Subjective cognitive decline is associated with altered patterns of brain activity and connectivity during performance of an old/new recognition memory task

INTRODUCTION

Subjective Cognitive Decline (SCD) is considered a preclinical stage within the AD continuum. Knowledge about the functional changes in the brain associated with episodic memory retrieval and novelty recognition in people with SCD is currently very limited.

METHOD

The study aimed to evaluate behavioural and neurofunctional changes in individuals with SCD, measured relative to a control group, during successful episodic memory retrieval and novelty recognition, as well as to compare the functional connectivity patterns related to these cognitive processes within the Default Mode Network (DMN) in both groups. Participants performed an old/new recognition memory task with words while the BOLD signal was acquired.

RESULTS

No between-group differences were observed in the performance of the episodic memory task. However, during the successful recognition of old words, the SCD group showed brain hypoactivity in the right rolandic operculum and reduced functional connectivity between the DMN and the fronto-parietal control network (FPCN). During the correct identification of new words, the SCD group also showed reduced connectivity between the DMN and the FPCN, and lower connectivity within the DMN.

CONCLUSION

Despite the absence of objective evidence of cognitive impairment, people with SCD display several changes in brain activity and connectivity associated with episodic memory retrieval and novelty recognition.

Unraveling the complexity of human brain: Structure, function in healthy and disease states

The human brain stands as an intricate organ, embodying a nexus of structure, function, development, and diversity. This review delves into the multifaceted landscape of the brain, spanning its anatomical intricacies, diverse functional capacities, dynamic developmental trajectories, and inherent variability across individuals. The dynamic process of brain development, from early embryonic stages to adulthood, highlights the nuanced changes that occur throughout the lifespan. The brain, a remarkably complex organ, is composed of various anatomical regions, each contributing uniquely to its overall functionality. Through an exploration of neuroanatomy, neurophysiology, and electrophysiology, this review elucidates how different brain structures interact to support a wide array of cognitive processes, sensory perception, motor control, and emotional regulation. Moreover, it addresses the impact of age, sex, and ethnic background on brain structure and function, and gender differences profoundly influence the onset, progression, and manifestation of brain disorders shaped by genetic, hormonal, environmental, and social factors. Delving into the complexities of the human brain, it investigates how variations in anatomical configuration correspond to diverse functional capacities across individuals. Furthermore, it examines the impact of neurodegenerative diseases on the structural and functional integrity of the brain. Specifically, our article explores the pathological processes underlying neurodegenerative diseases, such as Alzheimer's, Parkinson's, and Huntington's diseases, shedding light on the structural alterations and functional impairments that accompany these conditions. We will also explore the current research trends in neurodegenerative diseases and identify the existing gaps in the literature. Overall, this article deepens our understanding of the fundamental principles governing brain structure and function and paves the way for a deeper understanding of individual differences and tailored approaches in neuroscience and clinical practice-additionally, a comprehensive understanding of structural and functional changes that manifest in neurodegenerative diseases.

Structural MRI analysis of age-related changes and sex differences in marmoset brain volume

The field of aging biology, which aims to extend healthy lifespans and prevent age-related diseases, has turned its focus to the Callithrix jacchus (common marmoset) to understand the aging process better. This study utilized magnetic resonance imaging (MRI) to non-invasively analyze the brains of 216 marmosets, investigating age-related changes in brain structure; the relationship between body weight and brain volume; and potential differences between males and females. The key findings revealed that, similar to humans, Callithrix jacchus experiences a reduction in total intracranial volume, cortex, subcortex, thalamus, and cingulate volumes as they age, highlighting site-dependent changes in brain tissue. Notably, the study also uncovered sex differences in cerebellar volume. These insights into the structural connectivity and volumetric changes in the marmoset brain throughout aging contribute to accumulating valuable knowledge in the field, promising to inform future aging research and interventions for enhancing healthspan.

Mnemonic brain state engagement is diminished in healthy aging

Healthy older adults typically show impaired episodic memory - memory for when and where an event oc-curred - but intact semantic memory - knowledge for general information and facts. As older adults also have difficulty inhibiting the retrieval of prior knowledge from memory, their selective decline in episodic memory may be due to a tendency to over engage the retrieval state, a brain state in which attention is focused internally in an attempt to access prior knowledge. The retrieval state trades off with the encoding state, a brain state which supports the formation of new memories. Therefore, episodic memory declines in older adults may be the result of differential engagement in mnemonic brain states. Our hypothesis is that older adults are biased toward a retrieval state. We recorded scalp electroencephalography while young, middle-aged and older adults performed a memory task in which they were explicitly directed to either encode the currently presented object stimulus or retrieve a previously presented, categorically-related object stimulus. We used multivariate pattern analysis of spectral activity to decode engagement in the retrieval vs. encoding state. We find that all three age groups can follow top-down instructions to selectively engage in encoding or retrieval and that we can decode mnemonic states for all age groups. However, we find that mnemonic brain state engagement is diminished for older adults relative to middle-aged adults. Our interpretation is that a combination of executive control deficits and a modest bias to retrieve modulates older adults' mnemonic state engagement. Together, these findings suggest that dif-ferential mnemonic state engagement may underlie age-related memory changes.

The effect of head motion on brain age prediction using deep convolutional neural networks

Deep learning can be used effectively to predict participants' age from brain magnetic resonance imaging (MRI) data, and a growing body of evidence suggests that the difference between predicted and chronological age-referred to as brain-predicted age difference (brain-PAD)-is related to various neurological and neuropsychiatric disease states. A crucial aspect of the applicability of brain-PAD as a biomarker of individual brain health is whether and how brain-predicted age is affected by MR image artifacts commonly encountered in clinical settings. To investigate this issue, we trained and validated two different 3D convolutional neural network architectures (CNNs) from scratch and tested the models on a separate dataset consisting of motion-free and motion-corrupted T1-weighted MRI scans from the same participants, the quality of which were rated by neuroradiologists from a clinical diagnostic point of view. Our results revealed a systematic increase in brain-PAD with worsening image quality for both models. This effect was also observed for images that were deemed usable from a clinical perspective, with brains appearing older in medium than in good quality images. These findings were also supported by significant associations found between the brain-PAD and standard image quality metrics indicating larger brain-PAD for lower-quality images. Our results demonstrate a spurious effect of advanced brain aging as a result of head motion and underline the importance of controlling for image quality when using brain-predicted age based on structural neuroimaging data as a proxy measure for brain health.

Registered report: Age-preserved semantic memory and the CRUNCH effect manifested as differential semantic control networks: An fMRI study

Semantic memory representations are generally well maintained in aging, whereas semantic control is thought to be more affected. To explain this phenomenon, this study tested the predictions of the Compensation-Related Utilization of Neural Circuits Hypothesis (CRUNCH), focusing on task demands in aging as a possible framework. The CRUNCH effect would manifest itself in semantic tasks through a compensatory increase in neural activation in semantic control network regions but only up to a certain threshold of task demands. This study compares 39 younger (20-35 years old) with 39 older participants (60-75 years old) in a triad-based semantic judgment task performed in an fMRI scanner while manipulating task demand levels (low versus high) through semantic distance. In line with the CRUNCH predictions, differences in neurofunctional activation and behavioral performance (accuracy and response times) were expected in younger versus older participants in the low- versus high-demand conditions, which should be manifested in semantic control Regions of Interest (ROIs). Our older participants had intact behavioral performance, as proposed in the literature for semantic memory tasks (maintained accuracy and slower response times (RTs)). Age-invariant behavioral performance in the older group compared to the younger one is necessary to test the CRUNCH predictions. The older adults were also characterized by high cognitive reserve, as our neuropsychological tests showed. Our behavioral results confirmed that our task successfully manipulated task demands: error rates, RTs and perceived difficulty increased with increasing task demands in both age groups. We did not find an interaction between age group and task demand, or a statistically significant difference in activation between the low- and high-demand conditions for either RTs or accuracy. As for brain activation, we did not find the expected age group by task demand interaction, or a significant main effect of task demand. Overall, our results are compatible with some neural activation in the semantic network and the semantic control network, largely in frontotemporoparietal regions. ROI analyses demonstrated significant effects (but no interactions) of task demand in the left and right inferior frontal gyrus, the left posterior middle temporal gyrus, the posterior inferior temporal gyrus and the prefrontal gyrus. Overall, our test did not confirm the CRUNCH predictions.

