Structural and functional differences in medial prefrontal cortex underlie distractibility and suppression deficits in ageing

Large-scale coupling of prefrontal activity patterns as a mechanism for cognitive control in health and disease: evidence from rodent models

Cognitive control of behavior is crucial for well-being, as allows subject to adapt to changing environments in a goal-directed way. Changes in cognitive control of behavior is observed during cognitive decline in elderly and in pathological mental conditions. Therefore, the recovery of cognitive control may provide a reliable preventive and therapeutic strategy. However, its neural basis is not completely understood. Cognitive control is supported by the prefrontal cortex, structure that integrates relevant information for the appropriate organization of behavior. At neurophysiological level, it is suggested that cognitive control is supported by local and large-scale synchronization of oscillatory activity patterns and neural spiking activity between the prefrontal cortex and distributed neural networks. In this review, we focus mainly on rodent models approaching the neuronal origin of these prefrontal patterns, and the cognitive and behavioral relevance of its coordination with distributed brain systems. We also examine the relationship between cognitive control and neural activity patterns in the prefrontal cortex, and its role in normal cognitive decline and pathological mental conditions. Finally, based on these body of evidence, we propose a common mechanism that may underlie the impaired cognitive control of behavior.

Aging pattern of the brainstem based on volumetric measurement and optimized surface shape analysis

The brainstem, a small and crucial structure, is connected to the cerebrum, spinal cord, and cerebellum, playing a vital role in regulating autonomic functions, transmitting motor and sensory information, and modulating cognitive processes, emotions, and consciousness. While previous research has indicated that changes in brainstem anatomy can serve as a biomarker for aging and neurodegenerative diseases, the structural changes that occur in the brainstem during normal aging remain unclear. This study aimed to examine the age- and sex-related differences in the global and local structural measures of the brainstem in 187 healthy adults (ranging in age from 18 to 70 years) using structural magnetic resonance imaging. The findings showed a significant negative age effect on the volume of the two major components of the brainstem: the medulla oblongata and midbrain. The shape analysis revealed that atrophy primarily occurs in specific structures, such as the pyramid, cerebral peduncle, superior and inferior colliculi. Surface area and shape analysis showed a trend of flattening in the aging brainstem. There were no significant differences between the sexes or sex-by-age interactions in brainstem structural measures. These findings provide a systematic description of age associations with brainstem structures in healthy adults and may provide a reference for future research on brain aging and neurodegenerative diseases.

Dual-functional network regulation underlies the central executive system in working memory

The frontoparietal network (FPN) and cingulo-opercular network (CON) may exert top-down regulation corresponding to the central executive system (CES) in working memory (WM); however, contributions and regulatory mechanisms remain unclear. We examined network interaction mechanisms underpinning the CES by depicting CON- and FPN-mediated whole-brain information flow in WM. We used datasets from participants performing verbal and spatial working memory tasks, divided into encoding, maintenance, and probe stages. We used general linear models to obtain task-activated CON and FPN nodes to define regions of interest (ROI); an online meta-analysis defined alternative ROIs for validation. We calculated whole-brain functional connectivity (FC) maps seeded by CON and FPN nodes at each stage using beta sequence analysis. We used Granger causality analysis to obtain the connectivity maps and assess task-level information flow patterns. For verbal working memory, the CON functionally connected positively and negatively to task-dependent and task-independent networks, respectively, at all stages. FPN FC patterns were similar only in the encoding and maintenance stages. The CON elicited stronger task-level outputs. Main effects were: stable CON→FPN, CON→DMN, CON→visual areas, FPN→visual areas, and phonological areas→FPN. The CON and FPN both up-regulated task-dependent and down-regulated task-independent networks during encoding and probing. Task-level output was slightly stronger for the CON. CON→FPN, CON→DMN, visual areas→CON, and visual areas→FPN showed consistent effects. The CON and FPN might together underlie the CES's neural basis and achieve top-down regulation through information interaction with other large-scale functional networks, and the CON may be a higher-level regulatory core in WM.

Stimulus specific cortical activity associated with ignoring distraction during working memory encoding and maintenance

Distraction disrupts Working Memory (WM) performance, but how the brain filters distraction is not known. One possibility is that neural activity associated with distractions is suppressed relative to a baseline/passive task (biased competition). Alternatively, distraction may be denied access to WM, with no suppression. Furthermore, behavioural work indicates separate mechanisms for ignoring distractions which occur (1) while we put information into WM (Encoding Distraction, ED) and (2) while we maintain already encoded information during the WM delay period (Delay Distraction, DD). Here we used fMRI in humans to measure category-sensitive cortical activity and probe the extent to which ED/DD mechanisms involve enhancement/suppression during a WM task. We observed significant enhancement of task-relevant activity, relative to a passive view task, which did not differ according to whether or when distractors appeared. For both ED and DD we found no evidence of suppression, but instead a robust increase in stimulus specific activity in response to additional stimuli presented during the passive view task, which was not seen for the WM task, when those additional stimuli were to be ignored. The results indicate that ED/DD resistance does not necessarily involve suppression of distractor-related activity. Rather, a rise in distractor-associated activity is prevented when distractors are presented, supporting models of input gating, and providing a potential mechanism by which input-gating might be achieved.

The effect of acute exercise on cognitive and motor inhibition - Does fitness moderate this effect?

BACKGROUND

Given the extensive evidence on improvements in cognitive inhibition immediately following exercise, and the literature indicating that cognitive and motor inhibitory functions are mediated by overlapping brain networks, the aim of this study was to assess, for the first time, the effect of moderate intensity acute aerobic exercise on multi-limb motor inhibition, as compared to cognitive inhibition.

METHOD

Participants were 36 healthy adults aged 40-60 years old (mean age 46.8 ± 5.7), who were randomly assigned to experimental or control groups. One-to-two weeks following baseline assessment, participants were asked to perform a three-limb (3-Limb) inhibition task and a vocal version of the Stroop before and after either acute moderate-intense aerobic exercise (experimental group) or rest (control).

RESULTS

Similar rates of improvement were observed among both groups from baseline to the pre-test. Conversely, a meaningful, yet non-significant trend was seen among the experimental group in their pretest to posttest improvement in both cognitive and motor tasks. In addition, exploratory analysis revealed significant group differences in favor of the experimental group among highly fit participants on the 3-Limb task. A significant correlation was indicated between the inhibition conditions, i.e., choice in the motor inhibition and color/word (incongruent) in the cognitive inhibition, especially in the improvement observed following the exercise.

