Memory in the aging brain: doubly dissociating the contribution of the hippocampus and entorhinal cortex

What does preferential viewing tell us about the neurobiology of recognition memory?

The two tests most widely used in nonhuman primates to assess the neurobiology of recognition memory produce conflicting results. Preferential viewing tests (e.g., visual paired comparison) produce robust impairments following hippocampal lesions, whereas matching tests (e.g., delayed nonmatching-to-sample) often show complete sparing. Here, we review the data, the proposed explanations for this discrepancy, and then critically evaluate those explanations. The most likely explanation is that preferential viewing tests are not a process-pure assessment of recognition memory, but also test elements of novelty-seeking, habituation, and motivation. These confounds likely explain the conflicting results. Thus, we propose that memory researchers should prefer explicit matching tests and readers interested in the neural substrates of recognition memory should give explicit matching tests greater interpretive weight.

An overview of the hallmarks of cognitive aging

Although the notion of cognitive aging is commonly associated with decline in popular culture, a wealth of scientific literature shows that cognitive aging is more aptly characterized as multidirectional, such that trajectories of cognitive changes include areas of stability and growth (e.g., general knowledge) in addition to decline (e.g., episodic long-term memory). This article overviews these multidirectional trajectories, the heterogeneous factors that moderate the rate of change across individual trajectories, and the extensive literature that has investigated the most important factors, such as working memory, that constrain cognition across the adult lifespan. In light of the multidirectional nature of cognitive change, increasing research has considered methods to leverage the often-overlooked benefits of getting older to ameliorate cognitive deficits.

The role of recollection, familiarity, and the hippocampus in episodic and working memory

The hippocampus plays an essential role in long-term episodic memory by supporting the recollection of contextual details, whereas surrounding regions such as the perirhinal cortex support familiarity-based recognition discriminations. Working memory - the ability to maintain information over very brief periods of time - is traditionally thought to rely heavily on frontoparietal attention networks, but recent work has shown that it can also rely on the hippocampus. However, the conditions in which the hippocampus becomes involved in working memory tasks are unclear and whether it contributes to recollection or familiarity-based responses in working memory is only beginning to be explored. In the current paper, we first review and contrast the existing amnesia literature examining recollection and familiarity in episodic and working memory. The results indicate that recollection and familiarity contribute to both episodic and working memory. However, in contrast to episodic memory, in working memory the hippocampus is particularly critical for familiarity-based rather than recollection-based discrimination. Moreover, the results indicate that the role of the hippocampus in working memory can be obscured due to 'criterion-induced process-masking' because it primarily supports intermediate-confidence recognition decisions. We then report results from a new working memory study examining the ability of amnesics to detect global and local changes in novel complex objects (i.e., fribbles), which indicates that the hippocampus plays an especially critical role in working memory when the task requires the detection of global rather than discrete changes. We conclude by considering the results in light of neurocomputational models and proposing a general framework for understanding the relationship between episodic and working memory.

Protective effects of sleep duration and physical activity on cognitive performance are influenced by β-amyloid and brain volume but not tau burden among cognitively unimpaired older adults

BACKGROUND AND OBJECTIVES

Sleep and physical activity have gained traction as modifiable risk factors for Alzheimer's disease. Sleep duration is linked to amyloid-β clearance while physical activity is associated with brain volume maintenance. We investigate how sleep duration and physical activity are associated with cognition by testing if the associations between sleep duration or physical activity to cognition are explained by amyloid-β burden and brain volume, respectively. Additionally, we explore the mediating role of tau deposition in sleep duration-cognition and physical activity-cognition relationships.

METHODS

This cross-sectional study obtained data from participants in the Anti-Amyloid Treatment in Asymptomatic Alzheimer's Disease (A4) study, a randomized clinical trial. In trial screening, cognitively unimpaired participants (age 65-85 years) underwent amyloid PET and brain MRI; APOE genotype and lifestyle questionnaire data were obtained. Cognitive performance was assessed using the Preclinical Alzheimer Cognitive Composite (PACC). Self-reported nightly sleep duration and weekly physical activity were the primary predictors. Regional Aβ and tau pathologies and volumes were the proposed variables influencing relationships between sleep duration or physical activity and cognition.

RESULTS

Aβ data were obtained from 4322 participants (1208 with MRI, 59% female, 29% amyloid positive). Sleep duration was associated with a Aβ composite score (β = -0.005, CI: (-0.01, -0.001)) and Aβ burden in the anterior cingulate (ACC) (β = -0.012, CI: (-0.017, -0.006)) and medial orbitofrontal cortices (MOC) (β = -0.009, CI: (-0.014, -0.005)). Composite (β = -1.54, 95% CI:(-1.93, -1.15)), ACC (β = -1.22, CI:(-1.54, -0.90)) and MOC (β = -1.44, CI:(-1.86, -1.02)) Aβ deposition was associated with PACC. Sleep duration-PACC association was explained by Aβ burden in path analyses. Physical activity was associated with hippocampal (β = 10.57, CI: (1.06, 20.08)), parahippocampal (β = 9.3, CI: (1.69, 16.91)), entorhinal (β = 14.68, CI: (1.75, 27.61), and fusiform gyral (β = 38.38, CI: (5.57, 71.18)) volumes, which were positively associated with PACC (p < 0.02 for hippocampus, entorhinal cortex and fusiform gyrus). Physical activity-cognition relationship was explained by regional volumes. PET tau imaging was available for 443 participants. No direct sleep duration-tau burden, physical activity by tau burden, or mediation by regional tau was observed in sleep duration-cognition or physical activity-cognition relationships.

DISCUSSION

Sleep duration and physical activity are associated with cognition through independent paths of brain Aβ and brain volume, respectively. These findings implicate neural and pathological mechanisms for the relationships between sleep duration and physical activity on cognition. Dementia risk reduction approaches that emphasize the adequate sleep duration and a physically active lifestyle may benefit those with risk for Alzheimer's disease.

Construct identification in the neuropsychological battery: What are we measuring?

OBJECTIVE

Major obstacles to data harmonization in neuropsychology include lack of consensus about what constructs and tests are most important and invariant across healthy and clinical populations. This study addressed these challenges using data from the National Neuropsychology Network (NNN).

METHOD

Data were obtained from 5,000 NNN participants and Pearson standardization samples. Analyses included variables from four instruments: Wechsler Adult Intelligence Scale, 4th Edition (WAIS-IV); Wechsler Memory Scale, 4th Edition (WMS-IV); California Verbal Learning Test, 3rd Edition (CVLT3); and Delis-Kaplan Executive Function System (D-KEFS). We used confirmatory factor analysis to evaluate models suggested by prior work and examined fit statistics and measurement invariance across samples. We examined relations of factor scores to demographic and clinical characteristics.