SuperAging functional connectomics from resting-state functional MRI

Understanding the relationship between functional connectivity (FC) of higher-order neurocognitive networks and age-related cognitive decline is a complex and evolving field of research. Decreases in FC have been associated with cognitive decline in persons with Alzheimer's disease and related dementias (ADRD). However, the contributions of FC have been less straightforward in typical cognitive aging. Some investigations suggest relatively robust FC within neurocognitive networks differentiates unusually successful cognitive aging from average aging, while others do not. Methodologic limitations in data processing and varying definitions of 'successful aging' may have contributed to the inconsistent results to date. The current study seeks to address previous limitations by optimized MRI methods to examine FC in the well-established SuperAging phenotype, defined by age and cognitive performance as individuals 80 and older with episodic memory performance equal to or better than 50-to-60-year-olds. Within- and between-network FC of large-scale neurocognitive networks were compared between 24 SuperAgers and 16 cognitively average older-aged control (OACs) with stable cognitive profiles using resting-state functional MRI (rs-fMRI) from a single visit. Group classification was determined based on measures of episodic memory, executive functioning, verbal fluency and picture naming. Inclusion criteria required stable cognitive status across two visits. First, we investigated the FC within and between seven resting-state networks from a common atlas parcellation. A separate index of network segregation was also compared between groups. Second, we investigated the FC between six subcomponents of the default mode network (DMN), the neurocognitive network commonly associated with memory performance and disrupted in persons with ADRD. For each analysis, FCs were compared across groups using two-sample independent t-tests and corrected for multiple comparisons. There were no significant between-group differences in demographic characteristics including age, sex and education. At the group-level, within-network FC, between-network FC, and segregation measurements of seven large-scale networks, including subcomponents of the DMN, were not a primary differentiator between cognitively average aging and SuperAging phenotypes. Thus, FC within or between large-scale networks does not appear to be a primary driver of the exceptional memory performance observed in SuperAgers. These results have relevance for differentiating the role of FC changes associated with cognitive aging from those associated with ADRD.

Age-Related Decline in Blood-Brain Barrier Function is More Pronounced in Males than Females in Parietal and Temporal Regions

The blood-brain barrier (BBB) plays a pivotal role in protecting the central nervous system (CNS), shielding it from potential harmful entities. A natural decline of BBB function with aging has been reported in both animal and human studies, which may contribute to cognitive decline and neurodegenerative disorders. Limited data also suggest that being female may be associated with protective effects on BBB function. Here we investigated age and sex-dependent trajectories of perfusion and BBB water exchange rate (kw) across the lifespan in 186 cognitively normal participants spanning the ages of 8 to 92 years old, using a non-invasive diffusion prepared pseudo-continuous arterial spin labeling (DP-pCASL) MRI technique. We found that the pattern of BBB kw decline with aging varies across brain regions. Moreover, results from our DP-pCASL technique revealed a remarkable decline in BBB kw beginning in the early 60s, which was more pronounced in males. In addition, we observed sex differences in parietal and temporal regions. Our findings provide in vivo results demonstrating sex differences in the decline of BBB function with aging, which may serve as a foundation for future investigations into perfusion and BBB function in neurodegenerative and other brain disorders.

Compensatory brain activity pattern is not present in older adults during the n-back task performance-Findings based on EEG frequency analysis

Introduction

Cognitive ability is one of the most important enablers for successful aging. At the same time, cognitive decline is a well-documented phenomenon accompanying the aging process. Nevertheless, it is acknowledged that aging can also be related to positive processes that allow one to compensate for the decline. These processes include the compensatory brain activity of older adults primarily investigated using fMRI and PET. To strengthen the cognitive interpretation of compensatory brain activity in older adults, we searched for its indicators in brain activity measured by EEG.

Methods

The study sample comprised 110 volunteers, including 50 older adults (60-75 years old) and 60 young adults (20-35 years old) who performed 1-back, 2-back, and 3-back tasks while recording the EEG signal. The study analyzed (1) the level of cognitive performance, including sensitivity index, the percentage of correct answers to the target, and the percentage of false alarm errors; (2) theta and alpha power for electrodes located in the frontal-midline (Fz, AF3, AF4, F3, F4, FC1, and FC2) and the centro-parietal (CP1, CP2, P3, P4, and Pz) areas.

Results

Cognitive performance was worse in older adults than in young adults, which manifested in a significantly lower sensitivity index and a significantly higher false alarm error rate at all levels of the n-back task difficulty. Simultaneously, performance worsened with increasing task difficulty regardless of age. Significantly lower theta power in the older participants was observed at all difficulty levels, even at the lowest one, where compensatory activity was expected. At the same time, at this difficulty level, cognitive performance was worse in older adults than in young adults, which could reduce the chances of observing compensatory brain activity. The significant decrease in theta power observed in both age groups with rising task difficulty can reflect a declining capacity for efficient cognitive functioning under increasing demands rather than adapting to this increase. Moreover, in young adults, alpha power decreased to some extent with increasing cognitive demand, reflecting adaptation to them, while in older adults, no analogous pattern was observed.

Discussion

In conclusion, based on the results of the current study, the presence of compensatory activity in older adults cannot be inferred.

Brain signal variability and executive functions across the life span

Neural variability is thought to facilitate survival through flexible adaptation to changing environmental demands. In humans, such capacity for flexible adaptation may manifest as fluid reasoning, inhibition of automatic responses, and mental set-switching-skills falling under the broad domain of executive functions that fluctuate over the life span. Neural variability can be quantified via the BOLD signal in resting-state fMRI. Variability of large-scale brain networks is posited to underpin complex cognitive activities requiring interactions between multiple brain regions. Few studies have examined the extent to which network-level brain signal variability across the life span maps onto high-level processes under the umbrella of executive functions. The present study leveraged a large publicly available neuroimaging dataset to investigate the relationship between signal variability and executive functions across the life span. Associations between brain signal variability and executive functions shifted as a function of age. Limbic-specific variability was consistently associated with greater performance across subcomponents of executive functions. Associations between executive function subcomponents and network-level variability of the default mode and central executive networks, as well as whole-brain variability, varied across the life span. Findings suggest that brain signal variability may help to explain to age-related differences in executive functions across the life span.

Healthy aging alters the oscillatory dynamics and fronto-parietal connectivity serving fluid intelligence

Fluid intelligence (Gf) involves logical reasoning and novel problem-solving abilities. Often, abstract reasoning tasks like Raven's progressive matrices are used to assess Gf. Prior work has shown an age-related decline in fluid intelligence capabilities, and although many studies have sought to identify the underlying mechanisms, our understanding of the critical brain regions and dynamics remains largely incomplete. In this study, we utilized magnetoencephalography (MEG) to investigate 78 individuals, ages 20-65 years, as they completed an abstract reasoning task. MEG data was co-registered with structural MRI data, transformed into the time-frequency domain, and the resulting neural oscillations were imaged using a beamformer. We found worsening behavioral performance with age, including prolonged reaction times and reduced accuracy. MEG analyses indicated robust oscillations in the theta, alpha/beta, and gamma range during the task. Whole brain correlation analyses with age revealed relationships in the theta and alpha/beta frequency bands, such that theta oscillations became stronger with increasing age in a right prefrontal region and alpha/beta oscillations became stronger with increasing age in parietal and right motor cortices. Follow-up connectivity analyses revealed increasing parieto-frontal connectivity with increasing age in the alpha/beta frequency range. Importantly, our findings are consistent with the parieto-frontal integration theory of intelligence (P-FIT). These results further suggest that as people age, there may be alterations in neural responses that are spectrally specific, such that older people exhibit stronger alpha/beta oscillations across the parieto-frontal network during abstract reasoning tasks.

