Associative recognition in Alzheimer's disease: evidence for impaired recall-to-reject

Examining the neural basis of unitization: A review

Associative memory refers to the ability to form and remember associations between individual pieces of information rather than memory for a single object or word. Encoding associations in memory tends to be a more difficult task than item (only) encoding, because associative memory requires encoding multiple items as well as the specific links amongst the items. Accordingly, researchers have worked to identify interventions and strategies to reduce the effort and neural resources required for successful associative memory processing. Unitization is one such strategy that has traditionally been defined as the process by which two or more discrete items are processed, or encoded, such that they are perceived as a single ensemble. The current review explores the neural research on unitization while considering the behavioral benefits that accompany the process.

Further advancing theories of retrieval of the personal past

In our target article, we presented the idea that involuntary autobiographical memories (IAMs) and déjà vu may both be based on the same retrieval processes. Our core claim was thus straightforward: Both can be described as "involuntary" or spontaneous cognitions, where IAMs deliver content and déjà vu delivers only the feeling of retrieval. Our proposal resulted in 27 commentaries covering a broad range of perspectives and approaches. The majority of them have not only amplified our key arguments but also pushed our ideas further by offering extensions, refinements, discussing possible implications and providing additional empirical, neuroscientific and clinical support. The discussion launched by the commentaries proves to us the importance of bringing IAMs and déjà vu into mainstream discussions of memory retrieval processes.

Unsupervised mobile cognitive testing for use in preclinical Alzheimer's disease

INTRODUCTION

Unsupervised digital cognitive testing is an appealing means to capture subtle cognitive decline in preclinical Alzheimer's disease (AD). Here, we describe development, feasibility, and validity of the Boston Remote Assessment for Neurocognitive Health (BRANCH) against in-person cognitive testing and amyloid/tau burden.

METHODS

BRANCH is web-based, self-guided, and assesses memory processes vulnerable in AD. Clinically normal participants (n = 234; aged 50-89) completed BRANCH; a subset underwent in-person cognitive testing and positron emission tomography imaging. Mean accuracy across BRANCH tests (Categories, Face-Name-Occupation, Groceries, Signs) was calculated.

RESULTS

BRANCH was feasible to complete on participants' own devices (primarily smartphones). Technical difficulties and invalid/unusable data were infrequent. BRANCH psychometric properties were sound, including good retest reliability. BRANCH was correlated with in-person cognitive testing (r = 0.617, P < .001). Lower BRANCH score was associated with greater amyloid (r = -0.205, P = .007) and entorhinal tau (r = -0.178, P = .026).

DISCUSSION

BRANCH reliably captures meaningful cognitive information remotely, suggesting promise as a digital cognitive marker sensitive early in the AD trajectory.

Memory decay distinguishes subtypes of gist

Memories are thought to become more gist-like over time. Multiple related memories might form generalized memory representations, losing specific details but enhancing or retaining gist. The time course within which gist memory emerges, however, is the subject of less consensus. To address this question, we focused our design on four kinds of gist: inferential gist (relations extracted across non-contiguous events), statistical learning (regularities extracted from a series), summary gist (a theme abstracted from a temporally contiguous series of items), and category gist (characterization of a stimulus at a higher level in the semantic hierarchy). Seventy participants completed memory encoding tasks addressing these types of gist and corresponding retrieval tasks the same evening, the morning after, and one week later, as well as an MRI at a later time point. We found little evidence that gist slowly emerges over time or that gist traces are more resistant to forgetting than detail traces. Instead, we found that initial gist memory shortly after encoding was either retained over time or decayed. Inferential gist and statistical learning were retained over a week, whereas memory for category and summary gist decayed. We discuss several interpretations for differences between these two subtypes of gist. Individual differences in REM or slow-wave sleep and hippocampal volumes did not predict changes in memory for these four kinds of gist in a healthy young adult population.

Strategic encoding and enhanced memory for positive value-location associations

People often need to remember the location of important objects or events, and also to remember locations that are associated with negative objects. In the current study, we examined how both positive and negative items might be selectively remembered in the visuospatial domain. Participants studied number-items ranging from -25 to +25 indicating point values in a grid display and were instructed to maximize their score (a summation of correctly remembered positive and negative information; incorrectly placed negative items resulted in a subtraction from the overall score). Items were presented in a sequential, simultaneous (Experiment 1), or self-regulated format (Experiment 2) where participants controlled which items to study and the length of study time per item. In Experiment 1, participants selectively recalled high-magnitude over low-magnitude items, but also displayed a positivity preference in memory. In Experiment 2, we were able to determine whether this positivity preference was a result of bottom-up, automatic, or top-down strategic processes. Results indicated that participants explicitly chose to study positive items more frequently and for more total time relative to negative items, suggesting a deliberate strategy to focus on positive information. This bias for highly positive information suggests an overt points-gained approach, as opposed to a loss-aversion approach, to remembering value in the visuospatial domain.

