Age differences in prefontal recruitment during verbal working memory maintenance depend on memory load

Prefrontal activation may predict working-memory training gain in normal aging and mild cognitive impairment

Cognitive training has been shown to result in improved behavioral performance in normal aging and mild cognitive impairment (MCI), yet little is known about the neural correlates of cognitive plasticity, or about individual differences in responsiveness to cognitive training. In this study, 21 healthy older adults and 14 patients with MCI received five weeks of adaptive computerized working-memory (WM) training. Before and after training, functional Near-Infrared Spectroscopy (fNIRS) was used to assess the hemodynamic response in left and right prefrontal cortex during performance of a verbal n-back task with varying levels of WM load. After training, healthy older adults demonstrated decreased prefrontal activation at high WM load, which may indicate increased processing efficiency. Although MCI patients showed improved behavioral performance at low WM load after training, no evidence was found for training-related changes in prefrontal activation. Whole-group analyses showed that a relatively strong hemodynamic response at low WM load was related to worse behavioral performance, while a relatively strong hemodynamic response at high WM load was related to higher training gain. Therefore, a 'youth-like' prefrontal activation pattern at older age may be associated with better behavioral outcome and cognitive plasticity.

Influence of age and cognitive performance on resting-state brain networks of older adults in a population-based cohort

Aging leads to global changes in brain structure and cognitive performance, with reorganization of functional brain networks. Importantly, these age-related changes show higher inter-individual variability in older subjects. To particularly address this variability is a challenge for studies on lifetime trajectories from early to late adulthood. The present study therefore had a dedicated focus on late adulthood to characterize the functional connectivity in resting-state networks (RSFC) in relation to age and cognitive performance in 711 older adults (55-85 years) from the 1000BRAINS project. The executive, left and right frontoparietal resting-state (RS) networks showed age-related increases in RSFC. However, older adults did not show changes in RSFC in the default mode network (DMN). Furthermore, lower performance in working memory (WM) was associated with higher RSFC in the left frontoparietal RS network. The results suggest age-related compensatory increases in RSFC which might help to maintain cognitive performance. Nevertheless, the negative correlation between RSFC and WM performance hints at limited cognitive reserve capacity in lower performing older adults. Consequently, the current results provide evidence for a functional reorganization of the brain until late adulthood that might additionally explain parts of the variability of cognitive abilities in older adults.

Dissociating Normal Aging from Alzheimer's Disease: A View from Cognitive Neuroscience

Both normal aging and Alzheimer's disease (AD) are associated with changes in cognition, grey and white matter volume, white matter integrity, neural activation, functional connectivity, and neurotransmission. Obviously, all of these changes are more pronounced in AD and proceed faster providing the basis for an AD diagnosis. Since these differences are quantitative, however, it was hypothesized that AD might simply reflect an accelerated aging process. The present article highlights the different neurocognitive changes associated with normal aging and AD and shows that, next to quantitative differences, there are multiple qualitative differences as well. These differences comprise different neurocognitive dissociations as different cognitive deficit profiles, different weights of grey and white matter atrophy, and different gradients of structural decline. These qualitative differences clearly indicate that AD cannot be simply described as accelerated aging process but on the contrary represents a solid entity.

The neural bases of proactive and reactive control processes in normal aging

INTRODUCTION

Research on cognitive control suggests an age-related decline in proactive control abilities (anticipatory control), whereas reactive control (following conflict detection) seems to remain intact. As proactive and reactive control abilities are associated with specific brain networks, this study investigated age-related effects on the neural substrates associated with each kind of control.

METHODS

In an event-related fMRI study, a modified version of the Stroop task was administered to groups of 20 young and 20 older healthy adults. Based on the theory of dual mechanisms of control, the Stroop task has been built to induce proactive or reactive control depending on task context.

RESULTS

Behavioral results (p<0.05) indicated faster processing of interfering items in the mostly incongruent (MI) than the mostly congruent (MC) context in both young and older participants. fMRI results showed that reactive control is associated with increased activity in left frontal areas for older participants. For proactive control, decreased activity in the bilateral anterior cingulate cortex was associated with more activity in the right middle frontal gyrus in the older than the younger group.

CONCLUSION

These observations support the hypothesis that aging affects the neural networks associated with reactive and proactive cognitive control differentially. These age-related changes are very similar to those observed in young adults with low dopamine availability, suggesting that a general mechanism (prefrontal dopamine availability) may modulate brain networks associated with various kinds of cognitive control.

Aging and the Resting State: Is Cognition Obsolete?

Recent years have seen the rise in popularity of the resting state approach to neurocognitive aging, with many studies examining age differences in functional connectivity at rest and relating these differences to cognitive performance outside the scanner. There are many advantages to the resting state that likely contribute to its popularity and indeed, many insights have been gained from this work. However, there are also several limitations of the resting state approach that restrict its ability to contribute to the study of neurocognitive aging. In this opinion piece, we consider some of those limitations and argue that task-based studies are still essential to developing a mechanistic understanding of how age affects the brain in a cognitively relevant manner - a fundamental goal of neuroscientific research into aging.

Functional neuroimaging of normal aging: Declining brain, adapting brain

Early functional neuroimaging research on normal aging brain has been dominated by the interest in cognitive decline. In this framework the age-related compensatory recruitment of prefrontal cortex, in terms of executive system or reduced lateralization, has been established. Further details on these compensatory mechanisms and the findings reflecting cognitive decline, however, remain the matter of intensive investigations. Studies in another framework where age-related neural alteration is considered adaptation to the environmental change are recently burgeoning and appear largely categorized into three domains. The age-related increase in activation of the sensorimotor network may reflect the alteration of the peripheral sensorimotor systems. The increased susceptibility of the network for the mental-state inference to the socioemotional significance may be explained by the age-related motivational shift due to the altered social perception. The age-related change in activation of the self-referential network may be relevant to the focused positive self-concept of elderly driven by a similar motivational shift. Across the domains, the concept of the self and internal model may provide the theoretical bases of this adaptation framework. These two frameworks complement each other to provide a comprehensive view of the normal aging brain.