Neural substrates of specific and general autobiographical memory retrieval in younger and older adults

Healthy aging is associated with a shift away from the retrieval of specific episodic autobiographical memories (AMs), towards more general and semanticized memories. Younger adults modulate activity in the default mode network according to the episodic specificity of AM retrieval. However, little is known about whether aging disrupts this neural modulation. In the current study we examine age-related changes in the modulation of whole-brain networks in response to three tasks falling along a gradient of episodic specificity. Younger and older adults retrieved specific (unique) AMs, general (routine) AMs, and semantic (general knowledge) memories. We found that both younger and older adults modulated default mode regions in response to varying episodic specificity. In addition, younger adults upregulated activity in several default mode regions with increasing episodic specificity, while older adults either did not modulate these regions, or downregulated activity in these regions. In contrast, older adults upregulated activity in the left temporal pole for tasks with higher episodic specificity. These brain activation patterns converge with prior findings that specific AMs are diminished in episodic richness with age, but are supplemented with conceptual and general information. Age-related reductions in the modulation of default mode regions might contribute to the shift away from episodic retrieval and towards semantic retrieval, resulting in reduced episodic specificity of personal memories.

Alterations of Audiovisual Integration in Alzheimer's Disease

Audiovisual integration is a vital information process involved in cognition and is closely correlated with aging and Alzheimer's disease (AD). In this review, we evaluated the altered audiovisual integrative behavioral symptoms in AD. We further analyzed the relationships between AD pathologies and audiovisual integration alterations bidirectionally and suggested the possible mechanisms of audiovisual integration alterations underlying AD, including the imbalance between energy demand and supply, activity-dependent degeneration, disrupted brain networks, and cognitive resource overloading. Then, based on the clinical characteristics including electrophysiological and imaging data related to audiovisual integration, we emphasized the value of audiovisual integration alterations as potential biomarkers for the early diagnosis and progression of AD. We also highlighted that treatments targeted audiovisual integration contributed to widespread pathological improvements in AD animal models and cognitive improvements in AD patients. Moreover, investigation into audiovisual integration alterations in AD also provided new insights and comprehension about sensory information processes.

A neural mechanism of cognitive reserve: The case of bilingualism

Cognitive Reserve (CR) refers to the preservation of cognitive function in the face of age- or disease-related neuroanatomical decline. While bilingualism has been shown to contribute to CR, the extent to which, and what particular aspect of, second language experience contributes to CR are debated, and the underlying neural mechanism(s) unknown. Intrinsic functional connectivity reflects experience-dependent neuroplasticity that occurs across timescales ranging from minutes to decades, and may be a neural mechanism underlying CR. To test this hypothesis, we used voxel-based morphometry and resting-state functional connectivity analyses of MRI data to compare structural and functional brain integrity between monolingual and bilingual older adults, matched on cognitive performance, and across levels of second language proficiency measured as a continuous variable. Bilingualism, and degree of second language proficiency specifically, were associated with lower gray matter integrity in a hub of the default mode network - a region that is particularly vulnerable to decline in aging and dementia - but preserved intrinsic functional network organization. Bilingualism moderated the association between neuroanatomical differences and cognitive decline, such that lower gray matter integrity was associated with lower executive function in monolinguals, but not bilinguals. Intrinsic functional network integrity predicted executive function when controlling for group differences in gray matter integrity and language status. Our findings confirm that lifelong bilingualism is a CR factor, as bilingual older adults performed just as well as their monolingual peers on tasks of executive function, despite showing signs of more advanced neuroanatomical aging, and that this is a consequence of preserved intrinsic functional network organization.

Inhibitory temporo-parietal effective connectivity is associated with explicit memory performance in older adults

Successful explicit memory encoding is associated with inferior temporal activations and medial parietal deactivations, which are attenuated in aging. Here we used dynamic causal modeling (DCM) of functional magnetic resonance imaging data to elucidate effective connectivity patterns between hippocampus, parahippocampal place area (PPA), and precuneus during encoding of novel visual scenes. In 117 young adults, DCM revealed pronounced activating input from the PPA to the hippocampus and inhibitory connectivity from the PPA to the precuneus during novelty processing, with both being enhanced during successful encoding. This pattern could be replicated in two cohorts (N = 141 and 148) of young and older adults. In both cohorts, older adults selectively exhibited attenuated inhibitory PPA-precuneus connectivity, which correlated negatively with memory performance. Our results provide insight into the network dynamics underlying explicit memory encoding and suggest that age-related differences in memory-related network activity are, at least partly, attributable to altered temporo-parietal neocortical connectivity.

The relationship between resting-state amplitude fluctuations and memory-related deactivations of the default mode network in young and older adults

The default mode network (DMN) typically exhibits deactivations during demanding tasks compared to periods of relative rest. In functional magnetic resonance imaging (fMRI) studies of episodic memory encoding, increased activity in DMN regions even predicts later forgetting in young healthy adults. This association is attenuated in older adults and, in some instances, increased DMN activity even predicts remembering rather than forgetting. It is yet unclear whether this phenomenon is due to a compensatory mechanism, such as self-referential or schema-dependent encoding, or whether it reflects overall reduced DMN activity modulation in older age. We approached this question by systematically comparing DMN activity during successful encoding and tonic, task-independent, DMN activity at rest in a sample of 106 young (18-35 years) and 111 older (60-80 years) healthy participants. Using voxel-wise multimodal analyses, we assessed the age-dependent relationship between DMN resting-state amplitude (mean percent amplitude of fluctuation, mPerAF) and DMN fMRI signals related to successful memory encoding, as well as their modulation by age-related hippocampal volume loss, while controlling for regional grey matter volume. Older adults showed lower resting-state DMN amplitudes and lower task-related deactivations. However, a negative relationship between resting-state mPerAF and subsequent memory effect within the precuneus was observed only in young, but not older adults. Hippocampal volumes showed no relationship with the DMN subsequent memory effect or mPerAF. Lastly, older adults with higher mPerAF in the DMN at rest tend to show higher memory performance, pointing towards the importance of a maintained ability to modulate DMN activity in old age.

Cooperation and competition between the default mode network and frontal parietal network in the elderly

Recent research has shown that the Default Mode Network (DMN) typically exhibits increased activation during processing of social and personal information but shows deactivation during working memory (WM) tasks. Previously, we reported the Frontal Parietal Network (FPN) and DMN showed coactivation during task preparation whereas the DMN exhibited deactivation during task execution in working memory tasks. Aging research has shown that older adults exhibited decreased functional connectivity in the DMN relative to younger adults. Here, we investigated whether age-related cognitive decline is related to a reduced relationship between the FPN and DMN using a working memory task during the execution period. First, we replicated our previous finding that the FPN and DMN showed coactivation during the preparation period, whereas the DMN showed deactivation during the execution period. The older adults showed reduced DMN activity during task preparation and reduced deactivation during task execution; however, they exhibited a higher magnitude of activation in the FPN than the young individuals during task execution. Functional connectivity analyses showed that the elderly group, compared to the young group, showed weaker correlations within the FPN and the DMN, weaker positive correlations between the FPN and DMN during task preparation, and weaker negative correlations between the FPN and DMN during execution. The results suggest that cognitive decline in the older adults might be related to reduced connectivity within the DMN as well as between the FPN and DMN.

Reduced memory precision in older age is associated with functional and structural differences in the angular gyrus

Decreased fidelity of mnemonic representations plays a critical role in age-related episodic memory deficits, yet the brain mechanisms underlying such reductions remain unclear. Using functional and structural neuroimaging, we examined how changes in two key nodes of the posterior-medial network, the hippocampus and the angular gyrus (AG), might underpin loss of memory precision in older age. Healthy young and older adults completed a memory task that involved reconstructing object features on a continuous scale. Investigation of blood-oxygen-level-dependent (BOLD) activity during retrieval revealed an age-related reduction in activity reflecting successful recovery of object features in the hippocampus, whereas trial-wise modulation of BOLD signal by graded memory precision was diminished in the AG. Gray matter volume of the AG further predicted individual differences in memory precision in older age, beyond likelihood of successful retrieval. These findings provide converging evidence for a role of functional and structural integrity of the AG in constraining the fidelity of episodic remembering in older age, yielding new insights into parietal contributions to age-related episodic memory decline.

