Efficiency, capacity, compensation, maintenance, plasticity: emerging concepts in cognitive reserve

Education is associated with sub-regions of the hippocampus and the amygdala vulnerable to neuropathologies of Alzheimer's disease

We evaluated the correlation of educational attainment with structural volume and shape morphometry of the bilateral hippocampi and amygdalae in a sample of 110 non-demented, older adults at elevated sociodemographic risk for cognitive and functional declines. In both men and women, no significant education-volume correlation was detected for either structure. However, when performing shape analysis, we observed regionally specific associations with education after adjusting for age, intracranial volume, and race. By sub-dividing the hippocampus and the amygdala into compatible subregions, we found that education was positively associated with size variations in the CA1 and subiculum subregions of the hippocampus and the basolateral subregion of the amygdala (p < 0.05). In addition, we detected a greater left versus right asymmetric pattern in the shape-education correlation for the hippocampus but not the amygdala. This asymmetric association was largely observed in men versus women. These findings suggest that education in youth may exert direct and indirect influences on brain reserve in regions that are most vulnerable to the neuropathologies of aging, dementia, and specifically, Alzheimer disease.

Compensatory Neural Activity in Response to Cognitive Fatigue

Prolonged continuous performance of a cognitively demanding task induces cognitive fatigue and is associated with a time-related deterioration of objective performance, the degree of which is referred to cognitive fatigability. Although the neural underpinnings of cognitive fatigue are poorly understood, prior studies report changes in neural activity consistent with deterioration of task-related networks over time. While compensatory brain activity is reported to maintain motor task performance in the face of motor fatigue and cognitive performance in the face of other stressors (e.g., aging) and structural changes, there are no studies to date demonstrating compensatory activity for cognitive fatigue. High-density electroencephalography was recorded from human subjects during a 160 min continuous performance of a cognitive control task. While most time-varying neural activity showed a linear decline over time, we identified an evoked potential over the anterior frontal region which demonstrated an inverted U-shaped time-on-task profile. This evoked brain activity peaked between 60 and 100 min into the task and was positively associated with better behavioral performance only during this interval. Following the peak and during subsequent decline of this anterior frontal activity, the rate of performance decline also accelerated. These findings demonstrate that this anterior frontal brain activity, which is not part of the primary task-related activity at baseline, is recruited to compensate for fatigue-induced impairments in the primary task-related network, and that this compensation terminates as cognitive fatigue further progresses. These findings may be relevant to understanding individual differences in cognitive fatigability and developing interventions for clinical conditions afflicted by fatigue.

SIGNIFICANCE STATEMENT

Fatigue refers to changes in objective performance and subjective effort induced by continuous task performance. We examined the neural underpinnings of cognitive fatigue in humans using a prolonged continuous performance task and high-density electroencephalography with the goal of determining whether compensatory processes exist to maintain performance in the face of fatigue. We identified brain activity demonstrating an inverted U-shaped time-on-task profile. This brain activity showed features consistent with a compensatory role including: peaking between 60 and 100 min into the task, a positive association with behavioral performance only during this interval, and accelerated performance decline following its peak. These findings may be relevant to understanding individual differences in cognitive fatigue and developing interventions for clinical conditions afflicted by fatigue.

Cerebral and cerebellar grey matter atrophy in Friedreich ataxia: the IMAGE-FRDA study

Friedreich ataxia (FRDA) is traditionally associated with neuropathology in the cerebellar dentate nucleus and spinal cord. Growing evidence also suggests involvement of the cerebral and cerebellar cortices, although reports of structural abnormalities remain mixed. This study assessed the structural integrity of cortical grey matter in FRDA, focussing on regions in which pathology may underlie the motor deficits characteristic of this disorder. T1-weighted anatomical magnetic resonance imaging scans were acquired from 31 individuals with FRDA and 37 healthy controls. Cortical thickness (FreeSurfer) and cortical volume (SPM-VBM) were measured in cerebral motor regions-of-interest (primary motor, dorsal and ventral premotor, and supplementary motor areas) alongside unconstrained exploratory analyses of the cerebral and cerebellar cortices. Correlations were assessed between cortical thickness/volume measures and each of disease severity, length of the causative genetic triplet-repeat expansion, and finger-tapping behavioural measures. Individuals with FRDA had significantly reduced cortical thickness, relative to controls, in the premotor and supplementary motor areas. Reduced cortical thickness and/or volume were also observed in the cuneus and precuneus, posterior aspects of the medial and lateral prefrontal cortices, insula, temporal poles, and cerebellar lobules V, VI, and VII. Measures of clinical severity, genetic abnormality, and motor dysfunction correlated with volume loss in the lateral cerebellar hemispheres. These results suggest that atrophy preferentially affects premotor relative to primary areas of the cortical motor system, and also extends to a range of non-motor brain regions. Furthermore, cortical thickness and cortical volume findings were largely divergent, suggesting that each is sensitive to different aspects of neuropathology in FRDA. Overall, this study supports a disease model involving neural aberrations within the cerebral and cerebellar cortices, beyond those traditionally associated with this disorder.

Reserve-related activities and MRI metrics in multiple sclerosis patients and healthy controls: an observational study

BACKGROUND

To examine whether past and current reserve-related activities make the brain less susceptible to MS pathology (i.e., lesions or disease-related atrophy).

METHODS

This secondary analysis of a cohort study included 276 healthy controls (HC), and 65 clinically isolated syndrome (CIS), 352 relapsing-remitting MS (RR) and 109 secondary- progressive MS (SPMS) patients. Past reserve-related activities comprised educational and occupational attainment. Current reserve-related activities comprised strenuous and non-strenuous activities. MRI was performed on 3 T scanner. Regression and non-parametric analysis examined relationships between MRI metrics and reserve-related activities.

