The neural correlates of recollection and retrieval monitoring: Relationships with age and recollection performance

Cross-cultural comparison of the neural correlates of true and false memory retrieval

Prior work has shown Americans have higher levels of memory specificity than East Asians. Neuroimaging studies have not investigated mechanisms that account for cultural differences at retrieval. In this study, we use fMRI to assess whether mnemonic discrimination, distinguishing novel from previously encountered stimuli, accounts for cultural differences in memory. Fifty-five American and 55 Taiwanese young adults completed an object recognition paradigm testing discrimination of old targets, similar lures and novel foils. Mnemonic discrimination was tested by comparing discrimination of similar lures from studied targets, and results showed the relationship between activity in right fusiform gyrus and behavioural discrimination between target and lure objects differed across cultural groups. Parametric modulation analyses of activity during lure correct rejections also indicated that groups differed in left superior parietal cortex response to variations in lure similarity. Additional analyses of old vs. new activity indicated that Americans and Taiwanese differ in the neural activity supporting general object recognition in the hippocampus, left inferior frontal gyrus and middle frontal gyrus. Results are juxtaposed against comparisons of the regions activated in common across the two cultures. Overall, Americans and Taiwanese differ in the extent to which they recruit visual processing and attention modulating brain regions.

Neural correlates of retrieval success and precision: an fMRI study

Prior studies examining the neural mechanisms underlying retrieval success and precision have yielded inconsistent results. Here, their neural correlates were examined using a memory task that assessed precision for spatial location. A sample of healthy young adults underwent fMRI scanning during a single study-test cycle. At study, participants viewed a series of object images, each placed at a randomly selected location on an imaginary circle. At test, studied images were intermixed with new images and presented to the participants. The requirement was to move a cursor to the location of the studied image, guessing if necessary. Participants then signaled whether the presented image as having been studied. Memory precision was quantified as the angle between the studied location and the location selected by the participant. A precision effect was evident in the left angular gyrus, where BOLD activity covaried across trials with location accuracy. Multi-voxel pattern analysis also revealed a significant item-level reinstatement effect for high-precision trials. There was no evidence of a retrieval success effect in the angular gyrus. BOLD activity in the hippocampus was insensitive to both success and precision. These findings are partially consistent with prior evidence that success and precision are dissociable features of memory retrieval.

Schema-congruency supports the formation of unitized representations: Evidence from event-related potentials

The main goal of the present study was to investigate whether schema-based encoding of novel word pairs (i.e., novel compound words) supports the formation of unitized representations and thus, associative familiarity-based recognition. We report two experiments that both comprise an incidental learning task, in which novel noun-noun compound words were presented in semantically congruent contexts, enabling schema-supported processing of both constituents, contrasted with a schema-neutral condition. In Experiment 1, the effects of schema congruency on memory performance were larger for associative memory performance than for item memory performance in a memory test in which intact, recombined, and new compound words had to be discriminated. This supports the view that schema congruency boosts associative memory by promoting unitization. When contrasting event-related potentials (ERPs) for hits with correct rejections or associative misses, an N400 attenuation effect (520-676 ms) indicating absolute familiarity was present in the congruent condition, but not in the neutral condition. In line with this, a direct comparison of ERPs on hits across conditions revealed more positive waveforms in the congruent than in the neutral condition. This suggests that absolute familiarity contributes to associative recognition memory when schema-supported processing is established. In Experiment 2, we tested whether schema congruency enables the formation of semantically overlapping representations. Therefore, we included semantically similar lure compound words in the test phase and compared false alarm rates to these lures across conditions. In line with our hypothesis, we found higher false alarm rates in the congruent as compared to the neutral condition. In conclusion, we provide converging evidence for the view that schema congruency enables the formation of unitized representations and supports familiarity-based memory retrieval.

Menopause Status and Within-Group Differences in Chronological Age Affect the Functional Neural Correlates of Spatial Context Memory in Middle-Aged Females

Reductions in the ability to encode and retrieve past experiences in rich spatial contextual detail (episodic memory) are apparent by midlife-a time when most females experience spontaneous menopause. Yet, little is known about how menopause status affects episodic memory-related brain activity at encoding and retrieval in middle-aged premenopausal and postmenopausal females, and whether any observed group differences in brain activity and memory performance correlate with chronological age within group. We conducted an event-related task fMRI study of episodic memory for spatial context to address this knowledge gap. Multivariate behavioral partial least squares was used to investigate how chronological age and retrieval accuracy correlated with brain activity in 31 premenopausal females (age range, 39.55-53.30 years; mean age, 44.28 years; SD age, 3.12 years) and 41 postmenopausal females (age range, 46.70-65.14 years; mean age, 57.56 years; SD age, 3.93 years). We found that postmenopausal status, and advanced age within postmenopause, was associated with lower spatial context memory. The fMRI analysis showed that only in postmenopausal females, advanced age was correlated with decreased activity in occipitotemporal, parahippocampal, and inferior parietal cortices during encoding and retrieval, and poorer spatial context memory performance. In contrast, only premenopausal females exhibited an overlap in encoding and retrieval activity in angular gyrus, midline cortical regions, and prefrontal cortex, which correlated with better spatial context retrieval accuracy. These results highlight how menopause status and chronological age, nested within menopause group, affect episodic memory and its neural correlates at midlife.SIGNIFICANCE STATEMENT This is the first fMRI study to examine how premenopause and postmenopause status affect the neural correlates of episodic memory encoding and retrieval, and how chronological age contributes to any observed group similarities and differences. We found that both menopause status (endocrine age) and chronological age affect spatial context memory and its neural correlates. Menopause status directly affected the direction of age-related and performance-related correlations with brain activity in inferior parietal, parahippocampal, and occipitotemporal cortices across encoding and retrieval. Moreover, we found that only premenopausal females exhibited cortical reinstatement of encoding-related activity in midline cortical, prefrontal, and angular gyrus, at retrieval. This suggests that spatial context memory abilities may rely on distinct brain systems at premenopause compared with postmenopause.