Cognitive Performance Deficits Are Associated with Clinically Significant Depression Symptoms in Older US Adults

Accumulating research has described cognitive impairment in adults with depression, however, few studies have focused on this relationship during older adulthood. Our cross-sectional study investigated the association between cognitive function performance and clinically significant depression symptoms in older adults. We analysed the data from the 2011 to 2014 National Health and Nutrition Examination Survey on older (aged 60 years and above) US adults. Cognitive function was assessed as a composite score and on a test-by-test basis based on the Consortium to Establish a Registry for Alzheimer's Disease Word List Learning Test, the Word List Recall Test, and Intrusion Word Count Test, the Animal Fluency Test, and the Digit Symbol Substitution Test (DSST). Depression was defined as clinically significant depression symptoms based on the standard cut-off point of the Patient Health Questionnaire-9 (PHQ-9) score of 10 or greater. Adjusted-logistic regression analysis was employed using survey weights to examine the former relationships. Sociodemographic factors, in addition to medical history and status in terms of self-reported chronic illness and the incidence of stroke or memory-cognitive function loss, were considered as covariates. Among 1622 participants of a survey-weighted 860,400 US older adults, cognitive performance was associated with clinically significant depression symptoms (p = 0.003) after adjustment. Most prominently, older adults with significant cognitive deficits had approximately two and a half times (OR: 2.457 [1.219-4.953]) higher odds for a PHQ-9 score above threshold compared to those with the highest performance. Particularly, those with lowest DSST score had increased odds of almost four times (OR: 3.824 [1.069-13.678]). Efforts to decipher the underlying aetiology of these negative disparities may help create opportunities and interventions that could alleviate the risks from depression, cognitive impairment, and associated consequences in older adults at a population level.

Age-related changes in midfrontal theta activity during steering control: A driving simulator study

Motor control, a ubiquitous part of driving, requires increased cognitive controlled processing in older adults relative to younger adults. However, the influence of aging on motor-related neural mechanisms in the context of driving has rarely been studied. The present study aimed to identify age-related changes in cognitive control and attention allocation during a simulated steering task, using electroencephalography. Midfrontal theta, a marker for cognitive control, and posterior alpha power, a marker for attention allocation, were measured in a total of 26 young, 25 middle-aged, and 28 older adults. By adapting driving speed, the difficulty level of this steering task was individualized for each participant. Results show age-related changes in midfrontal theta power, but not in posterior alpha power, despite similar steering accuracy across age groups. Specifically, only younger and, to a lesser extent, middle-aged adults exhibited increased theta power while driving through more demanding curved segments relative to straight segments. In contrast, theta power upregulation was absent in older adults, suggesting a saturation of cognitive resources while driving, possibly due to a limitation in resource capacity, or less automatic motor-related neural processing.

Age-varying association between depression and cognitive function among a national sample of older U.S. immigrant adults: the potential moderating role of physical activity

OBJECTIVES

This study aimed to (1) investigate age-associated trends in depression and cognition, (2) determine whether the association between depression and cognition varies across age, and (3) test whether this association is moderated by different levels of physical activity among older U.S. immigrant adults aged 60 to 80 years.

METHODS

Using national data on elderly U.S. immigrants (N = 375) from the 2011-2014 NHANES, we employed weighted intercept-only linear time-varying effect modeling (TVEM) and weighted linear TVEM to address our research questions.

RESULTS

Weighted intercept-only linear TVEM indicated no trend in depression, but its mean peaked at age 67. Cognition consistently decreased with age, reaching its lowest point at age 78. Weighted linear TVEM revealed a significant inverse association between depression and cognition at some age ranges, with the strongest association at around age 66. Yet, we did not find the moderational relation of physical activity to this age-varying association.

CONCLUSIONS

Although we observed a significant inverse relationship between depression and cognition at a certain age point, physical activity did not moderate the age-varying association. Understanding of age-varying effects on the depression-cognition interaction will promote prevention efforts targeting aging immigrant populations at highest risk for these health outcomes. Further work is needed to test moderating effects of other health behaviors on this association across age.

Supplemental data for this article is available online at https://doi.org/10.1080/13607863.2022.2056139 .

Neural Contributions to Reduced Fluid Intelligence across the Adult Lifespan

Fluid intelligence, the ability to solve novel, complex problems, declines steeply during healthy human aging. Using fMRI, fluid intelligence has been repeatedly associated with activation of a frontoparietal brain network, and impairment following focal damage to these regions suggests that fluid intelligence depends on their integrity. It is therefore possible that age-related functional differences in frontoparietal activity contribute to the reduction in fluid intelligence. This paper reports on analysis of the Cambridge Center for Ageing and Neuroscience data, a large, population-based cohort of healthy males and females across the adult lifespan. The data support a model in which age-related differences in fluid intelligence are partially mediated by the responsiveness of frontoparietal regions to novel problem-solving. We first replicate a prior finding of such mediation using an independent sample. We then precisely localize the mediating brain regions, and show that mediation is specifically associated with voxels most activated by cognitive demand, but not with voxels suppressed by cognitive demand. We quantify the robustness of this result to potential unmodeled confounders, and estimate the causal direction of the effects. Finally, exploratory analyses suggest that neural mediation of age-related differences in fluid intelligence is moderated by the variety of regular physical activities, more reliably than by their frequency or duration. An additional moderating role of the variety of nonphysical activities emerged when controlling for head motion. A better understanding of the mechanisms that link healthy aging with lower fluid intelligence may suggest strategies for mitigating such decline.SIGNIFICANCE STATEMENT Global populations are living longer, driving urgency to understand age-related cognitive declines. Fluid intelligence is of prime importance because it reflects performance across many domains, and declines especially steeply during healthy aging. Despite consensus that fluid intelligence is associated with particular frontoparietal brain regions, little research has investigated suggestions that under-responsiveness of these regions mediates age-related decline. We replicate a recent demonstration of such mediation, showing specific association with brain regions most activated by cognitive demand, and robustness to moderate confounding by unmodeled variables. By showing that this mediation model is moderated by the variety of regular physical activities, more reliably than by their frequency or duration, we identify a potential modifiable lifestyle factor that may help promote successful aging.

Age interferes with sensorimotor timing and error correction in the supra-second range

Introduction

Precise motor timing including the ability to adjust movements after changes in the environment is fundamental to many daily activities. Sensorimotor timing in the sub-and supra-second range might rely on at least partially distinct brain networks, with the latter including the basal ganglia (BG) and the prefrontal cortex (PFC). Since both structures are particularly vulnerable to age-related decline, the present study investigated whether age might distinctively affect sensorimotor timing and error correction in the supra-second range.

Methods

A total of 50 healthy right-handed volunteers with 22 older (age range: 50-60 years) and 28 younger (age range: 20-36 years) participants synchronized the tap-onsets of their right index finger with an isochronous auditory pacing signal. Stimulus onset asynchronies were either 900 or 1,600 ms. Positive or negative step-changes that were perceivable or non-perceivable were occasionally interspersed to the fixed intervals to induce error correction. A simple reaction time task served as control condition.

Results and Discussion

In line with our hypothesis, synchronization variability in trials with supra-second intervals was larger in the older group. While reaction times were not affected by age, the mean negative asynchrony was significantly smaller in the elderly in trials with positive step-changes, suggesting more pronounced tolerance of positive deviations at older age. The analysis of error correction by means of the phase correction response (PCR) suggests reduced error correction in the older group. This effect emerged in trials with supra-second intervals and large positive step-changes, only. Overall, these results support the hypothesis that sensorimotor synchronization in the sub-second range is maintained but synchronization accuracy and error correction in the supra-second range is reduced in the elderly as early as in the fifth decade of life suggesting that these measures are suitable for the early detection of age-related changes of the motor system.

Brain Network Organization and Aging

Despite recent substantial progress in neuroscience, the mechanisms and principles of the complex structure, functions, and the relationship between the brain and cognitive functions have not been fully understood. The modeling method of brain network can provide a new perspective for neuroscience research, and it is possible to provide new solutions to the related research problems. On this basis, the researchers define the concept of human brain connectome to highlight and emphasize the importance of network modeling methods in neuroscience. For example, using diffusion-weighted magnetic resonance imaging (dMRI) technology and fiber tractography methods, a white matter connection network of the whole brain can be constructed. From the perspective of brain function, functional magnetic resonance imaging (fMRI) data can build the brain functional connection network. A structural covariation modeling method is used to obtain a brain structure covariation network, and it appears to reflect developmental coordination or synchronized maturation between areas of the brain. In addition, network modeling and analysis methods can also be applied to other types of image data, such as positron emission tomography (PET), electroencephalogram (EEG), and magnetoencephalography (MEG). This chapter mainly reviews the research progress of researchers on brain structure, function, and other aspects at the network level in recent years.