Frontostriatal anatomical connections predict age- and difficulty-related differences in reinforcement learning

Reinforcement learning (RL) is supported by a network of striatal and frontal cortical structures that are connected through white-matter fiber bundles. With age, the integrity of these white-matter connections declines. The role of structural frontostriatal connectivity in individual and age-related differences in RL is unclear, although local white-matter density and diffusivity have been linked to individual differences in RL. Here we show that frontostriatal tract counts in young human adults (aged 18-28), as assessed noninvasively with diffusion-weighted magnetic resonance imaging and probabilistic tractography, positively predicted individual differences in RL when learning was difficult (70% valid feedback). In older adults (aged 63-87), in contrast, learning under both easy (90% valid feedback) and difficult conditions was predicted by tract counts in the same frontostriatal network. Furthermore, network-level analyses showed a double dissociation between the task-relevant networks in young and older adults, suggesting that older adults relied on different frontostriatal networks than young adults to obtain the same task performance. These results highlight the importance of successful information integration across striatal and frontal regions during RL, especially with variable outcomes.

Male veterans with PTSD exhibit aberrant neural dynamics during working memory processing: an MEG study

BACKGROUND

Posttraumatic stress disorder (PTSD) is associated with executive functioning deficits, including disruptions in working memory. In this study, we examined the neural dynamics of working memory processing in veterans with PTSD and a matched healthy control sample using magnetoencephalography (MEG).

METHODS

Our sample of recent combat veterans with PTSD and demographically matched participants without PTSD completed a working memory task during a 306-sensor MEG recording. The MEG data were preprocessed and transformed into the time-frequency domain. Significant oscillatory brain responses were imaged using a beamforming approach to identify spatiotemporal dynamics.

RESULTS

Fifty-one men were included in our analyses: 27 combat veterans with PTSD and 24 controls. Across all participants, a dynamic wave of neural activity spread from posterior visual cortices to left frontotemporal regions during encoding, consistent with a verbal working memory task, and was sustained throughout maintenance. Differences related to PTSD emerged during early encoding, with patients exhibiting stronger α oscillatory responses than controls in the right inferior frontal gyrus (IFG). Differences spread to the right supramarginal and temporal cortices during later encoding where, along with the right IFG, they persisted throughout the maintenance period.

LIMITATIONS

This study focused on men with combat-related PTSD using a verbal working memory task. Future studies should evaluate women and the impact of various traumatic experiences using diverse tasks.

CONCLUSION

Posttraumatic stress disorder is associated with neurophysiological abnormalities during working memory encoding and maintenance. Veterans with PTSD engaged a bilateral network, including the inferior prefrontal cortices and supramarginal gyri. Right hemispheric neural activity likely reflects compensatory processing, as veterans with PTSD work to maintain accurate performance despite known cognitive deficits associated with the disorder.

Listening and Learning: Cognitive Contributions to the Rehabilitation of Older Adults With and Without Audiometrically Defined Hearing Loss

Here, we describe some of the ways in which aging negatively affects the way sensory input is transduced and processed within the aging brain and how cognitive work is involved when listening to a less-than-perfect signal. We also describe how audiologic rehabilitation, including hearing aid amplification and listening training, is used to reduce the amount of cognitive resources required for effective auditory communication and conclude with an example of how listening effort is being studied in research laboratories for the purpose(s) of informing clinical practice.

β-Amyloid Deposition Is Associated with Decreased Right Prefrontal Activation during Task Switching among Cognitively Normal Elderly

The accumulation of β-amyloid (Aβ) peptides, a pathological hallmark of Alzheimer's disease (AD), has been associated with functional alterations, often in an episodic memory system with a particular emphasis on medial temporal lobe function. The topography of Aβ deposition, however, largely overlaps with frontoparietal control (FPC) regions implicated in cognitive control that has been shown to be impaired in early mild AD. To understand the neural mechanism underlying early changes in cognitive control with AD, we examined the impact of Aβ deposition on task-evoked FPC activation using functional magnetic resonance imaging (fMRI) in humans. Forty-three young and 62 cognitively normal older adults underwent an fMRI session during an executive contextual task in which task difficulty varied: single (either letter case or vowel/consonant judgment task) vs dual (switching between letter case and vowel/consonant decisions) task. Older subjects additionally completed (18)F-florbetaben positron emission tomography scans and were classified as either amyloid positive (Aβ+) or negative (Aβ-). Consistent with previous reports, age-related increases in brain activity were found in FPC regions commonly identified across groups. For both task conditions, Aβ-related increases in brain activity were found compared with baseline activity. For higher cognitive control load, however, Aβ+ elderly showed reduced task-switching activation in the right inferior frontal cortex. Our findings suggest that with Aβ deposition, brain activation in the cognitive control region reaches a maximum with lower control demand and decreases with higher control demand, which may underlie early impairment in cognitive control with AD progression.

SIGNIFICANCE STATEMENT

The accumulation of β-amyloid (Aβ) peptides, a pathological hallmark of Alzheimer's disease, spatially overlaps with frontoparietal control (FPC) regions implicated in cognitive control, but the impact of Aβ deposition on FPC regions is largely unknown. Using functional magnetic resonance imaging with a task-switching task, we found Aβ-related increases in FPC regions compared with baseline activity. For higher cognitive control load, however, Aβ-related hypoactivity was found in the right inferior frontal cortex, a region highly implicated in cognitive control. The findings suggest that with Aβ deposition, task-related brain activity may reach a plateau early and undergo downstream pathways of neural dysfunction, which may relate to the early impairment of cognitive control seen in the progression of Aβ pathology.

Preclinical Magnetic Resonance Imaging and Spectroscopy Studies of Memory, Aging, and Cognitive Decline

Neuroimaging provides for non-invasive evaluation of brain structure and activity and has been employed to suggest possible mechanisms for cognitive aging in humans. However, these imaging procedures have limits in terms of defining cellular and molecular mechanisms. In contrast, investigations of cognitive aging in animal models have mostly utilized techniques that have offered insight on synaptic, cellular, genetic, and epigenetic mechanisms affecting memory. Studies employing magnetic resonance imaging and spectroscopy (MRI and MRS, respectively) in animal models have emerged as an integrative set of techniques bridging localized cellular/molecular phenomenon and broader in vivo neural network alterations. MRI methods are remarkably suited to longitudinal tracking of cognitive function over extended periods permitting examination of the trajectory of structural or activity related changes. Combined with molecular and electrophysiological tools to selectively drive activity within specific brain regions, recent studies have begun to unlock the meaning of fMRI signals in terms of the role of neural plasticity and types of neural activity that generate the signals. The techniques provide a unique opportunity to causally determine how memory-relevant synaptic activity is processed and how memories may be distributed or reconsolidated over time. The present review summarizes research employing animal MRI and MRS in the study of brain function, structure, and biochemistry, with a particular focus on age-related cognitive decline.