RESULTS

Multivariate models (HC as referent) revealed significant interactions in predicting strenuous reserve-related activities with chronic lesion burden (for CIS), brain- (for RR & SPMS), subcortical- (for CIS, RR, & SPMS) and amygdala- (for RR) volumes. Maximal Lifetime Brain Growth was higher for RR patients who engaged in running before and after diagnosis, rather than only before or never. Residual Brain Volume was higher in RR patients who did weights-exercise before and after diagnosis, as compared to only before.

CONCLUSIONS

Reserve-related activities are related to brain health cross-sectionally in all MS subgroups, and longitudinally in RR patients. Consistent with reserve theory, RR patients who maintained strenuous activities had higher Maximal Lifetime Brain Growth and Residual Brain Volume. The study's limitations are discussed, including the potential for recall bias and design limitations that preclude causal inference.

The Indirect Effect of Age Group on Switch Costs via Gray Matter Volume and Task-Related Brain Activity

Healthy aging simultaneously affects brain structure, brain function, and cognition. These effects are often investigated in isolation ignoring any relationships between them. It is plausible that age related declines in cognitive performance are the result of age-related structural and functional changes. This straightforward idea is tested in within a conceptual research model of cognitive aging. The current study tested whether age-related declines in task-performance were explained by age-related differences in brain structure and brain function using a task-switching paradigm in 175 participants. Sixty-three young and 112 old participants underwent MRI scanning of brain structure and brain activation. The experimental task was an executive context dual task with switch costs in response time as the behavioral measure. A serial mediation model was applied voxel-wise throughout the brain testing all pathways between age group, gray matter volume, brain activation and increased switch costs, worsening performance. There were widespread age group differences in gray matter volume and brain activation. Switch costs also significantly differed by age group. There were brain regions demonstrating significant indirect effects of age group on switch costs via the pathway through gray matter volume and brain activation. These were in the bilateral precuneus, bilateral parietal cortex, the left precentral gyrus, cerebellum, fusiform, and occipital cortices. There were also significant indirect effects via the brain activation pathway after controlling for gray matter volume. These effects were in the cerebellum, occipital cortex, left precentral gyrus, bilateral supramarginal, bilateral parietal, precuneus, middle cingulate extending to medial superior frontal gyri and the left middle frontal gyri. There were no significant effects through the gray matter volume alone pathway. These results demonstrate that a large proportion of the age group effect on switch costs can be attributed to individual differences in gray matter volume and brain activation. Therefore, age-related neural effects underlying cognitive control are a complex interaction between brain structure and function. Furthermore, the analyses demonstrate the feasibility of utilizing multiple neuroimaging modalities within a conceptual research model of cognitive aging.

Facial emotion recognition and its relationship to cognition and depressive symptoms in patients with Parkinson's disease

BACKGROUND

Impairments in facial emotion recognition (FER) have been detected in patients with Parkinson disease (PD). Presently, we aim at assessing differences in emotion recognition performance in PD patient groups with and without mild forms of cognitive impairment (MCI) compared to healthy controls.

METHODS

Performance on a concise emotion recognition test battery (VERT-K) of three groups of 97 PD patients was compared with an age-equivalent sample of 168 healthy controls. Patients were categorized into groups according to two well-established classifications of MCI according to Petersen's (cognitively intact vs. amnestic MCI, aMCI, vs. non-amnestic MCI, non-aMCI) and Litvan's (cognitively intact vs. single-domain MCI, sMCI, vs. multi-domain MCI, mMCI) criteria. Patients and controls underwent individual assessments using a comprehensive neuropsychological test battery examining attention, executive functioning, language, and memory (Neuropsychological Test Battery Vienna, NTBV), the Beck Depression Inventory, and a measure of premorbid IQ (WST).

RESULTS

Cognitively intact PD patients and patients with MCI in PD (PD-MCI) showed significantly worse emotion recognition performance when compared to healthy controls. Between-groups effect sizes were substantial, showing non-trivial effects in all comparisons (Cohen's ds from 0.31 to 1.22). Moreover, emotion recognition performance was higher in women, positively associated with premorbid IQ and negatively associated with age. Depressive symptoms were not related to FER.

CONCLUSIONS

The present investigation yields further evidence for impaired FER in PD. Interestingly, our data suggest FER deficits even in cognitively intact PD patients indicating FER dysfunction prior to the development of overt cognitive dysfunction. Age showed a negative association whereas IQ showed a positive association with FER.

Education as protector against dementia, but what exactly do we mean by education?

OBJECTIVES

even though a great number of research studies have shown that high education has protective effects against dementia, some studies did not observe such a significant effect. In that respect, the aim of our study was to investigate and compare various operationalisation approaches of education and how they impact dementia risk within one sample.

METHODS

data were derived from the Leipzig longitudinal study of the aged (LEILA75+). Individuals aged 75 and older underwent six cognitive assessments at an interval of 1.5 years and a final follow-up 15 years after the baseline assessment. We operationalised education according to different approaches used in previous studies and analysed the impact on dementia incidence via multivariate cox regression modelling.

RESULTS

the results showed that whether education is identified as significant protector against dementia strongly depends on the operationalisation of education. Whereas the pure number of years of education showed statistically significant protective effects on dementia risk, other more complex categorical classification approaches did not. Moreover, completing >10 years of education or a tertiary level seems to be an important threshold to significantly reduce dementia risk.

CONCLUSION

findings suggest a protective effect of more years of education on a lower dementia risk with a particular critical threshold of completing >10 years of education. Further, the findings highlight that, when examining risks and protective factors of dementia, a careful consideration of the underlying definitions and operationalisation approaches is required.

