biomarkers that were both modifiable (e.g., functional) and non-modifiable (e.g., genetic). Comparing, integrating and identifying important multi-modal predictors may lead to novel combinations of complex risk profiles potentially indicative of neuropathological changes in asymptomatic or preclinical AD.

Genetic markers of dopaminergic transmission predict performance for older males but not females

Mobility and memory declines with aging can limit independence. Several single-nucleotide polymorphisms have been associated with cognitive performance, but studies investigating motor function are scant. We examined 4 single-nucleotide polymorphisms involved in dopaminergic metabolism: BDNF (Val66Met), DRD3 (Ser9Gly), DBH (C>T), and COMT (Val158Met) for their relationship to motor and cognitive function in healthy older adults (n = 4605 and n = 7331) who participated in the U.S. Health and Retirement Study. Individuals with genotypes associated with reduced dopamine metabolism exhibited poorer balance and memory. We found the most pronounced effects in the oldest participants (aged 85+ years), supporting the notion that age-related declines in dopamine availability contribute to magnified genotype effects with advancing age. Moreover, males demonstrated stronger associations than did females between a number of beneficial dopamine alleles and cognitive scores, suggesting that sex differences in dopaminergic transmission interact with genotype to influence performance. These findings point to common genetic variants related to dopaminergic metabolism that characterizes individual differences in motor and cognitive function in older adults.

Influence of the DRD2/ANKK1 Taq1A polymorphism on caudate volume in older adults without dementia

Dopaminergic neuromodulation is critically important for brain and cognitive integrity. The DRD2/ANKK1 Taq1A polymorphism is associated with striatal dopamine (DA) D2 receptor availability. Some previous studies have found that the A allele of the Taq1A polymorphism influences brain structure, but the results are inconsistent, likely due to population heterogeneity and small sample sizes. We investigated the genetic effect on caudate volume in a large sample of older adults without dementia. Results show that A-allele carriers have smaller caudate volume compared to non-carriers in relatively older adults (n = 167; Mage = 77.8 years), whereas the genotype did not influence caudate volume in a younger age group (n = 220; Mage = 62.8 years). Cognitive performance was not significantly affected by the DRD2 gene. Our findings extend previous observations by showing magnified genetic effects on brain volume in old age, and provide evidence for a link between a DA-related genetic polymorphism and grey matter volume in a brain region within the nigrostriatal dopaminergic pathway.

Curiosity in old age: A possible key to achieving adaptive aging

Curiosity is a fundamental part of human motivation that supports a variety of human intellectual behaviors ranging from early learning in children to scientific discovery. However, there has been little attention paid to the role of curiosity in aging populations. By bringing together broad but sparse neuroscientific and psychological literature on curiosity and related concepts (e.g., novelty seeking in older adults), we propose that curiosity, although it declines with age, plays an important role in maintaining cognitive function, mental health, and physical health in older adults. We identify the dopaminergic reward system and the noradrenergic system as the key brain systems implicated in curiosity processing and discuss how these brain systems contribute to the relationship between curiosity and adaptive aging.

White Matter Microstructural Changes and Episodic Memory Disturbances in Late-Onset Bipolar Disorder

Background: Bipolar disorder (BD) has been associated with distributed network disruption, but little is known on how different clinical subtypes, particularly those with an earlier and later onset of disease, are related to connectivity changes in white matter (WM) tracts. Methods: Diffusion tensor imaging (DTI) and volumetric measures were carried out in early-onset bipolar patients [(EOD) (n = 16)], late-onset bipolar disorder [(LOD)(n = 14)] and healthy controls (n = 32). We also computed ROI analysis of gray matter (GM) and white matter (WM) volumes using the regions with significant group differences in the DTI parameters. Cognitive and behavior measurements were analyzed between groups. Results: Lower fraction of anisotropy (FA) in the right hemisphere comprising anterior thalamic radiation, fornix, posterior cingulate, internal capsule, splenium of corpus callosum was observed in the LOD in comparison with EOD; additionally, lower FA was also found in the LOD in comparison with healthy controls, mostly in the right hemisphere and comprising fibers of the splenium of the corpus callosum, cingulum, superior frontal gyrus and posterior thalamic radiation; LOD also showed worse episodic memory performance than EOD; no statistical significant differences between mood symptoms, WM and GM volumes were found between BD groups. Conclusion: Even after correcting for age differences, LOD was associated with more extensive WM microstructural changes and worse episodic memory performance than EOD; these findings suggest that changes in the WM fiber integrity may be associated with a later presentation of BD, possibly due to mechanisms other than neuroprogression. However, these findings deserve replication in larger, prospective, studies.