DISCUSSION

Moderate-intensity acute aerobic exercise is a potential stimulator of both multi-limb motor inhibition and cognitive inhibition. It appears that high-fit participants benefit from exercise more than low-fit people. Additionally, performance on behavioral tasks that represent motor and cognitive inhibition is related. This observation suggests that fitness levels and acute exercise contribute to the coupling between cognitive and motor inhibition. Neuroimaging methods would allow examining brain-behavior associations of exercise-induced changes in the brain.

Dissociable neural mechanisms of cognition and well-being in youth versus healthy aging

Mental health, cognition, and their underlying neural processes in healthy aging are rarely studied simultaneously. Here, in a sample of healthy younger (n = 62) and older (n = 54) adults, we compared subjective mental health as well as objective global cognition across several core cognitive domains with simultaneous electroencephalography (EEG). We found significantly greater symptoms of anxiety, depression, and loneliness in youth and in contrast, greater mental well-being in older adults. Yet, global performance across core cognitive domains was significantly worse in older adults. EEG-based source imaging of global cognitive task-evoked processing showed reduced suppression of activity in the anterior medial prefrontal default mode network (DMN) region in older adults relative to youth. Global cognitive performance efficiency was predicted by greater activity in the right dorsolateral prefrontal cortex in younger adults and in contrast, by greater activity in right inferior frontal cortex in older adults. Furthermore, greater mental well-being in older adults related to lesser global task-evoked activity in the posterior DMN. Overall, these results suggest dissociated neural mechanisms underlying global cognition and mental well-being in youth versus healthy aging. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

How musical rhythm training improves short-term memory for faces

Playing a musical instrument engages numerous cognitive abilities, including sensory perception, selective attention, and short-term memory. Mounting evidence indicates that engaging these cognitive functions during musical training will improve performance of these same functions. Yet, it remains unclear the extent these benefits may extend to nonmusical tasks, and what neural mechanisms may enable such transfer. Here, we conducted a preregistered randomized clinical trial where nonmusicians underwent 8 wk of either digital musical rhythm training or word search as control. Only musical rhythm training placed demands on short-term memory, as well as demands on visual perception and selective attention, which are known to facilitate short-term memory. As hypothesized, only the rhythm training group exhibited improved short-term memory on a face recognition task, thereby providing important evidence that musical rhythm training can benefit performance on a nonmusical task. Analysis of electroencephalography data showed that neural activity associated with sensory processing and selective attention were unchanged by training. Rather, rhythm training facilitated neural activity associated with short-term memory encoding, as indexed by an increased P3 of the event-related potential to face stimuli. Moreover, short-term memory maintenance was enhanced, as evidenced by increased two-class (face/scene) decoding accuracy. Activity from both the encoding and maintenance periods each highlight the right superior parietal lobule (SPL) as a source for training-related changes. Together, these results suggest musical rhythm training may improve memory for faces by facilitating activity within the SPL to promote how memories are encoded and maintained, which can be used in a domain-general manner to enhance performance on a nonmusical task.

Aberrant resting-state connectivity of auditory, ventral attention/salience and default-mode networks in adults with attention deficit hyperactivity disorder

Background

Numerous resting-state studies on attention deficit hyperactivity disorder (ADHD) have reported aberrant functional connectivity (FC) between the default-mode network (DMN) and the ventral attention/salience network (VA/SN). This finding has commonly been interpreted as an index of poorer DMN regulation associated with symptoms of mind wandering in ADHD literature. However, a competing perspective suggests that dysfunctional organization of the DMN and VA/SN may additionally index increased sensitivity to the external environment. The goal of the current study was to test this latter perspective in relation to auditory distraction by investigating whether ADHD-adults exhibit aberrant FC between DMN, VA/SN, and auditory networks.

Methods

Twelve minutes of resting-state fMRI data was collected from two adult groups: ADHD (n = 17) and controls (n = 17); from which the FC between predefined regions comprising the DMN, VA/SN, and auditory networks were analyzed.

Results

A weaker anticorrelation between the VA/SN and DMN was observed in ADHD. DMN and VA/SN hubs also exhibited aberrant FC with the auditory network in ADHD. Additionally, participants who displayed a stronger anticorrelation between the VA/SN and auditory network at rest, also performed better on a cognitively demanding behavioral task that involved ignoring a distracting auditory stimulus.

Conclusion

Results are consistent with the hypothesis that auditory distraction in ADHD is linked to aberrant interactions between DMN, VA/SN, and auditory systems. Our findings support models that implicate dysfunctional organization of the DMN and VA/SN in the disorder and encourage more research into sensory interactions with these major networks.

Structural and functional variations in the prefrontal cortex are associated with learning in pre-adolescent common marmosets (Callithrix jacchus)

There is substantial evidence linking the prefrontal cortex (PFC) to a variety of cognitive abilities, with adolescence being a critical period in its development. In the current study, we investigated the neural basis of differences in learning in pre-adolescent common marmosets. At 8 months old, marmosets were given anatomical and resting state MRI scans (n=24). At 9 months old, association learning and inhibitory control was tested using a 'go/no go' visual discrimination (VD) task. Marmosets were grouped into 'learners' (n=12) and 'non-learners' (n=12), and associations between cognitive performance and sub-regional PFC volumes, as well as PFC connectivity patterns, were investigated. 'Learners' had significantly (p<0.05) larger volumes of areas 11, 25, 47 and 32 than 'non-learners', although 'non-learners' had significantly larger volumes of areas 24a and 8v than 'learners'. There was also a significant correlation between average % correct responses to the 'punished' stimulus and volume of area 47. Further, 'non-learners' had significantly greater global PFC connections, as well as significantly greater numbers of connections between the PFC and basal ganglia, cerebellum and hippocampus, compared to 'non-learners'. These results suggest that larger sub-regions of the orbitofrontal cortex and ventromedial PFC, as well more refined PFC connectivity patterns to other brain regions associated with learning, may be important in successful response inhibition. This study therefore offers new information on the neurodevelopment of individual differences in cognition during pre-adolescence in non-human primates.