Neuropsychology of aging, past, present and future: Contributions of Morris Moscovitch

In this review we provide a broad overview of major trends in the cognitive neuroscience of aging and illustrate their roots in the pioneering ideas and discoveries of Morris Moscovitch and his close collaborators, especially Gordon Winocur. These trends include an on-going focus on the specific and dissociable contributions of medial temporal and frontal lobe processes to cognitive aging, especially in the memory domain, the role of individual variability stemming from different patterns of underlying neural decline, the possibility of compensatory neural and cognitive influences that alter the expression of neurobiological aging, and the investigation of lifestyle and psychosocial factors that affect plasticity and may contribute to the rate and level of neurocognitive decline. These prescient ideas, evident in the early work of Moscovitch and Winocur, continue to drive on-going research efforts in the cognitive neuroscience of aging.

Walking while Performing Working Memory Tasks Changes the Prefrontal Cortex Hemodynamic Activations and Gait Kinematics

BACKGROUND

Increasing evidence suggests that walking while performing a concurrent task negatively influences gait performance. However, it remains unclear how higher-level cognitive processes and coordination of limb movements are altered in challenging walking environments. This study investigated the influence of cognitive task complexity and walking road condition on the neutral correlates of executive function and postural control in dual-task walking.

METHODS

Twenty-four healthy young adults completed a series of overground walks with three walking road conditions (wide, narrow, with obstacles) with and without the concurrent n-back working memory tasks of two complexity levels (1-back and 3-back). Prefrontal brain activation was assessed by functional near-infrared spectroscopy. A three-dimensional motion analysis system was used simultaneously to measure gait performance and lower-extremity kinematics. Repeated measures analysis of variance were performed to examine the differences between the conditions.

RESULTS

In comparison with standing still, participants showed lower n-back task accuracy while walking, with the worst performance from the road with obstacles. Spatiotemporal gait parameters, lower-extremity joint movements, and the relative changes in oxygenated hemoglobin (HbO) concentration levels were all significantly different across the task complexity and walking path conditions. While dual-tasking participants were found to flex their hips and knees less, leading to a slower gait speed, longer stride time, shorter step length, and greater gait variability than during normal walking. For narrow-road walking, smaller ankle dorsiflexion and larger hip flexion were observed, along with a reduced gait speed. Obstacle negotiation was mainly characterized by increased gait variability than other conditions. HbO levels appeared to be lower during dual-task walking than normal walking. Compared to wide and obstacle conditions, walking on the narrow road was found to elicit a smaller decrement in HbO levels.

CONCLUSION

The current study provided direct evidence that, in young adults, neural correlates of executive function and dynamic postural control tend to be altered in response to the cognitive load imposed by the walking environment and the concurrent task during ambulation. A shift of brain activation patterns between functionally connected networks may occur when facing challenging cognitive-motor interaction.

The functional connectome of cognitive reserve

Cognitive Reserve (CR) designates the brain's capacity to actively cope with insults through a more efficient use of its resources/networks. It was proposed in order to explain the discrepancies between the observed cognitive ability and the expected capacity for an individual. Typical proxies of CR include education and Intelligence Quotient but none totally account for the variability of CR and no study has shown if the brain's greater efficiency associated with CR can be measured. We used a validated model to estimate CR from the residual variance in memory and general executive functioning, accounting for both brain anatomical (i.e., gray matter and white matter signal abnormalities volume) and demographic variables (i.e., years of formal education and sex). Functional connectivity (FC) networks and topological properties were explored for associations with CR. Demographic characteristics, mainly accounted by years of formal education, were associated with higher FC, clustering, local efficiency and strength in parietal and occipital regions and greater network transitivity. Higher CR was associated with a greater FC, local efficiency and clustering of occipital regions, strength and centrality of the inferior temporal gyrus and higher global efficiency. Altogether, these findings suggest that education may facilitate the brain's ability to form segregated functional groups, reinforcing the view that higher education level triggers more specialized use of neural processing. Additionally, this study demonstrated for the first time that CR is associated with more efficient processing of information in the human brain and reinforces the existence of a fine balance between segregation and integration. Hum Brain Mapp 37:3310–3322, 2016.. © 2016 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.

The impact of PICALM genetic variations on reserve capacity of posterior cingulate in AD continuum

Phosphatidylinositolbinding clathrin assembly protein (PICALM) gene is one novel genetic player associated with late-onset Alzheimer’s disease (LOAD), based on recent genome wide association studies (GWAS). However, how it affects AD occurrence is still unknown. Brain reserve hypothesis highlights the tolerant capacities of brain as a passive means to fight against neurodegenerations. Here, we took the baseline volume and/or thickness of LOAD-associated brain regions as proxies of brain reserve capacities and investigated whether PICALM genetic variations can influence the baseline reserve capacities and the longitudinal atrophy rate of these specific regions using data from Alzheimer’s Disease Neuroimaging Initiative (ADNI) dataset. In mixed population, we found that brain region significantly affected by PICALM genetic variations was majorly restricted to posterior cingulate. In sub-population analysis, we found that one PICALM variation (C allele of rs642949) was associated with larger baseline thickness of posterior cingulate in health. We found seven variations in health and two variations (rs543293 and rs592297) in individuals with mild cognitive impairment were associated with slower atrophy rate of posterior cingulate. Our study provided preliminary evidences supporting that PICALM variations render protections by facilitating reserve capacities of posterior cingulate in non-demented elderly.

