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

Better together: Left and right hemisphere engagement to reduce age-related memory loss

Episodic memory is a cognitive function that appears more susceptible than others to the effects of aging. The main aim of this study is to investigate if the magnitude of functional hemispheric lateralization during episodic memory test was positively correlated with memory performance, proving the presence of a beneficial pattern of neural processing in high-performing older adults but not in low-performing participants. We have applied anodal transcranial Direct Current Stimulation (tDCS) or sham stimulation over left and right hemisphere in a group of young subjects and in high-performing and low-performing older participants during an experimental verbal episodic memory task. Remarkably, young individuals and high-performing older adults exhibited similar performances on episodic memory tasks and both groups showed symmetrical recruitment of left and right areas during memory retrieval. In contrast, low-performing older adults, who obtained lower scores on the memory tasks, demonstrated a greater engagement of the left hemisphere during verbal memory task. Furthermore, structural equation model was performed for analyzing the interrelations between the index of interhemispheric asymmetry and several neuropsychological domains. We found that the bilateral engagement of dorsolateral prefrontal cortex and parietal cortex regions had a direct correlation with memory and executive functions evaluated as latent constructs. These findings drew attention to brain maintenance hypothesis. The potential of neurostimulation in cognitive enhancement is particularly promising to prevent memory loss during aging.

Lifelong bilingualism and neural reserve against Alzheimer's disease: a review of findings and potential mechanisms

Alzheimer's disease (AD) is a progressive brain disorder that initially affects medial temporal lobe circuitry and memory functions. Current drug treatments have only modest effects on the symptomatic course of the disease. In contrast, a growing body of evidence suggests that lifelong bilingualism may delay the onset of clinical AD symptoms by several years. The purpose of the present review is to summarize evidence for bilingualism as a reserve variable against AD and discuss potential underlying neurocognitive mechanisms. Evidence is reviewed suggesting that bilingualism may delay clinical AD symptoms by protecting frontostriatal and frontoparietal executive control circuitry rather than medial temporal lobe memory circuitry. Cellular and molecular mechanisms that may contribute to bilingual cognitive reserve effects are discussed, including those that may affect neuronal metabolic functions, dynamic neuronal-glial interactions, vascular factors, myelin structure and neurochemical signaling. Future studies that may test some of these potential mechanisms of bilingual CR effects are proposed.

Cognitive function in a general population of men and women: a cross sectional study in the European Investigation of Cancer-Norfolk cohort (EPIC-Norfolk)

Background

Although ageing is strongly associated with cognitive decline, a wide range of cognitive ability is observed in older populations with varying rates of change across different cognitive domains.

Methods

Cognitive function was measured as part of the third health examination of the European Prospective Investigation of Cancer in Norfolk (EPIC-Norfolk 3) between 2006 and 2011 (including measures from the pilot phase from 2004 to 2006). This was done using a battery consisting of seven previously validated cognitive function tests assessing both global function and specific domains. The battery included a shortened version of the Extended Mental State Exam (SF-EMSE); letter cancellation task; Hopkins Verbal Learning Test (HVLT); Cambridge Neuropsychological Test Automated Battery Paired Associates Learning Test (CANTAB-PAL); Visual Sensitivity Test (VST); Shortened version of the National Adult Reading Test (Short-NART) and a task to test for prospective memory. We report the distribution of cognitive function in different cognitive domains by age and sex and compare the utility of a number of assessment tests in a general population of older men and women.

Results

Cognitive test data were available for 8585 men and women taking part in EPIC-Norfolk 3. Increasing age was generally associated with declining mean cognitive function, but there was a wide range observed within each age group as well as variability across different cognitive domains. Some sex differences were also observed.

Conclusion

Descriptive data are presented for this general population sample of older men and women. There is a wide range of cognitive performance seen in this population. Though average performance declines with age, there is large individual variability across different cognitive domains. These variations may provide insights into the determinants of cognitive function in later life.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2318-14-142) contains supplementary material, which is available to authorized users.

Life experience and demographic influences on cognitive function in older adults

OBJECTIVE

We examined the influence of a broad spectrum of life experiences on longitudinal cognitive trajectories in a demographically diverse sample of older adults.

METHOD

Participants were 333 educationally, ethnically, and cognitively diverse older adults enrolled in a longitudinal aging study. Mixed-effects regression was used to measure baseline status in episodic memory, executive functioning, and semantic memory and change in a global cognition factor defined by change in these 3 domain-specific measures. We examined effects of life experience variables (literacy, childhood socioeconomic status, morphometric measures of physical development, life course physical and recreational activity) on longitudinal cognitive trajectories, covarying for age, apolipoprotein E (APOE) genotype and demographics (education, ethnicity, language).