Healthy minds from 0-100 years: Optimising the use of European brain imaging cohorts ("Lifebrain")

The main objective of "Lifebrain" is to identify the determinants of brain, cognitive and mental (BCM) health at different stages of life. By integrating, harmonising and enriching major European neuroimaging studies across the life span, we will merge fine-grained BCM health measures of more than 5,000 individuals. Longitudinal brain imaging, genetic and health data are available for a major part, as well as cognitive and mental health measures for the broader cohorts, exceeding 27,000 examinations in total. By linking these data to other databases and biobanks, including birth registries, national and regional archives, and by enriching them with a new online data collection and novel measures, we will address the risk factors and protective factors of BCM health. We will identify pathways through which risk and protective factors work and their moderators. Exploiting existing European infrastructures and initiatives, we hope to make major conceptual, methodological and analytical contributions towards large integrative cohorts and their efficient exploitation. We will thus provide novel information on BCM health maintenance, as well as the onset and course of BCM disorders. This will lay a foundation for earlier diagnosis of brain disorders, aberrant development and decline of BCM health, and translate into future preventive and therapeutic strategies. Aiming to improve clinical practice and public health we will work with stakeholders and health authorities, and thus provide the evidence base for prevention and intervention.

Effects of PER3 clock gene polymorphisms on aging-related changes of the cerebral cortex

Considerable evidence suggests that circadian rhythmicity is progressively disrupted in senescence. Among clock genes, Period3 (PER3) has been associated with circadian phenotypes, homeostatic regulation of sleep, and cognitive performance in young adults. However, the effects of PER3 genotype on aging-related changes in both cognitive function and cortical integrity remain largely unknown. To shed light into this issue, we have investigated differences in cognitive performance, patterns of cortical thickness, and cortical glucose consumption in normal elderly subjects homozygous carriers of the short (PER3^4/4, n = 32) and long repeat alleles (PER3^5/5, n = 32). Relationships between cognitive performance and cortical thickness/metabolism were further explored for each PER3 genotype. We found that PER3^5/5 carriers had poorer cognitive performance (attention, executive function, semantic memory, and verbal fluency) and lower cortical integrity (structural and functional) than PER3^4/4. PER3^5/5 further showed thinning of temporo-parietal areas, and reductions of glucose consumption in fronto-temporo-parietal regions bilaterally. Moreover, PER3^5/5 subjects exhibited significant correlations between decreased glucose metabolism in fronto-parietal regions and poorer cognitive flexibility, though only correlations with lower glucose consumption of the supramarginal gyrus distinguished PER3^5/5 from PER3^4/4 groups. Overall, these findings enhance our understanding on the gene-brain interaction in aging, and may have further implications for the detection of subclinical cognitive decline associated with PER3 genotypes in late life.

Genetic variants specific to aging-related verbal memory: Insights from GWASs in a population-based cohort

Verbal memory is typically studied using immediate recall (IR) and delayed recall (DR) scores, although DR is dependent on IR capability. Separating these components may be useful for deciphering the genetic variation in age-related memory abilities. This study was conducted to (a) construct individual trajectories in IR and independent aspects of delayed recall, or residualized-DR (rDR), across older adulthood; and (b) identify genetic markers that contribute to four estimated phenotypes: IR and rDR levels and changes after age 60. A cognitively intact sample (N = 20,650 with 125,164 observations) was drawn from the U.S. Health and Retirement Study, a nationally representative study of adults aged 50 and older. Mixed effects regression models were constructed using repeated measures from data collected every two years (1996–2012) to estimate level at age 60 and change in memory post-60 in IR and rDR. Genome-wide association scans (GWAS) were conducted in the genotypic subsample (N = 7,486) using ~1.2 million single nucleotide polymorphisms (SNPs). One SNP (rs2075650) in TOMM40 associated with rDR level at the genome-wide level (p = 5.0x10^-08), an effect that replicated in an independent sample from the English Longitudinal Study on Ageing (N = 6,898 with 41,328 observations). Meta-analysis of rDR level confirmed the association (p = 5.0x10^-11) and identified two others in TOMM40 (rs71352238 p = 1.0x10^-10; rs157582 p = 7.0x10^-09), and one in APOE (rs769449 p = 3.1 x10^-12). Meta-analysis of IR change identified associations with three of the same SNPs in TOMM40 (rs157582 p = 8.3x10^-10; rs71352238 p = 1.9x10^-09) and APOE (rs769449 p = 2.2x10^-08). Conditional analyses indicate GWAS signals on rDR level were driven by APOE, whereas signals on IR change were driven by TOMM40. Additionally, we found that TOMM40 had effects independent of APOE e4 on both phenotypes. Findings from this first U.S. population-based GWAS study conducted on both age-related immediate and delayed verbal memory merit continued examination in other samples and additional measures of verbal memory.