Changes in the modulation of brain activity during context encoding vs. context retrieval across the adult lifespan

Age-related deficits in context memory may arise from neural changes underlying both encoding and retrieval of context information. Although age-related functional changes in the brain regions supporting context memory begin at midlife, little is known about the functional changes with age that support context memory encoding and retrieval across the adult lifespan. We investigated how age-related functional changes support context memory across the adult lifespan by assessing linear changes with age during successful context encoding and retrieval. Using functional magnetic resonance imaging (fMRI), we compared young, middle-aged and older adults during both encoding and retrieval of spatial and temporal details of faces. Multivariate behavioral partial least squares (B-PLS) analysis of fMRI data identified a pattern of whole-brain activity that correlated with a linear age term and a pattern of whole-brain activity that was associated with an age-by-memory phase (encoding vs. retrieval) interaction. Further investigation of this latter effect identified three main findings: 1) reduced phase-related modulation in bilateral fusiform gyrus, left superior/anterior frontal gyrus and right inferior frontal gyrus that started at midlife and continued to older age, 2) reduced phase-related modulation in bilateral inferior parietal lobule that occurred only in older age, and 3) changes in phase-related modulation in older but not younger adults in left middle frontal gyrus and bilateral parahippocampal gyrus that was indicative of age-related over-recruitment. We conclude that age-related reductions in context memory arise in midlife and are related to changes in perceptual recollection and changes in fronto-parietal retrieval monitoring.

Aging modulates the oscillatory dynamics underlying successful working memory encoding and maintenance

Working memory is central to the execution of many daily functions and is typically divided into three phases: encoding, maintenance, and retrieval. While working memory performance has been repeatedly shown to decline with age, less is known regarding the underlying neural processes. We examined age-related differences in the neural dynamics that serve working memory by recording high-density magnetoencephalography (MEG) in younger and older adults while they performed a modified, high-load Sternberg working memory task with letters as stimuli. MEG data were evaluated in the time-frequency domain and significant oscillatory responses were imaged using a beamformer. A hierarchical regression was performed to investigate whether age moderated the relationship between oscillatory activity and accuracy on the working memory task. Our results indicated that the spatiotemporal dynamics of oscillatory activity in language-related areas of the left fronto-temporal cortices were similar across groups. Age-related differences emerged during early encoding in the right-hemispheric homologue of Wernicke's area. Slightly later, group differences emerged in the homologue of Broca's area and these persisted throughout memory maintenance. Additionally, occipital alpha activity during maintenance was stronger, occurred earlier, and involved more cortical tissue in older adults. Finally, age significantly moderated the relationship between accuracy and neural activity in the prefrontal cortices. In younger adults, as prefrontal activity decreased, accuracy tended to increase. Our results are consistent with predictions of the compensation-related utilization of neural circuits hypothesis (CRUNCH). Such differences in the oscillatory dynamics could reflect compensatory mechanisms, which would aid working memory performance in older age. Hum Brain Mapp 37:2348-2361, 2016. © 2016 Wiley Periodicals, Inc.

Robust Resilience of the Frontotemporal Syntax System to Aging

Brain function is thought to become less specialized with age. However, this view is largely based on findings of increased activation during tasks that fail to separate task-related processes (e.g., attention, decision making) from the cognitive process under examination. Here we take a systems-level approach to separate processes specific to language comprehension from those related to general task demands and to examine age differences in functional connectivity both within and between those systems. A large population-based sample (N = 111; 22-87 years) from the Cambridge Centre for Aging and Neuroscience (Cam-CAN) was scanned using functional MRI during two versions of an experiment: a natural listening version in which participants simply listened to spoken sentences and an explicit task version in which they rated the acceptability of the same sentences. Independent components analysis across the combined data from both versions showed that although task-free language comprehension activates only the auditory and frontotemporal (FTN) syntax networks, performing a simple task with the same sentences recruits several additional networks. Remarkably, functionality of the critical FTN is maintained across age groups, showing no difference in within-network connectivity or responsivity to syntactic processing demands despite gray matter loss and reduced connectivity to task-related networks. We found no evidence for reduced specialization or compensation with age. Overt task performance was maintained across the lifespan and performance in older, but not younger, adults related to crystallized knowledge, suggesting that decreased between-network connectivity may be compensated for by older adults' richer knowledge base.

SIGNIFICANCE STATEMENT

Understanding spoken language requires the rapid integration of information at many different levels of analysis. Given the complexity and speed of this process, it is remarkably well preserved with age. Although previous work claims that this preserved functionality is due to compensatory activation of regions outside the frontotemporal language network, we use a novel systems-level approach to show that these "compensatory" activations simply reflect age differences in response to experimental task demands. Natural, task-free language comprehension solely recruits auditory and frontotemporal networks, the latter of which is similarly responsive to language-processing demands across the lifespan. These findings challenge the conventional approach to neurocognitive aging by showing that the neural underpinnings of a given cognitive function depend on how you test it.

Young and Middle-Aged Schoolteachers Differ in the Neural Correlates of Memory Encoding and Cognitive Fatigue: A Functional MRI Study

This investigation was inspired by growing evidence that middle-aged persons in a cognitively demanding profession might be characterized by subtle cognitive fatigue. We studied young and middle-aged male schoolteachers. They were compared in a study with functional magnetic resonance imaging to evaluate differences during successful memory encoding. The schoolteachers were additionally subjected to an induced fatigue condition involving the sustained performance of cognitively demanding tasks and to a control condition. Results showed age-related brain activation differences underlying behavioral performance including: (1) greater activation in middle-aged vs. young teachers in bilateral prefrontal cortex (PFC) areas; and (2) differential fatigue effects in the left anterior cingulate cortex (ACC) depending on age group. Middle-aged schoolteachers showed decreased ACC activation in the fatigue compared to the control condition, whereas no change in activation was found in young teachers. Findings demonstrate age effects in these middle-aged subjects that are typically found in older adults, specifically in PFC over-activation. Findings also indicate that already in middle age cognitive aging may be associated with greater resource depletion following sustained task performance. The findings underscore the notion that persons in a cognitively demanding profession can experience subtle age effects, which are evident on fMRI and which impact daily functioning. Possible practical implications for middle-aged schoolteachers are discussed.

