An analysis of diversity in the cognitive performance of elderly community dwellers: individual differences in change scores as a function of age

Characterizing Cognitive Dispersion and Its Correlates Across the Adult Lifespan in MIDUS

OBJECTIVES

Although research has shown that higher levels of within-person variability across cognitive tasks (dispersion) are associated with cognitive decline in clinical samples, little is known about dispersion in comparatively younger, nonclinical, and national samples. A better understanding of dispersion is needed to elucidate for whom and under what circumstances dispersion can be used as a reliable indicator of cognitive health.

METHOD

We used data from the Midlife in the United States Study (MIDUS; n = 2,229; Mage = 56 years, range = 33-83; 56% female) to: (a) characterize dispersion and its cross-sectional correlates in a nonclinical, adult lifespan sample and (b) examine changes in dispersion over time to determine for whom changes in dispersion may reflect better or worse cognitive aging.

RESULTS

Correlations showed higher levels of dispersion were associated with higher levels of mean performance at both waves (rs = 0.28-0.29). Autoregressive main effect models showed that increases in dispersion were associated with less decline in mean performance over the 2-wave, 9-year follow-up period (β = 0.17, p < .001). Moderation models showed that the link between change in dispersion and change in mean performance was pronounced in comparatively older adults (β = 0.28), women (β = 0.27), individuals with less education (β = 0.23), and those with lower income (β = 0.23; all ps < .001).

DISCUSSION

Findings suggest that increases in dispersion may not always be maladaptive in normative, adult lifespan samples and may reflect healthier cognitive profiles in individuals who are at greater risk for cognitive impairment.

Cognitive engagement may slow clinical progression and brain atrophy in Huntington's disease

Lifelong cognitive engagement conveys benefits in Huntington's disease (HD) and may positively affect non-cognitive domains in other populations. However, the effect of lifelong cognitive engagement on the progression of motor and psychiatric domains in HD remains unknown, as is its neurobiological basis. Forty-five HD individuals completed the Cognitive Reserve Questionnaire (CRQ) and longitudinal clinical evaluation (maximum total of six visits, mean inter-assessment duration of 13.53 ± 4.1 months). Of these, thirty-three underwent longitudinal neuroimaging (18 ± 6 months follow-up). Generalized linear mixed-effects models were executed to predict the effect of individual differences in lifelong cognitive engagement on HD clinical progression and voxel-based morphometry to explore the impact of lifelong cognitive engagement on whole-brain gray matter volume atrophy. Controlling for age, disease stage, and sex, higher CRQ scores were associated with reduced overall severity and longitudinal progression across cognitive, motor, and psychiatric domains. Those with higher CRQ scores demonstrated reduced gray matter volume loss in the middle frontal gyrus, supplementary motor area, and middle cingulate. This putative impact on HD clinical progression may be conferred by preservation of brain volume in neural hubs that integrate executive function with action initiation and behavioral regulation, providing support for early cognitive engagement, even prior to diagnosis.

Differential sensitivity of intraindividual variability dispersion and global cognition in the prediction of functional outcomes and mortality in precariously housed and homeless adults

OBJECTIVE

To examine cognitive intraindividual variability (IIV) dispersion as a predictor of everyday functioning and mortality in persons who are homeless or precariously housed.

METHOD

Participants were 407 community-dwelling adults, followed for up to 13 years. Neurocognition was assessed at baseline and IIV dispersion was derived using a battery of standardized tests. Functional outcomes (social, physical) were obtained at baseline and last follow-up. Mortality was confirmed with Coroner's reports and hospital records (N  = 103 deaths). Linear regressions were used to predict current social and physical functioning from IIV dispersion. Repeated measures Analysis of Covariance were used to predict long-term change in functioning. Cox regression models examined the relation between IIV dispersion and mortality. Covariates included global cognition (i.e. mean-level performance), age, education, and physical comorbidities.

RESULTS

Higher IIV dispersion predicted poorer current physical functioning (B = -0.46 p = .010), while higher global cognition predicted better current (B  = 0.21, p = .015) and change in social functioning over a period of up to 13 years (F  = 4.23, p = .040). Global cognition, but not IIV dispersion, predicted mortality in individuals under 55 years old (HR = 0.50, p = .013).

CONCLUSIONS

Our findings suggest that indices of neurocognitive functioning (i.e. IIV dispersion and global cognition) may be differentially related to discrete dimensions of functional outcomes in an at-risk population. IIV dispersion may be a complimentary marker of emergent physical health dysfunction in precariously housed adults and may be best used in conjunction with traditional neuropsychological indices.

Variability across subjects in free recall versus cued recall

Memory scientists usually compare mean performance on some measure(s) (accuracy, confidence, latency) as a function of experimental condition. Some researchers have made within-subject variability in task performance a focal outcome measure (e.g., Yao et al., Journal of Clinical and Experimental Neuropsychology, 38, 227-237, 2016). Here, we explored between-subject variability in accuracy as a function of experimental conditions. This work was inspired by an incidental finding in a previous study, in which we observed greater variability in accuracy of memory performance on cued recall (CR) versus free recall (FR) of English animal/object nouns (Mah et al., Frontiers in Psychology, 14, 1146200, 2023). Here we report experiments designed to assess the reliability of that pattern and to explore its causes (e.g., differential interpretation of instructions, [un]relatedness of CR word pairs, encoding time). In Experiment 1 (N = 120 undergraduates), we replicated the CR:FR variability difference with a more representative set of English nouns. In Experiments 2A (N = 117 Prolific participants) and 2B (N = 127 undergraduates), we found that the CR:FR variability difference persisted in a forced-recall procedure. In Experiment 3 (N = 260 Prolific participants), we used meaningfully related word pairs and still found greater variability in CR than in FR performance. In Experiment 4 (N = 360 Prolific participants), we equated CR and FR study phases by having all participants study pairs and, again, observed greater variability in CR than FR. The same was true in Experiment 5 (N = 120 undergraduates), in which study time was self-paced. Comparisons of variability across subjects can yield insights into the mechanisms underlying task performance.