Color vision predicts processing modes of goal activation during action cascading

One of the most important functions of cognitive control is action cascading: the ability to cope with multiple response options when confronted with various task goals. A recent study implicates a key role for dopamine (DA) in this process, suggesting higher D1 efficiency shifts the action cascading strategy toward a more serial processing mode, whereas higher D2 efficiency promotes a shift in the opposite direction by inducing a more parallel processing mode (Stock, Arning, Epplen, & Beste, 2014). Given that DA is found in high concentration in the retina and modulation of retinal DA release displays characteristics of D2-receptors (Peters, Schweibold, Przuntek, & Müller, 2000), color vision discrimination might serve as an index of D2 efficiency. We used color discrimination, assessed with the Lanthony Desaturated Panel D-15 test, to predict individual differences (N = 85) in a stop-change paradigm that provides a well-established measure of action cascading. In this task it is possible to calculate an individual slope value for each participant that estimates the degree of overlap in task goal activation. When the stopping process of a previous task goal has not finished at the time the change process toward a new task goal is initiated (parallel processing), the slope value becomes steeper. In case of less overlap (more serial processing), the slope value becomes flatter. As expected, participants showing better color vision were more prone to activate goals in a parallel manner as indicated by a steeper slope. Our findings suggest that color vision might represent a predictor of D2 efficiency and the predisposed processing mode of goal activation during action cascading.

Sensorimotor Learning: Neurocognitive Mechanisms and Individual Differences

Here we provide an overview of findings and viewpoints on the mechanisms of sensorimotor learning presented at the 2016 Biomechanics and Neural Control of Movement (BANCOM) conference in Deer Creek, OH. This field has shown substantial growth in the past couple of decades. For example it is now well accepted that neural systems outside of primary motor pathways play a role in learning. Frontoparietal and anterior cingulate networks contribute to sensorimotor adaptation, reflecting strategic aspects of exploration and learning. Longer term training results in functional and morphological changes in primary motor and somatosensory cortices. Interestingly, re-engagement of strategic processes once a skill has become well learned may disrupt performance.

Efforts to predict individual differences in learning rate have enhanced our understanding of the neural, behavioral, and genetic factors underlying skilled human performance. Access to genomic analyses has dramatically increased over the past several years. This has enhanced our understanding of cellular processes underlying the expression of human behavior, including involvement of various neurotransmitters, receptors, and enzymes. Surprisingly our field has been slow to adopt such approaches in studying neural control, although this work does require much larger sample sizes than are typically used to investigate skill learning. We advocate that individual differences approaches can lead to new insights into human sensorimotor performance. Moreover, a greater understanding of the factors underlying the wide range of performance capabilities seen across individuals can promote personalized medicine and refinement of rehabilitation strategies, which stand to be more effective than “one size fits all” treatments.

Vulnerability of white matter tracts and cognition to the SOD2 polymorphism: A preliminary study of antioxidant defense genes in brain aging

Oxidative stress is a key mechanism of the aging process that can cause damage to brain white matter and cognitive functions. Polymorphisms in the superoxide dismutase 2 (SOD2) and catalase (CAT) genes have been associated with abnormalities in antioxidant enzyme activity in the aging brain, suggesting a risk for enhanced oxidative damage to white matter and cognition among older individuals with these genetic variants. The present study compared differences in white matter microstructure and cognition among 96 older adults with and without genetic risk factors of SOD2 (rs4880) and CAT (rs1001179). Results revealed higher radial diffusivity in the anterior thalamic radiation among SOD2 CC genotypes compared to CT/TT genotypes. Further, the CC genotype moderated the relationship between the hippocampal cingulum and processing speed, though this did not survive multiple test correction. The CAT polymorphism was not associated with brain outcomes in this cohort. These results suggest that the CC genotype of SOD2 is an important genetic marker of suboptimal brain aging in healthy individuals.

