Age-related Changes In Brain Activity Research Articles

Inter- and Intra-Hemispheric Age-Related Remodeling in Visuo-Spatial Working Memory.

Electroencephalography (EEG) studies investigating visuo-spatial working memory (vWM) in aging typically adopt an event-related potential (ERP) analysis approach that has shed light on the age-related changes during item retention and retrieval. However, this approach does not fully enable a detailed description of the time course of the neural dynamics related to aging. The most frequent age-related changes in brain activity have been described by two influential models of neurocognitive aging, the Hemispheric Asymmetry Reduction in Older Adults (HAROLD) and the Posterior-Anterior Shift in Aging (PASA). These models posit that older adults tend to recruit additional brain areas (bilateral as predicted by HAROLD and anterior as predicted by PASA) when performing several cognitive tasks. We tested younger (N = 36) and older adults (N = 35) in a typical vWM task (delayed match-to-sample) where participants have to retain items and then compare them to a sample. Through a data-driven whole scalp EEG analysis we aimed at characterizing the temporal dynamics of the age-related activations predicted by the two models, both across and within different stages of stimulus processing. Behaviorally, younger outperformed older adults. The EEG analysis showed that older adults engaged supplementary bilateral posterior and frontal sites when processing different levels of memory load, in line with both HAROLD and PASA-like activations. Interestingly, these age-related supplementary activations dynamically developed over time. Indeed, they varied across different stages of stimulus processing, with HAROLD-like modulations being mainly present during item retention, and PASA-like activity during both retention and retrieval. Overall, the present results suggest that age-related neural changes are not a phenomenon indiscriminately present throughout all levels of cognitive processing.

Salience and default-mode network connectivity during threat and safety processing in older adults.

The appropriate assessment of threat and safety is important for decision‐making but might be altered in old age due to neurobiological changes. The literature on threat and safety processing in older adults is sparse and it is unclear how healthy ageing affects the brain's functional networks associated with affective processing. We measured skin conductance responses as an indicator of sympathetic arousal and used functional magnetic resonance imaging and independent component analysis to compare young and older adults' functional connectivity in the default mode (DMN) and salience networks (SN) during a threat conditioning and extinction task. While our results provided evidence for differential threat processing in both groups, they also showed that functional connectivity within the SN – but not the DMN – was weaker during threat processing in older compared to young adults. This reduction of within‐network connectivity was accompanied by an age‐related decrease in low frequency spectral power in the SN and a reduction in inter‐network connectivity between the SN and DMN during threat and safety processing. Similarly, we found that skin conductance responses were generally lower in older compared to young adults. Our results are the first to demonstrate age‐related changes in brain activation during aversive conditioning and suggest that the ability to adaptively filter affective information is reduced in older adults.

Motor neuroplasticity: A MEG-fMRI study of motor imagery and execution in healthy ageing

Age-related decline in motor function is associated with over-activation of the sensorimotor circuitry. Using a multimodal MEG-fMRI paradigm, we investigated whether this neural over-recruitment in old age would be related to changes in movement-related beta desynchronization (MRBD), a correlate of the inhibitory neurotransmitter γ-aminobutyric acid (GABA), and whether it would characterize compensatory recruitment or a reduction in neural specialization (dedifferentiation). We used MEG to assess age-related changes in beta band oscillations in primary motor cortices, fMRI to localize age-related changes in brain activity, and the Finger Configuration Task to measure task performance during overt and covert motor processing: motor execution (ME) and motor imagery (MI). The results are threefold: first, showing age-related neuroplasticity during ME of older adults, compared to young adults, as evidenced by increased MRBD in motor cortices and over-recruitment of sensorimotor areas; second, showing similar age-related neuroplastic changes during MI; and finally, showing signs of dedifferentiation during ME in older adults whose performance negatively correlated with connectivity to bilateral primary motor cortex. Together, these findings demonstrate that elevated MRBD levels, reflecting greater GABAergic inhibitory activity, and over-activation of the sensorimotor network during ME may not be compensatory, but rather might reflect an age-related decline of the quality of the underlying neural signal.