The shared and unique neural correlates of personal semantic, general semantic, and episodic memory

One of the most common distinctions in long-term memory is that between semantic (i.e., general world knowledge) and episodic (i.e., recollection of contextually specific events from one's past). However, emerging cognitive neuroscience data suggest a surprisingly large overlap between the neural correlates of semantic and episodic memory. Moreover, personal semantic memories (i.e., knowledge about the self and one's life) have been studied little and do not easily fit into the standard semantic-episodic dichotomy. Here, we used fMRI to record brain activity while 48 participants verified statements concerning general facts, autobiographical facts, repeated events, and unique events. In multivariate analysis, all four types of memory involved activity within a common network bilaterally (e.g., frontal pole, paracingulate gyrus, medial frontal cortex, middle/superior temporal gyrus, precuneus, posterior cingulate, angular gyrus) and some areas of the medial temporal lobe. Yet the four memory types differentially engaged this network, increasing in activity from general to autobiographical facts, from autobiographical facts to repeated events, and from repeated to unique events. Our data are compatible with a component process model, in which declarative memory types rely on different weightings of the same elementary processes, such as perceptual imagery, spatial features, and self-reflection.

Age differences in the neural correlates of recollection: transient versus sustained fMRI effects

Prior functional magnetic resonance imaging findings in young adults indicate that recollection-sensitive neural regions dissociate according to the time courses of their respective recollection effects. Here, we examined whether such dissociations are also evident in older adults. Young and older participants encoded a series of word-image pairs, judging which of the denoted objects was the smaller. At the test, participants judged whether each of a series of test words was old or new. If a word was old, the requirement was to recall the associated image and maintain it over a variable delay period. Older adults demonstrated significantly lower associative memory performance than young adults. Transient recollection effects were identified in the left hippocampus, medial prefrontal cortex, and posterior cingulate, while sustained effects were widespread across left lateral cortex and were also evident in the bilateral striatum. Except for those in the left insula, all effects were age-invariant. These findings suggest that both transient and sustained recollection effects are largely stable across much of the healthy adult life span.

Relationships between age, fMRI correlates of familiarity and familiarity-based memory performance under single and dual task conditions

Using fMRI, we investigated the effects of age and divided attention on the neural correlates of familiarity and their relationship with memory performance. At study, word pairs were visually presented to young and older participants under the requirement to make a relational judgment on each pair. Participants were then scanned while undertaking an associative recognition test under single and dual (auditory tone detection) task conditions. The test items comprised studied, rearranged (words from different studied pairs) and new word pairs. fMRI familiarity effects were operationalized as greater activity elicited by studied pairs incorrectly identified as 'rearranged' than by correctly rejected new pairs. The reverse contrast was employed to identify 'novelty' effects. Behavioral familiarity estimates were equivalent across age groups and task conditions. Robust fMRI familiarity effects were identified in several regions, including medial and superior lateral parietal cortex, dorsal medial and left lateral prefrontal cortex, and bilateral caudate. fMRI novelty effects were identified in the anterior medial temporal lobe. Both familiarity and novelty effects were largely age-invariant and did not vary, or varied minimally, according to task condition. In addition, the familiarity effects correlated positively with a behavioral estimate of familiarity strength irrespective of age. These findings extend a previous report from our laboratory, and converge with prior behavioral reports, in demonstrating that the factors of age and divided attention have little impact on behavioral and neural estimates of familiarity.

Relationships between age, fMRI correlates of familiarity and familiarity-based memory performance under single and dual task conditions

Using fMRI, we investigated the effects of age and divided attention on the neural correlates of familiarity and their relationship with memory performance. At study, word pairs were visually presented to young and older participants under the requirement to make a relational judgment on each pair. Participants were then scanned while undertaking an associative recognition test under single and dual (auditory tone detection) task conditions. The test items comprised studied, rearranged (words from different studied pairs) and new word pairs. fMRI familiarity effects were operationalized as greater activity elicited by studied pairs incorrectly identified as 'rearranged' than by correctly rejected new pairs. The reverse contrast was employed to identify 'novelty' effects. Behavioral familiarity estimates were equivalent across age groups and task conditions. Robust fMRI familiarity effects were identified in several regions, including medial and superior lateral parietal cortex, dorsal medial and left lateral prefrontal cortex, and bilateral caudate. fMRI novelty effects were identified in the anterior medial temporal lobe. Both familiarity and novelty effects were age-invariant and did not vary according to task condition. In addition, the familiarity effects correlated positively with a behavioral estimate of familiarity strength irrespective of age. These findings extend a previous report from our laboratory, and converge with prior behavioral reports, in demonstrating that the factors of age and divided attention have minimal impact on behavioral and neural estimates of familiarity.

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

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

The effects of age on neural correlates of recollection: transient versus sustained fMRI effects

Prior fMRI findings in young adults indicate that recollection-sensitive neural regions dissociate according to the time courses of their respective recollection effects. Here, we examined whether such dissociations are also evident in older adults. Young and older participants encoded a series of word-object image pairs, judging which of the denoted objects was the smaller. At test, participants first judged whether a test word was old or new. For items judged old, they were required to recall the associated image and hold it in mind across a variable delay period. A post-delay cue denoted which of three judgments should be made on the retrieved image. Older adults demonstrated significantly lower associative memory performance than young adults. Replicating prior findings, transient recollection effects were identified in the left hippocampus, medial prefrontal cortex and posterior cingulate, while sustained effects were widespread across left lateral cortex and were also evident in the bilateral striatum. With the exception of those in the left insula, all effects were age-invariant. These findings add to the evidence that recollection-related BOLD effects in different neural regions can be temporally dissociated. Additionally, the findings suggest that both transient and sustained recollection effects are largely stable across much of the healthy adult lifespan.

Patterns of retrieval-related cortico-striatal connectivity are stable across the adult lifespan

Memory retrieval effects in the striatum are well documented and robust across experimental paradigms. However, the functional significance of these effects, and whether they are moderated by age, remains unclear. We used functional magnetic resonance imaging paired with an associative recognition task to examine retrieval effects in the striatum in a sample of healthy young, middle-aged, and older adults. We identified anatomically segregated patterns of enhanced striatal blood oxygen level-dependent (BOLD) activity during recollection- and familiarity-based memory judgments. Successful recollection was associated with enhanced BOLD activity in bilateral putamen and nucleus accumbens, and neither of these effects were reliably moderated by age. Familiarity effects were evident in the head of the caudate nucleus bilaterally, and these effects were attenuated in middle-aged and older adults. Using psychophysiological interaction analyses, we observed a monitoring-related increase in functional connectivity between the caudate and regions of the frontoparietal control network, and between the putamen and bilateral retrosplenial cortex and intraparietal sulcus. In all instances, monitoring-related increases in cortico-striatal connectivity were unmoderated by age. These results suggest that the striatum, and the caudate in particular, couples with the frontoparietal control network to support top-down retrieval-monitoring operations, and that the strength of these inter-regional interactions is preserved in later life.