RESULTS

For each instrument, we identified four first-order and one second-order factor. Optimal models in patients generally paralleled the best-fitting models in the standardization samples, including task-specific factors. Analysis of the NNN data prompted specification of a Recognition-Familiarity factor on the WMS-IV and an Inhibition-Switching factor on the D-KEFS. Analyses showed strong to strict factorial invariance across samples with expected differences in factor means and variances. The Recognition-Familiarity factor correlated with age more strongly in NNN than in the standardization sample.

CONCLUSIONS

Factor models derived from healthy groups generally fit well in patients. NNN data helped identify novel Recognition-Familiarity and Inhibition-Switching factors that were also invariant across samples and may be clinically useful. The findings support efforts to identify evidence-based and optimally efficient measurements of neuropsychological constructs that are valid across groups. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Forgetting rate for the familiarity and recollection components of recognition in amnestic mild cognitive impairment: A longitudinal study

Here we aimed to investigate the rate of forgetting of the familiarity and recollection components of recognition in patients at the onset of medial temporal lobe (MTL) pathology and destined to convert to Alzheimer's disease (AD). For this purpose, we conducted a longitudinal study of 13 patients who were diagnosed with amnestic mild cognitive impairment (a-MCI) at the first assessment and followed-up for 3 years. During this time, five patients converted to AD and eight remained in a stable condition of cognitive impairment. A group of 15 healthy subjects were enrolled as the control group (HC). In order to separately quantify the contribution of recollection and familiarity to recognition memory performance, the experimental sample was submitted to a modified version of Huppert and Piercy's procedure that included a Remember/Know paradigm. Data demonstrated that both stable and converter a-MCI patients forgot memory traces relative to the familiarity components of recognition at the same rate as HC. Conversely, converter a-MCI patients showed accelerated long-term forgetting specifically for the recollection component of recognition compared to stable a-MCI and HC. This is the first empirical demonstration that familiarity and recollection components of declarative memory are subject to different rates of forgetting in a-MCI patients as a function of their longitudinal clinical outcome. Our finding of accelerated long-term forgetting of the recollection component of recognition disclosed by converter a-MCI patients suggests that atrophy in the MTL not only interferes with the storage aspects but also disrupts the consolidation of memory traces.

Trajectories of cognitive decline and dementia development: A 12-year longitudinal study

INTRODUCTION

Mapping the preclinical dementia phase is important for early detection and evaluation of interventions. We assessed the trajectories of cognitive decline in preclinical dementia over 12 years and investigated whether being a fast decliner across 6 years is associated with increased risk of dementia the following 6 years.

METHODS

Rates of cognitive decline were determined using mixed-effects models for 1646 participants from the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K) cohort. Cox regression was used to assess the future likelihood of dementia for fast decliners (declining ≥1.5 standard deviations [SDs] faster than the age-specific rates).

RESULTS

Participants in a preclinical phase of dementia showed increased rates of decline in all cognitive tests compared to the no-dementia group, particularly closer (0-6 years) to diagnosis. Participants declining fast in three or more cognitive tests 12-6 years before diagnosis demonstrated a high risk of dementia 6 years later (hazard ratio [HR] 3.90, 95% confidence interval [CI] 2.28-6.69).

DISCUSSION

Being a fast decliner is linked to increased risk of future dementia.

Understanding associative false memories in aging using multivariate analyses

Age-related declines in associative memory are ubiquitous, with decreases in behavioral discriminability largely arising from increases in false memories for recombined lures. Using representational similarity analyses to examine the neural basis of associative false memories in aging, the current study found that neural pattern similarity between Hits and FAs and Hits and CRs differed as a function of age in occipital ROIs, such that older adults exhibited a smaller difference between the two similarity metrics than did younger adults. Additionally, greater Hit-FA representational similarity correlated with increases in associative FAs across several ROIs. Results suggest that while neural representations underlying targets may not differ across ages, greater pattern similarity between the neural representation of targets and lures may reflect reduced distinctiveness of the information encoded in memory, such that old and new items are more difficult to discriminate, leading to more false alarms.

A novel computer adaptive word list memory test optimized for remote assessment: Psychometric properties and associations with neurodegenerative biomarkers in older women without dementia

Introduction

This study established the psychometric properties and preliminary validity of the Stricker Learning Span (SLS), a novel computer adaptive word list memory test designed for remote assessment and optimized for smartphone use.

Methods

Women enrolled in the Mayo Clinic Specialized Center of Research Excellence (SCORE) were recruited via e-mail or phone to complete two remote cognitive testing sessions. Convergent validity was assessed through correlation with previously administered in-person neuropsychological tests (n = 96, ages 55-79) and criterion validity through associations with magnetic resonance imaging measures of neurodegeneration sensitive to Alzheimer's disease (n = 47).

Results

SLS performance significantly correlated with the Auditory Verbal Learning Test and measures of neurodegeneration (temporal meta-regions of interest and entorhinal cortical thickness, adjusting for age and education). Test-retest reliabilities across two sessions were 0.71-0.76 (two-way mixed intraclass correlation coefficients).

Discussion

The SLS is a valid and reliable self-administered memory test that shows promise for remote assessment of aging and neurodegenerative disorders.

Standardization and normative data for a new test of visual long-term recognition memory

The assessment of recognition memory is useful in several neurological conditions, but normative data for visual recognition memory of complex figures are still missing for the Italian population. The aim of this study is to present a new short test of visual recognition memory that consists in a supplementary task to be administered after the free delayed recall trial of the Modified Taylor Complex Figure (MTCF). The MTCF-Recognition Trial (MTCF-RT) includes 10 tables, each with a sub-component of the MTCF coupled with two interfering stimuli. Participants are asked to point, for each triplet, the item that was part of the original picture. Normative data were collected from a sample of 280 healthy Italian native speakers ranging in age from 18 to 89 years. The mean recognition score on the MTCF-RT was 9.125 ± 0.996. Results from multiple regression analyses showed that age and education (but not gender) were significant predictors of performance. Therefore, we provided correction grids to adjust raw scores for age and education and computed equivalent scores for the use of the MTCF-RT in the clinical assessment of recognition memory.

Lesion of the hippocampus selectively enhances LEC's activity during recognition memory based on familiarity

The sense of familiarity for events is crucial for successful recognition memory. However, the neural substrate and mechanisms supporting familiarity remain unclear. A major controversy in memory research is whether the parahippocampal areas, especially the lateral entorhinal (LEC) and the perirhinal (PER) cortices, support familiarity or whether the hippocampus (HIP) does. In addition, it is unclear if LEC, PER and HIP interact within this frame. Here, we especially investigate if LEC and PER's contribution to familiarity depends on hippocampal integrity. To do so, we compare LEC and PER neural activity between rats with intact hippocampus performing on a human to rat translational task relying on both recollection and familiarity and rats with hippocampal lesions that have been shown to then rely on familiarity to perform the same task. Using high resolution Immediate Early Gene imaging, we report that hippocampal lesions enhance activity in LEC during familiarity judgments but not PER’s. These findings suggest that different mechanisms support familiarity in LEC and PER and led to the hypothesis that HIP might exert a tonic inhibition on LEC during recognition memory that is released when HIP is compromised, possibly constituting a compensatory mechanism in aging and amnesic patients.