Object individuation and compensation in healthy aging

Theories on neural compensation suggest that aged participants overactivate the brain areas involved in a task to compensate for the age-related decline. In this electrophysiological study, we investigated the temporal locus of neural overactivation in aging during multiple target processing. We measured performance and three event-related brain potential responses (N1, N2pc, and contralateral delay activity) in young and old adults, while they enumerated a variable number (1-4) of targets presented in an easy (distractor absent) or difficult (distractor present) condition. The main results indicated that although N2pc (∼200 ms) increased in amplitude in the distractor-present condition in the young group, no modulation occurred for the old group. Old participants were associated with larger N2pc amplitudes than young participants in the distractor-absent condition, where both groups had comparable levels of accuracy. These effects were not present for N1 and contralateral delay activity. Overall, the data suggest that in enumeration, aging is associated with compensatory effects that rely on the selection mechanism responsible for target individuation.

Age differences in behavioral and neural correlates of proactive interference: Disentangling the role of overall working memory performance

Reliable performance in working memory (WM) critically depends on the ability to resist proactive interference (PI) from previously relevant WM contents. Both WM performance and PI susceptibility are subject to cognitive decline at older adult age. However, the behavioral and neural processes underlying these co-evolving developmental changes and their potential interdependencies are not yet understood. Here, we investigated PI using a recent-probes WM paradigm and functional MRI in a cross-sectional sample of younger (n=18, 10 female, 23.4 ± 2.7 years) and older adults (n=18, 10 female, 70.2 ± 2.7 years). As expected, older adults showed lower WM performance and higher PI susceptibility than younger adults. Resolution of PI activated a mainly bilateral frontal network across all participants. Significant interactions with age indicated reduced neural activation in older adults for PI resolution. A second analysis in a selection of younger and older adults (n=12 each) with matched WM performance also revealed significant differences in PI between both age groups and - on a descriptive level - again a hypo-activation of the older adults' PI network. But the differential effect of age on the neural PI effects did not reach significance in this smaller sample most likely to the reduced statistical power. However, given the highly similar patterns in both the overall and the WM-matched samples, we propose that the hypo-activation of the PI network in the older adults may not be attributable to age-related differences in overall WM performance, hence suggesting that higher PI susceptibility in older adult age does not directly depend on their lower WM performance.

The Effect of Task-Irrelevant Fearful-Face Distractor on Working Memory Processing in Mild Cognitive Impairment versus Healthy Controls: An Exploratory fMRI Study in Female Participants

In mild cognitive impairment (MCI), a risk state for Alzheimer's disease, patients have objective cognitive deficits with relatively preserved functioning. fMRI studies have identified anomalies during working memory (WM) processing in individuals with MCI. The effect of task-irrelevant emotional face distractor on WM processing in MCI remains unclear. We aim to explore the impact of fearful-face task-irrelevant distractor on WM processing in MCI using fMRI. Hypothesis. Compared to healthy controls (HC), MCI patients will show significantly higher BOLD signal in a priori identified regions of interest (ROIs) during a WM task with a task-irrelevant emotional face distractor. Methods. 9 right-handed female participants with MCI and 12 matched HC performed a WM task with standardized task-irrelevant fearful versus neutral face distractors randomized and counterbalanced across WM trials. MRI images were acquired during the WM task and BOLD signal was analyzed using statistical parametric mapping (SPM) to identify signal patterns during the task response phase. Results. Task-irrelevant fearful-face distractor resulted in higher activation in the amygdala, anterior cingulate, and frontal areas, in MCI participants compared to HC. Conclusions. This exploratory study suggests altered WM processing as a result of fearful-face distractor in MCI.

Mild cognitive impairment affects motor control and skill learning

Mild cognitive impairment (MCI) is a transitional phase between normal cognitive aging and dementia. As the world population is aging rapidly, more MCI patients will be identified, posing significant problems to society. Normal aging is associated with cognitive and motor decline, and MCI brings additional impairments. Compared to healthy older adults, MCI patients show poorer motor control in a variety of tasks. Efficient motor control and skill learning are essential for occupational and leisure purposes; degradation of motor behaviors in MCI patients often adversely affects their health and quality of life. In this article, we first define MCI and describe its pathology and neural correlates. After this, we review cognitive changes and motor control and skill learning in normal aging. This section is followed by a discussion of MCI-related degradation of motor behaviors. Finally, we propose that multicomponent interventions targeting both cognitive and motor domains can improve MCI patients’ motor functions. Future research directions are also raised.

Age-Related Differences in the Reliance on Executive Control in Working Memory: Role of Task Demand

We examined the hypothesis that age-related differences in the reliance on executive control may be better explained by variations of task demand than by a mechanism specifically linked to aging. To this end, we compared the relationship between the performance of young and older adults on two executive functioning tests and an updating working-memory task with different load levels. The results revealed a significant interaction between age, task demand, and individual executive capacities, indicating that executive resources were only involved at lower loads in older adults, and only at higher loads in young adults. Overall, the results are not consistent with the proposition that cognition places greater demand on executive control in older adults. However, they support the view that how much young and older adults rely on executive control to accomplish cognitive tasks depends on task demand. Finally, interestingly these results are consistent with the CRUNCH model accounting for age-related differences in brain activations.

Aβ-related hyperactivation in frontoparietal control regions in cognitively normal elderly

The accumulation of amyloid-beta (Aβ) peptides, a pathologic hallmark of Alzheimer's disease, has been associated with functional alterations in cognitively normal elderly, most often in the context of episodic memory with a particular emphasis on the medial temporal lobes. The topography of Aβ deposition, however, highly overlaps with frontoparietal control (FPC) regions implicated in cognitive control/working memory. To examine Aβ-related functional alternations in the FPC regions during a working memory task, we imaged 42 young and 57 cognitively normal elderly using functional magnetic resonance imaging during a letter Sternberg task with varying load. Based on (18)F-florbetaben-positron emission tomography scan, we determined older subjects' amyloid positivity (Aβ+) status. Within brain regions commonly recruited by all subject groups during the delay period, age and Aβ deposition were independently associated with load-dependent frontoparietal hyperactivation, whereas additional compensatory Aβ-related hyperactivity was found beyond the FPC regions. The present results suggest that Aβ-related hyperactivation is not specific to the episodic memory system but occurs in the PFC regions as well.