RESULTS

Non-Latino Whites had higher baseline cognition, but life experience variables attenuated ethnic differences in cognitive scores. Age, literacy, childhood socioeconomic status, and physical activity significantly influenced baseline cognition. Age, APOE ε4, and decline in intellectually and socially stimulating recreational activity from mid to late life were independently associated with increased late life cognitive decline. Higher literacy and late life recreational activity were associated with less decline. Literacy had similar effects for English and Spanish readers/speakers. Bilingual English and Spanish speakers did not differ from English Speakers in cognitive performance.

CONCLUSIONS

Life experience variables, especially literacy level, were strongly related to baseline cognition and substantially attenuated effects of race/ethnicity and education. Cognitive change was best explained by age, APOE ε4, literacy, and current recreational activities. Literacy had robust associations with baseline cognition and cognitive change in both English and Spanish speakers.

Quantity and structure of word knowledge across adulthood

Cross-sectional and longitudinal data from moderately large samples of healthy adults confirmed prior findings of age-related declines in measures of the quantity of word knowledge beginning around age 65. Additional analyses were carried out to investigate the interrelations of different types of vocabulary knowledge at various periods in adulthood. Although the organizational structures were similar in adults of different ages, scores on tests with different formats had weaker relations to a higher-order vocabulary construct beginning when adults were in their 60's. The within-person dispersion among different vocabulary test scores was also greater after about 65 years of age. The discovery of quantitative decreases in amount of knowledge occurring at about the same age as qualitative shifts in the structure of knowledge raises the possibility that the two types of changes may be causally linked.

A low cortisol response to acute stress is related to worse basal memory performance in older people

Age-related memory decline has been associated with a faulty regulation of the hypothalamus-pituitary-adrenal axis (HPA-axis). The aim of this study was to investigate whether the magnitude of the stress-induced cortisol increase is related to memory performance when memory is measured in non-stressful conditions. To do so, declarative and working memory performance were measured in 31 men and 35 women between 55 and 77 years of age. On a different day, the magnitude of their cortisol response to acute psychosocial stress was measured. The relationship between the cortisol response and memory performance was U shaped: a low cortisol response to stress was related to poorer declarative and working memory performance, whereas those who did not increase their cortisol levels and those who had the largest cortisol increase had better declarative and working memory capabilities. Sex did not moderate these relationships. These results suggest that a low cortisol response to stress could reflect a defective HPA-axis response to stressors that is accompanied by poorer memory performance. Conversely, a high cortisol response seems to reflect a correct functioning of the HPA-axis and may protect against memory deficits in the later stages of human life.

Preserved fine-tuning of face perception and memory: evidence from the own-race bias in high- and low-performing older adults

Previous research suggests specific deficits in face perception and memory in older adults, which could reflect a dedifferentiation in the context of a general broadening of cognitive architecture with advanced age. Such dedifferentiation could manifest in a less specialized face processing system. A promising tool to investigate the fine-tuning of face processing in older age is the own-race bias (ORB), a phenomenon reflecting more accurate memory for own-relative to other-race faces, which is related to an expertise-based specialization of early perceptual stages. To investigate whether poor face memory in older age is accompanied by reduced expertise-based specialization of face processing, we assessed event-related brain potential correlates of the ORB in high- vs. low-performing older adults (mean age = 69 years; N = 24 per group). Intriguingly, both older groups demonstrated an equivalent pattern of a behavioral ORB, and a parallel increase in N170 for other-race faces, reflecting less efficient early perceptual processing for this face category. Group differences only emerged independent of face ethnicity: whereas low-performers exhibited a right-lateralized N170, high-performers showed a more bilateral response. This finding may suggest a compensatory mechanism counteracting age-related decline in face perception enabling more efficient encoding into memory in high performers. Overall, our results demonstrate that even a less efficient face processing system in older adults can exhibit preserved expertise-related specialization toward own-race faces.

Cortical Amyloid Beta in Cognitively Normal Elderly Adults is Associated with Decreased Network Efficiency within the Cerebro-Cerebellar System

BACKGROUND

Deposition of cortical amyloid beta (Aβ) is a correlate of aging and a risk factor for Alzheimer disease (AD). While several higher order cognitive processes involve functional interactions between cortex and cerebellum, this study aims to investigate effects of cortical Aβ deposition on coupling within the cerebro-cerebellar system.

METHODS

We included 15 healthy elderly subjects with normal cognitive performance as assessed by neuropsychological testing. Cortical Aβ was quantified using (11)carbon-labeled Pittsburgh compound B positron-emission-tomography late frame signals. Volumes of brain structures were assessed by applying an automated parcelation algorithm to three dimensional magnetization-prepared rapid gradient-echo T1-weighted images. Basal functional network activity within the cerebro-cerebellar system was assessed using blood-oxygen-level dependent resting state functional magnetic resonance imaging at the high field strength of 7 T for measuring coupling between cerebellar seeds and cerebral gray matter. A bivariate regression approach was applied for identification of brain regions with significant effects of individual cortical Aβ load on coupling.