Influence of target-distractor neural similarity on working memory performance in older and younger adults

According to the inhibitory deficit hypothesis, older adults often fail to selectively inhibit distractors and attend to relevant information in working memory, leading to poorer memory of target items but better recall of irrelevant distractors compared to younger adults. Here, we explored how neural similarity of activity patterns between relevant and irrelevant stimulus categories impacts memory performance. We found evidence that older adults may benefit from failing to inhibit distractors that are similar to targets, perhaps because sustained neural activation of distractors partially supports maintenance of targets when they share neural resources, allowing for better subsequent recognition of studied target items. We also found increased category-specific multivoxel pattern activity in medial temporal regions in younger compared to older adults as category similarity increased. We propose that this reduced category-specific activation in medial temporal regions in older adults may reflect more blended representations of all the information available in working memory.

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.

Age Differences of the Hierarchical Cognitive Control and the Frontal Rostro-Caudal Functional Brain Activation

Age-related differences in the functional hierarchical organization of the frontal lobe remain unclear. We adopted task-related functional magnetic resonance imaging (fMRI) to investigate age differences in the functional hierarchical organization of the frontal lobe. Behavioral results report both reaction time and efficiency declined as the levels of abstraction increased in the selection of a set of stimulus–response mappings in older adults compared with young adults. fMRI findings suggest trends of the hierarchical organization along the rostro–caudal axis in both groups, and brain–behavior correlation further suggests neural dedifferentiation in older adults when performing at the highest level of control demands experiment. Behavioral performances and age difference overactivations at the highest level of control demands were both associated with working memory capacity, suggesting the working memory capacity is important for processing the highest task demands. Region-of-interest analysis revealed age differences in brain overactivation and common activation across experiments in the primary motor cortex, parietal lobule, and the fusiform gyrus may serve as shared mechanisms underlying tasks that are required for the selection of stimulus–response mapping sets. Overall, older adults reflect maladaptive overactivation in task-irrelevant regions that are detrimental to performance with the highest control demands.

Prefrontal cortex and cognitive aging in macaque monkeys

Cognitive impairments that accompany aging, even in the absence of neurodegenerative diseases, include deficits in executive function and memory mediated by the prefrontal cortex. Because of the unique differentiation and expansion of the prefrontal cortex in primates, investigations of the neurobiological basis of cognitive aging in nonhuman primates have been particularly informative about the potential basis for age-related cognitive decline in humans. We review the cognitive functions mediated by specific subregions of prefrontal cortex, and their corresponding connections, as well as the evidence for age-related alterations in specific regions of prefrontal cortex. We also discuss evidence for similarities and differences in the effects of aging on prefrontal cortex across species.

MRI of healthy brain aging: A review

We present a review of the characterization of healthy brain aging using MRI with an emphasis on morphology, lesions, and quantitative MR parameters. A scope review found 6612 articles encompassing the keywords "Brain Aging" and "Magnetic Resonance"; papers involving functional MRI or not involving imaging of healthy human brain aging were discarded, leaving 2246 articles. We first consider some of the biogerontological mechanisms of aging, and the consequences of aging in terms of cognition and onset of disease. Morphological changes with aging are reviewed for the whole brain, cerebral cortex, white matter, subcortical gray matter, and other individual structures. In general, volume and cortical thickness decline with age, beginning in mid-life. Prevalent silent lesions such as white matter hyperintensities, microbleeds, and lacunar infarcts are also observed with increasing frequency. The literature regarding quantitative MR parameter changes includes T₁ , T₂ , T₂ *, magnetic susceptibility, spectroscopy, magnetization transfer, diffusion, and blood flow. We summarize the findings on how each of these parameters varies with aging. Finally, we examine how the aforementioned techniques have been used for age prediction. While relatively large in scope, we present a comprehensive review that should provide the reader with sound understanding of what MRI has been able to tell us about how the healthy brain ages.

Long-term maintenance of multitasking abilities following video game training in older adults

The use of cognitive interventions to remediate deficient cognitive functions, or to enhance or preserve intact cognitive abilities, has been explored for some time, especially in older adults. However, few studies have investigated the long-term persistence of any positive benefits, with none examining whether changes in functional brain activity persist several years later. Here, we assessed whether enhanced cognitive abilities and potential underlying neural changes attained via the use of a custom-made video game (NeuroRacer) played by older adults (60-85 years old) continued to be elevated beyond control participants 6 years later. The NeuroRacer group continued to show reduced multitasking costs beyond control participants, with a neural signature of cognitive control, midline frontal theta power, also continuing to show heightened activity. However, previously evidenced performance benefits that had extended to untrained cognitive control abilities (i.e., enhanced sustained attention and working memory) did not persist, highlighting sustainability limitations. These findings continue to demonstrate the robust plasticity of the prefrontal cognitive control system in the aging brain, a potential neural mechanism underlying enhanced performance over time, and the possible long-term impact that digital therapeutics can have.

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.

Effects of age on goal-dependent modulation of episodic memory retrieval

Retrieval gating refers to the ability to modulate the retrieval of features of a single memory episode according to behavioral goals. Recent findings demonstrate that younger adults engage retrieval gating by attenuating the representation of task-irrelevant features of an episode. Here, we examine whether retrieval gating varies with age. Younger and older adults incidentally encoded words superimposed over scenes or scrambled backgrounds that were displayed in one of three spatial locations. Participants subsequently underwent fMRI as they completed two memory tasks: the background task, which tested memory for the word's background, and the location task, testing memory for the word's location. Employing univariate and multivariate approaches, we demonstrated that younger, but not older adults, exhibited attenuated reinstatement of scene information when it was goal-irrelevant (during the location task). Additionally, in younger adults only, the strength of scene reinstatement in the parahippocampal place area during the background task was related to item and source memory performance. Together, these findings point to an age-related decline in the ability to engage retrieval gating.