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

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

Trying to Put the Puzzle Together: Age and Performance Level Modulate the Neural Response to Increasing Task Load within Left Rostral Prefrontal Cortex

Age-related working memory decline is associated with functional cerebral changes within prefrontal cortex (PFC). Kind and meaning of these changes are heavily discussed since they depend on performance level and task load. Hence, we investigated the effects of age, performance level, and load on spatial working memory retrieval-related brain activation in different subregions of the PFC. 19 younger (Y) and 21 older (O) adults who were further subdivided into high performers (HP) and low performers (LP) performed a modified version of the Corsi Block-Tapping test during fMRI. Brain data was analyzed by a 4 (groups: YHP, OHP, YLP, and OLP) × 3 (load levels: loads 4, 5, and 6) ANOVA. Results revealed significant group × load interaction effects within rostral dorsolateral and ventrolateral PFC. YHP showed a flexible neural upregulation with increasing load, whereas YLP reached a resource ceiling at a moderate load level. OHP showed a similar (though less intense) pattern as YHP and may have compensated age-effects at high task load. OLP showed neural inefficiency at low and no upregulation at higher load. Our findings highlight the relevance of age and performance level for load-dependent activation within rostral PFC. Results are discussed in the context of the compensation-related utilization of neural circuits hypothesis (CRUNCH) and functional PFC organization.

Prefrontal Engagement and Reduced Default Network Suppression Co-occur and Are Dynamically Coupled in Older Adults: The Default-Executive Coupling Hypothesis of Aging

Reduced executive control is a hallmark of neurocognitive aging. Poor modulation of lateral pFC activity in the context of increasing task challenge in old adults and a "failure to deactivate" the default network during cognitive control tasks have been observed. Whether these two patterns represent discrete mechanisms of neurocognitive aging or interact into older adulthood remains unknown. We examined whether altered pFC and default network dynamics co-occur during goal-directed planning over increasing levels of difficulty during performance on the Tower of London task. We used fMRI to investigate task- and age-related changes in brain activation and functional connectivity across four levels of task challenge. Frontoparietal executive control regions were activated and default network regions were suppressed during planning relative to counting performance in both groups. Older adults, unlike young, failed to modulate brain activity in executive control and default regions as planning demands increased. Critically, functional connectivity analyses revealed bilateral dorsolateral pFC coupling in young adults and dorsolateral pFC to default coupling in older adults with increased planning complexity. We propose a default-executive coupling hypothesis of aging. First, this hypothesis suggests that failure to modulate control and default network activity in response to increasing task challenge are linked in older adulthood. Second, functional brain changes involve greater coupling of lateral pFC and the default network as cognitive control demands increase in older adults. We speculate that these changes reflect an adaptive shift in cognitive approach as older adults come to rely more upon stored representations to support goal-directed task performance.

A review of causal mechanisms underlying the link between age-related hearing loss and cognitive decline

Accumulating evidence points to a link between age-related hearing loss and cognitive decline, but their relationship is not clear. Does one cause the other, or does some third factor produce both? The answer has critical implications for prevention, rehabilitation, and health policy but has been difficult to establish for several reasons. First, determining a causal relationship in natural, correlational samples is problematic, and hearing and cognition are difficult to measure independently. Here, we critically review the evidence for a link between hearing loss and cognitive decline. We conclude that the evidence is convincing, but that the effects are small when hearing is measured audiometrically. We review four different directional hypotheses that have been offered as explanations for such a link, and conclude that no single hypothesis is sufficient. We introduce a framework that highlights that hearing and cognition rely on shared neurocognitive resources, and relate to each other in several different ways. We also discuss interventions for sensory and cognitive decline that may permit more causal inferences.

The Dynamic Aging Mind: Revelations From Functional Neuroimaging Research

The conception of the aging mind that emerged from behavioral and structural imaging studies portrayed the mind as a victim of passive deterioration and decline with age, with a few domains of preserved function. The advent of functional neuroimaging has demonstrated that the aging brain is an adaptive and plastic structure that responds dynamically to cognitive challenge and structural deterioration-thus, fundamentally changing views of cognitive aging. In addition, a neural theory of the aging mind based on behavioral data-the dedifferentiation view of cognitive aging-was largely confirmed when neuroimaging technology became available to test it. We argue that functional neuroimaging has advanced cognitive aging theories by creating a stronger emphasis on compensatory mechanisms related to brain plasticity and potential reorganization as evidenced by the resurgence of interest and research in cognitive training research designed to improve cognition through enhancement of neural structures or reorganization of functional circuitry.

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.

Age-related striatal BOLD changes without changes in behavioral loss aversion

Loss aversion (LA), the idea that negative valuations have a higher psychological impact than positive ones, is considered an important variable in consumer research. The literature on aging and behavior suggests older individuals may show more LA, although it is not clear if this is an effect of aging in general (as in the continuum from age 20 and 50 years), or of the state of older age (e.g., past age 65 years). We also have not yet identified the potential biological effects of aging on the neural processing of LA. In the current study we used a cohort of subjects with a 30 year range of ages, and performed whole brain functional MRI (fMRI) to examine the ventral striatum/nucleus accumbens (VS/NAc) response during a passive viewing of affective faces with model-based fMRI analysis incorporating behavioral data from a validated approach/avoidance task with the same stimuli. Our a priori focus on the VS/NAc was based on (1) the VS/NAc being a central region for reward/aversion processing; (2) its activation to both positive and negative stimuli; (3) its reported involvement with tracking LA. LA from approach/avoidance to affective faces showed excellent fidelity to published measures of LA. Imaging results were then compared to the behavioral measure of LA using the same affective faces. Although there was no relationship between age and LA, we observed increasing neural differential sensitivity (NDS) of the VS/NAc to avoidance responses (negative valuations) relative to approach responses (positive valuations) with increasing age. These findings suggest that a central region for reward/aversion processing changes with age, and may require more activation to produce the same LA behavior as in younger individuals, consistent with the idea of neural efficiency observed with high IQ individuals showing less brain activation to complete the same task.

