Is retaining the youthful functional anatomy underlying speed of information processing a signature of successful cognitive ageing? An event-related fMRI study of inspection time performance

P3b correlates of inspection time

Both P3b and the inspection time (IT) are related with intelligence, yet the P3b correlates of IT are not well understood. This event-related potential study addressed this question by asking participants (N = 28) to perform an IT task. There were three IT conditions with different levels of discriminative stimulus duration, i.e., 33 ms, 67 ms, and 100 ms, and a control condition with no target presentation (0 ms condition). We also measured participants' processing speed with four Elementary Cognitive Tests (ECTs), including a Simple Reaction Time task (SRT), two Choice Reaction Time tasks (CRTs), and a Pattern Discrimination task (PD). Results revealed that an increase in P3b latency with longer duration of the discriminative stimulus. Moreover, the P3b latency was negatively correlated with the accuracy of the IT task in the 33 ms condition, but not evident in the 67 and 100 ms conditions. Furthermore, the P3b latency of the 33 ms condition was positively correlated with the RT of the SRT, but not related with the RTs of CRTs or PD. A significant main effect of duration on the amplitude of P1 was also found. We conclude that the present study provides the neurophysiological correlates of the IT task, and those who are able to accurately perceive and process very briefly presented stimuli have a higher speed of information process, reflected by the P3b latency, yet this relationship is more obvious in the most difficult condition. Combined, our results suggest that P3b is related with the closure of a perceptual epoch to form the neural representation of a stimulus, in support of the "context closure" hypothesis.

Cognitive Aging: How the Brain Ages?

Cognitive aging refers to the cognitive changes or functional decline that comes with age. The relation between aging and functional declines involves various aspects of cognition, including memory, attention, processing speed, and executive function. In this chapter, we have introduced several dimensions about cognitive aging trajectories. Meanwhile, we have reviewed the history of the study of cognitive aging and expatiated two trends that are particularly noteworthy in the effort to elucidate the process of aging. One is that the differences between components of mental abilities have become gradually specified. The other one is a growing interest in the neural process, which relates changes in the brain structure to age-related changes in cognition. Lastly, as the basis of cognitive function, brain structures and functions change during aging, and these changes are reflected in a corresponding decline in cognitive function. We have discussed the patterns of reorganization of various structural and functional aging processes of the brain and their relationship with cognitive function.

Separation of memory span and learning rate: Evidence from behavior and spontaneous brain activity in older adults

It is unclear how the ability to initially acquire information in a first learning trial relates to learning rate in subsequent repeated trials. The separation of memory span and learning rate is an important psychological dilemma that remains unaddressed. Given the potential effects of aging on memory and learning, this study investigated the separation of memory span and learning rate from behavior and spontaneous brain activity in older adults. We enrolled a total of 758 participants, including 707 healthy older adults and 51 mild cognitive impairment (MCI) patients. Sixty-five participants out of 707 completed resting-state functional magnetic resonance imaging (fMRI) scanning. Behaviorally, memory span and learning rate were not correlated with each other in the paired-associative learning test (PALT) but were negatively correlated in the auditory verbal learning test (AVLT). This indicated that the relationship between memory span and learning rate for item memory might be differentially affected by aging. Interaction analysis confirmed that these two capacities were differentially affected by test type (associative memory vs. item memory). Additionally, at three progressive brain activity indexes (ALFF, ReHo, and DC), the right brain regions (right inferior temporal gyrus and right middle frontal gyrus) were more negatively correlated with memory span, whereas, the left precuneus was more positively correlated with learning rate. Regarding pathological aging, none of the correlations between memory span and learning rate were significant in either PALT or AVLT in MCI. This study provides novel evidence for the dissociation of memory span and learning rate at behavioral and brain activity levels, which may have useful applications in detecting cognitive deficits or conducting cognitive interventions.