Greater individual variability in functional brain activity during working memory performance in Schizophrenia Spectrum Disorders (SSD)

Heterogeneity has been a persistent challenge in understanding Schizophrenia Spectrum Disorders (SSD). Traditional case-control comparisons often show variable results, and may not map well onto individuals. To better understand heterogeneity and group differences in SSD compared to typically developing controls (TDC), we examined variability in functional brain activity during a working memory (WM) task with known deficits in SSD. Neuroimaging and behavioural data were extracted from two datasets collectively providing 34 TDC and 56 individuals with SSD (n = 90). Functional activity in response to an N-Back WM task (3-Back vs 1-Back) was examined between and within groups. Individual variability was calculated via the correlational distance of fMRI activity maps between participants; mean correlational distance from one participant to all others was defined as a 'variability score'. Greater individual variability in functional activity was found in SSD compared to TDC (p = 0.00090). At the group level, a case-control comparison suggested SSD had reduced activity in task positive and task negative networks. However, when SSD were divided into high and low variability subgroups, the low variability groups showed no differences relative to TDC while the high variability group showed little activity at the group level. Our results imply prior case-control differences may be driven by a subgroup of SSD who do not show specific impairments but instead show more 'idiosyncratic' activity patterns. In SSD but not TDC, variability was also related to cognitive performance and age. This novel approach focusing on individual variability has important implications for understanding the neurobiology of SSD.

Sex- and age-specific associations between cardiometabolic risk and white matter brain age in the UK Biobank cohort

Cardiometabolic risk (CMR) factors are associated with accelerated brain aging and increased risk for sex-dimorphic illnesses such as Alzheimer's disease (AD). Yet, it is unknown how CMRs interact with sex and apolipoprotein E-ϵ4 (APOE4), a known genetic risk factor for AD, to influence brain age across different life stages. Using age prediction based on multi-shell diffusion-weighted imaging data in 21,308 UK Biobank participants, we investigated whether associations between white matter Brain Age Gap (BAG) and body mass index (BMI), waist-to-hip ratio (WHR), body fat percentage (BF%), and APOE4 status varied (i) between males and females, (ii) according to age at menopause in females, and (iii) across different age groups in males and females. We report sex differences in associations between BAG and all three CMRs, with stronger positive associations among males compared to females. Independent of APOE4 status, higher BAG (older brain age relative to chronological age) was associated with greater BMI, WHR, and BF% in males, whereas in females, higher BAG was associated with greater WHR, but not BMI and BF%. These divergent associations were most prominent within the oldest group of females (66-81 years), where greater BF% was linked to lower BAG. Earlier menopause transition was associated with higher BAG, but no interactions were found with CMRs. In conclusion, the findings point to sex- and age-specific associations between CMRs and brain age. Incorporating sex as a factor of interest in studies addressing CMR may promote sex-specific precision medicine, consequently improving health care for both males and females.

Aging-Related Differences in Structural and Functional Interhemispheric Connectivity

There is substantial evidence of age-related declines in anatomical connectivity during adulthood, with associated alterations in functional connectivity. But the relation of those functional alterations to the structural reductions is unclear. The complexities of both the structural and the functional connectomes make it difficult to determine such relationships. We pursue this question with methods, based on animal research, that specifically target the interhemispheric connections between the visual cortices. We collect t1- and diffusion-weighted imaging data from which we assess the integrity of the white matter interconnecting the bilateral visual cortices. Functional connectivity between the visual cortices is measured with electroencephalography during the presentation of drifting sinusoidal gratings that agree or conflict across hemifields. Our results show age-related reductions in the integrity of the white matter interconnecting the visual cortices, and age-related increases in the difference in functional interhemispheric lagged coherence between agreeing versus disagreeing visual stimuli. We show that integrity of the white matter in the splenium of the corpus callosum predicts the differences in lagged coherence for the agreeing versus disagreeing stimuli; and that this relationship is mediated by age. These results give new insight into the causal relationship between age and functional connectivity.

Across the adult lifespan the ipsilateral sensorimotor cortex negative BOLD response exhibits decreases in magnitude and spatial extent suggesting declining inhibitory control

Ipsilateral sensorimotor (iSM1) cortex negative BOLD responses (NBR) are observed to unilateral tasks and are thought to reflect a functionally relevant component of sensorimotor inhibition. Evidence suggests that sensorimotor inhibitory mechanisms degrade with age, along with aspects of motor ability and dexterity. However, understanding of age-related changes to NBR is restricted by limited comparisons between young vs old adults groups with relatively small samples sizes. Here we analysed a BOLD fMRI dataset (obtained from the CamCAN repository) of 581 healthy subjects, gender-balanced, sampled from the whole adult lifespan performing a motor response task to an audio-visual stimulus. We aimed to investigate how sensorimotor and default-mode NBR characteristics of magnitude, spatial extent and response shape alter at every decade of the aging process. A linear decrease in iSM1 NBR magnitude was observed across the whole lifespan whereas the contralateral sensorimotor (cSM1) PBR magnitude was unchanged. An age-related decrease in the spatial extent of NBR and an increase in the ipsilateral positive BOLD response (PBR) was observed. This occurred alongside an increasing negative correlation between subject's iSM1 NBR and cSM1 PBR magnitude, reflecting a change in the balance between cortical excitation and inhibition. Conventional GLM analysis, using a canonical haemodynamic response (HR) function, showed disappearance of iSM1 NBR in subjects over 50 years of age. However, a deconvolution analysis showed that the shape of the iSM1 HR altered throughout the lifespan, with delayed time-to-peak and decreased magnitude. The most significant decreases in iSM1 HR magnitude occurred in older age (>60 years) but the first changes in shape and timing occurred as early as 30 years, suggesting possibility of separate mechanisms underlying these alterations. Reanalysis using data-driven HRs for each decade detected significant sensorimotor NBR into late older age, showing the importance of taking changes in HR morphology into account in fMRI aging studies. These results may reflect fMRI measures of the age-related decreases in transcollosal inhibition exerted upon ipsilateral sensorimotor cortex and alterations to the excitatory-inhibitory balance in the sensorimotor network.

Network-specific differences in transient brain activity at rest are associated with age-related reductions in motor performance

Multiple functional changes occur in the brain with increasing age. Among those, older adults typically display more restricted fluctuations of brain activity, both during resting-state and task execution. These altered dynamic patterns have been linked to reduced task performance across multiple behavioral domains. Windowed functional connectivity, which is typically employed in the study of connectivity dynamics, however, might not be able to properly characterize moment-to-moment variations of individual networks. In the present study, we used innovation-driven co-activation patterns (ICAP) to overcome this limitation and investigate the length (duration) and frequency (innovation) in which various brain networks emerged across the adult lifespan (N= 92) during a resting-state period. We identified a link between increasing age and a tendency to engage brain areas with distinct functional associations simultaneously as a single network. The emergence of isolated and spatially well-defined visual, motor, frontoparietal, and posterior networks decreased with increased age. This reduction in dynamics of specialized networks mediated age-related performance decreases (i.e., increases in interlimb interference) in a bimanual motor task. Altogether, our findings demonstrated that older compared to younger adults tend to activate fewer network configurations, which include multiple functionally distinct brain areas. The reduction in independent emergence of functionally well-defined and task-relevant networks may reflect an expression of brain dedifferentiation and is likely associated with functional modulatory deficits, negatively impacting motor behavior.

The role of the arousal system in age-related differences in cortical functional network architecture

A common finding in the aging literature is that of the brain's decreased within- and increased between-network functional connectivity. However, it remains unclear what is causing this shift in network organization with age. Given the essential role of the ascending arousal system (ARAS) in cortical activation and previous findings of disrupted ARAS functioning with age, it is possible that age differences in ARAS functioning contribute to disrupted cortical connectivity. We test this possibility here using resting state fMRI data from over 500 individuals across the lifespan from the Cambridge Center for Aging and Neuroscience (Cam-CAN) population-based cohort. Our results show that ARAS-cortical connectivity declines with age and, consistent with our expectations, significantly mediates some age-related differences in connectivity within and between association networks (specifically, within the default mode and between the default mode and salience networks). Additionally, connectivity between the ARAS and association networks predicted cognitive performance across several tasks over and above the effects of age and connectivity within the cortical networks themselves. These findings suggest that age differences in cortical connectivity may be driven, at least in part, by altered arousal signals from the brainstem and that ARAS-cortical connectivity relates to cognitive performance with age.