Aging effects on electrical and hemodynamic responses in the sensorimotor network during unilateral proximal upper limb functional tasks

Healthy aging leads to poorer performance in upper limb (UL) daily living movements. Understanding the neural correlates linked with UL functional movements may help to better understand how healthy aging affects motor control. Two non-invasive neuroimaging methods allow for monitoring the movement-related brain activity: functional near-infrared spectroscopy (fNIRS) and electroencephalography (EEG), respectively based on the hemodynamic response and electrical activity of brain regions. Coupled, they provide a better spatiotemporal mapping. The aim of this study was to evaluate the effect of healthy aging on the bilateral sensorimotor (SM1) activation patterns of functional proximal UL movements. Twenty-one young and 21 old healthy participants realized two unilateral proximal UL movements during: i) a paced reaching target task and ii) a circular steering task to capture the speed-accuracy trade-off. Combined fNIRS-EEG system was synchronised with movement capture system to record SM1 activation while moving. The circular steering task performance was significantly lower for the older group. The rate of increase in hemodynamic response was longer in the older group with no difference on the amplitude of fNIRS signal for the two tasks. The EEG results showed aging related reduction of the alpha-beta rhythms synchronisation but no desynchronisation modification. In conclusion, this study uncovers the age-related changes in brain electrical and hemodynamic response patterns in the bilateral sensorimotor network during two functional proximal UL movements using two complementary neuroimaging methods. This opens up the possibility to utilise combined fNIRS-EEG for monitoring the movement-related neuroplasticity in clinical practice.

Hippocampal and motor regions contribute to memory benefits after enacted encoding: cross-sectional and longitudinal evidence

The neurobiological underpinnings of action-related episodic memory and how enactment contributes to efficient memory encoding are not well understood. We examine whether individual differences in level (n = 338) and 5-year change (n = 248) in the ability to benefit from motor involvement during memory encoding are related to gray matter (GM) volume, white matter (WM) integrity, and dopamine-regulating genes in a population-based cohort (age range = 25-80 years). A latent profile analysis identified 2 groups with similar performance on verbal encoding but with marked differences in the ability to benefit from motor involvement during memory encoding. Impaired ability to benefit from enactment was paired with smaller HC, parahippocampal, and putamen volume along with lower WM microstructure in the fornix. Individuals with reduced ability to benefit from encoding enactment over 5 years were characterized by reduced HC and motor cortex GM volume along with reduced WM microstructure in several WM tracts. Moreover, the proportion of catechol-O-methyltransferase-Val-carriers differed significantly between classes identified from the latent-profile analysis. These results provide converging evidence that individuals with low or declining ability to benefit from motor involvement during memory encoding are characterized by low and reduced GM volume in regions critical for memory and motor functions along with altered WM microstructure.

Signatures of Neuropsychological Test Results in the Long Life Family Study: A Cluster Analysis

BACKGROUND

Discovering patterns of cognitive domains and characterizing how these patterns associate with other risk factors and biomarkers can improve our understanding of the determinants of cognitive aging.

OBJECTIVE

To discover patterns of cognitive domains using neuropsychological test results in Long Life Family Study (LLFS) and characterize how these patterns associate with aging markers.

METHODS

5,086 LLFS participants were administered neuropsychological tests at enrollment. We performed a cluster analysis of six baseline neuropsychological test scores and tested the association between the identified clusters and various clinical variables, biomarkers, and polygenic risk scores using generalized estimating equations and the Chi-square test. We used Cox regression to correlate the clusters with the hazard of various medical events. We investigated whether the cluster information could enhance the prediction of cognitive decline using Bayesian beta regression.

RESULTS

We identified 12 clusters with different cognitive signatures that represent profiles of performance across multiple neuropsychological tests. These signatures significantly correlated with 26 variables including polygenic risk scores, physical and pulmonary functions, and blood biomarkers and were associated with the hazard of mortality (p < 0.01), cardiovascular disease (p = 0.03), dementia (p = 0.01), and skin cancer (p = 0.03).

CONCLUSION

The identified cognitive signatures capture multiple domains simultaneously and provide a holistic vision of cognitive function, showing that different patterns of cognitive function can coexist in aging individuals. Such patterns can be used for clinical intervention and primary care.

The effect of memory cue duration on performance in the directed forgetting task in healthy aging

Although forgetting is usually considered a memory error, intentional forgetting can function as an adaptive mechanism. The current study examined the effect of increased processing time on directed forgetting in aging as a mechanism to compensate for age-related forgetting. Specifically, an item-method directed forgetting paradigm was used in conjunction with Remember/Know/New responding to examine the effect of cue duration (1, 3, 5 s) on directed forgetting and remembering in younger and older adults. Results indicated that increased processing time improved performance in both age groups. Critically, older adults exhibited a linear increase in directed remembering performance across all cue durations which was related to individual differences in cognitive reserve. Specifically, those older adults with the highest levels of cognitive functioning showed the greatest memory benefit in the longest cue duration condition. These findings indicate the importance of processing time in accounting for intentional memory performance in older adults.

Novel Functional, Health, and Genetic Determinants of Cognitive Terminal Decline: Kuakini Honolulu Heart Program/Honolulu-Asia Aging Study

To investigate interindividual differences in cognitive terminal decline and identify determinants including functional, health, and genetic risk and protective factors, data from the Honolulu Heart Program/Honolulu-Asia Aging Study, a prospective cohort study of Japanese American men, were analyzed. The sample was recruited in 1965-1968 (ages 45-68 years). Longitudinal performance of cognitive abilities and mortality status were assessed from Exam 4 (1991-1993) through June 2014. Latent class analysis revealed 2 groups: maintainers retained relatively high levels of cognitive functioning until death and decliners demonstrated significant cognitive waning several years prior to death. Maintainers were more likely to have greater education, diagnosed coronary heart disease, and presence of the apolipoprotein E (APOE) ε2 allele and FOXO3 G allele (SNP rs2802292). Decliners were more likely to be older and have prior stroke, Parkinson's disease, dementia, and greater depressive symptoms at Exam 4, and the APOE ε4 allele. Findings support terminal decline using distance to death as the basis for modeling change. Significant differences were observed between maintainers and decliners 15 years prior to death, a finding much earlier compared to the majority of previous investigations.