Cognitive reserve and brain maintenance in aging and dementia: An integrative review

This research is an integrative review of scientific evidence differentiating between cognitive reserve (CR) and brain maintenance concepts. Thus, we have examined how CR socio-behavioral proxies (i.e. education, occupational attainment, and leisure activities) may help to cope with age-related cognitive decline and negative consequences of brain pathology. We also analyze lifestyle factors associated with brain maintenance or the relative absence of change in neural resources over time. Medline and Web of Science databases were used for the bibliographic search in the last 20 years. Observational cohort studies were selected to analyze the effect of different CR proxies on cognitive decline, including dementia incidence, whereas studies employing functional neuroimaging (fMRI) were used to display the existence of compensation mechanisms. Besides, structural MRI studies were used to test the association between lifestyle factors and neural changes. Our findings suggest that education, leisure activities, and occupational activity are protective factors against cognitive decline and dementia. Moreover, functional neuroimaging studies have verified the existence of brain networks that may underlie CR. Therefore, CR may be expressed either through a more efficient utilization (neural reserve) of brain networks or the recruitment of additional brain regions (compensation). Finally, lifestyle factors such as abstaining from smoking, lower alcohol consumption, and physical activity contributed to brain maintenance and were associated with the preservation of cognitive function. Advances in multimodal neuroimaging studies, preferably longitudinal design, will allow a better understanding of the neural mechanisms associated with the prevention of cognitive decline and preservation of neural resources in aging.

Fronto-cerebellar connectivity mediating cognitive processing speed

Processing speed is an important construct in understanding cognition. This study was aimed to control task specificity for understanding the neural mechanisms underlying cognitive processing speed. Forty young adult subjects performed attention tasks of two modalities (auditory and visual) and two levels of task rules (compatible and incompatible). Block-design fMRI captured BOLD signals during the tasks. Thirteen regions of interest were defined with reference to publicly available activation maps for processing speed tasks. Cognitive speed was derived from task reaction times, which yielded six sets of connectivity measures. Mixed-effect LASSO regression revealed six significant paths suggestive of a cerebello-frontal network predicting the cognitive speed. Among them, three are long range (two fronto-cerebellar, one cerebello-frontal), and three are short range (fronto-frontal, cerebello-cerebellar, and cerebello-thalamic). The long-range connections are likely to relate to cognitive control, and the short-range connections relate to rule-based stimulus-response processes. The revealed neural network suggests that automaticity, acting on the task rules and interplaying with effortful top-down attentional control, accounts for cognitive speed.

Longitudinal Functional Brain Mapping in Supernormals

Prevention of age-related cognitive decline is an increasingly important topic. Recently, increased attention is being directed at understanding biological models of successful cognitive aging. Here, we examined resting-state brain regional low-frequency oscillations using functional magnetic resonance imaging in 19 older adults with excellent cognitive abilities (Supernormals), 28 older adults with normative cognition, 57 older adults with amnestic mild cognitive impairment, and 26 with Alzheimer's disease. We identified a "Supernormal map", a set of regions whose oscillations were resistant to the aging-associated neurodegenerative process, including the right fusiform gyrus, right middle frontal gyrus, right anterior cingulate cortex, left middle temporal gyrus, left precentral gyrus, and left orbitofrontal cortex. The map was unique to the Supernormals, differentiated this group from cognitive average-ager comparisons, and predicted a 1-year change in global cognition (indexed by the Montreal Cognitive Assessment scores, adjusted R2 = 0.68). The map was also correlated to Alzheimer's pathophysiological features (beta-amyloid/pTau ratio, adjusted R2 = 0.66) in participants with and without cognitive impairment. These findings in phenotypically successful cognitive agers suggest a divergent pattern of brain regions that may either reflect inherent neural integrity that contributes to Supernormals' cognitive success, or alternatively indicate adaptive reorganization to the demands of aging.

The Role of Cognitive Reserve in Alzheimer's Disease and Aging: A Multi-Modal Imaging Review

Comforts in modern society have generally been associated with longer survival rates, enabling individuals to reach advanced age as never before in history. With the increase in longevity, however, the incidence of neurodegenerative diseases, especially Alzheimer's disease, has also doubled. Nevertheless, most of the observed variance, in terms of time of clinical diagnosis and progression, often remains striking. Only recently, differences in the social, educational and occupational background of the individual, as proxies of cognitive reserve (CR), have been hypothesized to play a role in accounting for such discrepancies. CR is a well-established concept in literature; lots of studies have been conducted in trying to better understand its underlying neural substrates and associated biomarkers, resulting in an incredible amount of data being produced. Here, we aimed to summarize recent relevant published work addressing the issue, gathering evidence for the existence of a common path across research efforts that might ease future investigations by providing a general perspective on the actual state of the arts. An innovative model is hereby proposed, addressing the role of CR across structural and functional evidences, as well as the potential implementation of non-invasive brain stimulation techniques in the causal validation of such theoretical frame.