RESULTS

Consistent with earlier reports, a significant degree of positive and negative coupling could be observed between cerebellar seeds and cerebral voxels. Significant positive effects of cortical Aβ load on cerebro-cerebellar coupling resulted for cerebral brain regions located in inferior temporal lobe, prefrontal cortex, hippocampus, parahippocampal gyrus, and thalamus.

CONCLUSION

Our findings indicate that brain amyloidosis in cognitively normal elderly subjects is associated with decreased network efficiency within the cerebro-cerebellar system. While the identified cerebral regions are consistent with established patterns of increased sensitivity for Aβ-associated neurodegeneration, additional studies are needed to elucidate the relationship between dysfunction of the cerebro-cerebellar system and risk for AD.

Memory deficits in aging and neurological diseases

Memory is central to our ability to perform daily life activities and correctly function in society. Improvements in public health and medical treatment for a variety of diseases have resulted in longer life spans; however, age-related memory impairments have been significant sources of morbidity. Loss in memory function is not only associated with aging population but is also a feature of neurodegenerative diseases such as Alzheimer's disease and other psychiatric and neurological disorders. Here, we focus on current understanding of the impact of normal aging on memory and what is known about its mechanisms, and further review pathological mechanisms behind the cause of dementia in Alzheimer's disease. Finally, we discuss schizophrenia and look into abnormalities in circuit function and neurotransmitter systems that contribute to memory impairment in this illness.

Identifying Mobility Types in Cognitively Heterogeneous Older Adults Based on GPS-Tracking: What Discriminates Best?

Heterogeneity in older adults' mobility and its correlates have rarely been investigated based on objective mobility data and in samples including cognitively impaired individuals. We analyzed mobility profiles within a cognitively heterogeneous sample of N = 257 older adults from Israel and Germany based on GPS tracking technology. Participants were aged between 59 and 91 years (M = 72.9; SD = 6.4) and were either cognitively healthy (CH, n = 146), mildly cognitively impaired (MCI, n = 76), or diagnosed with an early-stage dementia of the Alzheimer's type (DAT, n = 35). Based on cluster analysis, we identified three mobility types ("Mobility restricted," "Outdoor oriented," "Walkers"), which could be predicted based on socio-demographic indicators, activity, health, and cognitive impairment status using discriminant analysis. Particularly demented individuals and persons with worse health exhibited restrictions in mobility. Our findings contribute to a better understanding of heterogeneity in mobility in old age.

Correlation between visual acuity and cognitive functions

A possible association between visual acuity (VA) and dementia was investigated in 2716 subjects who were aged between 53 and 102 at first visit and had varying degrees of dementia. Better VA was found to be significantly correlated with a lower dementia level (person coefficient range 0.146-0.261 over 10 years of follow-up, all correlations are significant, p<0.0001) as well as with a higher global cognitive score (person coefficient range -0.254 to -0.318 over 10 years of follow-up, all correlations are significant, p<0.0001), a grade encompassing 19 different cognitive tests. This correlation remained significant after adjustment for age, years of education, gender, use of ophthalmic drugs and years of follow-up.

Lifelong bilingualism contributes to cognitive reserve against white matter integrity declines in aging

Recent evidence suggests that lifelong bilingualism may contribute to cognitive reserve (CR) in normal aging. However, there is currently no neuroimaging evidence to suggest that lifelong bilinguals can retain normal cognitive functioning in the face of age-related neurodegeneration. Here we explored this issue by comparing white matter (WM) integrity and gray matter (GM) volumetric patterns of older adult lifelong bilinguals (N=20) and monolinguals (N=20). The groups were matched on a range of relevant cognitive test scores and on the established CR variables of education, socioeconomic status and intelligence. Participants underwent high-resolution structural imaging for assessment of GM volume and diffusion tensor imaging (DTI) for assessment of WM integrity. Results indicated significantly lower microstructural integrity in the bilingual group in several WM tracts. In particular, compared to their monolingual peers, the bilingual group showed lower fractional anisotropy and/or higher radial diffusivity in the inferior longitudinal fasciculus/inferior fronto-occipital fasciculus bilaterally, the fornix, and multiple portions of the corpus callosum. There were no group differences in GM volume. Our results suggest that lifelong bilingualism contributes to CR against WM integrity declines in aging.

Gray-matter macrostructure in cognitively healthy older persons: associations with age and cognition

A deeper understanding of brain macrostructure and its associations with cognition in persons who are considered cognitively healthy is critical to the early detection of persons at risk of developing dementia. Few studies have examined the associations of all three gray-matter macrostructural brain indices (volume, thickness, surface area) with age and cognition, in the same persons who are over the age of 65 and do not have cognitive impairment. We performed automated morphometric reconstruction of total gray matter, cortical gray matter, subcortical gray matter and 84 individual regions in 186 persons (60 % over the age of 80) without cognitive impairment. Morphometric measures were scaled and expressed as difference per decade of age and an adjusted score was created to identify those regions in which there was greater atrophy per decade of age compared to cortical or subcortical brain averages. The results showed that there is substantial total volume loss and cortical thinning in cognitively healthy older persons. Thinning was more widespread than volume loss, but volume loss, particularly in temporoparietal and hippocampal regions, was more strongly associated with cognition.