Cognitive Reserve in Dementia: Implications for Cognitive Training

Cognitive reserve (CR) is a potential mechanism to cope with brain damage. The aim of this study was to evaluate the effect of CR on a cognitive training (CT) in a group of patients with dementia. Eighty six participants with mild to moderate dementia were identified by their level of CR quantified by the CR Index questionnaire (CRIq) and underwent a cycle of CT. A global measure of cognition mini mental state examination (MMSE) was obtained before (T0) and after (T1) the training. Multiple linear regression analyses highlighted CR as a significant factor able to predict changes in cognitive performance after the CT. In particular, patients with lower CR benefited from a CT program more than those with high CR. These data show that CR can modulate the outcome of a CT program and that it should be considered as a predictive factor of neuropsychological rehabilitation training efficacy in people with dementia.

Advanced activities of daily living and incidence of cognitive decline in the elderly: the SABE Study

The objective of this study was to evaluate the association between advanced activities of daily living (AADL) and incidence of cognitive decline. The sample consisted of non-institutionalized older adults who participated in the second (2006) and third (2010) waves of the Health, Wellbeing, and Aging (SABE) cohort study in São Paulo, Brazil. Cognitive decline was measured using a modified Mini-Mental State Examination. Advanced activities of daily living covered 12 social, productive, physical, and leisure-time activities that involve higher cognitive functions. Other covariates included socio-demographic conditions, overall health, lifestyle, and functional disability. The association between the independent variables and incidence of cognitive decline was assessed by multiple Poisson regression. Incidence of cognitive decline was 7.9%. Mean number of AADL in 2006 was significantly higher among elders who had not developed cognitive decline. Multivariate analysis showed that the number of AADL performed was a significant inverse predictor of cognitive decline.

Neural correlates of training and transfer effects in working memory in older adults

As indicated by previous research, aging is associated with a decline in working memory (WM) functioning, related to alterations in fronto-parietal neural activations. At the same time, previous studies showed that WM training in older adults may improve the performance in the trained task (training effect), and more importantly, also in untrained WM tasks (transfer effects). However, neural correlates of these transfer effects that would improve understanding of its underlying mechanisms, have not been shown in older participants as yet. In this study, we investigated blood-oxygen-level-dependent (BOLD) signal changes during n-back performance and an untrained delayed recognition (Sternberg) task following 12sessions (45min each) of adaptive n-back training in older adults. The Sternberg task used in this study allowed to test for neural training effects independent of specific task affordances of the trained task and to separate maintenance from updating processes. Thirty-two healthy older participants (60-75years) were assigned either to an n-back training or a no-contact control group. Before (t1) and after (t2) training/waiting period, both the n-back task and the Sternberg task were conducted while BOLD signal was measured using functional Magnetic Resonance Imaging (fMRI) in all participants. In addition, neuropsychological tests were performed outside the scanner. WM performance improved with training and behavioral transfer to tests measuring executive functions, processing speed, and fluid intelligence was found. In the training group, BOLD signal in the right lateral middle frontal gyrus/caudal superior frontal sulcus (Brodmann area, BA 6/8) decreased in both the trained n-back and the updating condition of the untrained Sternberg task at t2, compared to the control group. fMRI findings indicate a training-related increase in processing efficiency of WM networks, potentially related to the process of WM updating. Performance gains in untrained tasks suggest that transfer to other cognitive tasks remains possible in aging.

Compensatory activation in fronto-parietal cortices among HIV-infected persons during a monetary decision-making task

HIV infection can cause direct and indirect damage to the brain and is consistently associated with neurocognitive disorders, including impairments in decision-making capacities. The tendency to devalue rewards that are delayed (temporal discounting) is relevant to a range of health risk behaviors. Making choices about delayed rewards engages the executive control network of the brain, which has been found to be affected by HIV. In this case-control study of 18 HIV-positive and 17 HIV-negative adults, we examined the effects of HIV on brain activation during a temporal discounting task. Functional MRI (fMRI) data were collected while participants made choices between smaller, sooner rewards and larger, delayed rewards. Choices were individualized based on participants' unique discount functions, so each participant experienced hard (similarly valued), easy (disparately valued), and control choices. fMRI data were analyzed using a mixed-effects model to identify group-related differences associated with choice difficulty. While there was no difference between groups in behavioral performance, the HIV-positive group demonstrated significantly larger increases in activation within left parietal regions and bilateral prefrontal regions during easy trials and within the right prefrontal cortex and anterior cingulate during hard trials. Increasing activation within the prefrontal regions was associated with lower nadir CD4 cell count and risk-taking propensity. These results support the hypothesis that HIV infection can alter brain functioning in regions that support decision making, providing further evidence for HIV-associated compensatory activation within fronto-parietal cortices. A history of immunosuppression may contribute to these brain changes. Hum Brain Mapp 37:2455-2467, 2016. © 2016 Wiley Periodicals, Inc.

Task-based neurofeedback training: A novel approach toward training executive functions

Cognitive training is an emergent approach to improve cognitive functions in various neurodevelopmental and neurodegenerative diseases. However, current training programs can be relatively lengthy, making adherence potentially difficult for patients with cognitive difficulties. Previous studies suggest that providing individuals with real-time feedback about the level of brain activity (neurofeedback) can potentially help them learn to control the activation of specific brain regions. In the present study, we developed a novel task-based neurofeedback training paradigm that benefits from the effects of neurofeedback in parallel with computerized training. We focused on executive function training given its core involvement in various developmental and neurodegenerative diseases. Near-infrared spectroscopy (NIRS) was employed for providing neurofeedback by measuring changes in oxygenated hemoglobin in the prefrontal cortex. Of the twenty healthy adult participants, ten received real neurofeedback (NFB) on prefrontal activity during cognitive training, and ten were presented with sham feedback (SHAM). Compared with SHAM, the NFB group showed significantly improved executive function performance including measures of working memory after four sessions of training (100min total). The NFB group also showed significantly reduced training-related brain activity in the executive function network including right middle frontal and inferior frontal regions compared with SHAM. Our data suggest that providing neurofeedback along with cognitive training can enhance executive function after a relatively short period of training. Similar designs could potentially be used for patient populations with known neuropathology, potentially helping them to boost/recover the activity in the affected brain regions.