A Systematic Review for Functional Neuroimaging Studies of Cognitive Reserve Across the Cognitive Aging Spectrum

Objective

Cognitive reserve has been proposed to explain the discrepancy between clinical symptoms and the effects of aging or Alzheimer's pathology. Functional magnetic resonance imaging (fMRI) may help elucidate how neural reserve and compensation delay cognitive decline and identify brain regions associated with cognitive reserve. This systematic review evaluated neural correlates of cognitive reserve via fMRI (resting-state and task-related) studies across the cognitive aging spectrum (i.e., normal cognition, mild cognitive impairment, and Alzheimer's disease).

Method

This review examined published articles up to March 2017. There were 13 cross-sectional observational studies that met the inclusion criteria, including relevance to cognitive reserve, subjects 60 years or older with normal cognition, mild cognitive impairment, and/or Alzheimer's disease, at least one quantitative measure of cognitive reserve, and fMRI as the imaging modality. Quality assessment of included studies was conducted using the Newcastle-Ottawa Scale adapted for cross-sectional studies.

Results

Across the cognitive aging spectrum, medial temporal regions and an anterior or posterior cingulate cortex-seeded default mode network were associated with neural reserve. Frontal regions and the dorsal attentional network were related to neural compensation. Compared to neural reserve, neural compensation was more common in mild cognitive impairment and Alzheimer's disease.

Conclusions

Neural reserve and compensation both support cognitive reserve, with compensation more common in later stages of the cognitive aging spectrum. Longitudinal and intervention studies are needed to investigate changes between neural reserve and compensation during the transition between clinical stages, and to explore the causal relationship between cognitive reserve and potential neural substrates.

Successful Memory Aging

For more than 50 years, psychologists, gerontologists, and, more recently, neuroscientists have considered the possibility of successful aging. How to define successful aging remains debated, but well-preserved age-sensitive cognitive functions, like episodic memory, is an often-suggested criterion. Evidence for successful memory aging comes from cross-sectional and longitudinal studies showing that some older individuals display high and stable levels of performance. Successful memory aging may be accomplished via multiple paths. One path is through brain maintenance, or relative lack of age-related brain pathology. Through another path, successful memory aging can be accomplished despite brain pathology by means of efficient compensatory and strategic processes. Genetic, epigenetic, and lifestyle factors influence memory aging via both paths. Some of these factors can be promoted throughout the life course, which, at the individual as well as the societal level, can positively impact successful memory aging.

Functional Brain Activity Changes after 4 Weeks Supplementation with a Multi-Vitamin/Mineral Combination: A Randomized, Double-Blind, Placebo-Controlled Trial Exploring Functional Magnetic Resonance Imaging and Steady-State Visual Evoked Potentials during Working Memory

This study explored the neurocognitive effects of 4 weeks daily supplementation with a multi-vitamin and -mineral combination (MVM) in healthy adults (aged 18–40 years). Using a randomized, double-blind, placebo-controlled design, participants underwent assessments of brain activity using functional Magnetic Resonance Imaging (fMRI; n = 32, 16 females) and Steady-State Visual Evoked Potential recordings (SSVEP; n = 39, 20 females) during working memory and continuous performance tasks at baseline and following 4 weeks of active MVM treatment or placebo. There were several treatment-related effects suggestive of changes in functional brain activity associated with MVM administration. SSVEP data showed latency reductions across centro-parietal regions during the encoding period of a spatial working memory task following 4 weeks of active MVM treatment. Complementary results were observed with the fMRI data, in which a subset of those completing fMRI assessment after SSVEP assessment (n = 16) demonstrated increased BOLD response during completion of the Rapid Visual Information Processing task (RVIP) within regions of interest including bilateral parietal lobes. No treatment-related changes in fMRI data were observed in those who had not first undergone SSVEP assessment, suggesting these results may be most evident under conditions of fatigue. Performance on the working memory and continuous performance tasks did not significantly differ between treatment groups at follow-up. In addition, within the fatigued fMRI sample, increased RVIP BOLD response was correlated with the change in number of target detections as part of the RVIP task. This study provides preliminary evidence of changes in functional brain activity during working memory associated with 4 weeks of daily treatment with a multi-vitamin and -mineral combination in healthy adults, using two distinct but complementary measures of functional brain activity.