Age-related changes in brain deactivation but not in activation after motor learning

It is poorly understood how healthy aging affects neural mechanisms underlying motor learning. We used blood-oxygen-level dependent (BOLD) contrasts to examine age-related changes in brain activation after acquisition and consolidation (24 h) of a visuomotor tracking skill. Additionally, structural magnetic resonance imaging and diffusion tensor imaging were used to examine age-related structural changes in the brain. Older adults had reduced gray matter volume (628 ± 57 ml) and mean white matter anisotropy (0.18 ± 0.03) compared with young adults (741 ± 59 ml and 0.22 ± 0.02, respectively). Although motor performance was 53% lower in older (n = 15, mean age 63.1 years) compared with young adults (n = 15, mean age 25.5 years), motor practice improved motor performance similarly in both age groups. While executing the task, older adults showed in general greater brain activation compared with young adults. BOLD activation decreased in parietal and occipital areas after skill acquisition but activation increased in these areas after consolidation in both age groups, indicating more efficient visuospatial processing immediately after skill acquisition. Changes in deactivation in specific areas were age-dependent after consolidating the motor skill into motor memory. Young adults showed greater deactivations from post-test to retention in parietal, occipital and temporal cortices, whereas older adults showed smaller deactivation in the frontal cortex. Since learning rate was similar between age groups, age-related changes in activation patterns may be interpreted as a compensatory mechanism for age-related structural decline.

Optimizing fMRI preprocessing pipelines for block-design tasks as a function of age

Functional Magnetic Resonance Imaging (fMRI) is a powerful neuroimaging tool, which is often hampered by significant noise confounds. There is evidence that our ability to detect activations in task fMRI is highly dependent on the preprocessing steps used to control noise and artifact. However, the vast majority of studies examining preprocessing pipelines in fMRI have focused on young adults. Given the widespread use of fMRI for characterizing the neurobiology of aging, it is critical to examine how the impact of preprocessing choices varies as a function of age. In this study, we employ the NPAIRS cross-validation framework, which optimizes pipelines based on metrics of prediction accuracy (P) and spatial reproducibility (R), to compare the effects of pipeline optimization between young (21–33 years) and older (61–82 years) cohorts, for three different block-design contrasts. Motion is shown to be a greater issue in the older cohort, and we introduce new statistical approaches to control for potential biases due to head motion during pipeline optimization. In comparison, data-driven methods of physiological noise correction show comparable benefits for both young and old cohorts. Using our optimization framework, we demonstrate that the optimal pipelines tend to be highly similar across age cohorts. In addition, there is a comparable, significant benefit of pipeline optimization across age cohorts, for (P, R) metrics and independent validation measures of activation overlap (both between-subject, within-session and within-subject, between-session). The choice of task contrast consistently shows a greater impact than the age cohort, for (P, R) metrics and activation overlap. Finally, adaptive pipeline optimization per task run shows improved sensitivity to age-related changes in brain activity, particularly for weaker, more complex cognitive contrasts. The current study provides the first detailed examination of preprocessing pipelines across age cohorts, demonstrating a significant benefit of adaptive pipeline optimization across age groups.

Age‐related changes in amygdala–frontal connectivity during emotional face processing from childhood into young adulthood

The ability to process and respond to emotional facial expressions is a critical skill for healthy social and emotional development. There has been growing interest in understanding the neural circuitry underlying development of emotional processing, with previous research implicating functional connectivity between amygdala and frontal regions. However, existing work has focused on threatening emotional faces, raising questions regarding the extent to which these developmental patterns are specific to threat or to emotional face processing more broadly. In the current study, we examined age-related changes in brain activity and amygdala functional connectivity during an fMRI emotional face matching task (including angry, fearful, and happy faces) in 61 healthy subjects aged 7-25 years. We found age-related decreases in ventral medial prefrontal cortex activity in response to happy faces but not to angry or fearful faces, and an age-related change (shifting from positive to negative correlation) in amygdala-anterior cingulate cortex/medial prefrontal cortex (ACC/mPFC) functional connectivity to all emotional faces. Specifically, positive correlations between amygdala and ACC/mPFC in children changed to negative correlations in adults, which may suggest early emergence of bottom-up amygdala excitatory signaling to ACC/mPFC in children and later development of top-down inhibitory control of ACC/mPFC over amygdala in adults. Age-related changes in amygdala-ACC/mPFC connectivity did not vary for processing of different facial emotions, suggesting changes in amygdala-ACC/mPFC connectivity may underlie development of broad emotional processing, rather than threat-specific processing. Hum Brain Mapp 37:1684-1695, 2016. © 2016 Wiley Periodicals, Inc.