Metamemory mediates the protective effect of cognitive reserve on episodic memory during aging

The present study investigated the impact of cognitive reserve on episodic memory and metamemory control during aging using a multidimensional index of cognitive reserve and a measure of metamemory control abilities. We tested the hypotheses that cognitive reserve may play a protective role against age-related differences in episodic memory and metamemory control and that metamemory control may mediate the effect of cognitive reserve on episodic memory during aging. Young and older adults carried out a readiness-recall task in which task difficulty was manipulated through a variation of the nature of the cue-target pair link (weak vs. strong semantic associates). Episodic memory was assessed through recall performance, and metamemory by a task difficulty index reflecting the ability to adjust study time to task difficulty. Results confirmed that older adults recall fewer words, indicating an age-related deficit in episodic memory, and that older adults adjust less to task difficulty, suggesting impaired metamemory control. Findings also showed that metamemory control moderates the age-related decline in episodic memory and that cognitive reserve plays a protective role against age-related deficits in episodic memory and metamemory control. In addition, metamemory abilities mediated the beneficial effect of cognitive reserve on episodic memory performance during aging. Hence, this study sheds new light on the mechanisms underlying the impact of cognitive reserve on cognitive aging, highlighting the role of metacognitive processes.

Intra-individual cognitive variability in neuropsychological assessment: a sign of neural network dysfunction

Intra-Individual Cognitive Variability (IICV) predicts progression in neurocognitive disorders . Given important clinical applications, we investigated the association between IICV and multiple brain metrics across 17 networks to better understand the brain mechanisms underlying this performance measure. Sixty-three middle-aged and older adults without dementia underwent a neuropsychological battery, resting-state fMRI, and structural MRI scans. In a linear mixed effect model, higher IICV was associated with lower functional connectivity in control C network relative to medial occipital network (the reference). A multivariate partial least squares analysis revealed that lower mean and higher variability were both associated with lower connectivity in sensorimotor and default mode networks, while higher mean and higher variability were associated with lower volume in default mode and limbic networks. This study suggests that IICV signals widespread network dysfunction across multiple brain networks. These brain abnormalities offer new insights into mechanisms of early cognitive dysfunction. Clinical implications are discussed.

Event-related brain potentials reveal strategy selection in younger and older adults

It is well-established that younger adults prioritize information accrued during different stages of stimulus evaluation ("early" versus "late") to optimize performance. The extent to which older adults flexibly adjust their processing strategies, however, is largely unexplored. Twenty-four younger and twenty-four older participants completed a cued flanker task in which one of three cues, indicating the probability that a congruent array would appear (75 %, 50 %, or 25 %), was presented on each trial. Behavioral and ERP (CNV, LRP, N2, and P3b) analyses allowed us to infer cue-driven changes in strategy selection. Results indicate that when both younger and older adults expected an incongruent array, they prioritized late, target information, resulting in a decreased susceptibility to the performance-impairing effect of distractors, extending the conclusions of Gratton et al. (1992) to older adults and supporting the claim that strategic control remains largely intact during healthy aging.

Strategies and cognitive reserve to preserve lexical production in aging

In the absence of any neuropsychiatric condition, older adults may show declining performance in several cognitive processes and among them, in retrieving and producing words, reflected in slower responses and even reduced accuracy compared to younger adults. To overcome this difficulty, healthy older adults implement compensatory strategies, which are the focus of this paper. We provide a review of mainstream findings on deficient mechanisms and possible neurocognitive strategies used by older adults to overcome the deleterious effects of age on lexical production. Moreover, we present findings on genetic and lifestyle factors that might either be protective or risk factors of cognitive impairment in advanced age. We propose that "aging-modulating factors" (AMF) can be modified, offering prevention opportunities against aging effects. Based on our review and this proposition, we introduce an integrative neurocognitive model of mechanisms and compensatory strategies for lexical production in older adults (entitled Lexical Access and Retrieval in Aging, LARA). The main hypothesis defended in LARA is that cognitive aging evolves heterogeneously and involves complementary domain-general and domain-specific mechanisms, with substantial inter-individual variability, reflected at behavioral, cognitive, and brain levels. Furthermore, we argue that the ability to compensate for the effect of cognitive aging depends on the amount of reserve specific to each individual which is, in turn, modulated by the AMF. Our conclusion is that a variety of mechanisms and compensatory strategies coexist in the same individual to oppose the effect of age. The role of reserve is pivotal for a successful coping with age-related changes and future research should continue to explore the modulating role of AMF.

Causal Prefrontal Contributions to Stop-Signal Task Performance in Humans

The frontal lobes have long been implicated in inhibitory control, but a full understanding of the underlying mechanisms remains elusive. The stop-signal task has been widely used to probe instructed response inhibition in cognitive neuroscience. The processes involved have been modeled and related to putative brain substrates. However, there has been surprisingly little human lesion research using this task, with the few existing studies implicating different prefrontal regions. Here, we tested the effects of focal prefrontal damage on stop-signal task performance in a large sample of people with chronic focal damage affecting the frontal lobes (n = 42) and demographically matched healthy individuals (n = 60). Patients with damage to the left lateral, right lateral, dorsomedial, or ventromedial frontal lobe had slower stop-signal RT compared to healthy controls. There were systematic differences in the patterns of impairment across frontal subgroups: Those with damage to the left or right lateral and dorsomedial frontal lobes, but not those with ventromedial frontal damage, were slower than controls to "go" as well as to stop. These findings suggest that multiple prefrontal regions make necessary but distinct contributions to stop-signal task performance. As a consequence, stop-signal RT slowing is not strongly localizing within the frontal lobes.

Spontaneous Eye Blinks Predict Executive Functioning in Seniors

As the world’s population is aging rapidly, cognitive training is an extensively used approach to attempt improvement of age-related cognitive functioning. With increasing numbers of older adults required to remain in the workforce, it is important to be able to reliably predict future functional decline, as well as the individual advantages of cognitive training. Given the correlation between age-related decline and striatal dopaminergic function, we investigated whether eye blink rate (EBR), a non-invasive, indirect indicator of dopaminergic activity, could predict executive functioning (response inhibition, switching and working memory updating) as well as trainability of executive functioning in older adults. EBR was collected before and after a cognitive flexibility training, cognitive training without flexibility, or a mock training. EBR predicted working memory updating performance on two measures of updating, as well as trainability of working memory updating, whereas performance and trainability in inhibition and switching tasks could not be predicted by EBR. Our findings tentatively indicate that EBR permits prediction of working memory performance in older adults. To fully interpret the relationship with executive functioning, we suggest future research should assess both EBR and dopamine receptor availability among seniors.

A Latent Transition Analysis Model to Assess Change in Cognitive States over Three Occasions: Results from the Rush Memory and Aging Project

BACKGROUND

Conceptualizing cognitive aging as a step-sequential process is useful in identifying particular stages of cognitive function and impairment.