Content-specific vulnerability of recent episodic memories in Alzheimer's disease

Endel Tulving's episodic memory framework emphasizes the multifaceted re-experiencing of personal events. Indeed, decades of research focused on the experiential nature of episodic memories, usually treating recent episodic memory as a coherent experiential quality. However, recent insights into the functional architecture of the medial temporal lobe show that different types of mnemonic information are segregated into distinct neural pathways in brain circuits empirically associated with episodic memory. Moreover, recent memories do not fade as a whole under conditions of progressive neurodegeneration in these brain circuits, notably in Alzheimer's disease. Instead, certain memory content seem particularly vulnerable from the moment of their encoding while other content can remain memorable consistently across individuals and contexts. We propose that these observations are related to the content-specific functional architecture of the medial temporal lobe and consequently to a content-specific impairment of memory at different stages of the neurodegeneration. To develop Endel Tulving's inspirational legacy further and to advance our understanding of how memory function is affected by neurodegenerative conditions such as Alzheimer's disease, we postulate that it is compelling to focus on the representational content of recent episodic memories.

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The functional anatomy of episodic memory segregates different memory content.

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Alzheimer's disease may cause content-specific loss of recent memories

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Content-specific memorability across individuals changes with Alzheimer's disease.

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Content-specific assessment could provide new insights into episodic memory in health and disease

Reliability and Validity of a Home-Based Self-Administered Computerized Test of Learning and Memory Using Speech Recognition

INTRODUCTION

The objective of this study is to evaluate the reliability and validity of the ReVeRe^TM word list recall test (RWLRT), which uses speech recognition, when administered remotely and unsupervised.

METHODS

Prospective cohort study. Participants included 249 cognitively intact community dwelling older adults. Measures included clinician administered neuropsychological assessments at baseline and unsupervised remotely administered tests of cognition from six time-points over six months.

RESULTS

The RWLRT showed acceptable validity. Reliability coefficients varied across time points, with poor reliability between times 1 and 2 and fair-to-good reliability across the remaining five testing sessions. Practice effects were observed with repeated administration as expected.

DISCUSSION

Unsupervised computerized tests of cognition, particularly word list learning and memory tests that use speech recognition, have significant potential for large scale early detection and long-term tracking of cognitive decline due to AD.

The influence of item familiarization on neural discriminability during associative memory encoding and retrieval

Associative memory requires one to encode and form memory representations not just for individual items, but for the association or link between those items. Past work has suggested that associative memory is facilitated when individual items are familiar rather than simultaneously learning the items and their associative link. The current study employed multivoxel pattern analyses (MVPA) to investigate whether item familiarization prior to associative encoding affects the distinctiveness of neural patterns, and whether that distinctiveness is also present during associative retrieval. Our results suggest that prior exposure to item stimuli impacts the representations of their shared association compared to stimuli that are novel at the time of associative encoding throughout most of the associative memory network. While this distinction was also present at retrieval, the overall extent of the difference was diminished. Overall the results suggest that stimulus familiarity influences the representation of associative pairings during memory encoding and retrieval, and the pair-specific representation is maintained across memory phases irrespective of this distinction.

Aging and binding in short-term memory: processes involved in conjunctive and relational binding

In visual short-term binding memory tasks, some studies suggested that aging disrupts relational binding more than conjunctive binding, whereas others report equivalent age-related differences in both types of binding. Yet, demands in controlled resources are potentially the greatest for relational short-term binding. In order to test the hypothesis that aging would affect preferentially tasks demanding in controlled processes, we assessed the contribution of controlled and automatic memory processes to relational and conjunctive short-term binding. Groups of young and older adults studied shape-colour (Exp.1 and 3) or object-colour (Exp.2) pairs in a relational condition in which items were linked to colour patches and a conjunctive condition where colour was integrated into the items. Memory for bindings was tested with a reconstruction task (Exp. 1 and 2) or with a recognition memory task (Exp. 3) under inclusion and exclusion instructions (Process Dissociation Procedure). The three experiments showed that the retrieval of both relational and conjunctive bindings relied primarily on controlled memory processes, the use of which was diminished in older participants. This study brings additional evidence that age-related differences in top-down control processes explain at least partly decreased short-term binding capacities.

Boundary extension as a tool for detection of cognitive change among individuals with mild cognitive impairment: A preliminary study

OBJECTIVES

Recent neuropathological research suggests that recognition memory supported by familiarity rather than recollection may be the earliest cognitive change in course of Alzheimer's disease (AD). Nonetheless, the findings on the issue of familiarity capacity in the prodromal AD remain inconsistent. Boundary extension (BE), in which the view recollected by the subject covers a wider angle than was actually observed, is a form of false memory. Given that BE occurs implicitly and automatically, it may be a candidate for assessing familiarity functioning in cases of AD. This was the issue explored in the current study.

METHODS

One-hundred and six participants comprising a younger adult group (YA, n = 40), a healthy older adult group (OA, n = 40), and a group of patients with mild cognitive impairment (MCI, n = 26) underwent testing for BE and neuropsychological functions. Parts of OA and MCI underwent analysis for plasma tau levels. Receiver-operating characteristic analysis was used to assess memory associated with familiarity and recollection among participants.

RESULTS

The OA and MCI groups could be differentiated by the degree of familiarity associated with BE, wherein the latter group displayed minimal familiarity. Among OAs, familiarity was positively associated with education level. We observed a correlation between plasma tau levels and various neuropsychological functions. Most of the associations between plasma tau levels and neuropsychological functions were mediated by education level.

CONCLUSIONS

Our findings indicate that BE could detect early decline in familiarity and assess preserved cognitive functions in aging.

Examining the Neural Basis of Congruent and Incongruent Configural Contexts during Associative Retrieval

Disrupting the configural context, or relative organization and orientation of paired stimuli, between encoding and retrieval negatively impacts memory. Using univariate and multivariate fMRI analyses, we examined the effect of retaining and manipulating the configural context on neural mechanisms supporting associative retrieval. Behavioral results showed participants had significantly higher hit rates for recollecting pairs in a contextually congruent, versus incongruent, configuration. In addition, contextual congruency between memory phases was a critical determinant to characterizing both the magnitude and patterns of neural activation within visual and parietal cortices. Regions within visual cortices also exhibited higher correlations between patterns of activity at encoding and retrieval when configural context was congruent across memory phases than incongruent. Collectively, these findings shed light on how manipulating configural context between encoding and retrieval affects associative recognition, with changes in the configural context leading to reductions in information transfer and increases in task difficulty.