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.

Investigation of age-related changes in brain activity during the divalent task-switching paradigm using functional MRI

This study compared the brain activation of young and older subjects during the use of the task-switching paradigm (TSP) at various task speeds to examine the relationship between task load and brain activation. Specifically, it attempted to examine whether the task load-dependent BOLD response gradient is a useful tool for functional magnetic resonance imaging-based assessments of age-related changes in cognitive function. We predicted that the extent of the activation of the brain regions responsible for task-set reconfiguration and the inhibition of task switching functions induced during the performance of a TSP-based task would vary according to age. Task difficulty was controlled by altering the inter-stimulus interval. Although similar brain regions were activated in both age groups, significant differences in the extent of the activation were detected between the young and older groups. In particular, some regions were activated in the older group, but not the young group. This study indicated that TSP-based task performance-induced activation of the brain regions linked to executive function increases with age and that the degree and pattern of such activation depend on the content and difficulty of the task being performed. This indicates that the age- and task difficulty-dependent augmentation of brain activation varies between brain regions.

Age-related changes in brain activity are specific for high order cognitive processes during successful encoding of information in working memory.

Memory capacity suffers an age-related decline, which is supposed to be due to a generalized slowing of processing speed and to a reduced availability of processing resources. Information encoding in memory has been demonstrated to be very sensitive to age-related changes, especially when carried out through self-initiated strategies or under high cognitive demands. However, most event-related potentials (ERP) research on age-related changes in working memory (WM) has used tasks that preclude distinction between age-related changes in encoding and retrieval processes. Here, we used ERP recording and a delayed match to sample (DMS) task with two levels of memory load to assess age-related changes in electrical brain activity in young and old adults during successful information encoding in WM. Age-related decline was reflected in lower accuracy rates and longer reaction times in the DMS task. Beside, only old adults presented lower accuracy rates under high than low memory load conditions. However, effects of memory load on brain activity were independent of age and may indicate an increased need of processing after stimulus classification as reflected in larger mean voltages in high than low load conditions between 550 and 1000 ms post-stimulus for young and old adults. Regarding age-related effects on brain activity, results also revealed smaller P2 and P300 amplitudes that may signal the existence of an age dependent reduction in the processing resources available for stimulus evaluation and categorization. Additionally, P2 and N2 latencies were longer in old than in young participants. Furthermore, longer N2 latencies were related to greater accuracy rates on the DMS task, especially in old adults. These results suggest that age-related slowing of processing speed may be specific for target stimulus analysis and evaluation processes. Thus, old adults seem to improve their performance the longer they take to evaluate the stimulus they encode in visual WM.

Age-related Increase in Activation of Effort-related Brain Areas During a Sustained Fatiguing Contraction.

Fatiguing contractions result in an overall increase in activation of the motor cortical areas. Older adults activate additional, ipsilateral areas during a non-fatiguing motor task. The activity pattern in older adults during a fatiguing motor task is not well studied. PURPOSE: To examine the effects of age on brain activation during a sustained fatiguing contraction with the right index finger abductor. METHODS: Thirty subjects (age-range: 19-64 years) performed a fatiguing maximal force task with their right first dorsal interosseous (FDI) in a 3 Tesla MR scanner during which the blood oxygen level dependent (BOLD) signal was recorded. The age-related changes in brain activation were determined using a one-sample t-test with age square as a covariate. RESULTS: The left inferior and superior parietal lobe, left rolandic operculum, left precuneus, left middle occipital gyrus, right hippocampus, bilateral parahippocampal gyrus, bilateral middle temporal gyrus, bilateral fusiform gyrus, bilateral insula and bilateral middle cingulate cortex were significantly more active with age (t>3.41, p<0.001 uncorrected). CONCLUSION: There is an age-related increase in brain activation, including the activation of several structures ipsilateral to the contracting hand, during a sustained fatiguing contraction. Most areas are thought to be involved in sensory-motor integration, effort- or cost-benefit analysis.