Higher brain BDNF gene expression is associated with slower cognitive decline in older adults

OBJECTIVES

We tested whether brain-derived neurotrophic factor (BDNF) gene expression levels are associated with cognitive decline in older adults.

METHODS

Five hundred thirty-five older participants underwent annual cognitive assessments and brain autopsy at death. BDNF gene expression was measured in the dorsolateral prefrontal cortex. Linear mixed models were used to examine whether BDNF expression was associated with cognitive decline adjusting for age, sex, and education. An interaction term was added to determine whether this association varied with clinical diagnosis proximate to death (no cognitive impairment, mild cognitive impairment, or dementia). Finally, we examined the extent to which the association of Alzheimer disease (AD) pathology with cognitive decline varied by BDNF expression.

RESULTS

Higher brain BDNF expression was associated with slower cognitive decline (p < 0.001); cognitive decline was about 50% slower with the 90th percentile BDNF expression vs 10th. This association was strongest in individuals with dementia. The level of BDNF expression was lower in individuals with pathologic AD (p = 0.006), but was not associated with macroscopic infarcts, Lewy body disease, or hippocampal sclerosis. BDNF expression remained associated with cognitive decline in a model adjusting for age, sex, education, and neuropathologies (p < 0.001). Furthermore, the effect of AD pathology on cognitive decline varied by BDNF expression such that the effect was strongest for high levels of AD pathology (p = 0.015); thus, in individuals with high AD pathology (90th percentile), cognitive decline was about 40% slower with the 90th percentile BDNF expression vs 10th.

CONCLUSIONS

Higher brain BDNF expression is associated with slower cognitive decline and may also reduce the deleterious effects of AD pathology on cognitive decline.

The neurobiology of HIV and its impact on cognitive reserve: A review of cognitive interventions for an aging population

The medications used to treat HIV have reduced the severity of cognitive deficits; yet, nearly half of adults with HIV still exhibit some degree of cognitive deficits, referred to as HIV-associated neurocognitive disorder or HAND. These cognitive deficits interfere with everyday functioning such as emotional regulation, medication adherence, instrumental activities of daily living, and even driving a vehicle. As adults are expected to live a normal lifespan, the process of aging in this clinical population may exacerbate such cognitive deficits. Therefore, it is important to understand the neurobiological mechanisms of HIV on cognitive reserve and develop interventions that are either neuroprotective or compensate for such cognitive deficits. Within the context of cognitive reserve, this article delivers a state of the science perspective on the causes of HAND and provides possible interventions for addressing such cognitive deficits. Suggestions for future research are also provided.

Motor Function Is Associated With Incident Disability in Older African Americans

BACKGROUND

Disability in older African American adults is common, but its basis is unclear. We tested the hypothesis that the level of motor function is associated with incident disability in older African Americans after adjusting for cognition.

METHODS

A prospective observational cohort study of 605 older community-dwelling African American adults without dementia was carried out. Baseline global motor score summarized 11 motor performances, cognition was based on 19 cognitive tests, and self-reported disability was obtained annually. We examined the association of motor function with incident disability (instrumental activities of daily living [IADL], activities of daily living [ADL], and mobility disability) with a series of Cox proportional hazards models which controlled for age, sex, and education.

RESULTS

Average follow-up was about 5 years. In proportional hazards models, a 1-SD increase in baseline level of global motor score was associated with about a 50% decrease in the risk of subsequent IADL, ADL, and mobility disability (all p values < .001). These associations were unchanged in analyses controlling for cognition and other covariates. Further, the association of global motor score and incident ADL disability varied with the level of cognition (estimate -5.541, SE 1.634, p < .001), such that higher motor function was more protective at higher levels of cognition. Mobility and dexterity components of global motor score were more strongly associated with incident disability than strength (all p values < .001).

CONCLUSIONS

Better motor function in older African Americans is associated with a decreased risk of developing disability. Moreover, the association of motor function and disability is stronger in individuals with better cognitive function.

Independent and combined effects of cognitive and physical activity on incident MCI

INTRODUCTION

The objective of this study was to examine the independent and combined influences of late-life cognitive activity (CA) and physical activity (PA) on the risk of incident mild cognitive impairment (MCI).

METHODS

We used interval censored survival modeling to examine the risk of incident MCI (Clinical Dementia Rating [CDR] = 0.5) as a function of CA (high vs. low) and at least moderate intensity PA (any vs. none) among 864 cognitively normal (CDR = 0) older adults.

RESULTS

During three annual follow-up waves, 72 participants developed MCI. Compared with low CA with no PA, significant reductions in risk for MCI were observed for high CA with any PA (hazards ratio (HR) = 0.20, 95% confidence interval (CI) 0.07-0.52) and low CA with any PA (HR = 0.52, 95% CI 0.29-0.93), but not for high CA without PA (HR = 0.94, 95% CI 0.45-1.95).

DISCUSSION

These findings suggest that a combination of CA and PA may be most efficacious at reducing the risk for cognitive impairment.

