Neurogenetic effects on cognition in aging brains: a window of opportunity for intervention?

The knowledge domain of cognitive neuroscience of aging: A Scientometric and bibliometric analysis

Cognitive neuroscience of aging (CNA) is a relatively young field compared with other branches of cognitive aging (CA). From the beginning of this century, scholars in CNA have contributed many valuable research to explain the cognitive ability decline in aging brains in terms of functional changes, neuromechanism, and neurodegenerative diseases. However, very few studies have systematically reviewed the research in the domain of CAN, with regard to its primary research topics, theories, findings, and future development. Therefore, this study used CiteSpace to conduct a bibliometric analysis of 1,462 published articles in CNA from Web of Science (WOS) and investigated the highly influential and potential research topics and theories of CNA, as well as important brain areas involved in CAN during 2000-2021. The results revealed that: (1) the research topics of "memory" and "attention" have been the focus of most studies, progressing into a fMRI-oriented stage; (2) the scaffolding theory and hemispheric asymmetry reduction in older adults model hold a key status in CNA, characterizing aging as a dynamic process and presenting compensatory relationships between different brain areas; and (3) age-related changes always occur in temporal (especially the hippocampus), parietal, and frontal lobes and the cognitive declines establish the compensation relationship between the anterior and posterior regions.

Amygdala subnuclei and healthy cognitive aging

Amygdala is a group of nuclei involved in the neural circuits of fear, reward learning, and stress. The main goal of this magnetic resonance imaging (MRI) study was to investigate the relationship between age and the amygdala subnuclei volumes in a large cohort of healthy individuals. Our second goal was to determine effects of the apolipoprotein E (APOE) and brain-derived neurotrophic factor (BDNF) polymorphisms on the amygdala structure. One hundred and twenty-six healthy participants (18-85 years old) were recruited for this study. MRI datasets were acquired on a 4.7 T system. Amygdala was manually segmented into five major subdivisions (lateral, basal, accessory basal nuclei, and cortical, and centromedial groups). The BDNF (methionine and homozygous valine) and APOE genotypes (ε2, homozygous ε3, and ε4) were obtained using single nucleotide polymorphisms. We found significant nonlinear negative associations between age and the total amygdala and its lateral, basal, and accessory basal nuclei volumes, while the cortical amygdala showed a trend. These age-related associations were found only in males but not in females. Centromedial amygdala did not show any relationship with age. We did not observe any statistically significant effects of APOE and BDNF polymorphisms on the amygdala subnuclei volumes. In contrast to APOE ε2 allele carriers, both older APOE ε4 and ε3 allele carriers had smaller lateral, basal, accessory basal nuclei volumes compared to their younger counterparts. This study indicates that amygdala subnuclei might be nonuniformly affected by aging and that age-related association might be gender specific.

Increased DNA Copy Number Variation Mosaicism in Elderly Human Brain

Aging is a complex process strongly determined by genetics. Previous reports have shown that the genome of neuronal cells displays somatic genomic mosaicism including DNA copy number variations (CNVs). CNVs represent a significant source of genetic variation in the human genome and have been implicated in several disorders and complex traits, representing a potential mechanism that contributes to neuronal diversity and the etiology of several neurological diseases and provides new insights into the normal, complex functions of the brain. Nonetheless, the features of somatic CNV mosaicism in nondiseased elderly brains have not been investigated. In the present study, we demonstrate a highly significant increase in the number of CNVs in nondiseased elderly brains compared to the blood. In two neural tissues isolated from paired postmortem samples (same individuals), we found a significant increase in the frequency of deletions in both brain areas, namely, the frontal cortex and cerebellum. Also, deletions were found to be significantly larger when present only in the cerebellum. The sizes of the variants described here were in the 150–760 kb range, and importantly, nearly all of them were present in the Database of Genomic Variants (common variants). Nearly all evidence of genome structural variation in human brains comes from studies detecting changes in single cells which were interpreted as derived from independent, isolated mutational events. The observations based on array-CGH analysis indicate the existence of an extensive clonal mosaicism of CNVs within and between the human brains revealing a different type of variation that had not been previously characterized.