Abstract Neural Representations of Category Membership beyond Information Coding Stimulus or Response

For decades, researchers have debated whether mental representations are symbolic or grounded in sensory inputs and motor programs. Certainly, aspects of mental representations are grounded. However, does the brain also contain abstract concept representations that mediate between perception and action in a flexible manner not tied to the details of sensory inputs and motor programs? Such conceptual pointers would be useful when concepts remain constant despite changes in appearance and associated actions. We evaluated whether human participants acquire such representations using fMRI. Participants completed a probabilistic concept learning task in which sensory, motor, and category variables were not perfectly coupled or entirely independent, making it possible to observe evidence for abstract representations or purely grounded representations. To assess how the learned concept structure is represented in the brain, we examined brain regions implicated in flexible cognition (e.g., pFC and parietal cortex) that are most likely to encode an abstract representation removed from sensory-motor details. We also examined sensory-motor regions that might encode grounded sensory-motor-based representations tuned for categorization. Using a cognitive model to estimate participants' category rule and multivariate pattern analysis of fMRI data, we found the left pFC and MT coded for category in the absence of information coding for stimulus or response. Because category was based on the stimulus, finding an abstract representation of category was not inevitable. Our results suggest that certain brain areas support categorization behavior by constructing concept representations in a format akin to a symbol that differs from stimulus-motor codes.

Pupillometry as an Objective Measure of Sustained Attention in Young and Older Listeners

The ability to sustain attention on a task-relevant sound source while avoiding distraction from concurrent sounds is fundamental to listening in crowded environments. We aimed to (a) devise an experimental paradigm with which this aspect of listening can be isolated and (b) evaluate the applicability of pupillometry as an objective measure of sustained attention in young and older populations. We designed a paradigm that continuously measured behavioral responses and pupillometry during 25-s trials. Stimuli contained a number of concurrent, spectrally distinct tone streams. On each trial, participants detected gaps in one of the streams while resisting distraction from the others. Behavior demonstrated increasing difficulty with time-on-task and with number/proximity of distractor streams. In young listeners (N = 20; aged 18 to 35 years), pupil diameter (on the group and individual level) was dynamically modulated by instantaneous task difficulty: Periods where behavioral performance revealed a strain on sustained attention were accompanied by increased pupil diameter. Only trials on which participants performed successfully were included in the pupillometry analysis so that the observed effects reflect task demands as opposed to failure to attend. In line with existing reports, we observed global changes to pupil dynamics in the older group (N = 19; aged 63 to 79 years) including decreased pupil diameter, limited dilation range, and reduced temporal variability. However, despite these changes, older listeners showed similar effects of attentive tracking to those observed in the young listeners. Overall, our results demonstrate that pupillometry can be a reliable and time-sensitive measure of attentive tracking over long durations in both young and (with caveats) older listeners.

The same, but different: Preserved distractor suppression in old age is implemented through an age-specific reactive ventral fronto-parietal network

Previous studies have shown age-related impairments in the ability to suppress salient distractors. One possibility is that this is mediated by age-related impairments in the recruitment of the left intraparietal sulcus (Left IPS), which has been shown to mediate the suppression of salient distractors in healthy, young participants. Alternatively, this effect may be due to a shift in engagement from proactive control to reactive control, possibly to compensate for age-related impairments in proactive control. Another possibility is that this is due to changes in the functional specificity of brain regions that mediate salience suppression, expressed in changes in spontaneous connectivity of these regions. We assessed these possibilities by having participants engage in a proactive distractor suppression task while in an fMRI scanner. Although we did not find any age-related differences in behavior, the young (N = 15) and older (N = 15) cohorts engaged qualitatively distinctive brain networks to complete the task. Younger participants engaged the predicted proactive control network, including the Left IPS. On the other hand, older participants simultaneously engaged both a proactive and a reactive network, but this was not a consequence of reduced network specificity as resting state functional connectivity was largely comparable in both age groups. Furthermore, improved behavioral performance for older adults was associated with increased resting state functional connectivity between these two networks. Overall, the results of this study suggest that age-related differences in the recruitment of a left lateralized ventral fronto-parietal network likely reflect the specific recruitment of reactive control mechanisms for distractor inhibition.

Neural capacity limits on the responses to memory interference during working memory in young and old adults

Advancing age affects the recruitment of task related neural resources thereby changing the efficiency, capacity and use of compensatory processes. With advancing age, brain activity may therefore increase within a region or be reorganized to utilize different brain regions. The different brain regions may be exclusive to old adults or accessible to young and old alike, but non-optimal. Interference during verbal working memory information retention recruits parahippocampal brain regions in young adults similar to brain activity recruited by old adults in the absence of external interference. The current work tests the hypothesis that old adults recruit neural resources to combat increases in age-related intrinsic noise that young adults recruit during high levels of interference during information retention. This experiment administered a verbal delayed item recognition task with low and high levels of an interfering addition task during information maintenance. Despite strong age-related behavioral effects, brain imaging results demonstrated no significant interaction effects between age group and the interference or memory tasks. Significant effects were only found for the interaction between interference level and memory load within the inferior frontal cortex, supplementary motor cortex and posterior supramarginal regions. Results demonstrate that neural resources were shared when facing increasing memory load and interference. The combined cognitive demands resulted in brain activity reaching a neural capacity limit which was similar for both age groups and which brain activation did not increase above. Despite significant behavioral differences the neural capacity limited the detection of age group differences in brain activity.

Holding On to the Past: Older Adults Show Lingering Neural Activation of No-Longer-Relevant Items in Working Memory

Goal-relevant information can be maintained in working memory over a brief delay interval to guide an upcoming decision. There is also evidence suggesting the existence of a complementary process: namely, the ability to suppress information that is no longer relevant to ongoing task goals. Moreover, this ability to suppress or inhibit irrelevant information appears to decline with age. In this study, we compared younger and older adults undergoing fMRI on a working memory task designed to address whether the modulation of neural representations of relevant and no-longer-relevant items during a delay interval is related to age and overall task performance. Following from the theoretical predictions of the inhibitory deficit hypothesis of aging, we hypothesized that older adults would show higher activation of no-longer-relevant items during a retention delay compared to young adults and that higher activation of these no-longer-relevant items would predict worse recognition memory accuracy for relevant items. Our results support this prediction and more generally demonstrate the importance of goal-driven modulation of neural activity in successful working memory maintenance. Furthermore, we showed that the largest age differences in the regulation of category-specific pattern activity during working memory maintenance were seen throughout the medial temporal lobe and prominently in the hippocampus, further establishing the importance of "long-term memory" retrieval mechanisms in the context of high-load working memory tasks that place large demands on attentional selection mechanisms.