OBJECTIVE

We applied latent transition analysis (LTA) to determine 1) whether the underlying structure of cognitive profiles found at every measurement occasion are uniform across three waves of assessment, 2) whether class-instability is predictive of distal outcomes, and 3) whether class-reversions from impaired to non-impaired using latent modelling is lower than when using clinical criteria of mild cognitive impairment (MCI).

METHODS

A mover-stayer LTA model with dementia as a distal outcome was specified to model transitions of ten neuropsychological measures over three annual waves in the Rush Memory and Aging Project (n = 1,661). The predictive validity of the mover-stayer status for incident Alzheimer's disease (AD) was then assessed.

RESULTS

We identified a five-class model across the three time-points: Mixed-Domain Impairment, Memory-Specific Impairment, Frontal Impairment, Average, and Superior Cognition. None of the individuals in the Impairment classes reverted to the Average or Superior classes. Conventional MCI classification identified 26.4% and 14.1% at Times 1 and 2 as false-positive cases. "Movers" had 87% increased risk of developing dementia compared to those classified as "Stayers".

CONCLUSION

Our findings support the use of latent variable modelling that incorporates comprehensive neuropsychological assessment to identify and classify cognitive impairment.

Slower Decline in Processing Speed Is Associated with Familial Longevity

INTRODUCTION

Cross-sectional analyses have associated familial longevity with better cognitive function and lower risk of cognitive impairment in comparison with individuals without familial longevity. The extent to which long-lived families also demonstrate slower rates of cognitive aging (i.e., change in cognition over time) is unknown. This study examined longitudinally collected data among 2 generations of the Long Life Family Study (LLFS) to compare rates of cognitive change across relatives and spouse controls.

METHODS

We analyzed change in 6 neuropsychological test scores collected approximately 8 years apart among LLFS family members (n = 3,972) versus spouse controls (n = 1,092) using a Bayesian hierarchical model that included age, years of follow-up, sex, education, generation, and field center and all possible pairwise interactions.

RESULTS

At a mean age of 88 years at enrollment in the older generation and 60 years in the younger generation, LLFS family members performed better than their spouses on the Digit Symbol Substitution Test (DSST) and the Logical Memory test. At follow-up, family members in the younger generation also showed slower decline than spouses on the DSST, whereas rates of change of Digit Span, fluency, and memory were similar between the 2 groups.

DISCUSSION/CONCLUSION

Individuals in families with longevity appear to have better cognitive performance than their spouses for cognitive processes including psychomotor processing, episodic memory, and retrieval. Additionally, they demonstrate longer cognitive health spans with a slower decline on a multifactorial test of processing speed, a task requiring the integration of processes including organized visual search, working and incidental memory, and graphomotor ability. Long-lived families may be a valuable cohort for studying resilience to cognitive aging.

Long-Term Music Exposure Prevents Age-Related Cognitive Deficits in Rats Independently of Hippocampal Neurogenesis

Cognitive decline appears across aging. While some studies report beneficial effects of musical listening and practice on cognitive aging, the underlying neurobiological mechanisms remain unknown. This study aims to determine whether chronic (6 h/day, 3 times/week) and long-lasting (4-8 months) music exposure, initiated at middle age in rats (15 months old), can influence behavioral parameters sensitive to age effects and reduce age-related spatial memory decline in rats. Spontaneous locomotor, circadian rhythmic activity, and anxiety-like behavior as well as spatial working and reference memory were assessed in 14-month-old rats and then after 4 and 8 months of music exposure (19 and 23 months old, respectively). Spatial learning and reference memory data were followed up by considering cognitive status of animals prior to music exposure (14 months old) given by K-means clustering of individual Z-score. Hippocampal cell proliferation and brain-derived neurotrophic factor (BDNF) level in the hippocampus and frontal cortex were measured. Results show that music exposure differentially rescues age-related deficits in spatial navigation tasks according to its duration without affecting spontaneous locomotor, circadian rhythmic activity, and anxiety-like behavior. Hippocampal cell proliferation as well as hippocampal and frontal cortex BDNF levels was not affected by music across aging. Cognitive improvement by music in aging rats may require distinct neurobiological mechanisms than hippocampal cell proliferation and BDNF.

Reproductive aging and executive functions in healthy women

The aim of this study was to analyze the influence of reproductive aging on executive functions. We assessed executive functions in three groups of healthy women in the premenopausal (n = 45, mean age = 30.89, SD = 10.5), perimenopausal (n = 31, mean age = 50.06, SD = 3.6) and postmenopausal (n = 24, mean age = 63.39, SD = 6.5) phase. No differences between groups were observed in working memory, verbal fluency, inhibitory control, planning, and cognitive flexibility. However, when the analyses were repeated with participants with occupations with lower intellectual demands, perimenopausal and postmenopausal women performed worse than premenopausal women in semantic verbal fluency. This study provides important evidence to understand the effects of reproductive aging on cognitive performance in healthy women. Our findings indicate that cognitive reserve-related factors may be important to understand the differences in executive functions associated with reproductive aging.

Neural distinctiveness declines with age in auditory cortex and is associated with auditory GABA levels

Neural activation patterns in the ventral visual cortex in response to different categories of visual stimuli (e.g., faces vs. houses) are less selective, or distinctive, in older adults than in younger adults, a phenomenon known as age-related neural dedifferentiation. In this study, we investigated whether neural dedifferentiation extends to the auditory cortex. Inspired by previous animal work, we also investigated whether individual differences in GABA are associated with individual differences in neural distinctiveness in humans. 20 healthy young adults (ages 18-29) and 23 healthy older adults (over 65) completed a functional magnetic resonance imaging (fMRI) scan, during which neural activity was estimated while they listened to music and foreign speech. GABA levels in the auditory, ventrovisual and sensorimotor cortex were estimated in the same individuals in a separate magnetic resonance spectroscopy (MRS) scan. Relative to the younger adults, the older adults exhibited both (1) less distinct activation patterns for music vs. speech stimuli and (2) lower GABA levels in the auditory cortex. Also, individual differences in auditory GABA levels (but not ventrovisual or sensorimotor GABA levels) were associated with individual differences in neural distinctiveness in the auditory cortex in the older adults. These results demonstrate that age-related neural dedifferentiation extends to the auditory cortex and suggest that declining GABA levels may play a role in neural dedifferentiation in older adults.