Disentangling Brain Graphs: A Note on the Conflation of Network and Connectivity Analyses

Understanding the human brain remains the holy grail in biomedical science, and arguably in all of the sciences. Our brains represent the most complex systems in the world (and some contend the universe) comprising nearly 100 billion neurons with septillions of possible connections between them. The structure of these connections engenders an efficient hierarchical system capable of consciousness, as well as complex thoughts, feelings, and behaviors. Brain connectivity and network analyses have exploded over the last decade due to their potential in helping us understand both normal and abnormal brain function. Functional connectivity (FC) analysis examines functional associations between time series pairs in specified brain voxels or regions. Brain network analysis serves as a distinct subfield of connectivity analysis, in which associations are quantified for all time series pairs to create an interconnected representation of the brain (a brain network), which allows studying its systemic properties. While connectivity analyses underlie network analyses, the subtle distinction between the two research areas has generally been overlooked in the literature, with them often being referred to synonymously. However, developing more useful analytic methods and allowing for more precise biological interpretations require distinguishing these two complementary domains.

Compensation in Preclinical Huntington's Disease: Evidence From the Track-On HD Study

BACKGROUND

Cognitive and motor task performance in premanifest Huntington's disease (HD) gene-carriers is often within normal ranges prior to clinical diagnosis, despite loss of brain volume in regions involved in these tasks. This indicates ongoing compensation, with the brain maintaining function in the presence of neuronal loss. However, thus far, compensatory processes in HD have not been modeled explicitly. Using a new model, which incorporates individual variability related to structural change and behavior, we sought to identify functional correlates of compensation in premanifest-HD gene-carriers.

METHODS

We investigated the modulatory effects of regional brain atrophy, indexed by structural measures of disease load, on the relationship between performance and brain activity (or connectivity) using task-based and resting-state functional MRI.

FINDINGS

Consistent with compensation, as atrophy increased performance-related activity increased in the right parietal cortex during a working memory task. Similarly, increased functional coupling between the right dorsolateral prefrontal cortex and a left hemisphere network in the resting-state predicted better cognitive performance as atrophy increased. Such patterns were not detectable for the left hemisphere or for motor tasks.

INTERPRETATION

Our findings provide evidence for active compensatory processes in premanifest-HD for cognitive demands and suggest a higher vulnerability of the left hemisphere to the effects of regional atrophy.

Interaction between years of education and APOE ε4 status on frontal and temporal metabolism

Objective:

To examine interactions between years of education and APOE ε4 status on gray matter volume and metabolism in cognitively healthy participants.

Methods:

Seventy-two healthy participants (28 APOE ε4 carriers and 44 noncarriers; from 23 to 84 years of age) with FDG-PET and structural MRI were included. A subgroup also underwent florbetapir-PET. We tested the interaction effect between years of education and APOE ε4 status (carrier vs noncarrier) on FDG-PET and structural MRI within the whole brain (voxel-wise) adjusting for age and sex. Computed florbetapir standardized uptake value ratios were used for complementary analyses.

Results:

We found an interaction between years of education and APOE ε4 status on frontotemporal FDG-PET metabolism, such that higher education was positively related to frontotemporal metabolism only in APOE ε4 carriers. Complementary analyses revealed that (1) this interaction was independent from amyloid load; (2) increased metabolism in APOE ε4 carriers in this region correlated with episodic memory performances; (3) lower educated APOE ε4 carriers showed decreased metabolism relative to noncarriers in medial temporal and prefrontal areas, while higher educated carriers were comparable to noncarriers in these areas and showed increased metabolism in the middle temporal lobe.

Conclusions:

Our results showed that education may counteract the effects of APOE ε4 on metabolism independently of amyloid deposition. Higher metabolism in higher (compared to lower) educated APOE ε4 carriers was found in regions that sustain episodic memory. Overall, our results point to education as a protective factor that may help to postpone cognitive changes in APOE ε4 carriers.

Cognitive reserve and lifestyle: moving towards preclinical Alzheimer's disease

The large majority of neuroimaging studies in Alzheimer’s disease (AD) patients have supported the idea that lifestyle factors may protect against the clinical manifestations of AD rather than influence AD neuropathological processes (the cognitive reserve hypothesis). This evidence argues in favor of the hypothesis that lifestyle factors act as moderators between AD pathology and cognition, i.e., through indirect compensatory mechanisms. In this review, we identify emerging evidence in cognitively normal older adults that relate lifestyle factors to established AD neuroimaging biomarkers. While some of these investigations are in agreement with the compensatory view of cognitive reserve, other studies have revealed new clues on the neural mechanisms underlying beneficial effects of lifestyle factors on the brain. Specifically, they provide novel evidence suggesting direct effects of lifestyle factors on AD neuropathological processes. We propose a tentative theoretical model where lifestyle factors may act via direct neuroprotective and/or indirect compensatory mechanisms. Importantly, we suggest that neuroprotective mechanisms may have a major role during early stages and compensatory mechanisms in later stages of the disease. In the absence of an effective treatment for AD and considering the potential of lifestyle factors in AD prevention, understanding the neural mechanisms underlying lifestyle effects on the brain seems crucial. We hope to provide an integrative view that may help to better understand the complex effects of lifestyle factors on AD neuropathological processes, starting from the preclinical stage.

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.

The Predictive Impact of Biological and Sociocultural Factors on Executive Processing: The Role of Age, Education, and Frequency of Reading and Writing Habits

Although the impact of education and age on executive functions (EF) has been widely studied, the influence of daily cognitive stimulation on EF has not been sufficiently investigated. Therefore, the aim of the present study was to evaluate whether the age, education, and frequency of reading and writing habits (FRWH) of healthy adults could predict their performance on measures of inhibition and cognitive flexibility. Inhibition speed, inhibitory control, and set shifting were assessed using speed, accuracy, and discrepancy scores on the Trail-Making Test (TMT) and Hayling Test. Demographic characteristics and the FRWH were assessed using specialized questionnaires. Regression analyses showed that age and the FRWH predicted speed and accuracy on the TMT. The FRWH predicted both speed and accuracy on the Hayling Test, for which speed and accuracy scores were also partly explained by age and education, respectively. Surprisingly, only the FRWH was associated with Hayling Test discrepancy scores, considered one of the purest EF measures. This highlights the importance of regular cognitive stimulation over the number of years of formal education on EF tasks. Further studies are required to investigate the role of the FRWH so as to better comprehend its relationship with EF and general cognition.