Early-life education may help bolster declarative memory in old age, especially for women

Although declarative memory declines with age, sex and education might moderate these weaknesses. We investigated effects of sex and education on nonverbal declarative (recognition) memory in 704 older adults (aged 58-98, 0-17 years of education). Items were drawings of real and made-up objects. Age negatively impacted declarative memory, though this age effect was moderated by sex and object-type: it was steeper for males than females, but only for real objects. Education was positively associated with memory, but also interacted with sex and object-type: education benefited women more than men (countering the age effects, especially for women), and remembering real more than made-up objects. The findings suggest that nonverbal memory in older adults is associated negatively with age but positively with education; both effects are modulated by sex, and by whether learning relates to preexisting or new information. The study suggests downstream benefits from education, especially for girls.

The importance of the ventromedial prefrontal cortex for associative memory in older adults: A latent structural equation analysis

Older adults show relatively minor age-related decline in memory for single items, while their memory for associations is markedly reduced. Inter-individual differences in memory function in older adults are substantial but the neurobiological underpinnings of such differences are not well understood. In particular, the relative importance of inter-individual differences in the medio-temporal lobe (MTL) and the lateral prefrontal cortex (PFC) for associative and item recognition in older adults is still ambiguous. We therefore aimed to first establish the distinction between inter-individual differences in associative memory (recollection-based) performance and item memory (familiarity-based) performance in older adults and subsequently link these two constructs to differences in cortical thickness in the MTL and lateral PFC regions, in a latent structural equation modelling framework. To this end, a sample of 160 older adults (65-75 years old) performed three intentional item-associative memory tasks, of which a subsample (n ​= ​72) additionally had cortical thickness measures in MTL and PFC regions of interest available. The results provided support for a distinction between familiarity-based item memory and recollection-based associative memory performance in older adults. Cortical thickness in the ventro-medial prefrontal cortex was positively correlated with associative recognition performance, above and beyond any relationship between item recognition performance and cortical thickness in the same region and between associative recognition performance and brain structure in the MTL (parahippocampus). The findings highlight the relative importance of the ventromedial prefrontal cortex in allowing for intentional recollection-based associative memory functioning in older adults.

Different types of associative encoding evoke differential processing in both younger and older adults: Evidence from univariate and multivariate analyses

Age-related deficits in associative processing are well-documented (e.g., Naveh-Benjamin, 2000) and have been assumed to be the result of a general deficit that affects all types of binding. However, recent behavioral research has indicated that the visual configuration of the information that is presented to older adults influences the degree to which this binding deficit is exhibited by older adults (Overman, Dennis et al, 2019; Overman, Dennis, et al., 2018). The purpose of the present study was to further clarify the neural underpinnings of the associative deficit in aging and to examine whether functional activity at encoding differs with respect to the visual configuration and the type of associative being encoded. Using both univariate and multi-voxel pattern analysis, we found differences in both the magnitude of activation and pattern of neural responses associated with the type of association encoded (item-item and item-context). Specifically, our results suggest that, when controlling for stimuli composition, patterns of activation in sensory and frontal regions within the associative encoding network are able to distinguish between different types of associations. With respect to the MTL, multivariate results suggest that only patterns of activation in the PrC in older, but not younger adults, can distinguish between associations types. These findings extend prior work regarding the neural basis of associative memory in young and older adults, and extends the predictions of the binding of item and context model (BIC; Diana, Yonelinas, Ranganath, 2007) to older adults.

Targeting age-related differences in brain and cognition with multimodal imaging and connectome topography profiling

Aging is characterized by accumulation of structural and metabolic changes in the brain. Recent studies suggest transmodal brain networks are especially sensitive to aging, which, we hypothesize, may be due to their apical position in the cortical hierarchy. Studying an open‐access healthy cohort (n = 102, age range = 30–89 years) with MRI and Aβ PET data, we estimated age‐related cortical thinning, hippocampal atrophy and Aβ deposition. In addition to carrying out surface‐based morphological and metabolic mapping experiments, we stratified effects along neocortical and hippocampal resting‐state functional connectome gradients derived from independent datasets. The cortical gradient depicts an axis of functional differentiation from sensory‐motor regions to transmodal regions, whereas the hippocampal gradient recapitulates its long‐axis. While age‐related thinning and increased Aβ deposition occurred across the entire cortical topography, increased Aβ deposition was especially pronounced toward higher‐order transmodal regions. Age‐related atrophy was greater toward the posterior end of the hippocampal long‐axis. No significant effect of age on Aβ deposition in the hippocampus was observed. Imaging markers correlated with behavioral measures of fluid intelligence and episodic memory in a topography‐specific manner, confirmed using both univariate as well as multivariate analyses. Our results strengthen existing evidence of structural and metabolic change in the aging brain and support the use of connectivity gradients as a compact framework to analyze and conceptualize brain‐based biomarkers of aging.

Automated segmentation of medial temporal lobe subregions on in vivo T1-weighted MRI in early stages of Alzheimer's disease

Medial temporal lobe (MTL) substructures are the earliest regions affected by neurofibrillary tangle pathology-and thus are promising biomarkers for Alzheimer's disease (AD). However, automatic segmentation of the MTL using only T1-weighted (T1w) magnetic resonance imaging (MRI) is challenging due to the large anatomical variability of the MTL cortex and the confound of the dura mater, which is commonly segmented as gray matter by state-of-the-art algorithms because they have similar intensity in T1w MRI. To address these challenges, we developed a novel atlas set, consisting of 15 cognitively normal older adults and 14 patients with mild cognitive impairment with a label explicitly assigned to the dura, that can be used by the multiatlas automated pipeline (Automatic Segmentation of Hippocampal Subfields [ASHS-T1]) for the segmentation of MTL subregions, including anterior/posterior hippocampus, entorhinal cortex (ERC), Brodmann areas (BA) 35 and 36, and parahippocampal cortex on T1w MRI. Cross-validation experiments indicated good segmentation accuracy of ASHS-T1 and that the dura can be reliably separated from the cortex (6.5% mislabeled as gray matter). Conversely, FreeSurfer segmented majority of the dura mater (62.4%) as gray matter and the degree of dura mislabeling decreased with increasing disease severity. To evaluate its clinical utility, we applied the pipeline to T1w images of 663 ADNI subjects and significant volume/thickness loss is observed in BA35, ERC, and posterior hippocampus in early prodromal AD and all subregions at later stages. As such, the publicly available new atlas and ASHS-T1 could have important utility in the early diagnosis and monitoring of AD and enhancing brain-behavior studies of these regions.