Neuroanatomical and neurocognitive changes associated with subjective cognitive decline

Introduction

Subjective Cognitive Decline (SCD) can progress to mild cognitive impairment (MCI) and Alzheimer's disease (AD) dementia and thus may represent a preclinical stage of the AD continuum. However, evidence about structural changes observed in the brain during SCD remains inconsistent.

Materials and methods

This cross-sectional study aimed to evaluate, in subjects recruited from the CompAS project, neurocognitive and neurostructural differences between a group of forty-nine control subjects and forty-nine individuals who met the diagnostic criteria for SCD and exhibited high levels of subjective cognitive complaints (SCCs). Structural magnetic resonance imaging was used to compare neuroanatomical differences in brain volume and cortical thickness between both groups.

Results

Relative to the control group, the SCD group displayed structural changes involving frontal, parietal, and medial temporal lobe regions of critical importance in AD etiology and functionally related to several cognitive domains, including executive control, attention, memory, and language.

Conclusion

Despite the absence of clinical deficits, SCD may constitute a preclinical entity with a similar (although subtle) pattern of neuroanatomical changes to that observed in individuals with amnestic MCI or AD dementia.

Effects of age on the neural correlates of encoding source and item information: An fMRI study

The effects of age on encoding-related neural activity predictive of accurate item and source memory judgments were examined with fMRI, with an a priori focus of the inferior frontal gyrus (IFG) and hippocampus. During a scanned study phase, young and older adults viewed a series of pictures of objects and made one of two judgments on each object. At test, which occurred outside of the scanner, an 'old/new' judgment on each test item was followed, for those items endorsed old, by a source judgment querying the study task. Neural activity predictive of accurate subsequent item and source memory judgments was identified in bilateral IFG, several other cortical regions and bilateral hippocampus. Cortical effects were graded in the young group (source > item > miss) but predicted item memory only in the older group. Hippocampal effects exclusively predicted source memory, and the magnitude of these effects did not reliably differ between the age groups. In the older group only, IFG and hippocampal encoding effects were positively correlated across participants with memory performance. Similar findings were evident in the extra-IFG regions demonstrating encoding effects. With the exception of the age-dependent relationship identified for hippocampal encoding effects, the present findings are broadly consistent with those from prior aging studies that employed verbal memoranda and tests of associative recognition. Thus, they extend these prior findings to include non-verbal materials and a different operationalization of episodic recollection. Additionally, the present findings suggest that the sensitivity in older adults of IFG encoding effects to subsequent memory performance reflects a more general tendency for cortical encoding effects to predict memory performance in this age group.

Healthy Middle-Aged Adults Have Preserved Mnemonic Discrimination and Integration, While Showing No Detectable Memory Benefits

Declarative memory abilities change across adulthood. Semantic memory and autobiographic episodic knowledge can remain stable or even increase from mid- to late adulthood, while episodic memory abilities decline in later adulthood. Although it is well known that prior knowledge influences new learning, it is unclear whether the experiential growth of knowledge and memory traces across the lifespan may drive favorable adaptations in some basic memory processes. We hypothesized that an increased reliance on memory integration may be an adaptive mechanism to handle increased interference from accumulating memory traces and knowledge across adulthood. In turn, this may confer an improved ability for integration, observable in middle-age, before the onset of major aging-related declines. We further tested whether the hypothesized increase would be associated with previously observed reductions in memory discrimination performance in midlife. Data from a sample of healthy middle-aged (40-50 years, n = 40) and younger adults (20-28 years, n = 41) did not support the hypothesis of improved integration, as assessed by an associative inference paradigm. Instead, age-equivalent performance on both integration and discrimination measures were observed [Bayes factors (BFs)10 = 0.19-0.25], along with expected higher verbal knowledge and slower perceptual speed for middle-aged [(BFs)10 = 8.52-73.52]. The results contribute to an increased understanding of memory processing in midlife, an understudied portion of the lifespan, and suggest that two core episodic memory processes, integration and discrimination, can be maintained in healthy middle-aged adults.

Continuous theta-burst stimulation over the right dorsolateral prefrontal cortex disrupts fear memory reconsolidation in humans

Continuous theta-burst stimulation (cTBS), a non-invasive brain stimulation technique, can induce long-lasting changes in synaptic plasticity, vital for memory reconsolidation. For this study, a total of 170 participants completed four experiments by a randomized controlled design. Succeeding fear conditioning, the subjects received cTBS over the right dorsolateral prefrontal cortex (dlPFC) or vertex (control) with or without exposure to the conditioned stimulus to reactivate the original fear memory, and then underwent fear response tests. Compared with cTBS over the vertex and without memory reactivation, only cTBS over the right dlPFC after reactivation decreased the fear response for both recent and remote fear memories. This procedure was effective only during the reconsolidation window. The disruptive effect of cTBS over the right dlPFC on fear memory reconsolidation was delay-dependent. These findings demonstrate that cTBS time-dependently and delay-dependently prevents the return of fear and may have clinical potential for treating fear-related disorders.

Divided attention at retrieval does not influence neural correlates of recollection in young or older adults

Age-related decline in episodic memory has been partially attributed to older adults' reduced domain general processing resources. In the present study, we examined the effects of divided attention (DA) - a manipulation assumed to further deplete the already limited processing resources of older adults - on the neural correlates of recollection in young and older adults. Participants underwent fMRI scanning while they performed an associative recognition test in single and dual (tone detection) task conditions. Recollection effects were operationalized as greater BOLD activity elicited by test pairs correctly endorsed as 'intact' than pairs correctly or incorrectly endorsed as 'rearranged'. Detrimental effects of DA on associative recognition performance were identified in older but not young adults. The magnitudes of recollection effects did not differ between the single and dual (tone detection) tasks in either age group. Across the task conditions, age-invariant recollection effects were evident in most members of the core recollection network. However, while young adults demonstrated robust recollection effects in left angular gyrus, angular gyrus effects were undetectable in the older adults in either task condition. With the possible exception of this result, the findings suggest that DA did not influence processes supporting the retrieval and representation of associative information in either young or older adults, and converge with prior behavioral findings to suggest that episodic retrieval operations are little affected by DA.