The BDNF Val66Met polymorphism moderates the relationship between cognitive reserve and executive function

The concept of cognitive reserve (CR) has been proposed to account for observed discrepancies between pathology and its clinical manifestation due to underlying differences in brain structure and function. In 433 healthy older adults participating in the Tasmanian Healthy Brain Project, we investigated whether common polymorphic variations in apolipoprotein E (APOE) or brain-derived neurotrophic factor (BDNF) influenced the association between CR contributors and cognitive function in older adults. We show that BDNF Val66Met moderates the association between CR and executive function. CR accounted for 8.5% of the variance in executive function in BDNF Val homozygotes, but CR was a nonsignificant predictor in BDNF Met carriers. APOE polymorphisms were not linked to the influence of CR on cognitive function. This result implicates BDNF in having an important role in capacity for building or accessing CR.

In vivo evidence for neuroplasticity in older adults

Neuroplasticity can be conceptualized as an intrinsic property of the brain that enables modification of function and structure in response to environmental demands. Neuroplastic strengthening of synapses is believed to serve as a critical mechanism underlying learning, memory, and other cognitive functions. Ex vivo work investigating neuroplasticity has been done on hippocampal slices using high frequency stimulation. However, in vivo neuroplasticity in humans has been difficult to demonstrate. Recently, a long-term potentiation-like phenomenon, a form of neuroplastic change, was identified in young adults by differences in visual evoked potentials (VEPs) that were measured before and after tetanic visual stimulation (TVS). The current study investigated whether neuroplastic changes in the visual pathway can persist in older adults. Seventeen healthy subjects, 65 years and older, were recruited from the community. Subjects had a mean age of 77.4 years, mean education of 17 years, mean MMSE of 29.1, and demonstrated normal performance on neuropsychological tests. 1Hz checkerboard stimulation, presented randomly to the right or left visual hemi-field, was followed by 2min of 9Hz stimulation (TVS) to one hemi-field. After 2min of rest, 1Hz stimulation was repeated. Temporospatial principal component analysis was used to identify the N1b component of the VEPs, at lateral occipital locations, in response to 1Hz stimulation pre- and post-TVS. Results showed that the amplitude of factors representing the early and late N1b component was substantially larger after tetanic stimulation. These findings indicate that high frequency visual stimulation can enhance the N1b in cognitively high functioning old adults, suggesting that neuroplastic changes in visual pathways can continue into late life. Future studies are needed to determine the extent to which this marker of neuroplasticity is sustained over a longer period of time, and is influenced by age, cognitive status, and neurodegenerative disease.

Longitudinal assessment of neuroanatomical and cognitive differences in young children with type 1 diabetes: association with hyperglycemia

Significant regional differences in gray and white matter volume and subtle cognitive differences between young diabetic and nondiabetic children have been observed. Here, we assessed whether these differences change over time and the relation with dysglycemia. Children ages 4 to <10 years with (n = 144) and without (n = 72) type 1 diabetes (T1D) had high-resolution structural MRI and comprehensive neurocognitive tests at baseline and 18 months and continuous glucose monitoring and HbA1c performed quarterly for 18 months. There were no differences in cognitive and executive function scores between groups at 18 months. However, children with diabetes had slower total gray and white matter growth than control subjects. Gray matter regions (left precuneus, right temporal, frontal, and parietal lobes and right medial-frontal cortex) showed lesser growth in diabetes, as did white matter areas (splenium of the corpus callosum, bilateral superior-parietal lobe, bilateral anterior forceps, and inferior-frontal fasciculus). These changes were associated with higher cumulative hyperglycemia and glucose variability but not with hypoglycemia. Young children with T1D have significant differences in total and regional gray and white matter growth in brain regions involved in complex sensorimotor processing and cognition compared with age-matched control subjects over 18 months, suggesting that chronic hyperglycemia may be detrimental to the developing brain.

The connectomics of brain disorders

Pathological perturbations of the brain are rarely confined to a single locus; instead, they often spread via axonal pathways to influence other regions. Patterns of such disease propagation are constrained by the extraordinarily complex, yet highly organized, topology of the underlying neural architecture; the so-called connectome. Thus, network organization fundamentally influences brain disease, and a connectomic approach grounded in network science is integral to understanding neuropathology. Here, we consider how brain-network topology shapes neural responses to damage, highlighting key maladaptive processes (such as diaschisis, transneuronal degeneration and dedifferentiation), and the resources (including degeneracy and reserve) and processes (such as compensation) that enable adaptation. We then show how knowledge of network topology allows us not only to describe pathological processes but also to generate predictive models of the spread and functional consequences of brain disease.