The role of hippocampal subfield volume and fornix microstructure in episodic memory across the lifespan

Advancing age is associated with both declines in episodic memory and degradation of medial temporal lobe (MTL) structure. The contribution of MTL to episodic memory is complex and depends upon the interplay among hippocampal subfields and surrounding structures that participate in anatomical connectivity to the cortex through inputs (parahippocampal and entorhinal cortices) and outputs (fornix). However, the differential contributions of MTL system components in mediating age effects on memory remain unclear. In a sample of 177 healthy individuals aged 20-94 we collected high-resolution T1-weighted, ultrahigh-resolution T2/PD, and diffusion tensor imaging (DTI) MRI sequences on a 3T Phillips Achieva scanner. Hippocampal subfield and entorhinal cortex (ERC) volumes were measured from T2/PD scans using a combination of manual tracings and training of a semiautomated pipeline. Parahippocampal gyrus volume was estimated using Freesurfer and DTI scans were used to obtain diffusion metrics from tractography of the fornix. Item and associative episodic memory constructs were formed from multiple tests. Competing structural equation models estimating differential association among these structural variables were specified and tested to investigate whether and how fornix diffusion and volume of parahippocampal gyrus, ERC, and hippocampal subfields mediate age effects on associative and/or item memory. The most parsimonious, best-fitting model included an anatomically based path through the MTL as well as a single hippocampal construct which combined all subfields. Results indicated that fornix microstructure independently mediated the effect of age on associative memory, but not item memory. Additionally, all regions and estimated paths (including fornix) combined to significantly mediate the age-associative memory relationship. These findings suggest that preservation of fornix connectivity and MTL structure with aging is important for maintenance of associative memory performance across the lifespan.

The effect of age on the FCSRT-IR and temporary visual memory binding

ABSTRACTBackground:Cognitive markers of early Alzheimer's disease (AD) should be sensitive and specific to memory impairments that are not associated with healthy cognitive aging. In the present study, we investigated the effect of healthy cognitive aging on two proposed cognitive markers of AD: the Free and Cued Selective Reminding Task with Immediate Recall (FCSRT-IR) and a temporary visual memory binding (TMB) task.

METHOD

Free recall and the cost of holding bound information in visual memory were compared between 24 younger and 24 older participants in a mixed, fully counterbalanced experiment.

RESULTS

A significant effect of age was observed on free recall in the FCSRT-IR only and not on the cost of binding in the TMB task.

CONCLUSIONS

Of these two cognitive markers, the TMB task is more likely to be specific to memory impairments that are independent of age.

Recognition memory: Cellular evidence of a massive contribution of the LEC to familiarity and a lack of involvement of the hippocampal subfields CA1 and CA3

A highly debated issue in memory research is whether familiarity is supported by the parahippocampal region, especially the lateral (LEC) and the perirhinal (PER) cortices, or whether it is supported by the same brain structure as recollection: the hippocampus. One reason for this is that conflicting results have emerged regarding the contribution of the hippocampus to familiarity. This might stem from the lack of dissociation between hippocampal subfields CA1 and CA3 as these areas are involved to a different extent in processes which are pertinent to familiarity. Another reason is that empirical evidence for a contribution of the LEC is still missing. Furthermore, it is unclear whether the superficial and the deep layers of the LEC would equally contribute to this process as these layers are differentially recruited during memory retrieval which partly relies on familiarity. To identify the specific contribution of the LEC, CA1, and CA3, we imaged with cellular resolution activity in the brain of rats performing a version of a standard human memory task adapted to rats that yields judgments based on familiarity. Using this translational approach, we report that in striking contrast to CA1 and CA3, the LEC is recruited for familiarity-judgments and that its contribution is comparable to that of the PER. These results show for the first time that the LEC, specifically its deep layers, contributes to familiarity and constitute the first cellular evidence that the hippocampus does not, thus establishing that familiarity does not share the same neural substrate as recollection.

Dopamine and memory dedifferentiation in aging

The dedifferentiation theory of aging proposes that a reduction in the specificity of neural representations causes declines in complex cognition as people get older, and may reflect a reduction in dopaminergic signaling. The present pharmacological fMRI study investigated episodic memory-related dedifferentiation in young and older adults, and its relation to dopaminergic function, using a randomized placebo-controlled double-blind crossover design with the agonist Bromocriptine (1.25mg) and the antagonist Sulpiride (400mg). We used multi-voxel pattern analysis to measure memory specificity: the degree to which distributed patterns of activity distinguishing two different task contexts during an encoding phase are reinstated during memory retrieval. As predicted, memory specificity was reduced in older adults in prefrontal cortex and in hippocampus, consistent with an impact of neural dedifferentiation on episodic memory representations. There was also a linear age-dependent dopaminergic modulation of memory specificity in hippocampus reflecting a relative boost to memory specificity on Bromocriptine in older adults whose memory was poorer at baseline, and a relative boost on Sulpiride in older better performers, compared to the young. This differed from generalized effects of both agents on task specificity in the encoding phase. The results demonstrate a link between aging, dopaminergic function and dedifferentiation in the hippocampus.

Recollection and familiarity in aging individuals: Gaining insight into relationships with medial temporal lobe structural integrity

Dual-process theories posit that two separate processes are involved in recognition, namely recollection and familiarity. Studies investigating the neuroanatomical substrates of these two processes have frequently revealed that, while recollection is functionally linked with the hippocampus, familiarity appears to be associated with perirhinal and/or entorhinal cortices integrity. Interestingly these regions are known to be sensitive to normal and neuropathological aging processes. The objective of this study was to examine the effects of aging on recollection and familiarity performance, as well as to investigate associations with the rate of false alarms. In older individuals, we further aimed to explore relationships between these recognition variables and structural integrity of the hippocampus and the entorhinal and perirhinal cortices. Younger (N = 56) and older (N = 59) adults were tested on a computerized recollection and familiarity task. In a separate session, older adults (N = 56) underwent a structural MRI. Hippocampal, entorhinal and perihinal cortices volumes were automatically segmented and then manually corrected to ensure validity of the volumetric assessment. Regional volumes were normalized for total intracranial volume. While the overall recognition performance did not significantly differ across groups, our results reveal a decrease in recollection, together with an increase in familiarity in older adults. The increase reliance on familiarity was significantly and positively associated with the rate of false alarms. In the older adult sample, significant positive associations were found between recollection estimates and normalized hippocampal volumes. The normalized total hippocampal volume accounted for 25% of the variance in recollection performance. No correlation was found between any recognition variables and perirhinal or entorhinal cortices volumes. Overall, our results suggest that the age-related impairment in recollection is linked with reduced hippocampal structural integrity.