Brain characteristics of individuals resisting age-related cognitive decline over two decades

Some elderly appear to resist age-related decline in cognitive functions, but the neural correlates of successful cognitive aging are not well known. Here, older human participants from a longitudinal study were classified as successful or average relative to the mean attrition-corrected cognitive development across 15-20 years in a population-based sample (n = 1561). Fifty-one successful elderly and 51 age-matched average elderly (mean age: 68.8 years) underwent functional magnetic resonance imaging while performing an episodic memory face-name paired-associates task. Successful older participants had higher BOLD signal during encoding than average participants, notably in the bilateral PFC and the left hippocampus (HC). The HC activation of the average, but not the successful, older group was lower than that of a young reference group (n = 45, mean age: 35.3 years). HC activation was correlated with task performance, thus likely contributing to the superior memory performance of successful older participants. The frontal BOLD response pattern might reflect individual differences present from young age. Additional analyses confirmed that both the initial cognitive level and the slope of cognitive change across the longitudinal measurement period contributed to the observed group differences in BOLD signal. Further, the differences between the older groups could not be accounted for by differences in brain structure. The current results suggest that one mechanism behind successful cognitive aging might be preservation of HC function combined with a high frontal responsivity. These findings highlight sources for heterogeneity in cognitive aging and may hold useful information for cognitive intervention studies.

Diversity, dispersion and inconsistency of reaction time measures: effects of age and task complexity

BACKGROUND AND AIMS

Performance variability of reaction time is regarded as an important parameter for cognitive functioning with aging. We investigated three types of variability, diversity (or variability between persons), dispersion (variability across trials within one task) and inconsistency (variability across testing occasions), while distinguishing between decision time and movement time and evaluating performance across comparable complexity levels.

METHODS

A single stratified reaction time test based on tasks with increasing complexity was used to evaluate inter- and intra-performance variability of 27 older (age 75+/-5 years) and 27 younger (age 29+/-7 years) participants, subdividing reaction time into decision and movement components.

RESULTS

There were consistent age and complexity differences for all variability types in our sample. When controlling for processing speed, which was slower in the older group, variability across age groups and task complexity tended to diminish and a more complex picture emerged. The elderly group showed a higher diversity of all reaction time measures, except for movement time, and a higher dispersion of decision time. Task complexity significantly affected the diversity of movement and overall reaction times and the dispersion of all reaction time measures, except for movement time.

CONCLUSIONS

These results highlight the importance of variability in cognitive functioning; it may be an important phenomenon for study and a useful indicator for cognitive deterioration. The reaction time test we propose is easy to use and can be applied in clinical practice.

Visual object pattern separation varies in older adults

Young and nondemented older adults completed a visual object continuous recognition memory task in which some stimuli (lures) were similar but not identical to previously presented objects. The lures were hypothesized to result in increased interference and increased pattern separation demand. To examine variability in object pattern separation deficits, older adults were divided into impaired and unimpaired groups based on performance on a standardized serial list-learning task. Impaired older adults showed intact recognition memory, but were impaired relative to young and unimpaired older adults when identifying similar lure stimuli, demonstrating that object pattern separation varies in older adults.

Cognitive reserve moderates the association between hippocampal volume and episodic memory in middle age

Cognitive reserve is hypothesized to help people withstand greater brain pathology without manifesting clinical symptoms, and may be regarded as a preventive factor of dementia. It is unclear whether the effect of cognitive reserve is evident only among the older adults or after conversion to dementia, or if it can also be seen earlier in life before the prominent effects of cognitive aging become apparent. While finding a main effect of cognitive reserve on cognitive outcome may be consistent with the reserve hypothesis, in our view, it is unnecessary to invoke the idea of reserve if only a main effect is present. Rather, it is the interaction between a measure of reserve and a brain measure on cognitive outcome that is key for confirming that the effects of brain pathology affect people differently according to their cognitive reserve. We studied whether general cognitive ability at an average age of 20 years, as a direct measure of cognitive reserve, moderates the association between hippocampal volume and episodic memory performance in 494 middle-aged men ages 51 to 60. Whereas there was no statistically significant direct relationship between hippocampal volume and episodic memory performance in middle age, we found a statistically significant interaction such that there was a positive association between hippocampal volume and episodic memory only among people with lower general cognitive ability at age 20, i.e., lower levels of cognitive reserve. Our results provide support for the hypothesis that cognitive reserve moderates the relationship between brain structure and cognition in middle age, well before the onset of dementia.