The microbiome and cognitive aging: a review of mechanisms

Gut microbiota plays an intrinsic role in communication between the gut and the brain and is capable of influencing the host brain by producing neurotransmitters and neurotrophins, the modulation of inflammatory processes amongst other key mechanisms. Increased age is also associated with changes in these key biological processes and impairments in a range of cognitive processes. We hypothesise several mechanisms in which gut microbiota may modulate changes in cognitive function with age. In this review, we discuss issues related to the measurement of cognition in the elderly and in particular outline a standardised model of cognition that could be utilised to better understand cognitive outcomes in future studies examining the relationship between gut microbiota and cognition in the elderly. We then review biological processes such as oxidative stress and inflammation which are related to cognitive changes with age and which are also influenced by our gut microbiota. Finally, we outline other potential mechanisms by which the gut microbiota may influence cognition.

Cognitive dispersion is a sensitive marker for early neurodegenerative changes and functional decline in nondemented older adults

OBJECTIVE

Intraindividual cognitive variability (IIV), a measure of within-person variability across cognitive measures at a single time point, is associated with mild cognitive impairment (MCI) and Alzheimer's disease (AD). Little is known regarding brain changes underlying IIV, or the relationship between IIV and functional ability. Therefore, we investigated the association between IIV and cerebral atrophy in AD-vulnerable regions and everyday functioning in nondemented older adults.

METHOD

736 Alzheimer's Disease Neuroimaging Initiative (ADNI) participants (285 cognitively normal [CN]; 451 MCI) underwent neuropsychological testing and serial MRI over 2 years. Linear mixed effects models examined the association between baseline IIV and change in entorhinal cortex thickness, hippocampal volume, and everyday functioning.

RESULTS

Adjusting for age, sex, apolipoprotein E genotype, amyloid-β positivity, and mean level of cognitive performance, higher baseline IIV predicted faster rates of entorhinal and hippocampal atrophy, as well as functional decline. Higher IIV was associated with both entorhinal and hippocampal atrophy among MCI participants but selective vulnerability of the entorhinal cortex among CN individuals.

CONCLUSIONS

IIV was associated with more widespread medial temporal lobe (MTL) atrophy in individuals with MCI relative to CN, suggesting that IIV may be tracking advancing MTL pathologic changes across the continuum of aging, MCI, and dementia. Findings suggest that cognitive dispersion may be a sensitive marker of neurodegeneration and functional decline in nondemented older adults. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Predictors of Source Memory Success and Failure in Older Adults

Source memory decline has been identified as one of the types of memory most seriously affected during older age. It refers to our capacity to recollect the contextual information in which our experiences take place. Although most elderly adults will be affected by progressive source memory decline, a subset of individuals will not follow this average pattern; instead, their source memory capabilities will remain functional. Likewise, a minority of individuals will manifest an extreme decay of their source memory abilities. The objective of the present study was to identify among 120 potential predictors that significantly contributed to these two extreme source memory outcomes. Spatial source memory was measured in a sample of 519 healthy individuals between 61 and 80 years old. Individuals who performed below the 20th and above the 80th percentiles in the source memory task were defined as individuals whose episodic memory failed and succeeded, respectively. Logistic models identified five and six significant predictors of source memory success and failure in older age, respectively. High source memory performance was mainly predicted by healthy cardiovascular markers and psychological traits, whereas low source memory performance was primarily predicted by consumption habits and by less engagement in mental activities. The models identified relevant biological and life experiences that underlie these unusual source memory outcomes in older age.

School Performance and Educational Attainment as Early-Life Predictors of Age-Related Memory Decline: Protective Influences in Later-Born Cohorts

Objectives

Evidence is accumulating that early-life characteristics and experiences contribute significantly to differences in cognitive aging. This study investigated whether school performance at age 12 predicted late-life level and rate of memory change over 15–25 years, and whether its potential protective influence on memory change was mediated by educational attainment or income.

Methods

Latent growth curve models were fitted to 15–25 year longitudinal memory data from a population-based sample, stratified on age cohorts (n = 227, born 1909–1935; n = 301, born 1938–1954).

Results

A latent-level school grade variable significantly predicted both memory level and slope in later-born cohorts. Higher grades were associated with higher level and reduced decline, measured between ages 45 and 70 years, on average. In the earlier-born cohorts, grades predicted memory level, but not slope, measured between ages 66 and 81 years. Follow-up analyses indicated that the protective influence of higher school grades in later-born cohorts was partially mediated by educational attainment, but independent of income.

Discussion

The results suggest that higher childhood school performance is protective against age-related cognitive decline in younger or later-born cohorts, for which further education has been more accessible. Education may exert such influence through increased cognitive reserve or more well-informed health- and lifestyle decisions.

Understanding the relationship between cognition and death: a within cohort examination of cognitive measures and mortality

Despite several studies demonstrating an independent and inverse association between cognition and mortality, the nature of this association still remains unclear. To examine the association of cognition and mortality after accounting for sociodemographic, health and lifestyle factors and to explore both test and population characteristics influencing this relationship. In a population based cohort of 8585 men and women aged 48-92 years, who had cognitive assessments in 2006-2011 and were followed up till 2016 for mortality, we examined the relationship between individual cognitive tests as well as a global cognition score to compare their ability in predicting mortality and whether these differed by population characteristics. Risk of death was estimated using Cox proportional hazard regression models including sociodemographic, lifestyle and health variables, and self-reported comorbidities, as covariates in the models. Poor cognitive performance (bottom quartile of combined cognition score) was associated with higher risk of mortality, Hazard Ratio = 1.32 (95% Confidence Interval 1.09, 1.60); individual cognitive tests varied in their mortality associations and also performed differently in middle-age and older age groups. Poor cognitive performance is independently associated with higher mortality. This association is observed for global cognition and for specific cognitive abilities. Associations vary depending on the cognitive test (and domain) as well as population characteristics, namely age and education.

The Relationship between Handgrip Strength and Cognitive Function in Elderly Koreans over 8 Years: A Prospective Population-Based Study Using Korean Longitudinal Study of Ageing

Background

Decreased physical performance, such as weakened handgrip strength and cognitive decline, is associated with disability and premature death in old age. We investigated the association between handgrip strength and cognitive impairment in Korean elderly adults with normal cognitive function.