The implications of age-related neurofunctional compensatory mechanisms in executive function and language processing including the new Temporal Hypothesis for Compensation

As the passage of time structurally alters one’s brain, cognition does not have to suffer the same faith, at least not to the same extent. Indeed, the existence of age-related compensatory mechanisms allow for some cognitive preservation. This paper attempts to coherently review the existing concepts of neurofunctional compensation when applied to two different cognitive domains, namely executive function and language processing. More precisely, we explore the Cognitive reserve (CR) model in healthy aging as well as its two underlying mechanisms: neural reserve and neural compensation. Furthermore, we review the Compensation-Related Utilization of Neural Circuits Hypothesis as well as the Growing Of Life Differences Explains Normal Aging model. Finally, we propose, based on some functional neuroimaging studies, the existence of another compensatory mechanism characterized by age-related delayed cerebral activation allowing for cognitive performance to be preserved at the expense of speed processing: the Temporal Hypothesis for Compensation.

Context Memory Decline in Middle Aged Adults is Related to Changes in Prefrontal Cortex Function

The ability to encode and retrieve spatial and temporal contextual details of episodic memories (context memory) begins to decline at midlife. In the current study, event-related fMRI was used to investigate the neural correlates of context memory decline in healthy middle aged adults (MA) compared with young adults (YA). Participants were scanned while performing easy and hard versions of spatial and temporal context memory tasks. Scans were obtained at encoding and retrieval. Significant reductions in context memory retrieval accuracy were observed in MA, compared with YA. The fMRI results revealed that overall, both groups exhibited similar patterns of brain activity in parahippocampal cortex, ventral occipito-temporal regions and prefrontal cortex (PFC) during encoding. In contrast, at retrieval, there were group differences in ventral occipito-temporal and PFC activity, due to these regions being more activated in MA, compared with YA. Furthermore, only in YA, increased encoding activity in ventrolateral PFC, and increased retrieval activity in occipital cortex, predicted increased retrieval accuracy. In MA, increased retrieval activity in anterior PFC predicted increased retrieval accuracy. These results suggest that there are changes in PFC contributions to context memory at midlife.

Social incentives improve deliberative but not procedural learning in older adults

Age-related deficits are seen across tasks where learning depends on asocial feedback processing, however plasticity has been observed in some of the same tasks in social contexts suggesting a novel way to attenuate deficits. Socioemotional selectivity theory suggests this plasticity is due to a deliberative motivational shift toward achieving well-being with age (positivity effect) that reverses when executive processes are limited (negativity effect). The present study examined the interaction of feedback valence (positive, negative) and social salience (emotional face feedback – happy; angry, asocial point feedback – gain; loss) on learning in a deliberative task that challenges executive processes and a procedural task that does not. We predict that angry face feedback will improve learning in a deliberative task when executive function is challenged. We tested two competing hypotheses regarding the interactive effects of deliberative emotional biases on automatic feedback processing: (1) If deliberative emotion regulation and automatic feedback are interactive we expect happy face feedback to improve learning and angry face feedback to impair learning in older adults because cognitive control is available. (2) If deliberative emotion regulation and automatic feedback are not interactive we predict that emotional face feedback will not improve procedural learning regardless of valence. Results demonstrate that older adults show persistent deficits relative to younger adults during procedural category learning suggesting that deliberative emotional biases do not interact with automatic feedback processing. Interestingly, a subgroup of older adults identified as potentially using deliberative strategies tended to learn as well as younger adults with angry relative to happy feedback, matching the pattern observed in the deliberative task. Results suggest that deliberative emotional biases can improve deliberative learning, but have no effect on procedural learning.

Functional correlates of preserved naming performance in amnestic Mild Cognitive Impairment

Naming abilities are typically preserved in amnestic Mild Cognitive Impairment (aMCI), a condition associated with increased risk of progression to Alzheimer's disease (AD). We compared the functional correlates of covert picture naming and word reading between a group of aMCI subjects and matched controls. Unimpaired picture naming performance was associated with more extensive activations, in particular involving the parietal lobes, in the aMCI group. In addition, in the condition associated with higher processing demands (blocks of categorically homogeneous items, living items), increased activity was observed in the aMCI group, in particular in the left fusiform gyrus. Graph analysis provided further evidence of increased modularity and reduced integration for the homogenous sets in the aMCI group. The functional modifications associated with preserved performance may reflect, in the case of more demanding tasks, compensatory mechanisms for the subclinical involvement of semantic processing areas by AD pathology.

Attention and the Cholinergic System: Relevance to Schizophrenia

Traditional methods of drug discovery often rely on a unidirectional, "bottom-up" approach: A search for molecular compounds that target a particular neurobiological substrate (e.g., a receptor type), the refinement of those compounds, testing in animal models using high-throughput behavioral screening methods, and then human testing for safety and effectiveness. Many attempts have found the "effectiveness" criterion to be a major stumbling block, and we and others have suggested that success may be improved by an alternative approach that considers the neural circuits mediating the effects of genetic and molecular manipulations on behavior and cognition. We describe our efforts to understand the cholinergic system's role in attention using parallel approaches to test main hypotheses in both rodents and humans as well as generating converging evidence using methods and levels of analysis tailored to each species. The close back-and-forth between these methods has enhanced our understanding of the cholinergic system's role in attention both "bottom-up" and "top-down"-that is, the basic neuroscience identifies potential neuronal circuit-based mechanisms of clinical symptoms, and the patient and genetic populations serve as natural experiments to test and refine hypotheses about its contribution to specific processes. Together, these studies have identified (at least) two major and potentially independent contributions of the cholinergic system to attention: a neuromodulatory component that influences cognitive control in response to challenges from distractors that either make detection more difficult or draw attention away from the distractor, and a phasic or transient cholinergic signal that instigates a shift from ongoing behavior and the activation of cue-associated response. Right prefrontal cortex appears to play a particularly important role in the neuromodulatory component integrating motivational and cognitive influences for top-down control across populations, whereas the transient cholinergic signal involves orbitofrontal regions associated with shifts between internal and external attention. Understanding how these two modes of cholinergic function interact and are perturbed in schizophrenia will be an important prerequisite for developing effective treatments.

Cognitive reserve modulates ERPs associated with verbal working memory in healthy younger and older adults

Although many epidemiological studies suggest the beneficial effects of higher cognitive reserve (CR) in reducing age-related cognitive decline and dementia risk, the neural basis of CR is poorly understood. To our knowledge, the present study represents the first electrophysiological investigation of the relationship between CR and neural reserve (i.e., neural efficiency and capacity). Specifically, we examined whether CR modulates event-related potentials associated with performance on a verbal recognition memory task with 3 set sizes (1, 4, or 7 letters) in healthy younger and older adults. Neural data showed that as task difficulty increased, the amplitude of the parietal P3b component during the probe phase decreased and its latency increased. Notably, the degree of these neural changes was negatively correlated with CR in both age groups, such that individuals with higher CR showed smaller changes in P3b amplitude and less slowing in P3b latency (i.e., smaller changes in the speed of neural processing) with increasing task difficulty, suggesting greater neural efficiency. These CR-related differences in neural efficiency may underlie reserve against neuropathology and age-related burden.