The cortisol awakening response and memory performance in older men and women

The activity and regulation of the hypothalamus-pituitary-adrenal axis has been related to cognitive decline during aging. This study investigated whether the cortisol awakening response (CAR) is related to memory performance among older adults. The sample was composed of 88 participants (44 men and 44 women) from 55 to 77 years old. The memory assessment consisted of two tests measuring declarative memory (a paragraph recall test and a word list learning test) and two tests measuring working memory (a spatial span test and a spatial working memory test). Among those participants who showed the CAR on two consecutive days, we found that a greater CAR was related to poorer declarative memory performance in both men and women, and to better working memory performance only in men. The results of our study suggest that the relationship between CAR and memory performance is negative in men and women when memory performance is largely dependent on hippocampal functioning (i.e. declarative memory), and positive, but only in men, when memory performance is largely dependent on prefrontal cortex functioning (i.e. working memory).

Neural correlates of changes in a visual search task due to cognitive training in seniors

This study aimed to elucidate the underlying neural sources of near transfer after a multidomain cognitive training in older participants in a visual search task. Participants were randomly assigned to a social control, a no-contact control and a training group, receiving a 4-month paper-pencil and PC-based trainer guided cognitive intervention. All participants were tested in a before and after session with a conjunction visual search task. Performance and event-related potentials (ERPs) suggest that the cognitive training improved feature processing of the stimuli which was expressed in an increased rate of target detection compared to the control groups. This was paralleled by enhanced amplitudes of the frontal P2 in the ERP and by higher activation in lingual and parahippocampal brain areas which are discussed to support visual feature processing. Enhanced N1 and N2 potentials in the ERP for nontarget stimuli after cognitive training additionally suggest improved attention and subsequent processing of arrays which were not immediately recognized as targets. Possible test repetition effects were confined to processes of stimulus categorisation as suggested by the P3b potential. The results show neurocognitive plasticity in aging after a broad cognitive training and allow pinpointing the functional loci of effects induced by cognitive training.

Dynamic associations of change in physical activity and change in cognitive function: coordinated analyses of four longitudinal studies

The present study used a coordinated analyses approach to examine the association of physical activity and cognitive change in four longitudinal studies. A series of multilevel growth models with physical activity included both as a fixed (between-person) and time-varying (within-person) predictor of four domains of cognitive function (reasoning, memory, fluency, and semantic knowledge) was used. Baseline physical activity predicted fluency, reasoning and memory in two studies. However, there was a consistent pattern of positive relationships between time-specific changes in physical activity and time-specific changes in cognition, controlling for expected linear trajectories over time, across all four studies. This pattern was most evident for the domains of reasoning and fluency.

Memory aging and brain maintenance

Episodic memory and working memory decline with advancing age. Nevertheless, large-scale population-based studies document well-preserved memory functioning in some older individuals. The influential ‘reserve’ notion holds that individual differences in brain characteristics or in the manner people process tasks allow some individuals to cope better than others with brain pathology and hence show preserved memory performance. Here, we discuss a complementary concept, that of brain maintenance (or relative lack of brain pathology), and argue that it constitutes the primary determinant of successful memory aging. We discuss evidence for brain maintenance at different levels: cellular, neurochemical, gray- and white-matter integrity, and systems-level activation patterns. Various genetic and lifestyle factors support brain maintenance in aging and interventions may be designed to promote maintenance of brain structure and function in late life.

Associations between variability of risk factors and health outcomes in longitudinal studies

Many statistical methods have been developed that treat within-subject correlation that accompanies the clustering of subjects in longitudinal data settings as a nuisance parameter, with the focus of analytic interest being on mean outcome or profiles over time. However, there is evidence that in certain settings, underlying variability in subject measures may also be important in predicting future health outcomes of interest. Here, we develop a method for combining information from mean profiles and residual variance to assess associations with categorical outcomes in a joint modeling framework. We consider an application to relating word recall measures obtained over time to dementia onset from the Health and Retirement Survey.

Brain training in progress: a review of trainability in healthy seniors

The cognitive deterioration associated with aging is accompanied by structural alterations and loss of functionality of the frontostriatal dopamine system. The question arises how such deleterious cognitive effects could be countered. Brain training, currently highly popular among young and old alike, promises that users will improve on certain neurocognitive skills, and this has indeed been confirmed in a number of studies. Based on these results, it seems reasonable to expect beneficial effects of brain training in the elderly as well. A selective review of the existing literature suggests, however, that the results are neither robust nor consistent, and that transfer and sustained effects thus far appear limited. Based on this review, we argue for a series of elements that hold potential for progress in successful types of brain training: (1) including flexibility and novelty as features of the training, (2) focusing on a number of promising, yet largely unexplored domains, such as decision-making and memory strategy training, and (3) tailoring the training adaptively to the level and progress of the individual. We also emphasize the need for covariance-based MRI methods in linking structural and functional changes in the aging brain to individual differences in neurocognitive efficiency and trainability in order to further uncover the underlying mechanisms.