Methods

This prospective study used the database from the Korean Longitudinal Study of Ageing. The participants included 2,378 adults aged 65 years or older with normal cognitive function (Korean Mini-Mental Status Evaluation [K-MMSE] score ≥21). Using a mixed-effects model, we examined the associations at baseline and over an 8-year follow-up period between handgrip strength and K-MMSE score. We investigated handgrip strength as a predictor of change in cognitive function.

Results

This study included 1,138 women (mean maximum handgrip strength 19.2 kg, mean K-MMSE score 25.1) and 1,240 men (mean maximum handgrip strength 30.7 kg, mean MMSE score 26.2). The baseline handgrip strength was positively associated with the baseline K-MMSE score (b=0.18, P<0.001). Using a mixed-effects model, we found that higher handgrip strength at baseline can predict MMSE scores positively over time (b=0.14, P<0.001) and the change of handgrip strength over time was a predictor of high MMSE scores over the study period (b=0.01, P<0.01).

Conclusion

We observed significant associations between baseline handgrip strength and baseline and change of cognition, as well as the longitudinal influence of handgrip strength on the change of cognitive function in elderly Korean adults with normal cognitive function.

Get a grip: individual variations in grip strength are a marker of brain health

Demonstrations that grip strength has predictive power in relation to a range of health conditions-even when these are assessed decades later-has motivated claims that hand-grip dynamometry has the potential to serve as a "vital sign" for middle-aged and older adults. Central to this belief has been the assumption that grip strength is a simple measure of physical performance that provides a marker of muscle status in general, and sarcopenia in particular. It is now evident that while differences in grip strength between individuals are influenced by musculoskeletal factors, "lifespan" changes in grip strength within individuals are exquisitely sensitive to integrity of neural systems that mediate the control of coordinated movement. The close and pervasive relationships between age-related declines in maximum grip strength and expressions of cognitive dysfunction can therefore be understood in terms of the convergent functional and structural mediation of cognitive and motor processes by the human brain. In the context of aging, maximum grip strength is a discriminating measure of neurological function and brain health.

Altered function of neuronal L-type calcium channels in ageing and neuroinflammation: Implications in age-related synaptic dysfunction and cognitive decline

The rapid developments in science have led to an increase in human life expectancy and thus, ageing and age-related disorders/diseases have become one of the greatest concerns in the 21st century. Cognitive abilities tend to decline as we get older. This age-related cognitive decline is mainly attributed to aberrant changes in synaptic plasticity and neuronal connections. Recent studies show that alterations in Ca²⁺ homeostasis underlie the increased vulnerability of neurons to age-related processes like cognitive decline and synaptic dysfunctions. Dysregulation of Ca²⁺ can lead to dramatic changes in neuronal functions. We discuss in this review, the recent advances on the potential role of dysregulated Ca²⁺ homeostasis through altered function of L-type voltage gated Ca²⁺ channels (LTCC) in ageing, with an emphasis on cognitive decline. This review therefore focuses on age-related changes mainly in the hippocampus, and with mention of other brain areas, that are important for learning and memory. This review also highlights age-related memory deficits via synaptic alterations and neuroinflammation. An understanding of these mechanisms will help us formulate strategies to reverse or ameliorate age-related disorders like cognitive decline.

Individual Differences in Developmental Change: Quantifying the Amplitude and Heterogeneity in Cognitive Change across Old Age

It is well known that cognitive decline in older adults is of smaller amplitude in longitudinal than in cross-sectional studies. Yet, the measure of interest rests generally with aggregated group data. A focus on individual developmental trajectories is rare, mainly because it is difficult to assess intraindividual change reliably. Individual differences in developmental trajectories may differ quantitatively (e.g., larger or smaller decline) or qualitatively (e.g., decline vs improvement), as well as in the degree of heterogeneity of change across different cognitive domains or different tasks. The present paper aims at exploring, within the Geneva Variability Study, individual change across several cognitive domains in 92 older adults (aged 59-89 years at baseline) over a maximum of seven years and a half. Two novel, complementary methods were used to explore change in cognitive performance while remaining entirely at the intra-individual level. A bootstrap based confidence interval was estimated, for each participant and for each experimental condition, making it possible to define three patterns: stability, increase or decrease in performance. Within-person ANOVAs were also conducted for each individual on all the tasks. Those two methods allowed quantifying the direction, the amplitude and the heterogeneity of change for each individual. Results show that trajectories differed widely among individuals and that decline is far from being the rule.

The influence of perceptual similarity and individual differences on false memories in aging

Previous false memory research has suggested that older adults' false memories are based on an overreliance on gist processing in the absence of item-specific details. Yet, false memory studies have rarely taken into consideration the precise role of item-item similarity on the cognitive and neural mechanisms underlying perceptual false memories in older adults. In addition, work in our laboratory has suggested that when investigating the neural basis of false memories in older adults, it is equally as critical to take into account interindividual variability in behavior. With both factors in mind, the present study was the first to examine how both controlled, systematic differences in perceptual relatedness between targets and lures and individual differences in true and false recognition contribute to the neural basis of both true and false memories in older adults. Results suggest that between-subject variability in memory performance modulates neural activity in key regions associated with false memories in aging, whereas systematic differences in perceptual similarity did not modulate neural activity associated with false memories.

Subacute ibuprofen treatment rescues the synaptic and cognitive deficits in advanced-aged mice

Aging is accompanied by increased neuroinflammation, synaptic dysfunction, and cognitive deficits both in rodents and humans, yet the onset and progression of these deficits throughout the life span remain unknown. These aging-related deficits affect the quality of life and present challenges to our aging society. Here, we defined age-dependent and progressive impairments of synaptic and cognitive functions and showed that reducing astrocyte-related neuroinflammation through anti-inflammatory drug treatment in aged mice reverses these events. By comparing young (3 months), middle-aged (18 months), aged (24 months), and advanced-aged wild-type mice (30 months), we found that the levels of an astrocytic marker, glial fibrillary acidic protein, progressively increased after 18 months of age, which preceded the decreases of the synaptic marker PSD-95. Hippocampal long-term potentiation was also suppressed in an age-dependent manner, where significant deficits were observed after 24 months of age. Fear conditioning tests demonstrated that associative memory in the context and cued conditions was decreased starting at the ages of 18 and 30 months, respectively. When the mice were tested on hidden platform water maze, spatial learning memory was significantly impaired after 24 months of age. Importantly, subacute treatment with the anti-inflammatory drug ibuprofen suppressed astrocyte activation and restored synaptic plasticity and memory function in advanced-aged mice. These results support the critical contribution of aging-related inflammatory responses to hippocampal-dependent cognitive function and synaptic plasticity, in particular during advanced aging. Our findings provide strong evidence that suppression of neuroinflammation could be a promising treatment strategy to preserve cognition during aging.