Quantifying mechanisms of cognition with an experiment and modeling ecosystem

Although there have been major strides toward uncovering the neurobehavioral mechanisms involved in cognitive functions like memory and decision making, methods for measuring behavior and accessing latent processes through computational means remain limited. To this end, we have created SUPREME (Sensing to Understanding and Prediction Realized via an Experiment and Modeling Ecosystem): a toolbox for comprehensive cognitive assessment, provided by a combination of construct-targeted tasks and corresponding computational models. SUPREME includes four tasks, each developed symbiotically with a mechanistic model, which together provide quantified assessments of perception, cognitive control, declarative memory, reward valuation, and frustrative nonreward. In this study, we provide validation analyses for each task using two sessions of data from a cohort of cognitively normal participants (N = 65). Measures of test-retest reliability (r: 0.58-0.75), stability of individual differences (ρ: 0.56-0.70), and internal consistency (α: 0.80-0.86) support the validity of our tasks. After fitting the models to data from individual subjects, we demonstrate each model's ability to capture observed patterns of behavioral results across task conditions. Our computational approaches allow us to decompose behavior into cognitively interpretable subprocesses, which we can compare both within and between participants. We discuss potential future applications of SUPREME, including clinical assessments, longitudinal tracking of cognitive functions, and insight into compensatory mechanisms.

Neuroimaging correlates of false memory in 'Alzheimer's disease: A preliminary systematic review

Alzheimer's disease (AD) is characterised by episodic memory impairment, but people also experience memory distortions, including false memories, which can impact on safety and reduce functioning. Understanding the neural networks that underpin false memories could help to predict the need for intervention and guide development of cognitive strategies to reduce memory errors. However, there is a relative absence of research into how the neuropathology of AD contributes to false memory generation. This paper systematically reviews the methodology and outcomes of studies investigating the neuroimaging correlates of false memory in AD. Four studies using structural imaging and three studies using functional imaging were identified. Studies were heterogenous in methodology and received mostly 'weak' quality assessment ratings. Combined, and consistent with neuroimaging findings in non-AD populations, results from identified studies provide preliminary support for the hypothesis that medial temporal lobe and prefrontal cortex dysfunction may lead to generation of false memories in AD. However, the small number of studies and significant heterogeneity within them means further study is necessary to assess replicability of results.

The Impact of Semantic Relatedness on Associative Memory in Aging Depending on the Semantic Relationships between the Memoranda

Background: Aging is characterized by a decline in associative memory. However, under some conditions, such as in the presence of semantic relatedness within the association, the age-related associative decline can be attenuated. In this study, we evaluated whether the nature of the semantic relationship between the memoranda (taxonomic versus thematic) could modulate the impact of semantic relatedness on older adults' associative memory. Methods: We assessed 40 young adults and 40 older adults' associative memory for associations that were either taxonomically-related, thematically-related, or unrelated. Results: While the main results showed age-related differences in all associative memory tasks without attenuation by semantic relatedness, the results after excluding 4 outlier older participants suggest that older adults' associative memory performance did not differ from that of young adults for thematically-related pairs, while there was an age-related difference in associative memory for taxonomically-related pairs as well as for unrelated pairs. Discussion: This could suggest that the nature of the semantic relationship between the memoranda can modulate the impact of semantic relatedness on older adults' associative memory performance, although the reason why this is not the case for all older participants still needs to be understood.

Cerebrospinal fluid amyloid levels are associated with delayed memory retention in cognitively normal biomarker-negative older adults

Alzheimer's disease is defined by abnormal levels of amyloid and tau biomarkers. Even cognitively normal older adults with clinically relevant amyloid and tau levels perform worse on memory tests. However, it is unclear if the relationship between biomarker level and memory extends below clinical thresholds. We hypothesized that even subclinical biomarker levels are associated with memory when measured with neuropsychological tests designed to detect dysfunction in preclinical disease states. In a group of cognitively normal, "biomarker-negative" older men and women, we investigated the relationship between cerebrospinal fluid biomarker levels and memory measured with the ModRey, a list-learning task designed to assess memory in preclinical and cognitively normal adults. Cerebrospinal amyloid levels were associated with ModRey memory retention, the proportion of information retained after a delay period. When older adults with mild impairment were included, cerebrospinal fluid tau levels were also associated with ModRey retention. The association of amyloid and tau levels with memory was independent of each other. These results suggest cognitive changes associated with Alzheimer's disease pathology might occur earlier than currently thought.

Do Alzheimer's Disease Patients Benefit From Prior-Knowledge in Associative Recognition Memory?