Effects of varying diagnostic criteria on prevalence of mild cognitive impairment in a community based sample

Mild cognitive impairment (MCI) is proposed to be a prodrome to dementia in some older adults. However, the presentation of MCI in the community can differ substantially from clinic-based samples. The aim of the current study is to demonstrate the effects of different operational definitions of MCI on prevalence estimates in community-dwelling older adults. A consecutive series of 200 participants aged 65 and over from the Adult Changes in Thought (ACT) community-based cohort were approached to undergo comprehensive neuropsychological and medical evaluation; 159 were included in the final analyses. Nondemented subjects were categorized using various diagnostic criteria for MCI. In a novel approach, neuropsychological test scores were evaluated using an individualized benchmark as a point of test comparison, as well as traditional methods that entail comparison to age-based normative data. Diagnostic criteria were further subdivided by severity of impairment (1.0 vs. 1.5 standard deviations [sd] below the benchmark) and extent of impairment (based on a single test or an average of tests within a cognitive domain). MCI prevalence rates in the sample were highly dependent on these diagnostic factors, and varied from 11% to 92% of the sample. Older groups tended to show higher prevalence rates, although this was not the case across all diagnostic schemes. The use of an individualized benchmark, less severe impairment cutoff, and impairment on only a single test all produced higher rates of MCI. Longitudinal follow-up will determine whether varying diagnostic criteria improves sensitivity and specificity of the MCI diagnosis as a predictor for dementia.

Association of grip strength with dementia in a Korean older population

BACKGROUND

Several studies have found that low grip strength is associated with dementia in Western populations. However, there have been few studies in Asian populations. This cross-sectional study aimed to examine whether grip strength is independently associated with dementia after controlling for other related factors in a Korean older population.

METHODS

One thousand thirty-eight community-dwelling older people aged 65 or over within a defined geographic area were screened for dementia. Data on grip strength, sit-to-stand score, body mass index (BMI), socio-demographic factors (age, gender, marital status, education), and medical conditions (diabetes, hypertension, heart disease, stroke) were collected. Dementia was diagnosed with the 10/66 dementia diagnostic algorithm.

RESULTS

Eleven percent of the participants were found to have dementia. After adjustment for other factors, grip strength (per 8-kg decrease) was independently associated with dementia (odds ratio, 1.59; 95% confidence interval, 1.19-2.14). Adjusted grip strength by BMI interaction terms showed marginal significance (p = 0.098); that is, older people with both reduced grip strength and low BMI were likely to be at higher risk for dementia.

CONCLUSIONS

Reduced grip strength was independently associated with dementia in a Korean older population. This association was partially influenced by BMI.

The contribution of set switching and working memory to sentence processing in older adults

This study evaluates the involvement of switching skills and working-memory capacity in auditory sentence processing in older adults. The authors examined 241 healthy participants, aged 55 to 88 years, who completed four neuropsychological tasks and two sentence-processing tasks. In addition to age and the expected contribution of working memory, switching ability, as measured by the number of perseverative errors on the Wisconsin Card Sorting Test, emerged as a strong predictor of performance on both sentence-processing tasks. Individuals with both low working-memory spans and more perseverative errors achieved the lowest accuracy scores. These findings are consistent with compensatory accounts of successful performance in older age.

Dissecting the age-related decline on spatial learning and memory tasks in rodent models: N-methyl-D-aspartate receptors and voltage-dependent Ca2+ channels in senescent synaptic plasticity

In humans, heterogeneity in the decline of hippocampal-dependent episodic memory is observed during aging. Rodents have been employed as models of age-related cognitive decline and the spatial water maze has been used to show variability in the emergence and extent of impaired hippocampal-dependent memory. Impairment in the consolidation of intermediate-term memory for rapidly acquired and flexible spatial information emerges early, in middle-age. As aging proceeds, deficits may broaden to include impaired incremental learning of a spatial reference memory. The extent and time course of impairment has been be linked to senescence of calcium (Ca²⁺) regulation and Ca²⁺-dependent synaptic plasticity mechanisms in region CA1. Specifically, aging is associated with altered function of N-methyl-D-aspartate receptors (NMDARs), voltage-dependent Ca²⁺ channels (VDCCs), and ryanodine receptors (RyRs) linked to intracellular Ca²⁺ stores (ICS). In young animals, NMDAR activation induces long-term potentiation of synaptic transmission (NMDAR-LTP), which is thought to mediate the rapid consolidation of intermediate-term memory. Oxidative stress, starting in middle-age, reduces NMDAR function. In addition, VDCCs and ICS can actively inhibit NMDAR-dependent LTP and oxidative stress enhances the role of VDCC and RyR-ICS in regulating synaptic plasticity. Blockade of L-type VDCCs promotes NMDAR-LTP and memory in older animals. Interestingly, pharmacological or genetic manipulations to reduce hippocampal NMDAR function readily impair memory consolidation or rapid learning, generally leaving incremental learning intact. Finally, evidence is mounting to indicate a role for VDCC-dependent synaptic plasticity in associative learning and the consolidation of remote memories. Thus, VDCC-dependent synaptic plasticity and extrahippocampal systems may contribute to incremental learning deficits observed with advanced aging.