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

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

The effects of age on neural correlates of recognition memory: An fMRI study

Studies examining the effects of age on the neural correlates of recognition memory have yielded mixed results. In the present study, we employed a modified remember-know paradigm to compare the fMRI correlates of recollection and familiarity in samples of healthy young and older adults. After studying a series of words, participants underwent fMRI scanning during a test phase in which they responded "remember" to a test word if any qualitative information could be recollected about the study event. When recollection failed, participants signaled how confident they were that the test item had been studied. Young and older adults demonstrated statistically equivalent estimates of recollection and familiarity strength, while recognition memory accuracy was significantly lower in the older adults. Robust, age-invariant fMRI effects were evident in two sets of a priori defined brain regions consistently reported in prior studies to be sensitive to recollection and familiarity respectively. In addition, the magnitudes of 'familiarity-attenuation effects' in perirhinal cortex demonstrated age-invariant correlations with estimates of familiarity strength and memory accuracy, replicating prior findings. Together, the present findings add to the evidence that the neural correlates of recognition memory are largely stable across much of the healthy human adult lifespan.

Transcranial magnetic stimulation of right dorsolateral prefrontal cortex does not affect associative retrieval in healthy young or older adults

We examined whether post-retrieval monitoring processes supporting memory performance are more resource limited in older adults than younger individuals. We predicted that older adults would be more susceptible to an experimental manipulation that reduced the neurocognitive resources available to support post-retrieval monitoring. Young and older adults received transcranial magnetic stimulation (TMS) to the right dorsolateral prefrontal cortex (DLPFC) or a vertex control site during an associative recognition task. The right DLPFC was selected as a TMS target because the region is held to be a key member of a network of regions engaged during retrieval monitoring and is readily accessible to administration of TMS. We predicted that TMS to the right DLPFC would lead to reduced associative recognition accuracy, and that this effect would be more prominent in older adults. The results did not support this prediction. Recognition accuracy was significantly reduced in older adults relative to their younger counterparts, but the magnitude of this age difference was unaffected following TMS to the right DLPFC or vertex. These findings suggest that TMS to the right DLPFC was insufficient to deplete the neurocognitive resources necessary to support post-retrieval monitoring.

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

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

Specific and general relationships between cortical thickness and cognition in older adults: a longitudinal study

Prior studies suggest that relationships between regional cortical thickness and domain-specific cognitive performance can be mediated by the relationship between global cortical thickness and domain-general cognition. Whether such findings extend to longitudinal cognitive change remains unclear. Here, we examined the relationships in healthy older adults between cognitive performance, longitudinal cognitive change over 3 years, and cortical thickness at baseline of the left and right inferior frontal gyrus (IFG) and left and right hemispheres. Both right IFG and right hemisphere thickness predicted baseline general cognition and domain-specific cognitive performance. Right IFG thickness was also predictive of longitudinal memory change. However, right IFG thickness was uncorrelated with cognitive performance and memory change after controlling for the mean thickness of other ipsilateral cortical regions. In addition, most identified associations between cortical thickness and specific cognitive domains were nonsignificant after controlling for the variance shared with other cognitive domains. Thus, relationships between right IFG thickness, cognitive performance, and memory change appear to be largely accounted for by more generic relationships between cortical thickness and cognition. This article is part of the Virtual Special Issue titled "COGNITIVE NEUROSCIENCE OF HEALTHY AND PATHOLOGICAL AGING". The full issue can be found on ScienceDirect athttps://www.sciencedirect.com/journal/neurobiology-of-aging/special-issue/105379XPWJP.

False recognitions in short-term memory - Age-differences in neural activity

While the knowledge on age-related differences in susceptibility to episodic false memories is extensive, little is known about this phenomenon in visual short-term memory (STM). Our previous behavioural research indicated that older adults are more confident of their erroneous STM recognitions than young adults. However, unlike in episodic memory, we did not find support for older adults' higher rate of false alarms. To further understand this specific age-difference, here we investigated its neural correlates. First, the pattern of behavioural results replicated the one from our previous experiment. Second, younger adults, when compared to older adults, exhibited higher false recognition-related activity of the visual cortex, the anterior cingulate cortex, the frontal operculum/insular cortex as well as regions within the anterior and dorsolateral prefrontal cortex. No age-differences were observed in hippocampal activity. Third, younger but not older adults presented higher activity in the anterior cingulate cortex and the frontal operculum/insular cortex for false recognitions when compared to highly confident correct rejections. Finally, frontal activity was influenced by both the individuals' performance and their metacognitive abilities. The results suggest that age-related differences in confidence of STM false recognitions may arise from age-differences in performance monitoring and uncertainty processing rather than in hippocampal-mediated binding.

Recognition memory performance can be estimated based on brain activation networks

BACKGROUND

Recognition memory is an essential ability for functioning in everyday life. Establishing robust brain networks linked to recognition memory performance can help to understand the neural basis of recognition memory itself and the interindividual differences in recognition memory performance.

METHODS

We analysed behavioural and whole-brain fMRI data from 1'410 healthy young adults during the testing phase of a picture-recognition task. Using independent component analysis (ICA), we decomposed the fMRI contrast for previously seen vs. new (old-new) pictures into networks of brain activity. This was done in two independent samples (training sample: N = 645, replication sample: N = 665). Next, we investigated the relationship between the identified brain networks and interindividual differences in recognition memory performance by conducting a prediction analysis. We estimated the prediction accuracy in a third independent sample (test sample: N = 100).

RESULTS

We identified 12 robust and replicable brain networks using two independent samples. Based on the activity of those networks we could successfully estimate interindividual differences in recognition memory performance with high accuracy in a third independent sample (r = 0.5, p = 1.29 × 10^-07).