Metabolic and Genetic Markers of Biological Age

Biological age is a concept that takes into account the heterogeneity of the aging process in different individuals that results in differences in survival and variations in relative health. Any measure of biological age must be better than chronological age at predicting mortality. Several quantitative measures of biological age have been developed. Among them are frailty indices, one of which called FI₃₄ is discussed here in greater detail. FI₃₄ increases exponentially with age reflecting decline in health and function ability. It readily depicts different patterns and trajectories of aging, and it is moderately heritable. Thus, it has been used to identify a genomic region on chromosome 12 associated with healthy aging. FI₃₄ has also been useful in describing the metabolic characteristics of this phenotype, revealing both sex and genetic differences. These differences give rise to specific, testable models regarding healthy aging, which involve cell and tissue damage and mitochondrial metabolism. FI₃₄ has been directly compared to various metrics based on DNA methylation as a predictor of mortality, demonstrating that it outperforms them uniformly. This and other frailty indices take a top-down, systems based view of aging that is cognizant of the integrated function of the complex aging system.

Aberrant interhemispheric functional connectivity within default mode network and its relationships with neurocognitive features in cognitively normal APOE ε 4 elderly carriers

BACKGROUND

Default mode network (DMN) is vulnerable to the effects of APOE genotype. Given the reduced brain volumes and APOE ε 4-related brain changes in elderly carriers, it is less known that whether these changes would influence the functional connectivity and to what extent. This study aimed to examine the functional connectivity within DMN, and its diagnostic value with age-related morphometric alterations considered.

METHODS

Whole brain and seed-based resting-state functional connectivity (RSFC) analysis were conducted in cognitively normal APOE ε 4 carriers and matched non-carriers (N=38). The absolute values of mean correlation coefficients (z-values) were used as a measure of functional connectivity strength (FCS) between DMN subregions, which were also used to estimate their diagnostic value by receiver-operating characteristic (ROC) curves.

RESULTS

APOE ε 4 carriers demonstrated decreased interhemispheric FCS, particularly between right hippocampal formation (R.HF) and left inferior parietal lobular (L.IPL) (t=3.487, p<0.001). ROC analysis showed that the FCS of R.HF and L.IPL could differentiate APOE ε 4 carriers from healthy counterparts (AUC value=0.734, p=0.025). Moreover, after adjusting the impact of morphometry, the differentiated value of FCS of R.HF and L.IPL was markedly improved (AUC value=0.828, p=0.002).

CONCLUSIONS

Our findings suggest that APOE ε 4 allele affects the functional connectivity within posterior DMN, particularly the atrophy-corrected interhemispheric FCS before the clinical expression of neurodegenerative disease.

APOE moderates compensatory recruitment of neuronal resources during working memory processing in healthy older adults

The APOE ε4 allele increases the risk for sporadic Alzheimer's disease and modifies brain activation patterns of numerous cognitive domains. We assessed cognitively intact older adults with a letter n-back task to determine if previously observed increases in ε4 carriers' working-memory-related brain activation are compensatory such that they serve to maintain working memory function. Using multiple regression models, we identified interactions of APOE variant and age in bilateral hippocampus independently from task performance: ε4 carriers only showed a decrease in activation with increasing age, suggesting high sensitivity of fMRI data for detecting changes in Alzheimer's disease-relevant brain areas before cognitive decline. Moreover, we identified ε4 carriers to show higher activations in task-negative medial and task-positive inferior frontal areas along with better performance under high working memory load relative to non-ε4 carriers. The increased frontal recruitment is compatible with models of neuronal compensation, extends on existing evidence, and suggests that ε4 carriers require additional neuronal resources to successfully perform a demanding working memory task.