COMT Val158Met polymorphism is associated with blood pressure and lipid levels in general families of Bama longevous area in China

To see the possible relationship between COMT Val158Met polymorphism and blood pressure (BP) and serum lipid levels and its putative role in human longevity, we genotyped COMT Val158Met (rs4680) by PCR-RFLP for members from Bama long-lived families (BLF, n = 1538), Bama non-long-lived families (BNLF, n = 600), Pingguo (a county outside Bama region) long-lived families (PLF, n = 538) and Pingguo non-long-lived families (PNLF, n = 403) after anthropometric measures were collected and serum lipid levels were detected. The distribution of genotypes and alleles among four family groups was significantly different (all P < 0.01), with GA/AA genotype and minor allele A presenting more frequently in Bama population than Pingguo Population (P < 0.01). The systolic blood pressure (SBP), pulse pressure (PP), total cholesterol (TC), triglyceride (TG) and low density lipoprotein-cholesterol (LDL-C) levels of GG genotype carriers were dramatically higher than non-GG carriers in BNLF (P < 0.05); the SBP and PP levels of GG carriers were lower (P < 0.05) while TC, LDL-C level were higher (P < 0.01) than that of non-GG carriers in PLF; no difference in blood pressure and lipids were observed between genotypes in BLF and PNLF (P > 0.05). Correlation analyses revealed that COMT Val158Met was mainly correlated negatively with SBP, diastolic blood pressure (DBP) and LDL-C in BNLF and negatively with TC level in BLF, BNLF and PLF. These data suggest that COMT Val158Met polymorphism may have more impact on the modulation of BP and lipid profiles in the average families than in the long-lived families in Bama region. The association between this SNP and other phenotypes (e.g. cognition) and its roles in the longevity in Bama area thus warrant further investigation.

Vascular Health and Genetic Risk Affect Mild Cognitive Impairment Status and 4-Year Stability: Evidence From the Victoria Longitudinal Study

OBJECTIVES

Mild cognitive impairment (MCI) is a high-risk condition for progression to Alzheimer's disease (AD). Vascular health is a key mechanism underlying age-related cognitive decline and neurodegeneration. AD-related genetic risk factors may be associated with preclinical cognitive status changes. We examine independent and cross-domain interactive effects of vascular and genetic markers for predicting MCI status and stability.

METHOD

We used cross-sectional and 2-wave longitudinal data from the Victoria Longitudinal Study, including indicators of vascular health (e.g., reported vascular diseases, measured lung capacity and pulse rate) and genetic risk factors-that is, apolipoprotein E (APOE; rs429358 and rs7412; the presence vs absence of ε4) and catechol-O-methyltransferase (COMT; rs4680; met/met vs val/val). We examined associations with objectively classified (a) cognitive status at baseline (not impaired congnitive (NIC) controls vs MCI) and (b) stability or transition of cognitive status across a 4-year interval (stable NIC-NIC vs chronic MCI-MCI or transitional NIC-MCI).

RESULTS

Using logistic regression, indicators of vascular health, both independently and interactively with APOE ε4, were associated with risk of MCI at baseline and/or associated with MCI conversion or MCI stability over the retest interval.

DISCUSSION

Several vascular health markers of aging predict MCI risk. Interactively, APOE ε4 may intensify the vascular health risk for MCI.

APOE and COMT polymorphisms are complementary biomarkers of status, stability, and transitions in normal aging and early mild cognitive impairment

Objective: Research has reported associations among selected genetic susceptibility biomarkers and risk of (a) normal cognitive aging decrements, (b) established mild cognitive impairment (MCI), and (c) sporadic Alzheimer's disease (AD). In focusing on the transitional normal-to-early MCI phase, we examine associations among three theoretically relevant polymorphisms (APOE [rs429358, rs7412], BDNF [rs6265], COMT [rs4680]) and both baseline cognitive status (MCI vs. normal aging) and two-wave (four-year) longitudinal stability or change profiles. The latter included three profiles: (a) stable as normal aging, (b) stable or chronic impairment (MCI-to-MCI), and (c) emergence of impairment (normal-to-MCI).