To boost or to CRUNCH? Effect of effortful encoding on episodic memory in older adults is dependent on executive functioning

It is essential to develop effective interventions aimed at ameliorating age-related cognitive decline. Previous studies found that effortful encoding benefits episodic memory in older adults. However, to date it is unclear whether this benefit is different for individuals with strong versus weak executive functioning (EF). Fifty-one older adults were recruited and divided into low (N = 26) and high (N = 25) functioning groups, based on their EF capacity. All participants performed a semantic and a perceptual incidental encoding task. Each encoding task was performed under four difficulty levels to establish different effort levels. Encoding was followed by a recognition task. Results showed that the high EF group benefitted from increased effort in both tasks. However, the low EF group only showed a beneficial effect under low levels of effort. Results are consistent with the Compensation-Related Utilization of Neural Circuits Hypothesis (CRUNCH) and suggest that future research directed at developing efficient memory strategies to reduce negative cognitive aging effects should take individual cognitive differences among older adults into account, such as differences in EF.

Effet paradoxal du vieillissement sur des tâches de mémoire prospective time-based en situation de laboratoire et en milieu naturel : Rôle des fonctions exécutives

The current study investigates the specific role of three executive functions in the explanation of performance variability on laboratory and naturalistic time-based prospective memory tasks in aging. Ninety people aged 18 to 80 years performed three executive tasks assessing inhibition, flexibility and updating, one laboratory time-based task and one naturalistic time-based task. The results indicate that age has a negative impact on the laboratory time-based task and a positive impact on the naturalistic task. The mediation analysis shows that inhibition and flexibility operate as a mediator in the negative relationship between age and the laboratory time-based task. Additionally, the hierarchical regression analyses show that, after controlling for age, none of the executive functions evaluated is predictive of performance of the naturalistic time-based task. Overall, these results seem to suggest that different cognitive processes underlie the performance on naturalistic and on laboratory time-based tasks. Future studies should confirm these results.

Using Cognitive Screening Tests in Audiology

PURPOSE

The population of the United States is aging. Those older adults are living longer than ever and have an increased desire for social participation. As a result, audiologists are likely to see an increased demand for service by older clients whose communication difficulty is caused by a combination of hearing loss and cognitive impairment. For these individuals, early detection of mild cognitive impairment is critical for providing timely medical intervention and social support.

METHOD

This tutorial provides information about cognition of older adults, mild cognitive impairment, and cognitive screening tests, with the purpose of assisting audiologists in identifying and appropriately referring potential cases of cognitive impairment.

RESULTS

Topics addressed also include how to administer cognitive screening tests on individuals with hearing loss, how to use test results in audiology practice, and the potential of using cognitive screening tests for evaluating the benefit of clinical interventions.

CONCLUSIONS

As health care professionals who serve the aging population, audiologists are likely to encounter cases of undiagnosed cognitive impairment. In order to provide timely referral for medical assistance as well as an optimized individual outcome of audiologic interventions, audiologists should be trained to recognize an abnormality in older clients' cognitive status.

Memory performance is related to the cortisol awakening response in older people, but not to the diurnal cortisol slope

There are large individual differences in age-related cognitive decline. Hypothalamic-pituitary-adrenal axis (HPA-axis) functioning has been suggested as one of the mechanisms underlying these differences. This study aimed to investigate the relationships between the diurnal cortisol cycle, measured as the cortisol awakening response (CAR), and the diurnal cortisol slope (DCS) and the memory performance of healthy older people. To do so, we assessed the verbal, visual, and working memory performance of 64 participants (32 men) from 57 to 76 years old who also provided 14 saliva samples on two consecutive weekdays to determine their diurnal cortisol cycle. The CAR was linearly and negatively associated with verbal (significantly) and visual (marginally) memory domains, but not with working memory. Sex did not moderate these relationships. Furthermore, no associations were found between the DCS and any of the three memory domains assessed. Our results indicate that the two components of the diurnal cortisol cycle have different relationships with memory performance, with the CAR being more relevant than DCS in understanding the link from HPA-axis activity and regulation to different types of memory. These results suggest that the CAR is related to memory domains dependent on hippocampal functioning (i.e., declarative memory), but not to those that are more dependent on prefrontal cortex functioning (i.e., working memory).

Dominant hemisphere functional networks compensate for structural connectivity loss to preserve phonological retrieval with aging

INTRODUCTION

Loss of hemispheric asymmetry during cognitive tasks has been previously demonstrated in the literature. In the context of language, increased right hemisphere activation is observed with aging. Whether this relates to compensation to preserve cognitive function or dedifferentiation implying loss of hemispheric specificity without functional consequence, remains unclear.

METHODS

With a multifaceted approach, integrating structural and functional imaging data during a word retrieval task, in a group of younger and older adults with equivalent cognitive performance, we aimed to establish whether interactions between hemispheres or reorganization of dominant hemisphere networks preserve function. We examined functional and structural connectivity on data from our previously published functional activation study. Functional connectivity was measured using psychophysiological interactions analysis from the left inferior frontal gyrus (LIFG) and the left insula (LINS), based on published literature, and the right inferior frontal gyrus (RIFG) based on our previous study.

RESULTS

Although RIFG showed increased activation, its connectivity decreased with age. Meanwhile, LIFG and LINS connected more bilaterally in the older adults. White matter integrity, measured by fractional anisotropy (FA) from diffusion tensor imaging, decreased significantly in the older group. Importantly, LINS functional connectivity to LIFG correlated inversely with FA.

CONCLUSIONS

We demonstrate that left hemispheric language areas show higher functional connectivity in older adults with intact behavioral performance, and thus, may have a role in preserving function. The inverse correlation of functional and structural connectivity with age is in keeping with emerging literature and merits further investigation with tractography studies and in other cognitive domains.