An exploratory study of the effects of spatial working-memory load on prefrontal activation in low- and high-performing elderly

Older adults show more bilateral prefrontal activation during cognitive performance than younger adults, who typically show unilateral activation. This over-recruitment has been interpreted as compensation for declining structure and function of the brain. Here we examined how the relationship between behavioral performance and prefrontal activation is modulated by different levels of working-memory load. Eighteen healthy older adults (70.8 ± 5.0 years; MMSE 29.3 ± 0.9) performed a spatial working-memory task (n-back). Oxygenated ([O₂Hb]) and deoxygenated ([HHb]) hemoglobin concentration changes were registered by two functional Near-Infrared Spectroscopy (fNIRS) channels located over the left and right prefrontal cortex. Increased working-memory load resulted in worse performance compared to the control condition. [O₂Hb] increased with rising working-memory load in both fNIRS channels. Based on the performance in the high working-memory load condition, the group was divided into low and high performers. A significant interaction effect of performance level and hemisphere on [O₂Hb] increase was found, indicating that high performers were better able to keep the right prefrontal cortex engaged under high cognitive demand. Furthermore, in the low performers group, individuals with a larger decline in task performance from the control to the high working-memory load condition had a larger bilateral increase of [O₂Hb]. The high performers did not show a correlation between performance decline and working-memory load related prefrontal activation changes. Thus, additional bilateral prefrontal activation in low performers did not necessarily result in better cognitive performance. Our study showed that bilateral prefrontal activation may not always be successfully compensatory. Individual behavioral performance should be taken into account to be able to distinguish successful and unsuccessful compensation or declined neural efficiency.

Combined frontal and parietal P300 amplitudes indicate compensated cognitive processing across the lifespan

In the present study the frontal and parietal P300, elicited in an auditory oddball paradigm were investigated in a large sample of healthy participants (N = 1572), aged 6–87. According to the concepts of the compensation-related utilization of neural circuits hypothesis (CRUNCH) it was hypothesized that the developmental trajectories of the frontal P300 would reach a maximum in amplitude at an older age than the amplitude of the parietal P300 amplitude. In addition, the amplitude of the frontal P300 was expected to increase with aging in adulthood in contrast to a decline in amplitude of the parietal P300 amplitude. Using curve-fitting methods, a comparison was made between the developmental trajectories of the amplitudes of the frontal and parietal P300. It was found that the developmental trajectories of frontal and parietal P300 amplitudes differed significantly across the lifespan. During adulthood, the amplitude of the parietal P300 declines with age, whereas both the frontal P300 amplitude and behavioral performance remain unaffected. A lifespan trajectory of combined frontal and parietal P300 amplitudes was found to closely resemble the lifespan trajectory of behavioral performance. Our results can be understood within the concepts of CRUNCH. That is, to compensate for declining neural resources, older participants recruit additional neural resources of prefrontal origin and consequently preserve a stable behavioral performance. Though, a direct relation between amplitude of the frontal P300 and compensatory mechanisms cannot yet be claimed.

Age trajectories of functional activation under conditions of low and high processing demands: an adult lifespan fMRI study of the aging brain

We examined functional activation across the adult lifespan in 316 healthy adults aged 20-89years on a judgment task that, across conditions, drew upon both semantic knowledge and ability to modulate neural function in response to cognitive challenge. Activation in core regions of the canonical semantic network (e.g., left IFG) were largely age-invariant, consistent with cognitive aging studies that show verbal knowledge is preserved across the lifespan. However, we observed a steady linear increase in activation with age in regions outside the core network, possibly as compensation to maintain function. Under conditions of increased task demands, we observed a stepwise reduction across the lifespan of modulation of activation to increasing task demands in cognitive control regions (frontal, parietal, anterior cingulate), paralleling the neural equivalent of "processing resources" described by cognitive aging theories. Middle-age was characterized by decreased modulation to task-demand in subcortical regions (caudate, nucleus accumbens, thalamus), and very old individuals showed reduced modulation to task difficulty in midbrain/brainstem regions (ventral tegmental, substantia nigra). These novel findings suggest that aging of activation to demand follows a gradient along the dopaminergic/nigrostriatal system, with earliest manifestation in fronto-parietal regions, followed by deficits in subcortical nuclei in middle-age and then to midbrain/brainstem dopaminergic regions in the very old.

Brain functional correlates of working memory: reduced load-modulated activation and deactivation in aging without hyperactivation or functional reorganization

We aimed to identify brain functional correlates of working memory performance in aging, in hopes of facilitating understanding of mechanisms that promote better versus worse working memory in late-life. Among 64 healthy adults, aged 23 to 78, we examined the relationship between age, working memory performance, and brain functional response during task performance. We focused on the association between working memory load-modulated functional response and individual differences in performance and whether these function-performance relationships differed with age. As expected, older age was associated with poorer working memory performance. Older age was also associated with reduced load-modulated activation including in bilateral prefrontal and parietal regions and left caudate as well as reduced deactivation including in the medial prefrontal cortex. Contrary to findings of hyperactivation in aging, we found no evidence of increased activation with older age. Positive associations identified between brain response and performance did not differ with age. Our findings suggest that the neural mechanisms underlying better versus worse working memory performance are age-invariant across adulthood, and argue against a pattern of functional reorganization in aging. Results are discussed within the broader literature, in which significant heterogeneity in findings between studies has been common.

Assessment of Adult Age differences in Task Engagement: The Utility of Systolic Blood Pressure

The constructs of effort and engagement are central to many theoretical frameworks associated with the study of aging. Age differences in the effort associated with effortful cognitive operations have been hypothesized to account for aging effects in ability, and shifting goals and motivation have been hypothesized to be associated with differential levels of engagement across situations in younger and older adults. Unfortunately, the assessment of effort and engagement-constructs that we view as relatively synonymous-has suffered in the field of aging due to the lack of well-validated measures. We suggest that systolic blood pressure might provide an easy and valid means for examining age differences in mental effort, and present evidence in support of its usage. Existing findings clearly support its potential utility, but further empirical and theoretical work is necessary.