Differential medial temporal lobe morphometric predictors of item- and relational-encoded memories in healthy individuals and in individuals with mild cognitive impairment and Alzheimer's disease

INTRODUCTION

Episodic memory processes are supported by different subregions of the medial temporal lobe (MTL). In contrast to a unitary model of memory recognition supported solely by the hippocampus, a current model suggests that item encoding engages perirhinal cortex, whereas relational encoding engages parahippocampal cortex and the hippocampus. However, this model has not been examined in the context of aging, neurodegeneration, and MTL morphometrics.

METHODS

Forty-four healthy subjects (HSs) and 18 cognitively impaired subjects (nine mild cognitive impairment [MCI] and nine Alzheimer's disease [AD] patients) were assessed with the relational and item-specific encoding task (RISE) and underwent 3T magnetic resonance imaging. The RISE assessed the differential contribution of relational and item-specific memory. FreeSurfer was used to obtain measures of cortical thickness of MTL regions and hippocampus volume.

RESULTS

Memory accuracies for both item and relational memory were significantly better in the HS group than in the MCI/AD group. In MCI/AD group, relational memory was disproportionately impaired. In HSs, hierarchical regressions demonstrated that memory was predicted by perirhinal thickness after item encoding, and by hippocampus volume after relational encoding (both at trend level) and significantly by parahippocampal thickness at associative recognition. The same brain morphometry profiles predicted memory accuracy in MCI/AD, although more robustly perirhinal thickness for item encoding (R² = 0.31) and hippocampal volume and parahippocampal thickness for relational encoding (R² = 0.31).

DISCUSSION

Our results supported a model of episodic memory in which item-specific encoding was associated with greater perirhinal cortical thickness, while relational encoding was associated with parahippocampal thickness and hippocampus volume. We identified these relationships not only in HSs but also in individuals with MCI and AD. In the subjects with cognitive impairment, reductions in hippocampal volume and impairments in relational memory were especially prominent.

Sleep does not facilitate insight in older adults

Sleep has been shown to foster the process of insight generation in young adults during problem solving activities. Aging is characterized by substantial changes in sleep architecture altering memory consolidation. Whether sleep might promote the occurrence of insight in older adults as well has not yet been tested experimentally. To address this issue, we tested healthy young and old volunteers on an insight problem solving task, involving both explicit and implicit features, before and after a night of sleep or a comparable wakefulness period. Data showed that insight emerged significantly less frequently after a night of sleep in older adults compared to young. Moreover, there was no difference in the magnitude of insight occurrence following sleep and daytime -consolidation in aged participants. We further found that acquisition of implicit knowledge in the task before sleep potentiated the gain of insight in young participants, but this effect was not observed in aged participants. Overall, present findings demonstrate that a period of sleep does not significantly promote insight in problem solving in older adults.

Material Specificity Drives Medial Temporal Lobe Familiarity But Not Hippocampal Recollection

The specific role of the perirhinal (PRC), entorhinal (ERC) and parahippocampal cortices (PHC) in supporting familiarity‐based recognition remains unknown. An fMRI study explored whether these medial temporal lobe (MTL) structures responded in the same way or differentially to familiarity as a function of stimulus type at recognition. A secondary aim was to explore whether the hippocampus responds in the same way to equally strong familiarity and recollection and whether this is influenced by the kind of stimulus involved. Univariate and multivariate analyses revealed that familiarity responses in the PRC, ERC, PHC and the amygdala are material‐specific. Specifically, the PRC and ERC selectively responded to object familiarity, while the PHC responded to both object and scene familiarity. The amygdala only responded to familiarity memory for faces. The hippocampus did not respond to stimulus familiarity for any of the three types of stimuli, but it did respond to recollection for all three types of stimuli. This was true even when recollection was contrasted to equally accurate familiarity. Overall, the findings suggest that the role of the MTL neocortices and the amygdala in familiarity‐based recognition depends on the kind of stimulus in memory, whereas the role of the hippocampus in recollection is independent of the type of cuing stimulus. © 2016 The Authors Hippocampus Published by Wiley Periodicals, Inc.

False memories with age: Neural and cognitive underpinnings

As we age we become increasingly susceptible to memory distortions and inaccuracies. Over the past decade numerous neuroimaging studies have attempted to illuminate the neural underpinnings of aging and false memory. Here we review these studies, and link their findings with those concerning the cognitive properties of age-related changes in memory accuracy. Collectively this evidence points towards a prominent role for age-related declines in medial temporal and prefrontal brain areas, and corresponding impairments in associative binding and strategic monitoring. A resulting cascade of cognitive changes contributes to the heightened vulnerability to false memories with age, including reduced recollective ability, a reliance on gist information and familiarity-based monitoring mechanisms, as well as a reduced ability to inhibit irrelevant information and erroneous binding of features between memory traces. We consider both theoretical and applied implications of research on aging and false memories, as well as questions remaining to be addressed in future research.

The effects of item familiarity on the neural correlates of successful associative memory encoding

Associative memory is considered to be resource-demanding, requiring individuals to learn individual items and the specific relationships between those items. Previous research has shown that prior studying of items aids in associative memory for pairs composed of those same items, as compared to pairs of items that have not been prelearned (e.g., Kilb & Naveh-Benjamin, 2011). In the present study, we sought to elucidate the neural correlates mediating this memory facilitation. After being trained on individual items, participants were scanned while encoding item pairs composed of items from the pretrained phase (familiarized-item pairs) and pairs whose items had not been previously learned (unfamiliarized-item pairs). Consistent with previous findings, the overall subsequent recollection showed the engagement of bilateral parahippocampal gyrus (PHG) and hippocampus, when compared to subsequent forgetting. However, a direct comparison between familiarized- and unfamiliarized-item pairs showed that subsequently recollected familiarized-item pairs were associated with decreased activity across much of the encoding network, including bilateral PHG, hippocampus, prefrontal cortex, and regions associated with item-specific processing within occipital cortex. Increased activity for familiarized-item pairs was found in a more limited set of regions, including bilateral parietal cortex, which has been associated with the formation of novel associations. Additionally, activity in the right parietal cortex correlated with associative memory success in the familiarized condition. Taken together, these results suggest that prior exposure to items can reduce the demands incurred on neural processing throughout the associative encoding network and can enhance associative memory performance by focusing resources within regions supporting the formation of associative links.