CONCLUSION

Given the robustness of the ICA decomposition as well as the high prediction estimate, the identified brain networks may be considered as potential biomarkers of recognition memory performance in healthy young adults and can be further investigated in the context of health and disease.

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.

Context Memory Encoding and Retrieval Temporal Dynamics are Modulated by Attention across the Adult Lifespan

Episodic memories are multidimensional, including simple and complex features. How we successful encode and recover these features in time, whether these temporal dynamics are preserved across age, even under conditions of reduced memory performance, and the role of attention on these temporal dynamics is unknown. In the current study, we applied time-resolved multivariate decoding to oscillatory electroencephalography (EEG) in an adult lifespan sample to investigate the temporal order of successful encoding and recognition of simple and complex perceptual context features. At encoding, participants studied pictures of black and white objects presented with both color (low-level/simple) and scene (high-level/complex) context features and subsequently made context memory decisions for both features. Attentional demands were manipulated by having participants attend to the relationship between the object and either the color or scene while ignoring the other context feature. Consistent with hierarchical visual perception models, simple visual features (color) were successfully encoded earlier than were complex features (scenes). These features were successfully recognized in the reverse temporal order. Importantly, these temporal dynamics were both dependent on whether these context features were in the focus of one's attention, and preserved across age, despite age-related context memory impairments. These novel results support the idea that episodic memories are encoded and retrieved successively, likely dependent on the input and output pathways of the medial temporal lobe (MTL), and attentional influences that bias activity within these pathways across age.

Hippocampal Theta Oscillations Support Successful Associative Memory Formation

Models of memory formation posit that episodic memory formation depends critically on the hippocampus, which binds features of an event to its context. For this reason, the contrast between study items that are later recollected with their associative pair versus those for which no association is made fails should reveal electrophysiological patterns in the hippocampus selectively involved in associative memory encoding. Extensive data from studies in rodents support a model in which theta oscillations fulfill this role, but results in humans have not been as clear. Here, we used an associative recognition memory procedure to identify hippocampal correlates of successful associative memory encoding and retrieval in patients (10 females and 9 males) undergoing intracranial EEG monitoring. We identified a dissociation between 2-5 Hz and 5-9 Hz theta oscillations, by which power increases in 2-5 Hz oscillations were uniquely linked with successful associative memory in both the anterior and posterior hippocampus. These oscillations exhibited a significant phase reset that also predicted successful associative encoding and distinguished recollected from nonrecollected items at retrieval, as well as contributing to relatively greater reinstatement of encoding-related patterns for recollected versus nonrecollected items. Our results provide direct electrophysiological evidence that 2-5 Hz hippocampal theta oscillations preferentially support the formation of associative memories, although we also observed memory-related effects in the 5-9 Hz frequency range using measures such as phase reset and reinstatement of oscillatory activity.SIGNIFICANCE STATEMENT Models of episodic memory encoding predict that theta oscillations support the formation of interitem associations. We used an associative recognition task designed to elicit strong hippocampal activation to test this prediction in human neurosurgical patients implanted with intracranial electrodes. The findings suggest that 2-5 Hz theta oscillatory power and phase reset in the hippocampus are selectively associated with associative memory judgments. Furthermore, reinstatement of oscillatory patterns in the hippocampus was stronger for successful recollection. Collectively, the findings support a role for hippocampal theta oscillations in human associative memory.

Neural correlates of post-retrieval monitoring in older adults are preserved under divided attention, but are decoupled from memory performance

Post-retrieval monitoring is associated with engagement of anterior cingulate and dorsolateral prefrontal cortex. Recent fMRI studies reported age-invariant monitoring effects in these regions and an age-invariant correlation between these effects and memory performance. The present study examined monitoring effects during associative recognition (difference in activity elicited by 'rearranged' and 'intact' test pairs) under single and dual (tone detection) task conditions in young and older adults (Ns = 28 per group). It was predicted that, for the older adults only, dual tasking would attenuate memory performance and monitoring effects and weaken their correlation. Consistent with this prediction, in the older group imposition of the secondary task led to lower memory performance and elimination of the relationship between monitoring effects and performance. However, the size of the effects did not differ between single and dual task conditions. The findings suggest that the decline in older adults' memory performance in the dual task condition resulted not from impaired monitoring, but from a different cause that also weakened the dependence of performance on monitoring.

Age Differences In Retrieval-Related Reinstatement Reflect Age-Related Dedifferentiation At Encoding

Age-related reductions in neural selectivity have been linked to cognitive decline. We examined whether age differences in the strength of retrieval-related cortical reinstatement could be explained by analogous differences in neural selectivity at encoding, and whether reinstatement was associated with memory performance in an age-dependent or an age-independent manner. Young and older adults underwent fMRI as they encoded words paired with images of faces or scenes. During a subsequent scanned memory test participants judged whether test words were studied or unstudied and, for words judged studied, also made a source memory judgment about the associated image category. Using multi-voxel pattern similarity analyses, we identified robust evidence for reduced scene reinstatement in older relative to younger adults. This decline was however largely explained by age differences in neural differentiation at encoding; moreover, a similar relationship between neural selectivity at encoding and retrieval was evident in young participants. The results suggest that, regardless of age, the selectivity with which events are neurally processed at the time of encoding can determine the strength of retrieval-related cortical reinstatement.

Recollection-related hippocampal fMRI effects predict longitudinal memory change in healthy older adults

Prior fMRI studies have reported relationships between memory-related activity in the hippocampus and in-scanner memory performance, but whether such activity is predictive of longitudinal memory change remains unclear. Here, we administered a neuropsychological test battery to a sample of cognitively healthy older adults on three occasions, the second and third sessions occurring one month and three years after the first session. Structural and functional MRI data were acquired between the first two sessions. The fMRI data were derived from an associative recognition procedure and allowed estimation of hippocampal effects associated with both successful associative encoding and successful associative recognition (recollection). Baseline memory performance and memory change were evaluated using memory component scores derived from a principal components analysis of the neuropsychological test scores. Across participants, right hippocampal encoding effects correlated significantly with baseline memory performance after controlling for chronological age. Additionally, both left and right hippocampal associative recognition effects correlated negatively with longitudinal memory decline after controlling for age, and the relationship with the left hippocampal effect remained after also controlling for left hippocampal volume. Thus, in cognitively healthy older adults, the magnitude of hippocampal recollection effects appears to be a robust predictor of future memory change.