Cerebral correlates of cognitive reserve

Cognitive reserve is a hypothetical concept introduced to explain discrepancies between severity of clinical dementia syndromes and the extent of dementia pathology. We examined cognitive reserve in a research programme that followed up a non-clinical sample born in 1921 or 1936 and IQ-tested age 11 years in 1932 or 1947. Structural MRI exams were acquired in about 50% of the sample from whom a subsample were recruited into an additional fMRI study. Here, we summarise findings from seven inter-related studies. These support an understanding of cognitive reserve as a balance between positive life course activity-driven experiences and the negative effects of brain pathologies including cerebrovascular disease and total and regional brain volume loss. Hypothesised structural equation models illustrate the relative causal effects of these positive and negative contributions. Cognitive reserve is considered in the context of choice of interventions to prevent dementia and the opposing effects of cerebrovascular disease and Alzheimer like brain appearances.

Processing speed and visuospatial executive function predict visual working memory ability in older adults

BACKGROUND/STUDY CONTEXT: Visual working memory (VWM) has been shown to be particularly age sensitive. Determining which measures share variance with this cognitive ability in older adults may help to elucidate the key factors underlying the effects of aging.

METHODS

Predictors of VWM (measured by a modified Visual Patterns Test) were investigated in a subsample (N = 44, mean age = 73) of older adults from the Lothian Birth Cohort 1936 (LBC1936; Deary et al., 2007 , BMC Geriatrics, 7, 28). Childhood intelligence (Moray House Test) and contemporaneous measures of processing speed (four-choice reaction time), executive function (verbal fluency; block design), and spatial working memory (backward spatial span), were assessed as potential predictors.

RESULTS

All contemporaneous measures except verbal fluency were significantly associated with VWM, and processing speed had the largest effect size (r = -.53, p < .001). In linear regression analysis, even after adjusting for childhood intelligence, processing speed and the executive measure associated with visuospatial organization accounted for 35% of the variance in VWM.

CONCLUSION

Processing speed may affect VWM performance in older adults via speed of encoding and/or rate of rehearsal, while executive resources specifically associated with visuospatial material are also important.

Neural Reorganization and Compensation in Aging

According to prominent theories of aging, the brain may reorganize to compensate for neural deterioration and prevent or offset cognitive decline. A frequent and striking finding in functional imaging studies is that older adults recruit additional regions relative to young adults performing the same task. This is often interpreted as evidence for functional reorganization, suggesting that, as people age, different regions or networks may support the same cognitive functions. Associations between additional recruitment and better performance in older adults have led to the suggestion that the additional recruitment may contribute to preserved cognitive function in old age and may explain some of the variation among individuals in preservation of function. However, many alternative explanations are possible, and recent findings and methodological developments have highlighted the need for more systematic approaches to determine whether reorganization occurs with age and whether it benefits performance. We reevaluate current evidence for compensatory functional reorganization in the light of recent moves to address these challenges.

A systematic review of type 2 diabetes mellitus and hypertension in imaging studies of cognitive aging: time to establish new norms