A theoretical framework for cognitive and non-cognitive interventions for older adults: stimulation versus compensation

BACKGROUND

Recently, interest in cognitive training for older adults has grown significantly, reflecting a need for preserving the quality of life into late adulthood. In spite of increasing interest in cognitive rehabilitation, recent meta-analyses have questioned reported training gains and determined that cognitive gain from cognitive training might be no larger than the gain observed from active controls such as unspecific, non-cognitive activities.

AIMS

This paper presents a theoretical framework for clarifying specificity of cognitive training by exploring mechanisms of current cognitive and non-cognitive interventions for older adults. By differentiating compensatory aspects from the components of specific and non-specific stimulation in current training, two related strategies of interventions for age-related cognitive decline, i.e., stimulation versus compensation, are proposed.

OVERVIEW

Current interventions for age-related cognitive decline are reviewed in terms of stimulation- and compensation-focused interventions. Stimulation-focused, cognitive and non-cognitive training, with or without specific targets, tend to result in general improvement in attention and sensory or other cognitive functions. Meanwhile, compensation-focused training is likely to be the most effective when the intervention specifically supports the frontally mediating activity in accordance with the direction of indigenous adjustments in the aging brain.

CONCLUSIONS

It can be inferred that stimulation-focused training is to ameliorate the adverse effects of neurological aging, whereas compensation-focused cognitive training is primarily to facilitate compensatory adaptation in the brain.

Age-related sensitivity to task-related modulation of language-processing networks

It is widely assumed that cognitive functions decline with age and that these decrements are associated with age-related changes in patterns of functional activity. However, these functional changes may be due to age-related increased responsiveness to task demands and not to other cognitive processes on which neural and behavioural responses rely, since many ageing studies use task paradigms that may not be orthogonal to the cognitive function being investigated. Here we test this hypothesis in adults aged 20–86 years by combining measures of language comprehension, functional connectivity and neural integrity to identify functional networks activated in two language experiments with varying task demands. In one, participants listened to spoken sentences without performing an overt task (the natural listening condition) while in the other they performed a task in response to the same sentences. Using task-based ICA of fMRI, we identified a left-lateralised frontotemporal network associated with syntactic analysis, which remained consistently activated regardless of task demands. In contrast, in the task condition only a separate set of components showed task-specific activity in Opercular, Frontoparietal, and bilateral PFC. Only the PFC showed age-related increases in activation which, furthermore, was strongly mediated by grey matter health. These results suggest that, contrary to prevailing views, age-related changes in cognitive activation may be due in part to differential responses to task-related processes.

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Ageing effects on brain activity may be over-estimated due to demands of tasks.

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Age differences in PFC network activity were present only during an active task.

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This age-related increase is largely accounted for by grey matter morphology.

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Results suggest that age-related changes may be due to task-related processes.

How does it STAC up? Revisiting the scaffolding theory of aging and cognition

"The Scaffolding Theory of Aging and Cognition (STAC)", proposed in 2009, is a conceptual model of cognitive aging that integrated evidence from structural and functional neuroimaging to explain how the combined effects of adverse and compensatory neural processes produce varying levels of cognitive function. The model made clear and testable predictions about how different brain variables, both structural and functional, were related to cognitive function, focusing on the core construct of compensatory scaffolding. The present paper provides a revised model that integrates new evidence about the aging brain that has emerged since STAC was published 5 years ago. Unlike the original STAC model, STAC-r incorporates life-course factors that serve to enhance or deplete neural resources, thereby influencing the developmental course of brain structure and function, as well as cognition, over time. Life-course factors also influence compensatory processes that are engaged to meet cognitive challenge, and to ameliorate the adverse effects of structural and functional decline. The revised model is discussed in relation to recent lifespan and longitudinal data as well as emerging evidence about the effects of training interventions. STAC-r goes beyond the previous model by combining a life-span approach with a life-course approach to understand and predict cognitive status and rate of cognitive change over time.

Age differences in the neural correlates of novelty processing: The effects of item-relatedness

Past research finds that age-related increases in false recognitions are a key contributor to age-related memory decline, suggesting that older adults have difficulty in correctly distinguishing between new and old information, particularly when new items at retrieval are semantically or perceptually related to items from encoding. However, little work has examined the neural mechanisms older adults engage to avoid false recognitions and successfully identify information as novel. In the present study, young and older adults were scanned during a retrieval task in which new items were exemplars from studied categories (related lures) or unstudied categories (unrelated lures) in order to detect age-related differences in the neural correlates of related and unrelated novelty processing. Results showed that, unlike young adults, older adults did not differentially recruit regions such as the anterior cingulate and bilateral middle/inferior temporal gyrus to capitalize on the salient categorical differences in unrelated items. Likewise, older adults did not differentially recruit regions of early visual cortex or anterior hippocampus, suggesting that older adults have difficulty using item-specific details to make successful related novelty decisions. Instead, older adults recruited bilateral ventrolateral prefrontal cortex differentially for successful novelty processing and particularly for related novelty processing. Overall, results suggest that age deficits in novelty processing may arise because older adults process related and unrelated lures similarly and do not capitalize on categorical or item-specific properties of novel items. Similar to aging patterns in memory retrieval, results also showed that older adults have the strongest novelty success activity in lateral PFC regions associated with control and monitoring processes. This article is part of a Special Issue entitled SI: Memory & Aging.

Age-related increase in brain activity during task-related and -negative networks and numerical inductive reasoning

OBJECTIVE

Recent neuroimaging studies have shown that elderly adults exhibit increased and decreased activation on various cognitive tasks, yet little is known about age-related changes in inductive reasoning.

METHODS

To investigate the neural basis for the aging effect on inductive reasoning, 15 young and 15 elderly subjects performed numerical inductive reasoning while in a magnetic resonance (MR) scanner.

RESULTS

Functional magnetic resonance imaging (fMRI) analysis revealed that numerical inductive reasoning, relative to rest, yielded multiple frontal, temporal, parietal, and some subcortical area activations for both age groups. In addition, the younger participants showed significant regions of task-induced deactivation, while no deactivation occurred in the elderly adults. Direct group comparisons showed that elderly adults exhibited greater activity in regions of task-related activation and areas showing task-induced deactivation (TID) in the younger group.

CONCLUSIONS

Our findings suggest an age-related deficiency in neural function and resource allocation during inductive reasoning.

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

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