Emerging Molecular Pathways Governing Dietary Regulation of Neural Stem Cells during Aging

Aging alters cellular and molecular processes, including those of stem cells biology. In particular, changes in neural stem cells (NSCs) are linked to cognitive decline associated with aging. Recently, the systemic environment has been shown to alter both NSCs regulation and age-related cognitive decline. Interestingly, a well-documented and naturally occurring way of altering the composition of the systemic environment is through diet and nutrition. Furthermore, it is well established that the presence of specific nutrients as well as the overall increase or reduction of calorie intake can modulate conserved molecular pathways and respectively reduce or increase lifespan. In this review, we examine these pathways in relation to their function on NSCs and cognitive aging. We highlight the importance of the Sirtuin, mTOR and Insulin/Insulin like growth factor-1 pathways as well as the significant role played by epigenetics in the dietary regulation of NSCs and the need for further research to exploit nutrition as a mode of intervention to regulate NSCs aging.

Executive function performance and change in aging is predicted by apolipoprotein E, intensified by catechol-O-methyltransferase and brain-derived neurotrophic factor, and moderated by age and lifestyle

Recent studies have reported several genetic, health, and aging interaction effects in predicting cognitive performance and change. We used an accelerated longitudinal design to examine interactions among genetic, lifestyle, and aging for executive function (EF) in non-demented older adults (n = 634; age range = 53-95 years). The polymorphisms were apolipoprotein E (APOE), catechol-O-methyltransferase (COMT), and brain-derived neurotrophic factor (BDNF). We tested (1) independent and additive effects of APOE, COMT, and BDNF and (2) APOE effect modification for COMT + BDNF, on EF performance and 9-year change as separated by age and lifestyle activities. First, APOE ε4+ carriers had poorer EF performance and steeper 9-year decline. Second, APOE ε4+ carriers with (1) BDNF Met/Met genotype and (2) increasing allelic risk in the COMT + BDNF risk panel had poorer EF performance; these effects were moderated by lifestyle activities (composite of everyday social, physical, and cognitive activities). Examining APOE effect modification for COMT + BDNF risk panel effects with other moderating factors may help identify complex neurobiological and genetic underpinnings of polygenic phenotypes such as EF in aging.

Dopamine Receptor Genes Modulate Associative Memory in Old Age

Previous research shows that associative memory declines more than item memory in aging. Although the underlying mechanisms of this selective impairment remain poorly understood, animal and human data suggest that dopaminergic modulation may be particularly relevant for associative binding. We investigated the influence of dopamine (DA) receptor genes on item and associative memory in a population-based sample of older adults (n = 525, aged 60 years), assessed with a face-scene item associative memory task. The effects of single-nucleotide polymorphisms of DA D1 (DRD1; rs4532), D2 (DRD2/ANKK1/Taq1A; rs1800497), and D3 (DRD3/Ser9Gly; rs6280) receptor genes were examined and combined into a single genetic score. Individuals carrying more beneficial alleles, presumably associated with higher DA receptor efficacy (DRD1 C allele; DRD2 A2 allele; DRD3 T allele), performed better on associative memory than persons with less beneficial genotypes. There were no effects of these genes on item memory or other cognitive measures, such as working memory, executive functioning, fluency, and perceptual speed, indicating a selective association between DA genes and associative memory. By contrast, genetic risk for Alzheimer disease (AD) was associated with worse item and associative memory, indicating adverse effects of APOE ε4 and a genetic risk score for AD (PICALM, BIN1, CLU) on episodic memory in general. Taken together, our results suggest that DA may be particularly important for associative memory, whereas AD-related genetic variations may influence overall episodic memory in older adults without dementia.

The effects of apolipoprotein ε 4 on aging brain in cognitively normal Chinese elderly: a surface-based morphometry study

BACKGROUND

Default mode network (DMN) has been reported to be susceptible to APOE ε 4 genotype. However, the APOE ε 4-related brain changes in young carriers are different from the ones in elderly carriers. The current study aimed to evaluate the cortical morphometry of DMN subregions in cognitively normal elderly with APOE ε 4.

METHOD

11 cognitively normal senior APOE ε 4 carriers and 27 matched healthy controls (HC) participated the neuropsychological tests, genotyping, and magnetic resonance imaging (MRI) scanning. Voxel-based morphometry (VBM) analysis was used to assess the global volumetric changes. Surface-based morphometry (SBM) analysis was performed to measure regional gray matter volume (GMV) and gray matter thickness (GMT).