Hippocampal and cortical mechanisms at retrieval explain variability in episodic remembering in older adults

Age-related episodic memory decline is characterized by striking heterogeneity across individuals. Hippocampal pattern completion is a fundamental process supporting episodic memory. Yet, the degree to which this mechanism is impaired with age, and contributes to variability in episodic memory, remains unclear. We combine univariate and multivariate analyses of fMRI data from a large cohort of cognitively normal older adults (N=100) to measure hippocampal activity and cortical reinstatement during retrieval of trial-unique associations. Trial-wise analyses revealed that (a) hippocampal activity scaled with reinstatement strength, (b) cortical reinstatement partially mediated the relationship between hippocampal activity and associative retrieval, (c) older age weakened cortical reinstatement and its relationship to memory behaviour. Moreover, individual differences in the strength of hippocampal activity and cortical reinstatement explained unique variance in performance across multiple assays of episodic memory. These results indicate that fMRI indices of hippocampal pattern completion explain within- and across-individual memory variability in older adults.

How Proactive Interference during New Associative Learning Impacts General and Specific Memory in Young and Old

Some prior research has found that older adults are more susceptible to proactive interference than young adults. The current study investigated whether age-related deficits in pFC-mediated cognitive control processes that act to detect and resolve interference underlie increased susceptibility to proactive interference in an associative memory task. Young and older adults were scanned while tasked with remembering which associate (face or scene) objects were paired with most recently during study, under conditions of high, low, or no proactive interference. After scanning, participants' memory was tested for varying levels of episodic detail about the pairings (i.e., target category vs. specific target category vs. specific target associate). Young and older adults were similarly susceptible to proactive interference. Memory for both the general target category and the specific target associate worsened as the level of proactive interference increased, with no robust age differences. For both young and older adults, the left ventrolateral pFC, which has been indicated in controlled retrieval of goal-relevant conceptual representations, was sensitive to increasing levels of interference during encoding but was insensitive to associative memory accuracy. Consistent with the Compensation-Related Utilization of Neural Circuits Hypothesis model of cognitive aging, the ventromedial pFC, which is involved in the monitoring of internally generated information, was recruited more by older than young adults to support the successful retrieval of target-object pairs at lower levels of proactive interference. Collectively, these results suggest that some older adults are able to engage in the cognitive control processes necessary to resolve proactive interference to the same extent as young adults.

Age differences in the neural correlates of the specificity of recollection: An event-related potential study

In young adults, the neural correlates of successful recollection vary with the specificity (or amount) of information retrieved. We examined whether the neural correlates of recollection are modulated in a similar fashion in older adults. We compared event-related potential (ERP) correlates of recollection in samples of healthy young and older adults (N = 20 per age group). At study, participants were cued to make one of two judgments about each of a series of words. Subsequently, participants completed a memory test for studied and unstudied words in which they first made a Remember/Know/New (RKN) judgment, followed by a source memory judgment when a word attracted a 'Remember' (R) response. In young adults, the 'left parietal effect' - a putative ERP correlate of successful recollection - was largest for test items endorsed as recollected (R judgment) and attracting a correct source judgment, intermediate for items endorsed as recollected but attracting an incorrect or uncertain source judgment, and, relative to correct rejections, absent for items endorsed as familiar only (K judgment). In marked contrast, the left parietal effect was not detectable in older adults. Rather, regardless of source accuracy, studied items attracting an R response elicited a sustained, centrally maximum negative-going deflection relative to both correct rejections and studied items where recollection failed (K judgment). A similar retrieval-related negativity has been described previously in older adults, but the present findings are among the few to link this effect specifically to recollection. Finally, relative to correct rejections, all classes of correctly recognized old items elicited an age-invariant, late-onsetting positive deflection that was maximal over the right frontal scalp. This finding, which replicates several prior results, suggests that post-retrieval monitoring operations were engaged to an equivalent extent in the two age groups. Together, the present results suggest that there are circumstances where young and older adults engage qualitatively distinct retrieval-related processes during successful recollection.

A Functional MRI Paradigm Suitable for Language and Memory Mapping in Pediatric Temporal Lobe Epilepsy

Functional Magnetic Resonance Imaging (fMRI) is a technique frequently used to determine the territories of eloquent tissue that serve critical functions, such as language. This can be particularly useful as part of the pre-surgical assessment for temporal lobe epilepsy (TLE) in order to predict cognitive outcome and guide surgical decision-making. Whereas language fMRI is widely used, memory fMRI is less frequently employed in adult TLE, and lacking in childhood TLE. We have developed a combined language/memory fMRI paradigm that is suitable for children, to provide clinically useful information for surgical planning in pediatric TLE. We evaluated this paradigm in 28 healthy children, aged 8 to 18 years. The advantages of this paradigm are: (a) it examines the functional mapping of language and memory networks within one scanning session, (b) provides assessment of both memory encoding- and retrieval-related neural networks, (c) examines recall-based retrieval to engage hippocampal involvement compared to recognition-based retrieval, and (d) provides overt verbal responses to monitor in-scanner memory performance. This novel fMRI paradigm was designed for language and memory mapping in pediatric TLE and could provide clinically useful information for surgical planning. Finally, parallel versions of the paradigm allow the comparison of brain activations pre- and post-surgical intervention.

Sex, Age, and Handedness Modulate the Neural Correlates of Active Learning

BACKGROUND

Self-generation of material compared to passive learning results in mproved memory performance; this may be related to recruitment of a fronto-temporal encoding network. Using a verbal paired-associate learning fMRI task, we examined the effects of sex, age, and handedness on the neural correlates of self-generation.

METHODS

Data from 174 healthy English-speaking participants (78M, 56 atypically handed; ages 19-76) were preprocessed using AFNI and FSL. Independent component analysis was conducted using GIFT (Group ICA fMRI Toolbox). Forty-one independent components were temporally sorted by task time series. Retaining correlations (r > 0.25) resulted in three task-positive ("generate") and three task-negative ("read") components. Using participants' back-projected components, we evaluated the effects of sex, handedness, and aging on activation lateralization and localization in task-relevant networks with two-sample t-tests. Further, we examined the linear relationship between sex and neuroimaging data with multiple regression, covarying for scanner, age, and handedness.