Repetition suppression in the medial temporal lobe and midbrain is altered by event overlap

Repeated encounters with the same event typically lead to decreased activation in the medial temporal lobe (MTL) and dopaminergic midbrain, a phenomenon known as repetition suppression. In contrast, encountering an event that overlaps with prior experience leads to increased response in the same regions. Such increased responding is thought to reflect an associative novelty signal that promotes memory updating to resolve differences between current events and stored memories. Here, we married these ideas to test whether event overlap significantly modulates MTL and midbrain responses-even when events are repeated and expected-to promote memory updating through integration. While undergoing high-resolution functional MRI, participants were repeatedly presented with objects pairs, some of which overlapped with other, intervening pairs and some of which contained elements unique from other pairs. MTL and midbrain regions showed widespread repetition suppression for nonoverlapping pairs containing unique elements; however, the degree of repetition suppression was altered for overlapping pairs. Entorhinal cortex, perirhinal cortex (PRc), midbrain, and PRc-midbrain connectivity showed repetition-related increases across overlapping pairs. Notably, increased PRc activation for overlapping pairs tracked individual differences in the ability to reason about the relationships among pairs-our behavioral measure of memory integration. Within the hippocampus, activation increases across overlapping pairs were unique to CA₁ , consistent with its hypothesized comparator function. These findings demonstrate that event overlap engages MTL and midbrain functions traditionally implicated in novelty processing, even when overlapping events themselves are repeated. Our findings further suggest that the MTL-midbrain response to event overlap may promote integration of new content into existing memories, leading to the formation of relational memory networks that span experiences. Moreover, the results inform theories about the division of labor within MTL, demonstrating that the role of PRc in episodic encoding extends beyond familiarity processing and item-level recognition. © 2016 Wiley Periodicals, Inc.

Fornix Microstructure and Memory Performance Is Associated with Altered Neural Connectivity during Episodic Recognition

OBJECTIVES

The purpose of this study was to assess whether age-related differences in white matter microstructure are associated with altered task-related connectivity during episodic recognition.

METHODS

Using functional magnetic resonance imaging and diffusion tensor imaging from 282 cognitively healthy middle-to-late aged adults enrolled in the Wisconsin Registry for Alzheimer's Prevention, we investigated whether fractional anisotropy (FA) within white matter regions known to decline with age was associated with task-related connectivity within the recognition network.

RESULTS

There was a positive relationship between fornix FA and memory performance, both of which negatively correlated with age. Psychophysiological interaction analyses revealed that higher fornix FA was associated with increased task-related connectivity amongst the hippocampus, caudate, precuneus, middle occipital gyrus, and middle frontal gyrus. In addition, better task performance was associated with increased task-related connectivity between the posterior cingulate gyrus, middle frontal gyrus, cuneus, and hippocampus.

CONCLUSIONS

The findings indicate that age has a negative effect on white matter microstructure, which in turn has a negative impact on memory performance. However, fornix microstructure did not significantly mediate the effect of age on performance. Of interest, dynamic functional connectivity was associated with better memory performance. The results of the psychophysiological interaction analysis further revealed that alterations in fornix microstructure explain-at least in part-connectivity among cortical regions in the recognition memory network. Our results may further elucidate the relationship between structural connectivity, neural function, and cognition.

Episodic memory in normal aging and Alzheimer disease: Insights from imaging and behavioral studies

Age-related cognitive changes often include difficulties in retrieving memories, particularly those that rely on personal experiences within their temporal and spatial contexts (i.e., episodic memories). This decline may vary depending on the studied phase (i.e., encoding, storage or retrieval), according to inter-individual differences, and whether we are talking about normal or pathological (e.g., Alzheimer disease; AD) aging. Such cognitive changes are associated with different structural and functional alterations in the human neural network that underpins episodic memory. The prefrontal cortex is the first structure to be affected by age, followed by the medial temporal lobe (MTL), the parietal cortex and the cerebellum. In AD, however, the modifications occur mainly in the MTL (hippocampus and adjacent structures) before spreading to the neocortex. In this review, we will present results that attempt to characterize normal and pathological cognitive aging at multiple levels by integrating structural, behavioral, inter-individual and neuroimaging measures of episodic memory.

[Influence of survival processing and delay on recollection and familiarity in recognition]

The survival processing effect is a robust memory phenomenon of memory whereby encouraging participants to judge words for relevance to a survival situation produces better recall than other processing tasks such as semantic or self-reference tasks (Nairne, Thompson, & Pandeirada, 2007). The present study separated memory performance into recollection and familiarity, and estimated the contribution of these two factors to the survival processing effect as adaptive memory by using a recognition test based on the dual-process signal detection model. This study also examined the long-term persistence of the effect by delay manipulation (immediate, after a week, after five weeks) of the recognition test. Under delayed conditions (after a week and five weeks), survival processing advantage occurred on recollection, but semantic processing had no effect. In contrast, for familiarity, there was no significant difference between survival and semantic processing. These findings suggest that the survival processing effect mainly relies on recollection.

Understanding age-related reductions in visual working memory capacity: examining the stages of change detection

Visual working memory (VWM) capacity is reduced in older adults. Research has shown age-related impairments to VWM encoding, but aging is likely to affect multiple stages of VWM. In the present study, we recorded the event-related potentials (ERPs) of younger and older adults during VWM maintenance and retrieval. We measured encoding-stage processing with the P1 component, maintenance-stage processing with the contralateral delay activity (CDA), and retrieval-stage processing by comparing the activity for old and new items (old-new effect). Older adults showed lower behavioral capacity estimates (K) than did younger adults, but surprisingly, their P1 components and CDAs were comparable to those of younger adults. This remarkable dissociation between neural activity and behavior in the older adults indicated that the P1 and CDA did not accurately assess their VWM capacity. However, the neural activity evoked during VWM retrieval yielded results that helped clarify the age-related differences. During retrieval, younger adults showed early old-new effects in frontal and occipital areas and a late central-parietal old-new effect, whereas older adults showed a late right-lateralized parietal old-new effect. The younger adults' early old-new effects strongly resembled an index of perceptual fluency, suggesting that perceptual implicit memory was activated. The activation of implicit memory could have facilitated the younger adults' behavior, and the lack of these early effects in older adults may suggest that they have much lower-resolution memory than do younger adults. From these data, we speculated that younger and older adults store the same number of items in VWM, but that younger adults store a higher-resolution representation than do older adults.

Modifications of recognition memory processes in preterm children: an event-related potential study

Prematurity may cause hippocampal compromise. Therefore, hippocampus-dependent memory processes (recollection-based retrieval) may be more impaired than hippocampus-independent processes (familiarity-based retrieval). The memory of 18 children born preterm with reduced hippocampal volumes, without neonatal complications (weeks of gestation < 34, weight < 1,600 g), and 15 controls (8-10 years) was tested using an item recognition task. While groups were equal in memory performance, dissociation was found: The event-related potential (ERP) correlate of familiarity was intact in the preterm group, whereas the correlate of recollection was attenuated. A follow-up experiment ruled out that this was due to general cognitive deficits. Furthermore, gestational age correlated with the ERP index of recollection. Thus, recognition memory in preterm children may be characterized by a compensation of attenuated recollection by familiarity.