Dysfunction of Inferior Parietal Lobule During Sensory Gating in Patients With Amnestic Mild Cognitive Impairment

Patients with amnestic mild cognitive impairment (aMCI) demonstrate significant cognitive deficits, especially in the memory aspect. The memory deficiency might be attributed to the difficulties in the inhibitory function to suppress redundant stimuli. Sensory gating (SG) refers to the attenuation of neural responses to the second identical stimulus in a paired-click paradigm, in which auditory stimuli are delivered in pairs with inter-stimulus intervals (ISI) of 500 ms and inter-pair intervals of 6-8 s. It is considered as an electrophysiological signal to reflect the brain's automatic response to gate out repetitive sensory inputs. However, there has been no study systematically investigating SG function in aMCI patients. Thus, the present study used magnetoencephalography (MEG) to record neuromagnetic responses to a paired-click paradigm in 23 healthy controls (HC) and 26 aMCI patients. The Stimulus 2/Stimulus 1 (S2/S1) amplitude ratio was used to represent the SG function. Compared to HC, aMCI patients showed M50 SG deficits in the left inferior frontal gyrus (IFG) and right inferior parietal lobule (IPL). M100 SG defects were also observed in the right IPL. Based on the ROIs showing significant between-group SG differences, we found that a more deficient M50 SG function in the right IPL was associated with poorer performance in the immediate recall of Logic Memory (LM), Chinese Version Verbal Learning Test (CVVLT) and Digit Span Backward (DSB) Test. Furthermore, the M50 SG ratios of the right IPL together with the neuropsychological performance of LM and CVVLT demonstrated very good accuracy in the discrimination of aMCI from HC. In conclusion, compared to HC, aMCI patients showed a significant SG deficit in the right IPL, which was correlated with the auditory short-term memory function. We suggest the combination of SG in the right IPL, LM and CVVLT to be sensitive indicators to differentiate aMCI patients from HC.

The Decline in Intrinsic Connectivity Between the Salience Network and Locus Coeruleus in Older Adults: Implications for Distractibility

We examined functional connectivity between the locus coeruleus (LC) and the salience network in healthy young and older adults to investigate why people become more prone to distraction with age. Recent findings suggest that the LC plays an important role in focusing processing on salient or goal-relevant information from multiple incoming sensory inputs (Mather et al., 2016). We hypothesized that the connection between LC and the salience network declines in older adults, and therefore the salience network fails to appropriately filter out irrelevant sensory signals. To examine this possibility, we used resting-state-like fMRI data, in which all task-related activities were regressed out (Fair et al., 2007; Elliott et al., 2019) and performed a functional connectivity analysis based on the time-course of LC activity. Older adults showed reduced functional connectivity between the LC and salience network compared with younger adults. Additionally, the salience network was relatively more coupled with the frontoparietal network than the default-mode network in older adults compared with younger adults, even though all task-related activities were regressed out. Together, these findings suggest that reduced interactions between LC and the salience network impairs the ability to prioritize the importance of incoming events, and in turn, the salience network fails to initiate network switching (e.g., Menon and Uddin, 2010; Uddin, 2015) that would promote further attentional processing. A chronic lack of functional connection between LC and salience network may limit older adults' attentional and executive control resources.

Multiscale Imaging Reveals Aberrant Functional Connectome Organization and Elevated Dorsal Striatal Arc Expression in Advanced Age

The functional connectome reflects a network architecture enabling adaptive behavior that becomes vulnerable in advanced age. The cellular mechanisms that contribute to altered functional connectivity in old age, however, are not known. Here we used a multiscale imaging approach to link age-related changes in the functional connectome to altered expression of the activity-dependent immediate-early gene Arc as a function of training to multitask on a working memory (WM)/biconditional association task (BAT). Resting-state fMRI data were collected from young and aged rats longitudinally at three different timepoints during cognitive training. After imaging, rats performed the WM/BAT and were immediately sacrificed to examine expression levels of Arc during task performance. Aged behaviorally impaired, but not young, rats had a subnetwork of increased connectivity between the anterior cingulate cortex (ACC) and dorsal striatum (DS) that was correlated with the use of a suboptimal response-based strategy during cognitive testing. Moreover, while young rats had stable rich-club organization across three scanning sessions, the rich-club organization of old rats increased with cognitive training. In a control group of young and aged rats that were longitudinally scanned at similar time intervals, but without cognitive training, ACC-DS connectivity and rich-club organization did not change between scans in either age group. These findings suggest that aberrant large-scale functional connectivity in aged animals is associated with altered cellular activity patterns within individual brain regions.

Neural markers of category-based selective working memory in aging

Working memory (WM) is essential for normal cognitive function, but shows marked decline in aging. The importance of selective attention in guiding WM performance is increasingly recognized. Studies so far are inconclusive about the ability to use selective attention during WM in aging. To investigate the neural mechanisms supporting selective attention in WM in aging, we tested a large group of older adults using functional magnetic resonance imaging whilst they performed a category-based (faces/houses) selective-WM task. Older adults were able to use attention to encode targets and suppress distractors to reach high levels of task performance. A subsequent, surprise recognition-memory task showed strong consequences of selective attention. Attended items in the relevant category were recognized significantly better than items in the ignored category. Neural measures also showed reliable markers of selective attention during WM. Purported control regions including the dorsolateral and inferior prefrontal and anterior cingulate cortex were reliably recruited for attention to both categories. Activation levels in category-sensitive visual cortex showed reliable modulation according to attentional demands, and positively correlated with subsequent memory measures of attention and WM span. Psychophysiological interaction analyses showed that activity in category-sensitive areas were coupled with non-sensory cortex known to be involved in cognitive control and memory processing, including regions in the prefrontal cortex and hippocampus. In summary, we found that older adults were able to recruit a network of brain regions involved in top-down attention during selective WM, and individual differences in attentional control corresponded to the degree of attention-related modulation in the brain.

Working memory revived in older adults by synchronizing rhythmic brain circuits

Understanding normal brain aging and developing methods to maintain or improve cognition in older adults are major goals of fundamental and translational neuroscience. Here we show a core feature of cognitive decline-working-memory deficits-emerges from disconnected local and long-range circuits instantiated by theta-gamma phase-amplitude coupling in temporal cortex and theta phase synchronization across frontotemporal cortex. We developed a noninvasive stimulation procedure for modulating long-range theta interactions in adults aged 60-76 years. After 25 min of stimulation, frequency-tuned to individual brain network dynamics, we observed a preferential increase in neural synchronization patterns and the return of sender-receiver relationships of information flow within and between frontotemporal regions. The end result was rapid improvement in working-memory performance that outlasted a 50 min post-stimulation period. The results provide insight into the physiological foundations of age-related cognitive impairment and contribute to groundwork for future non-pharmacological interventions targeting aspects of cognitive decline.