RESULTS

Task-positive components identified using ICA revealed a fronto-parietal network involved with self-generation, while task-negative components reflecting passive reading showed temporo-occipital involvement. Compared to older adults, younger adults exhibited greater task-positive involvement of the left inferior frontal gyrus and insula, whereas older adults exhibited reduced prefrontal lateralization. Greater involvement of the left angular gyrus in task-positive encoding networks among right-handed individuals suggests the reliance on left dominant semantic processing areas may be modulated by handedness. Sex effects on task-related encoding networks while controlling for age and handedness suggest increased right hemisphere recruitment among males compared to females, specifically in the paracentral lobe during self-generation and the suparmarginal gyrus during passive reading.

IMPLICATIONS

Identified neuroimaging differences suggest that sex, age, and handedness are factors in the differential recruitment of encoding network regions for both passive and active learning.

Neural evidence for age-related differences in representational quality and strategic retrieval processes

Mounting behavioral evidence suggests that declines in both representational quality and controlled retrieval processes contribute to episodic memory decline with age. The present study sought neural evidence for age-related change in these factors by measuring neural differentiation during encoding of paired associates and changes in regional blood oxygenation level-dependent activity and functional connectivity during retrieval conditions that placed low (intact pairs) and high (recombined pairs) demands on controlled retrieval processes. Pattern similarity analysis revealed age-related declines in the differentiation of stimulus representations at encoding, manifesting as both reduced pattern similarity between closely related events and increased pattern similarity between distinct events. During retrieval, both groups increased recruitment of areas within the core recollection network when endorsing studied pairs, including the hippocampus and angular gyrus. In contrast, only younger adults increased recruitment of, and hippocampal connectivity with, lateral prefrontal regions during correct rejections of recombined pairs. These results provide evidence for age-related changes in representational quality and in the neural mechanisms supporting memory retrieval under conditions of high, but not low, control demand.

Age moderates the relationship between cortical thickness and cognitive performance

Findings from cross-sectional and longitudinal magnetic resonance imaging (MRI) studies indicate that cortical thickness declines across the adult lifespan, with regional differences in rate of decline. Global and regional thickness have also been found to co-vary with cognitive performance. Here we examined the relationships between age, mean cortical thickness, and associative recognition performance across three age groups (younger, middle-aged and older adults; total n = 133). Measures of cortical thickness were obtained using a semi-automated method. Older age was associated with decreased memory performance and a reduction in mean cortical thickness. After controlling for the potentially confounding effects of head motion, mean cortical thickness was negatively associated with associative memory performance in the younger participants, but was positively correlated with performance in older participants. A similar but weaker pattern was evident in the relationships between cortical thickness and scores on four cognitive constructs derived from a neuropsychological test battery. This pattern is consistent with prior findings indicating that the direction of the association between cortical thickness and cognitive performance reverses between early and later adulthood. In addition, head motion was independently and negatively correlated with associative recognition performance in younger and middle-aged, but not older, participants, suggesting that variance in head motion is determined by multiple factors that vary in their relative influences with age.

Effects of pioglitazone on mnemonic hippocampal function: A blood oxygen level-dependent functional magnetic resonance imaging study in elderly adults

Introduction

Mitochondrial dysfunction is implicated in the pathophysiology of Alzheimer's disease (AD). Accordingly, drugs that positively influence mitochondrial function are being evaluated in delay-of-onset clinical trials with at-risk individuals. Such ongoing clinical research can be advanced by developing a better understanding of how these drugs affect intermediate brain phenotypes associated with both AD risk and pathophysiology.

Methods

Using a randomized, parallel-group, placebo-controlled design in 55 healthy elderly volunteers, we explored the effects of oral, low-dose pioglitazone, a thiazolidinedione with promitochondrial effects, on hippocampal activity measured with functional magnetic resonance imaging during the encoding of novel face–name pairs.

Results

Compared with placebo, 0.6 mg of pioglitazone (but not 2.1 mg, 3.9 mg, or 6.0 mg) administered daily for 14 days was associated with significant increases in right hippocampal activation during encoding of novel face–name pairs at day 7 and day 14, relative to baseline.

Discussion

Our exploratory analyses suggest that low-dose pioglitazone has measurable effects on mnemonic brain function associated with AD risk and pathophysiology.

•

Right hippocampal activity increased after 7 and 14 days of 0.6 mg of oral pioglitazone administration.

•

Pioglitazone-associated hippocampal effects were not manifested at the level of memory performance.

•

Nonspecific increases in distributed brain activity at higher pioglitazone doses (>0.6 mg).

Development and Decline of the Hippocampal Long-Axis Specialization and Differentiation During Encoding and Retrieval of Episodic Memories

Change in hippocampal function is a major factor in life span development and decline of episodic memory. Evidence indicates a long-axis specialization where anterior hippocampus is more engaged during encoding than during retrieval, and posterior more engaged during retrieval than during encoding. We tested the life span trajectory of hippocampal long-axis episodic memory-related activity and functional connectivity (FC) in 496 participants (6.8–80.8 years) encoding and retrieving associative memories. We found evidence for a long-axis encoding–retrieval specialization that declined linearly during development and aging, eventually vanishing in the older adults. This was mainly driven by age effects on retrieval, which was associated with gradually lower activity from childhood to adulthood, followed by positive age relationships until 70 years. This pattern of age effects characterized task engagement regardless of memory success or failure. Especially for retrieval, children engaged posterior hippocampus more than anterior, while anterior was relatively more activated already in teenagers. Significant intrahippocampal connectivity was found during task, which declined with age. The results suggest that hippocampal long-axis differentiation and communication during episodic memory tasks develop rapidly during childhood, are different in older compared with younger adults, and that the age effects are related to task engagement, not the successful retrieval of episodic memories specifically.