Relationship of medial temporal lobe atrophy, APOE genotype, and cognitive reserve in preclinical Alzheimer's disease

This study evaluated the utility of baseline and longitudinal magnetic resonance imaging (MRI) measures of medial temporal lobe brain regions collected when participants were cognitively normal and largely in middle age (mean age 57 years) to predict the time to onset of clinical symptoms associated with mild cognitive impairment (MCI). Furthermore, we examined whether the relationship between MRI measures and clinical symptom onset was modified by apolipoprotein E (ApoE) genotype and level of cognitive reserve (CR). MRI scans and measures of CR were obtained at baseline from 245 participants who had been followed for up to 18 years (mean follow-up 11 years). A composite score based on reading, vocabulary, and years of education was used as an index of CR. Cox regression models showed that lower baseline volume of the right hippocampus and smaller baseline thickness of the right entorhinal cortex predicted the time to symptom onset independently of CR and ApoE-ɛ4 genotype, which also predicted the onset of symptoms. The atrophy rates of bilateral entorhinal cortex and amygdala volumes were also associated with time to symptom onset, independent of CR, ApoE genotype, and baseline volume. Only one measure, the left entorhinal cortex baseline volume, interacted with CR, such that smaller volumes predicted symptom onset only in individuals with lower CR. These results suggest that MRI measures of medial temporal atrophy, ApoE-ɛ4 genotype, and the protective effects of higher CR all predict the time to onset of symptoms associated with MCI in a largely independent, additive manner during the preclinical phase of Alzheimer's disease.

A randomized controlled trial of brain training with non-action video games in older adults: results of the 3-month follow-up

This randomized controlled study (ClinicalTrials.gov NCT02007616) investigated the maintenance of training effects of 20 1-hr non-action video game training sessions with selected games from a commercial package on several age-declining cognitive functions and subjective wellbeing after a 3-month no-contact period. Two groups of cognitively normal older adults participated in both the post-training (posttest) and the present follow-up study, the experimental group who received training and the control group who attended several meetings with the research team during the study but did not receive training. Groups were similar at baseline on demographics, vocabulary, global cognition, and depression status. Significant improvements in the trained group, and no variation in the control group had been previously found at posttest, in processing speed, attention and visual recognition memory, as well as in two dimensions of subjective wellbeing. In the current study, improvement from baseline to 3 months follow-up was found only in wellbeing (Affection and Assertivity dimensions) in the trained group whereas there was no change in the control group. Previous significant improvements in processing speed, attention and spatial memory become non-significant after the 3-month interval. Training older adults with non-action video games enhanced aspects of cognition just after training but this effect disappeared after a 3-month no-contact follow-up period. Cognitive plasticity can be induced in older adults by training, but to maintain the benefits periodic boosting sessions would be necessary.

Modeling cognitive reserve in healthy middle-aged and older adults: the Tasmanian Healthy Brain Project

BACKGROUND

Cognitive reserve (CR) is a protective factor that supports cognition by increasing the resilience of an individual's cognitive function to the deleterious effects of cerebral lesions. A single environmental proxy indicator is often used to estimate CR (e.g. education), possibly resulting in a loss of the accuracy and predictive power of the investigation. Furthermore, while estimates of an individual's prior CR can be made, no operational measure exists to estimate dynamic change in CR resulting from exposure to new life experiences.

METHODS

We aimed to develop two latent measures of CR through factor analysis: prior and current, in a sample of 467 healthy older adults.

RESULTS

The prior CR measure combined proxy measures traditionally associated with CR, while the current CR measure combined variables that had the potential to reflect dynamic change in CR due to new life experiences. Our main finding was that the analyses uncovered latent variables in hypothesized prior and current models of CR.

CONCLUSIONS

The prior CR model supports multivariate estimation of pre-existing CR and may be applied to more accurately estimate CR in the absence of neuropathological data. The current CR model may be applied to evaluate and explore the potential benefits of CR-based interventions prior to dementia onset.

Physical activity, motor function, and white matter hyperintensity burden in healthy older adults

OBJECTIVE

To test the hypothesis that physical activity modifies the association between white matter hyperintensity (WMH) burden and motor function in healthy older persons without dementia.

METHODS

Total daily activity (exercise and nonexercise physical activity) was measured for up to 11 days with actigraphy (Actical; Philips Respironics, Bend, OR) in 167 older adults without dementia participating in the Rush Memory and Aging Project. Eleven motor performances were summarized into a previously described global motor score. WMH volume was expressed as percent of intracranial volume. Linear regression models, adjusted for age, education, and sex, were performed with total WMH volume as the predictor and global motor score as the outcome. Terms for total daily physical activity and its interaction with WMH volume were then added to the model.

RESULTS

Higher WMH burden was associated with lower motor function (p = 0.006), and total daily activity was positively associated with motor function (p = 0.002). Total daily activity modified the association between WMH and motor function (p = 0.007). WMH burden was not associated with motor function in persons with high activity (90th percentile). By contrast, higher WMH burden remained associated with lower motor function in persons with average (50th percentile; estimate = -0.304, slope = -0.133) and low (10th percentile; estimate = -1.793, slope = -0.241) activity.

CONCLUSIONS

Higher levels of physical activity may reduce the effect of WMH burden on motor function in healthy older adults.

Regression-Based Norms for a Bi-factor Model for Scoring the Brief Test of Adult Cognition by Telephone (BTACT)

The current study developed regression-based normative adjustments for a bi-factor model of the The Brief Test of Adult Cognition by Telephone (BTACT). Archival data from the Midlife Development in the United States-II Cognitive Project were used to develop eight separate linear regression models that predicted bi-factor BTACT scores, accounting for age, education, gender, and occupation-alone and in various combinations. All regression models provided statistically significant fit to the data. A three-predictor regression model fit best and accounted for 32.8% of the variance in the global bi-factor BTACT score. The fit of the regression models was not improved by gender. Eight different regression models are presented to allow the user flexibility in applying demographic corrections to the bi-factor BTACT scores. Occupation corrections, while not widely used, may provide useful demographic adjustments for adult populations or for those individuals who have attained an occupational status not commensurate with expected educational attainment.