Transcranial magnetic stimulation (TMS) for geriatric depression

BACKGROUND

The prevalence of treatment-resistant geriatric depression (GD) highlights the need for treatments that preserve cognitive functions and recognize polypharmacy in elderly, yet effectively reduce symptom burden. Transcranial magnetic stimulation (TMS) is a proven intervention for treatment-resistant depression in younger adults but the efficacy of TMS to treat depressed older adults is still unclear. This review provides an updated view on the efficacy of TMS treatment for GD, discusses methodological differences between trials in TMS application, and explores avenues for optimization of TMS treatment in the context of the ageing brain.

METHODS

A systematic review was conducted to identify published literature on the antidepressant efficacy of TMS for GD. Databases PubMed, Embase, and PsycINFO were searched for English language articles in peer-reviewed journals in March 2021.

RESULTS

Seven randomized controlled trials (RCTs) (total n = 260, active n = 148, control n = 112) and seven uncontrolled trials (total n = 160) were included. Overall, we found substantial variability in the clinical response, ranging from 6.7% to 54.3%.

CONCLUSIONS

The reviewed literature highlights large heterogeneity among studies both in terms of the employed TMS dosage and the observed clinical efficacy. This highlights the need for optimizing TMS dosage by recognizing the unique clinical features of GD. We showcase a set of novel approaches for the optimization of the TMS protocol for depression and discuss the possibility for a standardized TMS protocol tailored for the treatment of GD.

Default mode network and neural phase synchronization in healthy aging: A resting state EEG study

Aging is associated with altered brain connectivity within the default mode network (DMN). Although research using functional magnetic resonance imaging has quantified age-related alterations in functional connectivity within this network during resting state, it is less clear how this may be reflected in electrophysiological measures, and how this relates to cognitive performance in older adults. The aim of this study was to quantify age differences in phase synchrony of the DMN during resting state, with particular focus on connectivity between the anterior node (i.e., medial prefrontal cortex, or mPFC) and other associated regions in this network. Electroencephalography was recorded from 55 younger adults (18-30 years, 28 females) and 34 older adults (64-88 years, 16 females) in two resting state conditions (eyes-open and -closed). Source-level functional connectivity was quantified using phase-locking value (PLV) with a spatial filter of six sources of interest, and were subjected to data-driven permutation testing between groups from 1 to 50 Hz. Older adults also completed tests of memory, language, executive functioning, and processing speed. Findings indicated decreased connectivity in the alpha2 range for older than younger adults between the mPFC and other DMN regions including the left angular gyrus and bilateral lateral temporal cortices, the latter of which were associated with lower performance in semantic fluency and executive functioning in older adults. Furthermore, greater PLV in theta and beta bands between the mPFC and posterior cingulate regions was found in older than younger adults. These results suggest age-related changes in DMN functional connectivity are non-uniform and frequency-dependent, and may reflect poorer performance in cognitive domains thought to decline with aging.

Hearing-Aid Directionality Improves Neural Speech Tracking in Older Hearing-Impaired Listeners

In recent years, a growing body of literature has explored the effect of hearing impairment on the neural processing of speech, particularly related to the neural tracking of speech envelopes. However, only limited work has focused on the potential usage of the method for evaluating the effect of hearing aids designed to amplify and process the auditory input provided to hearing-impaired listeners. The current study investigates how directional sound processing in hearing-aids, denoted directionality, affects the neural tracking and encoding of speech in EEG recorded from 11 older hearing-impaired listeners. Behaviorally, the task performance improved when directionality was applied, while subjective ratings of listening effort were not affected. The reconstruction of the to-be-attended speech envelopes improved significantly when applying directionality, as well as when removing the background noise altogether. When inspecting the modelled response of the neural encoding of speech, a faster transition was observed between the early bottom-up response and the later top-down attentional-driven responses when directionality was applied. In summary, hearing-aid directionality affects both the neural speech tracking and neural encoding of to-be-attended speech. This result shows that hearing-aid signal processing impacts the neural processing of sounds and that neural speech tracking is indicative of the benefits associated with applying hearing-aid processing algorithms.

Changes in brain activity related to episodic memory retrieval in adults with single domain amnestic mild cognitive impairment

The present fMRI study aimed to characterize the performance and the brain activity changes related to episodic memory retrieval in adults with single domain aMCI (sdaMCI), relative to cognitively unimpaired adults. Participants performed an old/new recognition memory task with words while BOLD signal was acquired. The sdaMCI group showed lower hits (correct recognition of old words), lower ability to discriminate old and new words, higher errors and longer reaction times for hits. This group also displayed brain hypoactivation in left precuneus and the left midcingulate cortex during the successful recognition of old words. These changes in brain activity suggest the presence of neural dysregulations in brain regions involved during successful episodic memory retrieval. Moreover, hypoactivation in these brain areas discriminated both groups with moderate sensitivity and specificity values, suggesting that it might constitute a potential neurocognitive biomarker of sdaMCI.

Brain Dynamics Underlying Cognitive Flexibility Across the Lifespan

The neural mechanisms contributing to flexible cognition and behavior and how they change with development and aging are incompletely understood. The current study explored intrinsic brain dynamics across the lifespan using resting-state fMRI data (n = 601, 6-85 years) and examined the interactions between age and brain dynamics among three neurocognitive networks (midcingulo-insular network, M-CIN; medial frontoparietal network, M-FPN; and lateral frontoparietal network, L-FPN) in relation to behavioral measures of cognitive flexibility. Hierarchical multiple regression analysis revealed brain dynamics among a brain state characterized by co-activation of the L-FPN and M-FPN, and brain state transitions, moderated the relationship between quadratic effects of age and cognitive flexibility as measured by scores on the Delis-Kaplan Executive Function System (D-KEFS) test. Furthermore, simple slope analyses of significant interactions revealed children and older adults were more likely to exhibit brain dynamic patterns associated with poorer cognitive flexibility compared with younger adults. Our findings link changes in cognitive flexibility observed with age with the underlying brain dynamics supporting these changes. Preventative and intervention measures should prioritize targeting these networks with cognitive flexibility training to promote optimal outcomes across the lifespan.

The Aging Brain and Executive Functions Revisited: Implications from Meta-analytic and Functional-Connectivity Evidence

Healthy aging is associated with changes in cognitive performance, including executive functions (EFs) and their associated brain activation patterns. However, it has remained unclear which EF-related brain regions are affected consistently, because the results of pertinent neuroimaging studies and earlier meta-analyses vary considerably. We, therefore, conducted new rigorous meta-analyses of published age differences in EF-related brain activity. Out of a larger set of regions associated with EFs, only left inferior frontal junction and left anterior cuneus/precuneus were found to show consistent age differences. To further characterize these two age-sensitive regions, we performed seed-based resting-state functional connectivity (RS-FC) analyses using fMRI data from a large adult sample with a wide age range. We also assessed associations of the two regions' whole-brain RS-FC patterns with age and EF performance. Although our results largely point toward a domain-general role of left inferior frontal junction in EFs, the pattern of individual study contributions to the meta-analytic results suggests process-specific modulations by age. Our analyses further indicate that the left anterior cuneus/precuneus is recruited differently by older (compared with younger) adults during EF tasks, potentially reflecting inefficiencies in switching the attentional focus. Overall, our findings question earlier meta-analytic results and suggest a larger heterogeneity of age-related differences in brain activity associated with EFs. Hence, they encourage future research that pays greater attention to replicability, investigates age-related differences in deactivation, and focuses on more narrowly defined EF subprocesses, combining multiple behavioral assessments with multimodal imaging.

The ironic effect of older adults' increased task motivation: Implications for neurocognitive aging

Recent work suggests that most older adults who volunteer to take part in cognitive experiments are more motivated to do well than are undergraduate students. This empirical evidence is echoed by the impressions of cognitive aging researchers. We surveyed a large group (N = 88) of researchers asking about their perceptions of younger and older adults' motivation to take part in lab-based research. Not only were older adults seen as more motivated than younger adults, but researchers thought that the two groups participate for different reasons: younger adults to obtain course credit or monetary compensation, older adults to get a sense of their cognitive health, to further science, and out of curiosity. However, older adults' greater motivation to do well on cognitive tasks may leave them vulnerable to stereotype threat, the phenomenon by which individuals underperform when they are put in a position to either confirm or deny a negative stereotype about their group. In this opinion piece, we argue that most cognitive experiments, not just those designed to measure stereotype threat, likely induce some form of performance-related anxiety in older adults. This anxiety likely leads to greater task-related interference, or thoughts about how one is doing on the task, resulting in poorer performance. We discuss some of the potential implications for our understanding of neurocognitive aging.