Neuroanatomical substrates of age-related cognitive decline

There are many reports of relations between age and cognitive variables and of relations between age and variables representing different aspects of brain structure and a few reports of relations between brain structure variables and cognitive variables. These findings have sometimes led to inferences that the age-related brain changes cause the age-related cognitive changes. Although this conclusion may well be true, it is widely recognized that simple correlations are not sufficient to warrant causal conclusions, and other types of correlational information, such as mediation and correlations between longitudinal brain changes and longitudinal cognitive changes, also have limitations with respect to causal inferences. These issues are discussed, and the existing results on relations of regional volume, white matter hyperintensities, and diffusion tensor imaging measures of white matter integrity to age and to measures of cognitive functioning are reviewed. It is concluded that at the current time the evidence that these aspects of brain structure are neuroanatomical substrates of age-related cognitive decline is weak. The final section contains several suggestions concerning measurement and methodology that may lead to stronger conclusions in the future.

The association of serum oestradiol level, age, and education with cognitive performance in peri- and late postmenopausal women

OBJECTIVES

To evaluate whether healthy women show cognitive changes after menopause and whether the possible changes are oestrogen-, age- or education-dependent.

METHODS

Forty-eight women, 21 perimenopausal (aged 43-51 years) and 27 late postmenopausal (aged 59-71 years), participated in the study. Verbal and visuomotor functions, visuoconstructive skills, visual and verbal episodic memory as well as attention were evaluated.

RESULTS

Perimenopausal women performed better than postmenopausal women. Serum oestradiol (E(2)) level was included in the model in perimenopausal women only given the lack of endogenous oestrogen in postmenopausal women who were also not using hormone therapy (HT). In perimenopausal women, lower E(2) was associated with better visual episodic memory (p<.05), and older age was related to poorer verbal episodic memory (p<.05). In postmenopausal women, more education was associated with better performance in verbal and visuomotor functions, attention as well as verbal episodic memory (p<.05), older age was related to poorer performance in the visuoconstructive test and visual episodic memory (p<.05).

CONCLUSIONS

Perimenopausal women had better cognitive performance compared to late postmenopausal women. In perimenopausal women the effect of E(2) was minor. In both groups, age modified cognitive performance, but more so in postmenopausal women. Education did not have any effect on cognitive performance in perimenopausal women, whereas in postmenopausal women education exceeded age as a source of variation. Thus the relevance of education for better cognition was accentuated after menopause.

Using cognitive decline in novel trial designs for primary prevention and early disease-modifying therapy trials of Alzheimer's disease

BACKGROUND

Ideally putative disease-modifying therapies for Alzheimer's disease (AD) should be tested in patients who have minimal morbidity. Current barriers to such trials in early disease include the lack of disease-specific early biomarkers, insensitivity of quantitative cognitive outcome measures, and expensive trial designs requiring large sample sizes and long duration. This paper describes principles and progress towards a novel trial design that overcomes these problems, utilizing wide-scale cognitive performance screening to define pre-trial cognitive decline trajectories which can serve as trial outcome measures to assess AD disease-modifying efficacy.

METHODS

Theoretical principles important for the detection of intra-individual cognitive decline and a practical example are described.

RESULTS

Serial evaluations of community-based volunteers demonstrate how a screening tool method to detect subtle cognitive decline can predict in vivo amyloid pathology as a trigger for etiological evaluation. Trajectories of decline appear consistent over at least two years, suggesting they could be used as a trial inclusion criterion and ameliorable outcome measure together with other AD biomarkers. Informative trial durations could be 6-12 months, or extend to incorporate staggered random withdrawal or start designs, with as few as 20 individuals per treatment arm.

CONCLUSIONS

This trial methodology offers significant advantages over current AD trial designs, including treatment at earlier stages of disease, shorter trial duration, obviation of informed consent difficulties, smaller sample sizes, reduced cost and--given adequate screening programs--sufficient subjects for multiple simultaneous trials. Importantly, it allows the rapid evaluation of putative treatments that may only be efficacious in pre-dementia states.

Emerging perspectives in social neuroscience and neuroeconomics of aging

This article introduces the special issue of 'Social Cognitive and Affective Neuroscience' on Aging Research, and offers a broad conceptual and methodological framework for considering advances in life course research in social neuroscience and neuroeconomics. The authors highlight key areas of inquiry where aging research is raising new insights about how to conceptualize and examine critical questions about the links between cognition, emotion and motivation in social and economic behavior, as well as challenges that need to be addressed when taking a life course perspective in these fields. They also point to several emerging approaches that hold the potential for addressing these challenges, through bridging approaches from laboratory and population-based science, bridging inquiry across life stages and expanding measurement of core psychological phenotypes.