Aging associated changes in the motor control of ankle movements in the brain

Although age-related gait changes have been well characterized, little is known regarding potential functional changes in central motor control of distal lower limb movements with age. We hypothesized that there are age-related changes in brain activity associated with the control of repetitive ankle movements, an element of gait feasible for study with functional magnetic resonance imaging. We analyzed standardized functional magnetic resonance imaging data from 102 right-foot dominant healthy participants aged 20–83 years for age-associated effects using FSL and a meta-analysis using coordinate-based activation likelihood estimation. For the first time, we have confirmed age-related changes in brain activity with this gait-related movement of the lower limb in a large population. Increasing age correlated strongly with increased movement-associated activity in the cerebellum and precuneus. Given that task performance did not vary with age, we interpret these changes as potentially compensatory for other age-related changes in the sensorimotor network responsible for control of limb function.

Different developmental trajectories for anticipation and receipt of reward during adolescence

Typical adolescent behaviour such as increased risk-taking and novelty-seeking is probably related to developmental changes in the brain reward system. This functional MRI study investigated how brain activation related to two components of reward processing (Reward Anticipation and Reward Outcome) changes with age in a sample of 39 children, adolescents and young adults aged 10–25. Our data revealed age-related changes in brain activity during both components of reward processing. Activation related to Reward Anticipation increased with age, while activation related to Reward Outcome decreased in various regions of the reward network. This shift from outcome to anticipation was confirmed by subsequent analyses showing positive correlations between age and the difference in activation between Reward Anticipation and Reward Outcome. The shift was predominantly present in striatal regions and was accompanied by a significant effect of age on behaviour, with older participants showing more response speeding on potentially rewarding trials than younger participants. This study provides evidence for functional changes in the reward system which may underlie typical adolescent behaviour.

The Relationship between P3 Amplitude and Working Memory Performance Differs in Young and Older Adults

While some elderly show deteriorations in cognitive performance, others achieve performance levels comparable to young adults. To examine whether age-related changes in brain activity varied with working memory performance efficiency, we recorded electroencephalography (EEG) from young and older healthy adults during performance on an n-back task with two loads (0- and 1-back) and two versions (identity and integrated). Young adults showed a typical P3 amplitude pattern with a parietal-maximum. Compared to young adults, the P3 amplitude of older adults was characterized by frontal hyperactivity coupled with posterior hypoactivity. Moreover, P3 amplitude in young and older adults varied with working memory performance efficiency. Among young adults, more efficient performance correlated with a larger P3 amplitude at parietal sites. In contrast, a higher P3 amplitude at midline electrode sites in older adults correlated with less efficient performance. Particularly, the enhanced frontal midline EEG activity in older adults during working memory performance seems to reflect inefficient use of neural resources due to frontal lobe dysfunction.

Partitioning age-related changes in brain activation using a virtual performance task to simulate complex movements