Age-preserved semantic memory and the CRUNCH effect manifested as differential semantic control networks: An fMRI study

Semantic memory representations are overall well-maintained in aging whereas semantic control is thought to be more affected. To explain this phenomenon, this study aims to test the predictions of the Compensation Related Utilization of Neural Circuits Hypothesis (CRUNCH) focusing on task demands in aging as a possible framework. The CRUNCH effect would manifest itself in semantic tasks through a compensatory increase in neural activation in semantic control network regions but only up to a certain threshold of task demands. This study will compare 40 young (20-35 years old) with 40 older participants (60-75 years old) in a triad-based semantic judgment task performed in an fMRI scanner while manipulating levels of task demands (low vs. high) through semantic distance. In line with the CRUNCH predictions, differences in neurofunctional activation and behavioral performance (accuracy and response times) are expected in young vs. old participants in the low- vs. high-demand conditions manifested in semantic control Regions of Interest.

Age-Related Differences in Functional Asymmetry During Memory Retrieval Revisited: No Evidence for Contralateral Overactivation or Compensation

Brain asymmetry is inherent to cognitive processing and seems to reflect processing efficiency. Lower frontal asymmetry is often observed in older adults during memory retrieval, yet it is unclear whether lower asymmetry implies an age-related increase in contralateral recruitment, whether less asymmetry reflects compensation, is limited to frontal regions, or predicts neurocognitive stability or decline. We assessed age-related differences in asymmetry across the entire cerebral cortex, using functional magnetic resonance imaging data from 89 young and 76 older adults during successful retrieval, and surface-based methods allowing direct homotopic comparison of activity between cortical hemispheres . An extensive left-asymmetric network facilitated retrieval in both young and older adults, whereas diverse frontal and parietal regions exhibited lower asymmetry in older adults. However, lower asymmetry was not associated with age-related increases in contralateral recruitment but primarily reflected either less deactivation in contralateral regions reliably signaling retrieval failure in the young or lower recruitment of the dominant hemisphere-suggesting that functional deficits may drive lower asymmetry in older brains, not compensatory activity. Lower asymmetry predicted neither current memory performance nor the extent of memory change across the preceding ~ 8 years in older adults. Together, these findings are inconsistent with a compensation account for lower asymmetry during retrieval and aging.

Functional brain changes associated with cognitive trajectories determine specific tDCS-induced effects among older adults

The combination of transcranial direct current stimulation (tDCS) with functional magnetic resonance imaging (fMRI) can provide original data to investigate age-related brain changes. We examined neural activity modulations induced by two multifocal tDCS procedures based on two distinct montages fitting two N-back task-based fMRI patterns ("compensatory" and "maintenance") related to high working memory (WM) in a previous publication (Fernández-Cabello et al. Neurobiol Aging (2016);48:23-33). We included 24 participants classified as stable or decliners according to their 4-year WM trajectories following a retrospective longitudinal approach. Then, we studied longitudinal fMRI differences between groups (stable and decliners) and across multifocal tDCS montages ("compensatory" and "maintenance") applied using a single-blind sham-controlled cross-over design. Decliners evidenced over-activation of non-related WM areas after 4 years of follow-up. Focusing on tDCS effects, among the decliner group, the "compensatory"-tDCS montage reduced the activity over the posterior regions where these subjects showed longitudinal hyperactivation. These results reinforce the notion that tDCS effects are characterized by an activity reduction and might be more noticeable in compromised systems. Importantly, the data provide novel evidence that cognitive trajectories predict tDCS effects in older adults.

Altered connectivity of the default mode network in cognitively stable adults with Down syndrome: "Accelerated aging" or a prelude to Alzheimer's disease?

INTRODUCTION

Most individuals with Down syndrome (DS) have the neuropathological changes of Alzheimer's disease (AD) by age 40 and will have developed dementia by age 60. Alterations of the intrinsic connectivity of the default mode network (DMN) are associated with AD in the neurotypical population. In this study, we sought to determine whether, and how, connectivity between the hubs of the DMN were altered in cognitively stable adults with DS who did not have evidence of either mild cognitive impairment or AD.

METHODS

Resting state functional MRI scans were collected from 26 healthy adults with DS and 26 healthy age-matched non-DS controls. Nodes comprising the DMN were generated as ROI's (regions of interest) and inter-nodal correlations estimated.

RESULTS

Analysis of intra-network connectivity of the DMN revealed anterior-posterior DMN dissociation and hyper- and hypo-connectivity, suggesting "accelerated aging" in DS.

DISCUSSION

Disruption of the DMN may serve as a prelude for AD in DS.

The Effects of Amyloid and Tau on Functional Network Connectivity in Older Populations

Background: Neuroimaging studies suggest that aged brains show altered connectivity within and across functional networks. Similar changes in functional network integrity are also linked to the accumulation of pathological proteins in the brain, such as amyloid-beta plaques and neurofibrillary tau tangles seen in Alzheimer's disease. However, less is known about the specific impacts of amyloid and tau on functional network connectivity in cognitively normal older adults who harbor these proteins. Methods: We briefly summarize recent neuroimaging studies of aging and then thoroughly review positron emission tomography and functional magnetic resonance imaging studies measuring the relationship between amyloid-tau pathology and functional connectivity in cognitively normal older individuals. Results: The literature overall suggests that amyloid-positive older individuals show minor cognitive dysfunction and aberrant default mode network connectivity compared with amyloid-negative individuals. Tau, however, is more closely associated with network hypoconnectivity and poorer cognition. Those with substantial amyloid and tau experience even greater cognitive decline compared with those with primarily amyloid or tau, suggesting a potential interaction. Multimodal neuroimaging studies suggest that older adults with pathological protein deposits show amyloid-related hyperconnectivity and tau-related hypoconnectivity in multiple functional networks, including the default mode and frontoparietal networks. Discussion: We propose an updated model considering the effects of amyloid and tau on functional connectivity in older individuals. Large, longitudinal neuroimaging studies with multiple levels of analysis are required to obtain a deeper understanding of the dynamic relationship between pathological protein accumulation and functional connectivity changes, as amyloid- and tau-induced connectivity alterations may have critical and time-varying effects on neurodegeneration and cognitive decline. Impact statement Amyloid and tau accumulation have been linked with altered functional connectivity in cognitively normal older adults. This review synthesized recent functional imaging literatures in a discussion of how amyloid and tau can interactively affect functional connectivity in nonlinear ways, which can explain previous conflicting findings. Changes in connectivity strength may depend on the accumulation of both amyloid and tau, and their integrative effects seem to have critical consequences on cognition. Elucidating the effects of these pathological proteins on brain functioning is paramount to understand the etiology of Alzheimer's disease and the aging process overall.

Sex differences in brain aging among adults with family history of Alzheimer's disease and APOE4 genetic risk

Emerging evidence suggests that Alzheimer's Disease (AD) risk factors may differentially contribute to disease trajectory in women than men. Determining the effect of AD risk factors on brain aging in women, compared to men, is critical for understanding whether there are sex differences in the pathways towards AD in cognitively intact but at-risk adults. Brain Age Gap (BAG) is a concept used increasingly as a measure of brain health; BAG is defined as the difference between predicted age (based on structural MRI) and chronological age, with negative values reflecting preserved brain health with age. Using BAG, we investigated whether there were sex differences in the brain effects of AD risk factors (i.e., family history of AD, and carrying an apolipoprotein E ε4 allele [+APOE4]) in cognitively intact adults, and if this relationship was moderated by modifiable factors (i.e. body mass index [BMI], blood pressure and physical activity). We undertook a cross-sectional study of structural MRIs from 1067 cognitively normal adults across four neuroimaging datasets. An elastic net regression model found that women with a family history of AD and +APOE4 genotype had more advanced brain aging than their male counterparts. In a sub-cohort of women with those risk factors, higher BMI was associated with less brain aging whereas lower BMI was not. In a sub-cohort of women and men with +APOE4, engaging in physical activity was more beneficial to men's brain aging than women's. Our results demonstrate that AD risk factors are associated with greater brain aging in women than men, although there may be more unexplored modifiable factors that influence this relationship. These findings suggest that the complex interplay between unmodifiable and modifiable AD risk factors can potentially protect against brain aging in women and men.