The rising prevalence of type 2 diabetes (T2DM) and hypertension in older adults, and the deleterious effect of these conditions on cerebrovascular and brain health, is creating a growing discrepancy between the "typical" cognitive aging trajectory and a "healthy" cognitive aging trajectory. These changing health demographics make T2DM and hypertension important topics of study in their own right, and warrant attention from the perspective of cognitive aging neuroimaging research. Specifically, interpretation of individual or group differences in blood oxygenation level dependent magnetic resonance imaging (BOLD MRI) or positron emission tomography (PET H2O(15)) signals as reflective of differences in neural activation underlying a cognitive operation of interest requires assumptions of intact vascular health amongst the study participants. Without adequate screening, inclusion of individuals with T2DM or hypertension in "healthy" samples may introduce unwanted variability and bias to brain and/or cognitive measures, and increase potential for error. We conducted a systematic review of the cognitive aging neuroimaging literature to document the extent to which researchers account for these conditions. Of the 232 studies selected for review, few explicitly excluded individuals with T2DM (9%) or hypertension (13%). A large portion had exclusion criteria that made it difficult to determine whether T2DM or hypertension were excluded (44 and 37%), and many did not mention any selection criteria related to T2DM or hypertension (34 and 22%). Of all the surveyed studies, only 29% acknowledged or addressed the potential influence of intersubject vascular variability on the measured BOLD or PET signals. To reinforce the notion that individuals with T2DM and hypertension should not be overlooked as a potential source of bias, we also provide an overview of metabolic and vascular changes associated with T2DM and hypertension, as they relate to cerebrovascular and brain health.

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.

Imaging approaches for dementia

Brain imaging has progressed from exclusion of rare treatable mass lesions to a specific antemortem diagnosis. MR imaging-derived hippocampal atrophy and WMH are regarded as imaging biomarkers of AD and CVD respectively. Abnormal FP-CIT SPECT or cardiac iodobenzamide SPECT is a useful supportive imaging feature in the diagnosis of DLB. Frontal and/or anterior temporal atrophy and anterior defects on molecular imaging with FDG-PET or perfusion SPECT are characteristic of FTDs. Whole-body FDG-PET may be helpful in patients with rapidly progressing "autoimmune dementias," and FLAIR and DWI are indicated in suspected CJD. A major role of imaging is in the development of new drugs and less costly biomarkers.

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.

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.

Cognitive functioning in newly presenting patients with supratentorial intracranial tumors: is there a role for inspection time?

Quantifying the extent of cognitive dysfunction in patients with intracranial tumors is important to monitor treatment effects and assess patients' needs. Inspection time, a measure of the efficiency of visual information processing, was evaluated, and its usefulness in patients with intracranial tumors was compared with that of other widely used cognitive tests. Newly presenting inpatients with supratentorial intracranial tumors (n = 118) underwent preoperative assessment using inspection time and a number of other measures of cognitive function, mood, and functional status. The brain tumor cohort was compared with patients admitted for elective spinal surgery (n = 85) and a healthy control group (n = 80). Analysis of covariance was used to compare the performance of the 3 groups. The brain tumor cohort had significantly lower inspection time scores than the spinal surgery group (P = .005) and the healthy volunteer control group (P < .001). The effect size was moderate. There was a large effect size of participant group for the Rey Auditory Verbal Learning Test, Digit Symbol-Coding, and Verbal Fluency (P = .002). The performance of patients with brain tumors was significantly worse than that of both of the control groups. Inspection time was well-tolerated by patients with intracranial tumors. However, inspection time is neither as easy to perform nor as sensitive as some other measures of cognitive function. Although its lack of any motor speed or coordination requirements, conceptual simplicity, repeatability, and relative lack of learning effect make inspection time a potentially useful tool in clinical neuro-oncology, practical considerations will limit its use.

Inter-individual differences in fMRI entropy measurements in old age

We investigated the association between individual differences in cognitive performance in old age and the approximate entropy (ApEn) measured from functional magnetic resonance imaging (fMRI) data acquired from 40 participants of the Aberdeen Birth Cohort 1936 (ABC1936), while undergoing a visual information processing task: inspection time (IT). Participants took a version of the Moray House Test (MHT) No. 12 at age 11, a valid measure of childhood intelligence. The same individuals completed a test of non-verbal reasoning (Raven's Standard Progressive Matrices [RPM]) aged about 68 years. The IT, MHT and RPM scores were used as indicators of cognitive performance. Our results show that higher regional signal entropy is associated with better cognitive performance. This finding was independent of ability in childhood but not independent of current cognitive ability. ApEn is used for the first time to identify a potential source of individual differences in cognitive ability using fMRI data.