Event Abstract Back to Event Partitioning age-related changes in brain activation using a virtual performance task to simulate complex movements Toshiharu Nakai1*, Ayuko Tanaka1, Mitsunobu Kunimi1, Sachiko Kiyama1 and Yoshiaki Shiraishi2 1 National Center for Geriatrics and Gerontology, Neuroimaging & Informatics, Japan 2 Nagoya Institute of Technology Graduate School of Engineering, Computer Science and Engineering, Japan Aging has become a serious social issue, especially in Asian countries. In order to maintain the activities of elderly people, social programs to promote physical and mental exercises are conducted. Although some investigations have reported that those activities potentially contribute to the prevention of cognitive decline [1], the neurological background has not been systematically verified. We investigated the availability of a virtual performance task designed from such exercises as a model to test age-related changes in brain function [2]. An event-related fMRI task representing the motor behavior in the bean transfer test (BTT), which is used as one component of the test battery to evaluate the physical ability of elderly in Japan, was designed. The task consisted of two operations using a 2 by 2 turnkey system. With the left-hand key, a small, round object (bean) is pinched with two lines representing chopsticks. Then, the object with chopsticks is moved to a round target (pot) with the right-hand key to put the bean in. The behavioral data were marked with 6 checkpoints (Fig.1). The onset of each trial was determined using the sum of two jittering factors, the execution time for each trial by the subject and periodically altering the interval time before the onset of each trial. fMRI data were obtained using the EPI sequence on a 3T MR scanner, and the data sets were analyzed using SPM8. fMRI data were obtained from 11 elderly (over 60, 6 females) and 7 non-elderly (under 54) volunteers. In the activation representing the total trial, the network for the upper visuo-spatial transformation tract and higher motor control was observed in the elderly (two-sample t-test, p<0.05). Differential peaks between the two age groups were detected as augmented activation in the left BA5 ([-23 -38 59]) and bilateral BA6 ([-60 -2 47], [60 2 38]) in the elderly group (Fig.2, CPall). In the partitioned maps, it was indicated that this difference was mostly contributed to by the first task switching point (CP2) and pinching the object (CP1). Activation of these areas was not significant in the CP3 and CP4 map in the elderly. On the other hand, activation was augmented in the dorsal visuo-motor pathway in the young subjects during these steps. It was suggested that these results represent: 1) a higher demand for visuo-spatial transformation by adjusting the asymmetric (two independent) rotation of the sticks, and 2) a lower frequency of object transference to the goal than pinching it in elderly subjects. By recording self-paced object manipulation in the interactive task, complex brain activation during a combined motor processing could be more precisely attributed to cognitive elements. This feature was useful to further partitioning age-related changes in brain activation. Figure 1 Figure 2 Acknowledgements This research was supported by a Grant-in-Aid for Scientific Research (KAKENHI) # 21300196 and 24300186 supported by MEXT.

Altered error-related brain activity in youth with major depression

Depression is associated with impairments in cognitive control including action monitoring processes, which involve the detection and processing of erroneous responses in order to adjust behavior. Although numerous studies have reported altered error-related brain activity in depressed adults, relatively little is known about age-related changes in error-related brain activity in depressed youth. This study focuses on the error-related negativity (ERN), a negative deflection in the event-related potential (ERP) that is maximal approximately 50 ms following errors. High-density ERPs were examined following responses on a flanker task in 24 youth diagnosed with MDD and 14 low-risk healthy controls (HC). Results indicate that compared to HC, MDD youth had significantly smaller ERN amplitudes and did not exhibit the normative increases in ERN amplitudes as a function of age. Also, ERN amplitudes were similar in depressed youth with and without comorbid anxiety. These results suggest that depressed youth exhibit different age-related changes in brain activity associated with action monitoring processes. Findings are discussed in terms of existing work on the neural correlates of action monitoring and depression and the need for longitudinal research studies investigating the development of neural systems underlying action monitoring in youth diagnosed with and at risk for depression.

PLASMA HOMOCYSTEINE LEVEL AND APATHY IN ALZHEIMER'S DISEASE

PLASMA HOMOCYSTEINE LEVEL AND APATHY IN ALZHEIMER'S DISEASE

Age-related changes in brain activation underlying single- and dual-task performance: Visuomanual drawing and mental arithmetic