Central role for NMDA receptors in redox mediated impairment of synaptic function during aging and Alzheimer's disease

Increased human longevity has magnified the negative impact that aging can have on cognitive integrity of older individuals experiencing some decline in cognitive function. Approximately 30% of the elderly will have cognitive problems that influence their independence. Impaired executive function and memory performance are observed in normal aging and yet can be an early sign of a progressive cognitive impairment of Alzheimer's disease (AD), the most common form of dementia. Brain regions that are vulnerable to aging exhibit the earliest pathology of AD. Senescent synaptic function is observed as a shift in Ca²⁺-dependent synaptic plasticity and similar mechanisms are thought to contribute to the early cognitive deficits associated with AD. In the case of aging, intracellular redox state mediates a shift in Ca²⁺ regulation including N-methyl-d-aspartate (NMDA) receptor hypofunction and increased Ca²⁺ release from intracellular stores to alter synaptic plasticity. AD can interact with these aging processes such that molecules linked to AD, β-amyloid (Aβ) and mutated presenilin 1 (PS1), can also degrade NMDA receptor function, promote Ca²⁺ release from intracellular stores, and may increase oxidative stress. Thus, age is one of the most important predictors of AD and brain aging likely contributes to the onset of AD. The focus of this review article is to provide an update on mechanisms that contribute to the senescent synapse and possible interactions with AD-related molecules, with special emphasis on regulation of NMDA receptors.

Association between handgrip strength and cognitive impairment in elderly Koreans: a population-based cross-sectional study

[Purpose] The purpose of this study was to investigate the association between handgrip strength and mild cognitive impairment in elderly adults. [Subjects] Study participants included 2,982 adults (1,366 males and 1,616 females), aged 65 years or older. [Methods] This population-based cross-sectional study used the baseline database from the Korean Longitudinal Study of Ageing. [Results] The odds ratio for mild cognitive impairment showed a significant linear decrease in relation to the quartile of handgrip strength, independent of potential covariates, in both men and women. Moreover, after excluding incident cases of mild cognitive impairment, the results showed that greater handgrip strength was associated with higher cognitive function scores in the elderly. [Conclusion] The findings presented here suggest that handgrip strength is associated with a risk of mild cognitive impairment in the Korean elderly. Moreover, greater handgrip strength is associated with higher cognitive function in cognitively normal elderly individuals.

Longitudinal Changes in Familiarity, Free and Cued Odor Identification, and Edibility Judgments for Odors in Aging Individuals

This longitudinal study investigated changes in olfaction as assessed by a set of tasks requiring different aspects of semantic information in normal aging individuals. Using 16 odorous items from a standardized olfactory test, the Scandinavian Odor Identification Test, 107 middle aged and older adults were assessed up to three times over a period of 6.5 years, requesting them to rate familiarity and edibility for each odorous item before identifying it with or without presenting verbal cues. Using linear mixed models, the longitudinal analyses revealed significant correlations between all olfactory measures. Furthermore, we found an almost parallel age-related decline in all olfactory tasks, although free identification performance indicated a trend toward faster decline with age. Women showed less decline compared with men, in particular for edibility judgments. The results corroborate earlier cross-sectional findings showing significant correlations between the olfactory tasks. In the present study of healthy middle-aged and older adults, we found a parallel longitudinal decline across different tests of olfaction.

Neural correlates of successful memory retrieval in aging: Do executive functioning and task difficulty matter?

The current experiment aimed to explore age differences in brain activity associated with successful memory retrieval in older adults with different levels of executive functioning, at different levels of task demand. Memory performance and fMRI activity during a recognition task were compared between a young group and two older groups characterized by a low (old-low group) vs. high (old-high group) level of executive functioning. Participants first encoded pictures, presented once (Hard condition) or twice (Easy condition), and then completed a recognition memory task. Old-low adults had poorer memory performance than the two other groups, which did not differ, in both levels of task demands. In the Easy condition, even though older adults demonstrated reduced activity compared to young adults in several regions, they also showed additional activations in the right superior frontal gyrus and right parietal lobule (positively correlated to memory accuracy) for the old-high group and in the right precuneus (negatively correlated to memory accuracy), right anterior cingulate gyrus and right supramarginal gyrus for the old-low group. In the Hard condition, some regions were also more activated in the young group than in the older groups. Vice versa, old-high participants demonstrated more activity than either the young or the old-low group in the right frontal gyrus, associated with more accurate memory performance, and in the left frontal gyrus. In sum, the present study clearly showed that age differences in the neural correlates of retrieval success were modulated by task difficulty, as suggested by the CRUNCH model, but also by interindividual variability, in particular regarding executive functioning.

Experienced stress produces inhibitory deficits in old adults' Flanker task performance: First evidence for lifetime stress effects beyond memory

Studies regarding aged individuals' performance on the Flanker task differ with respect to reporting impaired or intact executive control. Past work has explained this discrepancy by hypothesising that elderly individuals use increased top-down control mechanisms advantageous to Flanker performance. This study investigated this mechanism, focussing on cumulative experienced stress as a factor that may impact on its execution, thereby leading to impaired performance. Thirty elderly and thirty young participants completed a version of the Flanker task paired with electroencephalographic recordings of the alpha frequency, whose increased synchronisation indexes inhibitory processes. Among high stress elderly individuals, findings revealed a general slowing of reaction times for congruent and incongruent stimuli, which correlated with alpha desynchronisation for both stimulus categories. Results found high performing (low stress) elderly revealed neither a behavioural nor electrophysiological difference compared to young participants. Therefore, rather than impacting on top-down compensatory mechanisms, findings indicate that stress may affect elderly participants' inhibitory control in attentional and sensorimotor domains.

Episodic memory in normal aging and Alzheimer disease: Insights from imaging and behavioral studies

Age-related cognitive changes often include difficulties in retrieving memories, particularly those that rely on personal experiences within their temporal and spatial contexts (i.e., episodic memories). This decline may vary depending on the studied phase (i.e., encoding, storage or retrieval), according to inter-individual differences, and whether we are talking about normal or pathological (e.g., Alzheimer disease; AD) aging. Such cognitive changes are associated with different structural and functional alterations in the human neural network that underpins episodic memory. The prefrontal cortex is the first structure to be affected by age, followed by the medial temporal lobe (MTL), the parietal cortex and the cerebellum. In AD, however, the modifications occur mainly in the MTL (hippocampus and adjacent structures) before spreading to the neocortex. In this review, we will present results that attempt to characterize normal and pathological cognitive aging at multiple levels by integrating structural, behavioral, inter-individual and neuroimaging measures of episodic memory.