Aging of the frontal lobe

Healthy aging is associated with numerous deficits in cognitive function, which have been attributed to changes within the prefrontal cortex (PFC). This chapter summarizes some of the most prominent cognitive changes associated with age-related alterations in the anatomy and physiology of the PFC. Specifically, aging of the PFC results in deficient aspects of cognitive control, including sustained attention, selective attention, inhibitory control, working memory, and multitasking abilities. Yet, not all cognitive functions associated with the PFC exhibit age-related declines, such as arithmetic, comprehension, emotion perception, and emotional control. Moreover, not all older adults exhibit declines in cognition. Multiple life-course and lifestyle factors, as well as genetics, play a role in the trajectory of cognitive performance across the life span. Thus many adults retain cognitive function well into advanced age. Moreover, the brain remains plastic throughout life and there is increasing evidence that most age-related declines in cognition can be remediated by various methods such as physical exercise, cognitive training, or noninvasive brain stimulation. Overall, because cognitive aging is associated with numerous life-course and lifestyle factors, successful aging likely begins in early life, while maintaining cognition or remediating declines is a life-long process.

Perforant Path Fiber Loss Results in Mnemonic Discrimination Task Deficits in Young Rats

The observation that entorhinal input to the hippocampus declines in old age is well established across human studies and in animal models. This loss of perforant path fibers is exaggerated in individuals with episodic memory deficits and Mild Cognitive Impairment, suggesting that perforant path integrity is associated with progression to Alzheimer's Disease. During normal aging, behaviors that measure the ability of a study participant to discriminate between stimuli that share features is particularly sensitive to perforant fiber loss. Evidence linking perforant path changes to cognitive decline, however, has been largely correlational. Thus, the current study tested the causative role of perforant path fiber loss in behavioral decline by performing a unilateral knife cut to disconnect the entorhinal cortex from the hippocampus in the right hemisphere in young male and female rats. This approach does not completely disconnect the hippocampus from the entorhinal cortex but rather reduces the effective connectivity between these two structures. Male and female rats were then tested on the rodent variant of the mnemonic discrimination task, which is believed to critically rely on perforant path fiber integrity. Right hemisphere perforant path transections produced a significant impairment in the abilities of lesioned animals to discriminate between objects with high levels of feature overlap. This deficit was not observed in the male and female sham groups that received a cut to cortex above the white matter. Together these data support the view that, across species, age-related perforant path fiber loss produces behavioral deficits in the ability to discriminate between stimuli with perceptual overlap.

Age differences in the neural response to emotional distraction during working memory encoding

Age-related declines in attention and working memory (WM) are well documented and may be worsened by the occurrence of distracting information. Emotionally valenced stimuli may have particularly strong distracting effects on cognition. We investigated age-related differences in emotional distraction using task-fMRI. WM performance in older adults was lower for emotional compared with neutral distractors, suggesting a disproportional impairment elicited by emotional task-irrelevant information. Critically, older adults were particularly distracted by task-irrelevant positive information, whereas the opposite pattern was found for younger adults. Age groups differed markedly in the brain response to emotional distractors; younger adults activated posterior cortical regions and the striatum, and older adults activated frontal regions. Also, an age by valence interaction was found for IFG and ACC, suggesting differential modulation of attention to task-relevant emotional information. These results provide new insights into age-related changes in emotional processing and the ability to resolve interference from emotional distraction.

Age-related changes in the ease of dynamical transitions in human brain activity

Executive functions, a set of cognitive processes that enable flexible behavioral control, are known to decay with aging. Because such complex mental functions are considered to rely on the dynamic coordination of functionally different neural systems, the age-related decline in executive functions should be underpinned by alteration of large-scale neural dynamics. However, the effects of age on brain dynamics have not been firmly formulated. Here, we investigate such age-related changes in brain dynamics by applying "energy landscape analysis" to publicly available functional magnetic resonance imaging data from healthy younger and older human adults. We quantified the ease of dynamical transitions between different major patterns of brain activity, and estimated it for the default mode network (DMN) and the cingulo-opercular network (CON) separately. We found that the two age groups shared qualitatively the same trajectories of brain dynamics in both the DMN and CON. However, in both of networks, the ease of transitions was significantly smaller in the older than the younger group. Moreover, the ease of transitions was associated with the performance in executive function tasks in a doubly dissociated manner: for the younger adults, the ability of executive functions was mainly correlated with the ease of transitions in the CON, whereas that for the older adults was specifically associated with the ease of transitions in the DMN. These results provide direct biological evidence for age-related changes in macroscopic brain dynamics and suggest that such neural dynamics play key roles when individuals carry out cognitively demanding tasks.

Chronic amphetamine treatment affects collicular-dependent behaviour

Distractibility can be defined as an attention deficit where orientation toward irrelevant targets cannot be inhibited. There is now mounting evidence that the superior colliculus is a key neural correlate of distractibility, with increased collicular-activity resulting in heightened distractibility. Heightened distractibility is reduced by amphetamine, which acutely suppresses collicular responsiveness. However, when amphetamine is used to treat distractibility, it is given chronically, yet no data exist on whether chronic amphetamine treatment affects the colliculus. Here, the effect of chronic amphetamine treatment was assessed in healthy hooded lister rats on two collicular dependent behaviours following a twenty-eight day treatment period: i) orienting to visual stimuli, and ii) height-dependent modulation of air-righting. We found no significant impact of amphetamine treatment on visual orienting despite showing dose-dependent decreases in orienting to repeated stimuli. However, we did find that treatment with amphetamine significantly reduced the ability to modulate righting according to the height the animal is dropped from - a function known to be dependent on the colliculus. We suggest that the results are in line with previous research showing acute amphetamine suppresses collicular activity and we speculate that the psychostimulant may increase receptive field size, altering time-to-impact calculations carried out by the colliculus during air-righting.