Recollection, not familiarity, decreases in healthy ageing: Converging evidence from four estimation methods

Although it is generally accepted that ageing is associated with recollection impairments, there is considerable disagreement surrounding how healthy ageing influences familiarity-based recognition. One factor that might contribute to the mixed findings regarding age differences in familiarity is the estimation method used to quantify the two mnemonic processes. Here, this issue is examined by having a group of older adults (N = 39) between 40 and 81 years of age complete remember/know (RK), receiver-operating characteristic (ROC) and process dissociation (PD) recognition tests. Estimates of recollection, but not familiarity, showed a significant negative correlation with chronological age. Inconsistent with previous findings, the estimation method did not moderate the relationship between age and estimates of recollection and familiarity. In a final analysis, recollection and familiarity were estimated as latent factors in a confirmatory factor analysis that modelled the covariance between measures of free recall and recognition, and the results converged with the results from the RK, PD and ROC tasks. These results are consistent with the hypothesis that episodic memory declines in older adults are primary driven by recollection deficits, and also suggest that the estimation method plays little to no role in age-related decreases in familiarity.

Brain network activity in monolingual and bilingual older adults

Bilingual older adults typically have better performance on tasks of executive control (EC) than do their monolingual peers, but differences in brain activity due to language experience are not well understood. Based on studies showing a relation between the dynamic range of brain network activity and performance on EC tasks, we hypothesized that life-long bilingual older adults would show increased functional connectivity relative to monolinguals in networks related to EC. We assessed intrinsic functional connectivity and modulation of activity in task vs. fixation periods in two brain networks that are active when EC is engaged, the frontoparietal control network (FPC) and the salience network (SLN). We also examined the default mode network (DMN), which influences behavior through reduced activity during tasks. We found stronger intrinsic functional connectivity in the FPC and DMN in bilinguals than in monolinguals. Although there were no group differences in the modulation of activity across tasks and fixation, bilinguals showed stronger correlations than monolinguals between intrinsic connectivity in the FPC and task-related increases of activity in prefrontal and parietal regions. This bilingual difference in network connectivity suggests that language experience begun in childhood and continued throughout adulthood influences brain networks in ways that may provide benefits in later life.

Age-related differences in medial temporal lobe involvement during conceptual fluency

Not all memory processes are equally affected by aging. A widely accepted hypothesis is that older adults rely more on familiarity-based processing, typically linked with the perirhinal cortex (PRC), in the context of impaired recollection, linked with the hippocampus (HC). However, according to the dedifferentiation hypothesis, healthy aging reduces the specialization of MTL memory subregions so that they may mediate different memory processes than in young adults. Using fMRI, we tested this possibility using a conceptual fluency manipulation known to induce familiarity-related PRC activity. The study yielded two main findings. First, although fluency equivalently affected PRC in both young (18-28; N=14) and older (62-80; N=15) adults, it also uniquely affected HC activity in older adults. Second, the fluency manipulation reduced functional connectivity between HC and PRC in young adults, but it increased it in older adults. Taken together, the results suggest that aging may result in reduced specialization of the HC for recollection, such that the HC may be recruited when fluency increases familiarity-based responding. This article is part of a Special Issue entitled SI: Memory & Aging.

The effects of healthy aging, amnestic mild cognitive impairment, and Alzheimer's disease on recollection and familiarity: a meta-analytic review

It is well established that healthy aging, amnestic Mild Cognitive Impairment (aMCI), and Alzheimer's Disease (AD) are associated with substantial declines in episodic memory. However, there is still debate as to how two forms of episodic memory - recollection and familiarity - are affected by healthy and pathological aging. To address this issue we conducted a meta-analytic review of the effect sizes reported in studies using remember/know (RK), receiver operating characteristic (ROC) and process dissociation (PD) methods to examine recollection and familiarity in healthy aging (25 published reports), aMCI (9 published reports), and AD (5 published reports). The results from the meta-analysis revealed that healthy aging is associated with moderate-to-large recollection impairments. Familiarity was not impaired in studies using ROC or PD methods but was impaired in studies that used the RK procedure. aMCI was associated with large decreases in recollection whereas familiarity only tended to show a decrease in studies with a patient sample comprised of both single-domain and multiple-domain aMCI patients. Lastly, AD was associated with large decreases in both recollection and familiarity. The results are consistent with neuroimaging evidence suggesting that the hippocampus is critical for recollection whereas familiarity is dependent on the integrity of the surrounding perirhinal cortex. Moreover, the results highlight the relevance of method selection when examining aging, and suggest that familiarity deficits might be a useful behavioral marker for identifying individuals that will develop dementia.

Memory reactivation in healthy aging: evidence of stimulus-specific dedifferentiation

We investigated how aging affects the neural specificity of mental replay, the act of conjuring up past experiences in one's mind. We used functional magnetic resonance imaging (fMRI) and multivariate pattern analysis to quantify the similarity between brain activity elicited by the perception and memory of complex multimodal stimuli. Young and older human adults viewed and mentally replayed short videos from long-term memory while undergoing fMRI. We identified a wide array of cortical regions involved in visual, auditory, and spatial processing that supported stimulus-specific representation at perception as well as during mental replay. Evidence of age-related dedifferentiation was subtle at perception but more salient during mental replay, and age differences at perception could not account for older adults' reduced neural reactivation specificity. Performance on a post-scan recognition task for video details correlated with neural reactivation in young but not in older adults, indicating that in-scan reactivation benefited post-scan recognition in young adults, but that some older adults may have benefited from alternative rehearsal strategies. Although young adults recalled more details about the video stimuli than older adults on a post-scan recall task, patterns of neural reactivation correlated with post-scan recall in both age groups. These results demonstrate that the mechanisms supporting recall and recollection are linked to accurate neural reactivation in both young and older adults, but that age affects how efficiently these mechanisms can support memory's representational specificity in a way that cannot simply be accounted for by degraded sensory processes.

Individual differences in forced-choice recognition memory: partitioning contributions of recollection and familiarity

In forced-choice recognition memory, two different testing formats are possible under conditions of high target-foil similarity: Each target can be presented alongside foils similar to itself (forced-choice corresponding; FCC), or alongside foils similar to other targets (forced-choice noncorresponding; FCNC). Recent behavioural and neuropsychological studies suggest that FCC performance can be supported by familiarity whereas FCNC performance is supported primarily by recollection. In this paper, we corroborate this finding from an individual differences perspective. A group of older adults were given a test of FCC and FCNC recognition for object pictures, as well as standardized tests of recall, recognition, and IQ. Recall measures were found to predict FCNC, but not FCC performance, consistent with a critical role for recollection in FCNC only. After the common influence of recall was removed, standardized tests of recognition predicted FCC, but not FCNC performance. This is consistent with a contribution of only familiarity in FCC. Simulations show that a two-process model, where familiarity and recollection make separate contributions to recognition, is 10 times more likely to give these results than a single-process model. This evidence highlights the importance of recognition memory test design when examining the involvement of recollection and familiarity.