Recollection-related increases in functional connectivity across the healthy adult lifespan

In young adults, recollection-sensitive brain regions exhibit enhanced connectivity with a widely distributed set of other regions during successful versus unsuccessful recollection, and the magnitude of connectivity change correlates with individual differences in recollection accuracy. Here, we examined whether recollection-related changes in connectivity and their relationship with performance varied across samples of young, middle-aged, and older adults. Psychophysiological interaction analyses identified recollection-related increases in connectivity both with recollection-sensitive seed regions and among regions distributed throughout the whole brain. The seed-based approach failed to identify age-related differences in recollection-related connectivity change. However, the whole-brain analysis revealed a number of age-related effects. Numerous pairs of regions exhibited a main effect of age on connectivity change, mostly due to decreased change with increasing age. After controlling for recollection accuracy, however, these effects of age were for the most part no longer significant, and those effects that were detected now reflected age-related increases in connectivity change. A subset of pairs of regions also exhibited an age by performance interaction, driven mostly by a weaker relationship between connectivity change and recollection accuracy with increasing age. We conjecture that these effects reflect age-related differences in neuromodulation.

Individual differences in associative memory among older adults explained by hippocampal subfield structure and function

Older adults experience impairments in episodic memory, ranging from mild to clinically significant. Given the critical role of the medial temporal lobe (MTL) in episodic memory, age-related changes in MTL structure and function may partially account for individual differences in memory. Using ultra-high-field 7T structural MRI and high-resolution 3T functional MRI (hr-fMRI), we evaluated MTL subfield thickness and function in older adults representing a spectrum of cognitive health. Participants performed an associative memory task during hr-fMRI in which they encoded and later retrieved face-name pairs. Motivated by prior research, we hypothesized that differences in performance would be explained by the following: (i) entorhinal cortex (ERC) and CA1 apical neuropil layer [CA1-stratum radiatum lacunosum moleculare (SRLM)] thickness, and (ii) activity in ERC and the dentate gyrus (DG)/CA3 region. Regression analyses revealed that this combination of factors significantly accounted for variability in memory performance. Among these metrics, CA1-SRLM thickness was positively associated with memory, whereas DG/CA3 retrieval activity was negatively associated with memory. Furthermore, including structural and functional metrics in the same model better accounted for performance than did single-modality models. These results advance the understanding of how independent but converging influences of both MTL subfield structure and function contribute to age-related memory impairment, complementing findings in the rodent and human postmortem literatures.

Dissociation between the neural correlates of recollection and familiarity in the striatum and hippocampus: Across-study convergence

In tests of recognition memory, neural activity in the striatum has consistently been reported to differ according to the study status of the test item. A full understanding of the functional significance of striatal 'retrieval success' effects is impeded by a paucity of evidence concerning whether the effects differ according to the nature of the memory signal supporting the recognition judgment (recollection vs. familiarity). Here, we address this issue through an analysis of retrieval-related striatal activity in three independent fMRI studies (total N = 88). Recollection and familiarity were operationalized in a different way in each study, allowing the identification of test-independent, generic recollection- and familiarity-related effects. While activity in a bilateral dorsal striatal region, mainly encompassing the caudate nucleus, was enhanced equally by recollected and 'familiar only' test items, activity in bilateral ventral striatum and adjacent subgenual frontal cortex was enhanced only in response to items that elicited successful recollection. By contrast, relative to familiar items, activity in anterior hippocampus was enhanced for both recollected and novel test items. Thus, recollection- and familiarity-driven recognition memory judgments are associated with anatomically distinct patterns of retrieval-related striatal activity, and these patterns are at least partially independent of recollection and novelty effects in the hippocampus.

Independent contributions of fMRI familiarity and novelty effects to recognition memory and their stability across the adult lifespan

The impact of age on the neural correlates of familiarity-driven recognition memory has received relatively little attention. Here, the relationships between age, the neural correlates of familiarity, and memory performance were investigated using an associative recognition test in young, middle-aged and older participants. Test items comprised studied, rearranged (items studied on different trials) and new word pairs. fMRI 'familiarity effects' were operationalized as greater activity for studied test pairs incorrectly identified as 'rearranged' than for correctly rejected new pairs. The reverse contrast was employed to identify 'novelty' effects. Estimates of familiarity strength were slightly but significantly lower for the older relative to the younger group. With the exception of one region in dorsal medial prefrontal cortex, fMRI familiarity effects (which were identified in medial and lateral parietal cortex, dorsal medial and left lateral prefrontal cortex, and bilateral caudate among other regions) did not differ significantly with age. Age-invariant 'novelty effects' were identified in the anterior hippocampus and the perirhinal cortex. When entered into the same regression model, familiarity and novelty effects independently predicted familiarity strength across participants, suggesting that the two classes of memory effect reflect functionally distinct mnemonic processes. It is concluded that the neural correlates of familiarity-based memory judgments, and their relationship with familiarity strength, are largely stable across much of the healthy adult lifespan.

Decoding the content of recollection within the core recollection network and beyond

Recollection - retrieval of qualitative information about a past event - is associated with enhanced neural activity in a consistent set of neural regions (the 'core recollection network') seemingly regardless of the nature of the recollected content. Here, we employed multi-voxel pattern analysis (MVPA) to assess whether retrieval-related functional magnetic resonance imaging (fMRI) activity in core recollection regions - including the hippocampus, angular gyrus, medial prefrontal cortex, retrosplenial/posterior cingulate cortex, and middle temporal gyrus - contain information about studied content and thus demonstrate retrieval-related 'reinstatement' effects. During study, participants viewed objects and concrete words that were subjected to different encoding tasks. Test items included studied words, the names of studied objects, or unstudied words. Participants judged whether the items were recollected, familiar, or new by making 'remember', 'know', and 'new' responses, respectively. The study history of remembered test items could be reliably decoded using MVPA in most regions, as well as from the dorsolateral prefrontal cortex, a region where univariate recollection effects could not be detected. The findings add to evidence that members of the core recollection network, as well as at least one neural region where mean signal is insensitive to recollection success, carry information about recollected content. Importantly, the study history of recognized items endorsed with a 'know' response could be decoded with equal accuracy. The results thus demonstrate a striking dissociation between mean signal and multi-voxel indices of recollection. Moreover, they converge with prior findings in suggesting that, as it is operationalized by classification-based MVPA, reinstatement is not uniquely a signature of recollection.