Neurocognitive variability in high-functioning individuals: implications for the practice of clinical neuropsychology

Knowledge of neurocognitive performance patterns of normal, healthy individuals is necessary, as clinicians may not always take into account normal intra-individual variability, demonstrated here in a sample of 20 healthy individuals with particularly high educational achievement (i.e., holding doctorate degrees). The data indicate that neurocognitive abilities are not equally distributed within a given individual. Some participants in the sample achieved some test scores at the intellectually disabled to borderline range but also some scores in the high average to superior range. The practice of deductive reasoning in clinical neuropsychology may be prone to false positive conclusions about neurocognitive functioning where base rates of neurocognitive impairments are low and pre-existing educational achievements are high.

Cognitive predictors of everyday functioning in older adults: results from the ACTIVE Cognitive Intervention Trial

OBJECTIVE

The present study sought to predict changes in everyday functioning using cognitive tests.

METHODS

Data from the Advanced Cognitive Training for Independent and Vital Elderly trial were used to examine the extent to which competence in different cognitive domains--memory, inductive reasoning, processing speed, and global mental status--predicts prospectively measured everyday functioning among older adults. Coefficients of determination for baseline levels and trajectories of everyday functioning were estimated using parallel process latent growth models.

RESULTS

Each cognitive domain independently predicts a significant proportion of the variance in baseline and trajectory change of everyday functioning, with inductive reasoning explaining the most variance (R2 = .175) in baseline functioning and memory explaining the most variance (R2 = .057) in changes in everyday functioning.

DISCUSSION

Inductive reasoning is an important determinant of current everyday functioning in community-dwelling older adults, suggesting that successful performance in daily tasks is critically dependent on executive cognitive function. On the other hand, baseline memory function is more important in determining change over time in everyday functioning, suggesting that some participants with low baseline memory function may reflect a subgroup with incipient progressive neurologic disease.

The role of diffusion tensor imaging in the study of cognitive aging

This chapter gives an overview of the role that diffusion tensor MRI (DTI) can play in the study of cognitive decline that is associated with advancing age. A brief overview of biological injury processes that impinge on the aging brain is provided, and their overall effect on the integrity of neural architecture is described. Cognitive decline associated with aging, and white matter connectivity degradation as a biological substrate for that decline, is then described. We then briefly describe the technology of DTI as a means for in vivo, non-invasive interrogation of white matter connectivity, and relate it to FLAIR, a more traditional MRI method for assessing white matter injury. We then survey the existing findings on relationships between aging-associated neuropathological processes and DTI measurements on one hand; and relationships between DTI measurements and late-life cognitive function on the other. We conclude with a summary of current research directions in relation to DTI studies of cognitive aging.

Neural specificity predicts fluid processing ability in older adults

We investigated whether individual differences in neural specificity-the distinctiveness of different neural representations-could explain individual differences in cognitive performance in older adults. Neural specificity was estimated based on how accurately multivariate pattern analysis identified neural activation patterns associated with specific experimental conditions. Neural specificity calculated from a same/different task on two categories of visual stimuli (faces and houses) significantly predicted performance on a range of fluid processing behavioral tasks (dot-comparison, digit-symbol, Trails-A, Trails-B, verbal-fluency) in older adults, whereas it did not correlate with a measure of crystallized knowledge (Shipley-vocabulary). In addition, the neural specificity measure accounted for 30% of the variance in a composite measure of fluid processing ability. These results are consistent with the hypothesis that loss of neural specificity, or dedifferentiation, contributes to reduced fluid processing ability in old age.

The effect of maintaining cognition on risk of disability and death

OBJECTIVES

To determine whether long-term maintenance of cognition is associated with health advantages such as lower mortality or incident disability in older adults.

DESIGN

Longitudinal cohort study.

SETTING

Community clinics at two sites.

PARTICIPANTS

Two thousand seven hundred thirty-three adults with a mean age of 74 at baseline and 80 at follow-up.

MEASUREMENTS

Cognitive function was assessed using the Modified Mini-Mental State Examination (3MS), a test of global cognition, at least two times. Three cognitive groups were defined based on 4-year participant-specific slopes (maintainers, slopes of >or=0; minor decliners, slopes <0 but no more than 1 standard deviation (SD) below the mean; major decliners, slopes >1 SD below the mean). Whether the cognitive groups differed in mortality and incident disability during the subsequent 3 years was determined.

RESULTS

Nine hundred eighty-four (36%) participants were maintainers, 1,314 (48%) were minor decliners, and 435 (16%) were major decliners. Maintainers had lower mortality (7% vs 14%, hazard ratio (HR)=0.48, 95% confidence interval (CI)=0.36-0.63) and incident disability (22% vs 29%, HR=0.74, 95% CI=0.62-0.89) than minor decliners. After adjustment for age, race, sex, education, apolipoprotein E epsilon4, depression, body mass index, stroke, hypertension, and diabetes mellitus, these differences remained. As expected, major decliners had greater mortality (20%) and incident disability (40%) than minor decliners.

CONCLUSION

A substantial proportion of older adults maintain cognitive function in their eighth and ninth decades of life. These older adults demonstrate lower risk of death and functional decline than those with minor cognitive decline, supporting the concept of "successful" cognitive aging.