A review of functional brain imaging correlates of successful cognitive aging

Preserved cognitive performance is a key feature of successful aging. Several theoretical models have been proposed to explain the putative underlying relationship between brain function and performance. We aimed to review imaging studies of the association between brain functional response and cognitive performance among healthy younger and older adults to understand the neural correlates of successful cognitive aging. MEDLINE-indexed articles published between January 1989 and December 2009 and bibliographies of these articles and related reviews were searched. Studies that measured brain function with functional magnetic resonance imaging or positron emission tomography, evaluated cognitive performance, analyzed how cognitive performance related to brain response, and studied healthy older individuals were included. Eighty of 550 articles met these criteria. Seventy percent of the studies reported some brain regions in which greater activation related to better cognitive performance among older participants. This association was not universal, however, and was seen mainly in frontal cortex brain response and seemed to be more common among older compared with younger individuals. This review supports the notion of compensatory increases in brain activity in old age resulting in better cognitive performance, as suggested by hemispheric asymmetry reduction and posterior-anterior shift models of functional brain aging. However, a simple model of bigger structure → greater brain response → better cognitive performance might not be accurate. Suggestions for future research are discussed.

How the 1932 and 1947 mental surveys of Aberdeen schoolchildren provide a framework to explore the childhood origins of late onset disease and disability

OBJECTIVES

To describe the discovery and development of the Aberdeen 1921 and 1936 birth cohort studies.

STUDY DESIGN

The Aberdeen birth cohort studies were started in 1998 when the Scottish Mental Survey archives of the Scottish Council for Research in Education were re-discovered and permissions granted to follow-up survivors born in 1921 or 1936 and then aged about 77 or 64 years and who had entered (or were about to enter) the age of greatest risk for Alzheimer's disease (AD).

MAIN OUTCOME MEASURES

Sources of attrition from the study, exposures to childhood adversity, nutritional, genetic and life style factors of possible relevance to extent of age-related cognitive decline and the timing of onset of dementia.

RESULTS

By 2010, the feasibility of following up more than 75% of Scottish Mental Survey survivors living in the Aberdeen area without dementia was well-established, dementia ascertainment to age about 88 years was completed in the 1921 birth cohort and was underway in the 1936 born cohort.

CONCLUSION

These databases are available to other bone fide research groups wishing to test specific hypotheses that may either replicate their own findings or make best use of the data collected in the Aberdeen studies.

Cognitive reserve modulates task-induced activations and deactivations in healthy elders, amnestic mild cognitive impairment and mild Alzheimer's disease

INTRODUCTION

Cognitive reserve (CR) reflects the capacity of the brain to endure neuropathology in order to minimize clinical manifestations. Previous studies showed that CR modulates the patterns of brain activity in both healthy and clinical populations. In the present study we sought to determine whether reorganizations of functional brain resources linked to CR could already be observed in amnestic mild cognitive impairment (a-MCI) and mild Alzheimer's disease (AD) patients when performing a task corresponding to an unaffected cognitive domain. We further investigated if activity in regions showing task-induced deactivations, usually identified as pertaining to the default-mode network (DMN), was also influenced by CR.

METHODS

Fifteen healthy elders, 15 a-MCI and 15 AD patients underwent functional magnetic resonance imaging (fMRI) during a speech comprehension task. Differences in the regression of slopes between CR proxies and blood-oxygen-level dependent (BOLD) signals across clinical groups were investigated for activation and deactivation areas. Correlations between significant fMRI results and a language comprehension test were also computed.

RESULTS

Among a-MCI and AD we observed positive correlations between CR measures and BOLD signals in task-induced activation areas directly processing speech, as well as greater deactivations in regions of the DMN. These relationships were inverted in healthy elders. We found no evidence that these results were mediated by gray matter volumes. Increased activity in left frontal areas and decreased activity in the anterior cingulate were related to better language comprehension in clinical evaluations.

CONCLUSIONS

The present findings provide evidence that the neurofunctional reorganizations related to CR among a-MCI and AD patients can be seen even when considering a preserved cognitive domain, being independent of gray matter atrophy. Areas showing both task-induced activations and deactivations are modulated by CR in an opposite manner when considering healthy elders versus patients. Brain reorganizations facilitated by CR may reflect behavioral compensatory mechanisms.