Selective attention on representations in working memory: cognitive and neural mechanisms

Selective attention and working memory are inter-dependent core cognitive functions. It is critical to allocate attention on selected targets during the capacity-limited working memory processes to fulfill the goal-directed behavior. The trends of research on both topics are increasing exponentially in recent years, and it is considered that selective attention and working memory share similar underlying neural mechanisms. Different types of attention orientation in working memory are introduced by distinctive cues, and the means using retrospective cues are strengthened currently as it is manipulating the representation in memory, instead of the perceptual representation. The cognitive and neural mechanisms of the retro-cue effects are further reviewed, as well as the potential molecular mechanism. The frontal-parietal network that is involved in both attention and working memory is also the neural candidate for attention orientation during working memory. Neural oscillations in the gamma and alpha/beta oscillations may respectively be employed for the feedforward and feedback information transfer between the sensory cortices and the association cortices. Dopamine and serotonin systems might interact with each other subserving the communication between memory and attention. In conclusion, representations which attention shifts towards are strengthened, while representations which attention moves away from are degraded. Studies on attention orientation during working memory indicates the flexibility of the processes of working memory, and the beneficial way that overcome the limited capacity of working memory.

Cognitive Control As a Double-Edged Sword

Cognitive control, the ability to limit attention to goal-relevant information, aids performance on a wide range of laboratory tasks. However, there are many day-to-day functions which require little to no control and others which even benefit from reduced control. We review behavioral and neuroimaging evidence demonstrating that reduced control can enhance the performance of both older and, under some circumstances, younger adults. Using healthy aging as a model, we demonstrate that decreased cognitive control benefits performance on tasks ranging from acquiring and using environmental information to generating creative solutions to problems. Cognitive control is thus a double-edged sword - aiding performance on some tasks when fully engaged, and many others when less engaged.

Brain Network Modularity Predicts Exercise-Related Executive Function Gains in Older Adults

Recent work suggests that the brain can be conceptualized as a network comprised of groups of sub-networks or modules. The extent of segregation between modules can be quantified with a modularity metric, where networks with high modularity have dense connections within modules and sparser connections between modules. Previous work has shown that higher modularity predicts greater improvements after cognitive training in patients with traumatic brain injury and in healthy older and young adults. It is not known, however, whether modularity can also predict cognitive gains after a physical exercise intervention. Here, we quantified modularity in older adults (N = 128, mean age = 64.74) who underwent one of the following interventions for 6 months (NCT01472744 on ClinicalTrials.gov): (1) aerobic exercise in the form of brisk walking (Walk), (2) aerobic exercise in the form of brisk walking plus nutritional supplement (Walk+), (3) stretching, strengthening and stability (SSS), or (4) dance instruction. After the intervention, the Walk, Walk+ and SSS groups showed gains in cardiorespiratory fitness (CRF), with larger effects in both walking groups compared to the SSS and Dance groups. The Walk, Walk+ and SSS groups also improved in executive function (EF) as measured by reasoning, working memory, and task-switching tests. In the Walk, Walk+, and SSS groups that improved in EF, higher baseline modularity was positively related to EF gains, even after controlling for age, in-scanner motion and baseline EF. No relationship between modularity and EF gains was observed in the Dance group, which did not show training-related gains in CRF or EF control. These results are consistent with previous studies demonstrating that individuals with a more modular brain network organization are more responsive to cognitive training. These findings suggest that the predictive power of modularity may be generalizable across interventions aimed to enhance aspects of cognition and that, especially in low-performing individuals, global network properties can capture individual differences in neuroplasticity.

Medial prefrontal-perirhinal cortical communication is necessary for flexible response selection

The ability to use information from the physical world to update behavioral strategies is critical for survival across species. The prefrontal cortex (PFC) supports behavioral flexibility; however, exactly how this brain structure interacts with sensory association cortical areas to facilitate the adaptation of response selection remains unknown. Given the role of the perirhinal cortex (PER) in higher-order perception and associative memory, the current study evaluated whether PFC-PER circuits are critical for the ability to perform biconditional object discriminations when the rule for selecting the rewarded object shifted depending on the animal's spatial location in a 2-arm maze. Following acquisition to criterion performance on an object-place paired association task, pharmacological blockade of communication between the PFC and PER significantly disrupted performance. Specifically, the PFC-PER disconnection caused rats to regress to a response bias of selecting an object on a particular side regardless of its identity. Importantly, the PFC-PER disconnection did not interfere with the capacity to perform object-only or location-only discriminations, which do not require the animal to update a response rule across trials. These findings are consistent with a critical role for PFC-PER circuits in rule shifting and the effective updating of a response rule across spatial locations.

Predictive cues and age-related declines in working memory performance

Older adults, compared to younger adults, do not benefit from predictive information regarding either what type of stimuli they will see or when to expect them, yet it is unclear whether older adults benefit when given both types of predictive information. Here, electroencephalogram recordings of older (aged 62-87 years) and younger (aged 20-32 years) adults were recorded during a working memory task. Each trial contained 2 faces and 2 scenes presented sequentially, followed by a 5-second delay and a probe stimulus. Participants were told what stimuli to remember/ignore and when they would appear. Predictive cues enabled older adults to remember stimuli as accurately as younger adults, although response times were significantly slower, even when corrected for general age-related slowing. Previously observed reductions in P1/N1 amplitude and latency suppression to irrelevant stimuli were not seen. Rather, older adults exhibited lowered P3 amplitudes to relevant stimuli; those with the greatest declines yielded the lowest accuracy and slowest response times. This shows that predictive information can help maintain accuracy, although not response times, which correspond to age-related declines in neural enhancement to relevant stimuli.

Attentional updating and monitoring and affective shifting are impacted independently by aging in macaque monkeys

One hallmark of the normal cognitive aging process involves alterations in executive function. Executive function can be divided into at least three separable components, including set shifting, attentional updating and monitoring, and inhibition of prepotent responses. The ability to study the neural basis of cognitive aging has been enriched by the use of animal models such as the macaque monkey. In aged macaques, changes in attentional updating and monitoring systems are poorly understood compared to changes in shifting and inhibition. A partial explanation for this is the fact that the tasks designed to study executive function in aged monkeys, to date, primarily have probed shifting and inhibition processes. Here we examine how aging impacts attentional updating and monitoring processes in monkeys using an interference task designed after a paradigm used to examine multi-tasking in older humans. Young and aged macaque monkeys were tested on this interference task as well as on an object reversal learning task to study these processes in the same animals. Relative to the young monkeys, aged animals were impaired on both tasks. Proactive and retroactive interference did not differ between age groups on an array of 40 object pairs presented each day in the object reversal learning task. The levels of performance on the interference task were not correlated with levels of performance in the object reversal task. These results suggest that attentional updating and monitoring and affective shifting are separable functions in the macaque, and that normal aging affects these mental operations independently.