RESULTS

Advancing age was associated with decreased GMV of DMN subregions. Compared to HC, APOE ε 4 carriers presented cortical atrophy in right cingulate gyrus (R_CG) (GMV: APOE carriers: 8475.23 ± 1940.73 mm3, HC: 9727.34 ± 1311.57 mm3, t = 2.314, p = 0.026, corrected) and left insular (GMT: APOE ε 4 carriers: 3.83 ± 0.37 mm, HC: 4.05 ± 0.25 mm, t = 2.197, p = 0.033, corrected).

CONCLUSIONS

Our results highlight the difference between different cortical measures and suggest that the cortical reduction of CG and insular maybe a potential neuroimaging marker for APOE 4 ε senior carriers, even in the context of relatively intact cognition.

Alzheimer disease genetic risk factor APOE e4 and cognitive abilities in 111,739 UK Biobank participants

BACKGROUND

the apolipoprotein (APOE) e4 locus is a genetic risk factor for dementia. Carriers of the e4 allele may be more vulnerable to conditions that are independent risk factors for cognitive decline, such as cardiometabolic diseases.

OBJECTIVE

we tested whether any association with APOE e4 status on cognitive ability was larger in older ages or in those with cardiometabolic diseases.

SUBJECTS

UK Biobank includes over 500,000 middle- and older aged adults who have undergone detailed medical and cognitive phenotypic assessment. Around 150,000 currently have genetic data. We examined 111,739 participants with complete genetic and cognitive data.

METHODS

baseline cognitive data relating to information processing speed, memory and reasoning were used. We tested for interactions with age and with the presence versus absence of type 2 diabetes (T2D), coronary artery disease (CAD) and hypertension.

RESULTS

in several instances, APOE e4 dosage interacted with older age and disease presence to affect cognitive scores. When adjusted for potentially confounding variables, there was no APOE e4 effect on the outcome variables.

CONCLUSIONS

future research in large independent cohorts should continue to investigate this important question, which has potential implications for aetiology related to dementia and cognitive impairment.

Neurocognitive functioning and genetic variation in patients with primary brain tumours

Impairment of neurocognitive functioning is a common result of cerebral neoplasms and treatment, although there is substantial heterogeneity in the pattern and severity of neurocognitive dysfunction across individuals and tumour types. The effects of many clinical and patient characteristics on neurocognitive functioning have been documented, but little research has been devoted to understanding the effect of genetic variation on neurocognitive outcomes in patients with brain tumours. This Review highlights preliminary evidence that suggests an association between various genes and risk of adverse neurocognitive outcomes in patients with brain tumours. Studies include genes specific to neuronal function, and those associated with more systemic cellular regulation. Related scientific literature in other disease populations is briefly discussed to indicate additional candidate genes. We consider methodological issues central to the study of neurocognitive functioning and genetic associations for patients with brain tumours, and emphasise the need for future research integrating novel investigative techniques.

Oral administration of d-galactose induces cognitive impairments and oxidative damage in rats

d-Galactose (d-gal) is a reducing sugar that can be used to mimic the characteristics of aging in rodents; however, the effects of d-gal administration by oral route are not clear. Therefore, the aim of this study was to elucidate if the oral administration of d-gal induces cognitive impairments, neuronal loss, and oxidative damage, mimicking an animal model of aging. Male adult Wistar rats (4 months old) received d-gal (100mg/kg) via the oral route for a period of 1, 2, 4, 6 or 8 weeks. The results showed cognitive impairments in the open-field test in the 4th and 6th weeks after d-gal administration, as well as an impairment in spatial memory in the radial maze test after the 6th week of d-gal administration. The results indicated increase of levels of thiobarbituric acid reactive species-TBARS-and carbonyl group content in the prefrontal cortex from the 4th week, and in all weeks of d-gal administration, respectively. An increase in the levels of TBARS and carbonyl group content was observed in the hippocampus over the entire period of d-gal treatment. In the 8th week of d-gal administration, we also observed reductions in synaptophysin and TAU protein levels in the prefrontal cortex. Thus, d-gal given by oral route caused cognitive impairments which were accompanied by oxidative damage. Therefore, these results indicate that orally administered d-gal can induce the behavioral and neurochemical alterations that are observed in the natural aging process. However, oral d-gal effect in rats deserve further studies to be better described.