Method: Genotyped older adults (n = 237 at baseline; age range = 64–91; 62% women) from the Victoria Longitudinal Study were examined for (a) independent and interactive associations of three genetic polymorphisms with (b) two objectively classified cognitive status groups (not-impaired controls (NIC) and MCI) at (c) both baseline and across a two-wave (four-year) longitudinal interval.

Results: First, logistic regression revealed that the presence of at least one APOE ε4 allele (the risk factor for AD) was linked to greater baseline risk of objective MCI. Second, multinomial logistic regression revealed that (a) the presence of an APOE ε4 allele was associated with an increased risk of 4-year MCI status stability (chronicity), and (b) the COMT homozygous risk genotype (G/G or Val/Val) was associated with an increased risk of both MCI-to-MCI stability (chronicity) and emerging NIC-to-MCI conversion.

Discussion: Both chronicity and emergence of objectively classified early cognitive impairment may be genetically heterogeneous phenomena, with influences from a panel of both normal cognitive aging (COMT) and AD-related (APOE) polymorphisms.

Age and sex related changes in episodic memory function in middle aged and older adults

Age-related change in episodic memory function is commonly reported in older adults. When detected on neuropsychological tests, it may still be difficult to distinguish normal from pathological changes. The present study investigates age-and sex-related changes in a group of healthy middle-aged and older adults, participating in a three-wave study on cognitive aging. The California Verbal Learning test (CVLT-II) was used to assess their episodic memory function. A cross-sectional analysis of results from the first wave showed higher performance in females than males, with a steeper age-related decline in males. This was confirmed in a longitudinal analysis using a mixed effects regression model, but with a lower age-related change and smaller difference between the sexes. Information about learning strategies and errors in the third wave turned out to contribute significantly to explain change in episodic memory function across the three waves. We argue that the results from the longitudinal analyses are generalizable to the population of healthy middle-aged and older individuals, and that they could be useful in guiding clinicians when evaluating individuals with respect to cognitive change.

From Neuroplasticity to Scaffolding

This paper is a review of cognitive aging research centred on the Scaffolding Theory of Aging and Cognition (STAC), a theory which brings together much of the previous research into cognitive aging over the past century and suggests directions for future work. From Santiago Ramon y Cajal, with his microscope and talented drawings, to today’s researchers with psychological and neurobiological methods and technology, particularly neuroimaging techniques, such as fMRI, sMRI, PET, etc., enormous progress has been made, through cognitive reserve, dedifferentiation, compensation, hemispherical asymmetry, inhibition and neurotransmission, to the Scaffolding theory of aging and cognition and beyond. Prior to 1990, research was almost entirely behavioural, but the advent of neuroimaging has boosted research and given rise to a new domain known as cognitive neuroscience, combining behavioural and neurobiological approaches to investigate structural and functional changes in the aging brain. Having reviewed the existing literature on cognitive aging research, the author concludes that although the scaffolding theory brings together a significant body of work and ideas, it is not yet the single, unifying theory for researchers. However, it does represent a giant step toward that theory.

Individual differences in cognition, affect, and performance: behavioral, neuroimaging, and molecular genetic approaches

We describe the use of behavioral, neuroimaging, and genetic methods to examine individual differences in cognition and affect, guided by three criteria: (1) relevance to human performance in work and everyday settings; (2) interactions between working memory, decision-making, and affective processing; and (3) examination of individual differences. The results of behavioral, functional MRI (fMRI), event-related potential (ERP), and molecular genetic studies show that analyses at the group level often mask important findings associated with sub-groups of individuals. Dopaminergic/noradrenergic genes influencing prefrontal cortex activity contribute to inter-individual variation in working memory and decision behavior, including performance in complex simulations of military decision-making. The interactive influences of individual differences in anxiety, sensation seeking, and boredom susceptibility on evaluative decision-making can be systematically described using ERP and fMRI methods. We conclude that a multi-modal neuroergonomic approach to examining brain function (using both neuroimaging and molecular genetics) can be usefully applied to understanding individual differences in cognition and affect and has implications for human performance at work.