Selective Attention and Sensory Modality in Aging: Curses and Blessings

The notion that selective attention is compromised in older adults as a result of impaired inhibitory control is well established. Yet it is primarily based on empirical findings covering the visual modality. Auditory and especially, cross-modal selective attention are remarkably underexposed in the literature on aging. In the past 5 years, we have attempted to fill these voids by investigating performance of younger and older adults on equivalent tasks covering all four combinations of visual or auditory target, and visual or auditory distractor information. In doing so, we have demonstrated that older adults are especially impaired in auditory selective attention with visual distraction. This pattern of results was not mirrored by the results from our psychophysiological studies, however, in which both enhancement of target processing and suppression of distractor processing appeared to be age equivalent. We currently conclude that: (1) age-related differences of selective attention are modality dependent; (2) age-related differences of selective attention are limited; and (3) it remains an open question whether modality-specific age differences in selective attention are due to impaired distractor inhibition, impaired target enhancement, or both. These conclusions put the longstanding inhibitory deficit hypothesis of aging in a new perspective.

Behavioral and Neural Markers of Flexible Attention over Working Memory in Aging

Working memory (WM) declines as we age and, because of its fundamental role in higher order cognition, this can have highly deleterious effects in daily life. We investigated whether older individuals benefit from flexible orienting of attention within WM to mitigate cognitive decline. We measured magnetoencephalography (MEG) in older adults performing a WM precision task with cues during the maintenance period that retroactively predicted the location of the relevant items for performance (retro-cues). WM performance of older adults significantly benefitted from retro-cues. Whereas WM maintenance declined with age, retro-cues conferred strong attentional benefits. A model-based analysis revealed an increase in the probability of recalling the target, a lowered probability of retrieving incorrect items or guessing, and an improvement in memory precision. MEG recordings showed that retro-cues induced a transient lateralization of alpha (8-14 Hz) and beta (15-30 Hz) oscillatory power. Interestingly, shorter durations of alpha/beta lateralization following retro-cues predicted larger cueing benefits, reinforcing recent ideas about the dynamic nature of access to WM representations. Our results suggest that older adults retain flexible control over WM, but individual differences in control correspond to differences in neural dynamics, possibly reflecting the degree of preservation of control in healthy aging.

Retrieval Goal Modulates Memory for Context

fMRI was employed to assess whether the contents of recollection vary according to retrieval goal. At study, visually presented words were superimposed on urban or rural scenes or a gray background. The word-background pairs were presented in one of three spatial locations. During a scanned test phase, studied and unstudied words were presented. Two different source memory tasks were randomly interleaved. In the "background" task, the requirement was to judge whether the word had been presented against one of the two classes of scene, as opposed to the alternate class or the gray background. In the "location" task, discrimination was between words presented in one of the two lateral locations and words presented in either of the alternate locations. In both tasks, unstudied words required a separate response. In the background task, words studied against scenes elicited greater activity in parahippocampal and retrosplenial cortex than did words studied against the gray background, consistent with prior reports of scene reinstatement effects. Reinstatement effects were also evident in the location task. Relative to the background task, however, the effects were attenuated in parahippocampal cortex. In other regions, including medial prefrontal and posterior cingulate cortex, activity elicited in the location task by items associated with scenes was lower than that elicited by items presented on the gray background. The findings are interpreted as evidence that contextual retrieval is partially modulated by retrieval goal.

Effects of aging on value-directed modulation of semantic network activity during verbal learning

While impairments in memory recall are apparent in aging, older adults show a remarkably preserved ability to selectively remember information deemed valuable. Here, we use fMRI to compare brain activation in healthy older and younger adults during encoding of high and low value words to determine whether there are differences in how older adults achieve value-directed memory selectivity. We find that memory selectivity in older adults is associated with value-related changes in activation during word presentation in left hemisphere regions that are involved in semantic processing, similar to young adults. However, highly selective young adults show a relatively greater increase in semantic network activity during encoding of high-value items, whereas highly selective older adults show relatively diminished activity during encoding of low-value items. Additionally, only younger adults showed value-related increases in activity in semantic and reward processing regions during presentation of the value cue preceding each to-be-remembered word. Young adults therefore respond to cue value more proactively than do older adults, yet the magnitude of value-related differences in cue period brain activity did not predict individual differences in memory selectivity. Thus, our data also show that age-related reductions in prestimulus activity do not always lead to inefficient performance.

Age-related changes in working memory and the ability to ignore distraction

A weakened ability to effectively resist distraction is a potential basis for reduced working memory capacity (WMC) associated with healthy aging. Exploiting data from 29,631 users of a smartphone game, we show that, as age increases, working memory (WM) performance is compromised more by distractors presented during WM maintenance than distractors presented during encoding. However, with increasing age, the ability to exclude distraction at encoding is a better predictor of WMC in the absence of distraction. A significantly greater contribution of distractor filtering at encoding represents a potential compensation for reduced WMC in older age.

Greater priming for previously distracting information in young than older adults when suppression is ruled out

The use of previously distracting information on memory tests with indirect instructions is usually age-equivalent, while young adults typically show greater explicit memory for such information. This could reflect qualitatively distinct initial processing (encoding) of distracting information by younger and older adults, but could also be caused by greater suppression of such information by younger adults on tasks with indirect instructions. In Experiment 1, young and older adults read stories containing distracting words, which they ignored, before studying a list of words containing previously distracting items for a free recall task. Half the participants were informed of the presence of previously distracting items in the study list prior to recall (direct instruction), and half were not (indirect instruction). Recall of previously distracting words was age-equivalent in the indirect condition, but young adults recalled more distracting words in the direct condition. In Experiment 2, participants performed the continuous identification with recognition task, which captures a measure of perceptual priming and recognition on each trial, and is immune to suppression. Priming and recognition of previously distracting words was greater in younger than older adults, suggesting that the young engage in more successful suppression of previously distracting information on tasks in which its relevance is not overtly signaled.