Depending on task combination, dual-tasking can either be performed successfully or can lead to performance decrements in one or both tasks. Interference is believed to be caused by limitations in central processing, i.e. structural interference between the neural activation patterns associated with each task. In the present study, single- and dual-task effects were addressed in the context of aging. Increasing evidence from research on motor and cognitive tasks has shown that aging is associated with an expansion of brain activation and an increased BOLD-signal. This may result in increased structural interference and higher dual-task interference in older adults. Functional magnetic resonance imaging was used to measure the BOLD-response in 20 old and 20 young healthy adults while performing tasks separately, or combined. Single tasks consisted of mental arithmetic cued by auditory tones, and a visuomotor task, drawing a circular shape with spatiotemporal constraints. Age-related brain activation increases were only apparent during performance of the visuomotor task. Elderly showed higher BOLD-responses in a frontoparietal network, pointing to an increased reliance on sensory feedback processing. However, no increased structural interference was found for the elderly during performance of the dual-task. Region of interest analysis involving a functional cluster within the (pre-) supplementary motor area, active during performance of both single-tasks, revealed that both groups were able to upregulate their brain activity for dual-as compared to single-task performance. We assume that this allowed both groups to maintain performance under dual-task conditions, leading to minimal dual-task interference.

Neural correlates of temporality: Default mode variability and temporal awareness

The continual background awareness of duration is an essential structure of consciousness, conferring temporal extension to the many objects of awareness within the evanescent sensory present. Seeking the possible neural correlates of ubiquitous temporal awareness, this article reexamines fMRI data from off-task "default mode" (DM) periods in 25 healthy subjects studied by Grady et al. ("Age-related Changes in Brain Activity across the Adult Lifespan,"Journal of Cognitive Neuroscience 18(2), 2005). "Brain reading" using support vector machines detected information specifying elapsed time, and further analysis specified distributed networks encoding implicit time. These networks fluctuate; none are continuously active during DM. However, the aggregate regions of greatest variability closely resemble the default mode network. It appears that the default mode network has an important role as a state-dependent monitor of temporality.

Prefrontal cortex and age-related changes in strategic processing

Event Abstract Back to Event Prefrontal cortex and age-related changes in strategic processing Brenda Kirchhoff1* 1 University of Missouri – St. Louis , United States Episodic memory impairments are one of the main cognitive changes associated with healthy and disordered aging. For example, healthy older adults typically remember fewer words following intentional encoding than young adults. Under-and over-recruitment of prefrontal cortex have also been reported during intentional encoding in older adults. There is growing evidence that changes in self-initiated encoding strategy use could play an important role in these age-related memory impairments and alterations in brain activity. Behavioral studies have suggested that older adults are less likely than young adults to spontaneously use effective encoding strategies during intentional encoding. In addition, age-related changes in brain activity during intentional encoding have been reported in prefrontal regions associated with self-initiated use of effective encoding strategies in young adults. To further explore the role that age-related changes in self-initiated encoding strategy use may play in age-related changes in brain activity in prefrontal cortex, we recently conducted a cognitive training study in which older adults were taught to use semantic encoding strategies. Strategy use training substantially improved older adults’ ability to consciously recollect studied words. Older adults reported greater self-initiated use of semantic encoding strategies following cognitive training, and were less likely to report not using any learning strategy. Brain activity in left inferior prefrontal regions increased following cognitive training, and individual differences in training-related changes in brain activity in these regions were associated with individual differences in training-related changes in memory performance.

The effect of age on word-stem cued recall: A behavioral and electrophysiological study

The present study investigated the effects of aging on behavioral cued-recall performance and on the neural correlates of explicit memory using event-related potentials (ERPs) under shallow and deep encoding conditions. At test, participants were required to complete old and new three-letter word stems using the letters as retrieval cues. The main results were as follows: (1) older participants exhibited the same level of explicit memory as young adults with the same high level of education. Moreover older adults benefited as much as young ones from deep processing at encoding; (2) brain activity at frontal sites showed that the shallow old/new effect developed and ended earlier for older than young adults. In contrast, the deep old/new effect started later for older than for young adults and was sustained up to 1000 ms in both age groups. Moreover, the results suggest that the frontal old/new effect was bilateral but greater over the right than the left electrode sites from 600 ms onward; (3) there were no differences at parietal sites between age groups: the old/new effect developed from 400 ms under both encoding conditions and was sustained up to 1000 ms under the deep condition but ended earlier (800 ms) under the shallow condition. These ERP results indicate significant age-related changes in brain activity associated with the voluntary retrieval of previously encoded information, in spite of similar behavioral performance of young and older adults.