Object-Location Memory Training in Older Adults Leads to Greater Deactivation of the Dorsal Default Mode Network

Substantial evidence indicates that cognitive training can be efficacious for older adults, but findings regarding training-related brain plasticity have been mixed and vary depending on the imaging modality. Recent years have seen a growth in recognition of the importance of large-scale brain networks on cognition. In particular, task-induced deactivation within the default mode network (DMN) is thought to facilitate externally directed cognition, while aging-related decrements in this neural process are related to reduced cognitive performance. It is not yet clear whether task-induced deactivation within the DMN can be enhanced by cognitive training in the elderly. We previously reported durable cognitive improvements in a sample of healthy older adults (age range = 60-75) who completed 6 weeks of process-based object-location memory training (N = 36) compared to an active control training group (N = 31). The primary aim of the current study is to evaluate whether these cognitive gains are accompanied by training-related changes in task-related DMN deactivation. Given the evidence for heterogeneity of the DMN, we examine task-related activation/deactivation within two separate DMN branches, a ventral branch related to episodic memory and a dorsal branch more closely resembling the canonical DMN. Participants underwent functional magnetic resonance imaging (fMRI) while performing an untrained object-location memory task at four time points before, during, and after the training period. Task-induced (de)activation values were extracted for the ventral and dorsal DMN branches at each time point. Relative to visual fixation baseline: (i) the dorsal DMN was deactivated during the scanner task, while the ventral DMN was activated; (ii) the object-location memory training group exhibited an increase in dorsal DMN deactivation relative to the active control group over the course of training and follow-up; (iii) changes in dorsal DMN deactivation did not correlate with task improvement. These results indicate a training-related enhancement of task-induced deactivation of the dorsal DMN, although the specificity of this improvement to the cognitive task performed in the scanner is not clear.

Investigating the effects of healthy cognitive aging on brain functional connectivity using 4.7 T resting-state functional magnetic resonance imaging

Functional changes in the aging human brain have been previously reported using functional magnetic resonance imaging (fMRI). Earlier resting-state fMRI studies revealed an age-associated weakening of intra-system functional connectivity (FC) and age-associated strengthening of inter-system FC. However, the majority of such FC studies did not investigate the relationship between age and network amplitude, without which correlation-based measures of FC can be challenging to interpret. Consequently, the main aim of this study was to investigate how three primary measures of resting-state fMRI signal-network amplitude, network topography, and inter-network FC-are affected by healthy cognitive aging. We acquired resting-state fMRI data on a 4.7 T scanner for 105 healthy participants representing the entire adult lifespan (18-85 years of age). To study age differences in network structure, we combined ICA-based network decomposition with sparse graphical models. Older adults displayed lower blood-oxygen-level-dependent (BOLD) signal amplitude in all functional systems, with sensorimotor networks showing the largest age differences. Our age comparisons of network topography and inter-network FC demonstrated a substantial amount of age invariance in the brain's functional architecture. Despite architecture similarities, old adults displayed a loss of communication efficiency in our inter-network FC comparisons, driven primarily by the FC reduction in frontal and parietal association cortices. Together, our results provide a comprehensive overview of age effects on fMRI-based FC.

Effects of aging on brain networks during swallowing: general linear model and independent component analyses

Swallowing disorders occur more frequently in older adults. However, the effects of the aging process on neural activation when swallowing are unclear. We aimed to identify neural regions activated during swallowing and evaluate changes in neural activation and neural networks with aging. Using a general linear model (GLM) and independent component (IC) analyses, blood oxygen level-dependent (BOLD) signals were observed in the lateral precentral gyrus, postcentral gyrus, anterior insular cortices, supramarginal gyri, and medial frontal gyrus during swallowing. The right thalamus and anterior cingulate gyri were found to be active areas by GLM and IC analyses, respectively. In the correlational analyses, age was negatively correlated with BOLD signals of the lateral precentral gyri, postcentral gyri, and insular cortices in swallowing tasks. Additionally, correlation analyses between ICs of all participants and age revealed negative correlations in the right supramarginal gyrus, both anterior cingulate cortices, putamen, and cerebellum. In the network analysis, the BOLD signal positively correlated with age in the default mode network (DMN), and was negatively correlated in the lateral precentral gyri, postcentral gyri, and insular cortices. The amplitude of low-frequency fluctuations was significantly decreased in the DMN and increased in swallowing-related areas during swallowing tasks. These results suggest that aging has negative effects on the activation of swallowing-related regions and task-induced deactivation of the DMN. These changes may be used to detect early functional decline during swallowing.

Age-related effects on the neural processing of semantic complexity in a continuous narrative: Modulation by gestures already present in young to middle-aged adults

The processing of semantically complex speech is a demanding task which can be facilitated by speech-associated arm and hand gestures. However, the role of age concerning the perception of semantic complexity and the influence of gestures in this context remains unclear. The goal of this study was to investigate if age-related differences are already present in early adulthood during the processing of semantic complexity and gestures. To this end, we analyzed fMRI images of a sample of 38 young and middle-aged participants (age-range: 19-55). They had the task to listen and to watch a narrative. The narrative contained segments varying in the degree of semantic complexity, and they were spontaneously accompanied by gestures. The semantic complexity of the story was measured by the idea density. Consistent with previous findings in young adults, we observed increased activation for passages with lower compared to higher complexity in bilateral temporal areas and the precuneus. BOLD signal in the left frontal and left parietal regions correlated during the perception of complex passages with increasing age. This correlation was reduced for passages presented with gestures. Median-split based post-hoc comparisons confirmed that group differences between younger (19-23 years) and older adults within the early adult lifespan (24-55 years) were significantly reduced in passages with gestures. Our results suggest that older adults within early adulthood adapt to the requirements of highly complex passages activating additional regions when no gesture information is available. Gestures might play a facilitative role with increasing age, especially when speech is complex.

Association of Missense Mutation in FOLH1 With Decreased NAAG Levels and Impaired Working Memory Circuitry and Cognition

OBJECTIVE

Altering the metabotropic glutamate receptor 3 (mGluR3) by pharmacology or genetics is associated with differences in learning and memory in animals and humans. GRM3 (the gene coding for mGluR3) is also genome-wide associated with risk for schizophrenia. The neurotransmitter N-acetyl-aspartyl-glutamate (NAAG) is the selective endogenous agonist of mGluR3, and increasing NAAG may improve cognition. Glutamate carboxypeptidase II (GCPII), coded by the gene folate hydrolase 1 (FOLH1), regulates the amount of NAAG in the synapse. The goal of this study was to determine the relationship between FOLH1, NAAG levels, measures of human cognition, and neural activity associated with cognition.

METHODS

The effects of genetic variation in FOLH1 on mRNA expression in human brain and NAAG levels using 7-T magnetic resonance spectroscopy (MRS) were measured. NAAG levels and FOLH1 genetic variation were correlated with measures of cognition in subjects with psychosis and unaffected subjects. Additionally, FOLH1 genetic variation was correlated with neural activity during working memory, as measured by functional MRI (fMRI).

RESULTS

A missense mutation in FOLH1 (rs202676 G allele) was associated with increased FOLH1 mRNA in the dorsolateral prefrontal cortex of brains from unaffected subjects and schizophrenia patients. This FOLH1 variant was associated with decreased NAAG levels in unaffected subjects and patients with psychosis. NAAG levels were positively correlated with visual memory performance. Carriers of the FOLH1 variant associated with lower NAAG levels had lower IQ scores. Carriers of this FOLH1 variant had less efficient cortical activity during working memory.

CONCLUSIONS

These data show that higher NAAG levels are associated with better cognition, suggesting that increasing NAAG levels through FOLH1/GCPII inhibition may improve cognition. Additionally, NAAG levels measured by MRS and cortical efficiency during working memory measured by fMRI have the potential to be neuroimaging biomarkers for future clinical trials.