OBJECTIVES

Although the influence of prior knowledge on associative memory in healthy aging has received great attention, it has never been studied in Alzheimer's disease (AD). This study aimed at assessing whether AD patients could benefit from prior knowledge in associative memory and whether such benefit would be related to the integrity of their semantic memory.

METHODS

Twenty-one AD patients and 21 healthy older adults took part in an associative memory task using semantically related and unrelated word pairs and were also submitted to an evaluation of their semantic memory.

RESULTS

While participants of both groups benefited from semantic relatedness in associative discrimination, related pairs recognition was significantly predicted by semantic memory integrity in healthy older adults only.

CONCLUSIONS

We suggest that patients benefitted from semantic knowledge to improve their performance in the associative memory task, but that such performance is not related to semantic knowledge integrity evaluation measures because the two tasks differ in the way semantic information is accessed: in an automatic manner for the associative memory task, with automatic processes thought to be relatively preserved in AD, and in a controlled manner for the semantic knowledge evaluation, with controlled processes thought to be impaired in AD. (JINS, 2019, 25, 443-452).

False memories in patients with mild cognitive impairment and mild Alzheimer's disease dementia: Can cognitive strategies help?

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that presents predominantly with impairments in learning and memory. Patients with AD are also susceptible to false memories, a clinically relevant memory distortion where a patient remembers an incorrect memory that they believe to be true. The use of cognitive strategies to improve memory performance among patients with AD by reducing false memories has taken on added importance given the lack of disease-modifying agents for AD. However, existing evidence suggests that cognitive strategies to reduce false memories in patients with AD are of limited effectiveness, although these strategies may be useful at earlier stages of the disease. The purpose of this review is to examine experimental findings of false memories and associated memory processes in patients with mild cognitive impairment due to AD and mild AD dementia. Cognitive strategies to reduce false memories in these patient populations are also reviewed. Approaches to clinically relevant future research are suggested and discussed.

Explicit and implicit memory for music in healthy older adults and patients with mild Alzheimer's disease

Introduction: Previous studies have found that music paired with lyrics at encoding may improve the memory performance of patients with mild Alzheimer's disease (AD). To further explore memory for different types of musical stimuli, the current study examined both implicit and explicit memory for music with and without lyrics compared to spoken lyrics. Method: In this mixed design, patients with probable mild AD (n = 15) and healthy older adults (n = 13) listened to auditory clips (song, instrumental, or spoken lyrics varied across three sessions) and then had their memory tested. Implicit memory was measured by the mere exposure effect. Explicit recognition memory was measured using a confidence-judgment receiver operating characteristic (ROC) paradigm, which allowed examination of the separate contributions made by familiarity and recollection. Results: A significant implicit memory mere exposure effect was found for both groups in the instrumental and song but not the spoken condition. Both groups had the best explicit memory performance in the spoken condition, followed by song, and then instrumental conditions. Healthy older adults demonstrated more recollection than patients with AD in the song and spoken conditions, but both groups performed similarly in the instrumental condition. Patients with AD demonstrated more familiarity in the instrumental and song conditions than in the spoken condition. Conclusions: The results have implications for memory interventions for patients with mild AD. The implicit memory findings suggest that patients with AD may still show a preference for information familiar to them. The explicit memory results support prior findings that patients with AD rely heavily on familiarity, but also suggest that there may be limitations on the benefits that music can provide to recognition memory performance.

Phonological false recognition produced by bottom-up automatic activation in young and older people

Two experiments explored a new procedure to implicitly induce phonological false memories in young and older people. On the study tasks, half of the words were formed from half of the letters in the alphabet, whereas the remaining words were formed from all the letters in the alphabet. On the recognition tests, there were three types of non-studied new words: critical lures formed from the same half of the letters as the studied words; distractors formed from the other half of the letters not used, and distractors formed from all the letters in the alphabet. In both experiments, the results showed that, in both young and older people, critical lures produced more false recognitions than distractors composed of all the letters in the alphabet, which, in turn, produced more false alarms than distractors composed of the letters not used during the study. These results support the predictions of the activation/monitoring models, which assume that false memories are partly due to activation spreading from items (semantically or phonologically) related to the critical words.

Impaired perceptual integration and memory for unitized representations are associated with perirhinal cortex atrophy in Alzheimer's disease

Unitization, the capacity to encode associations as one integrated entity, can enhance associative memory in populations with an associative memory deficit by promoting familiarity-based associative recognition. Patients with Alzheimer's disease (AD) are typically impaired in associative memory compared with healthy controls but do not benefit from unitization strategies. Using fragmented pictures of objects, this study aimed at assessing which of the cognitive processes that compose unitization is actually affected in AD: the retrieval of unitized representations itself, or some earlier stages of processing, such as the integration process at a perceptual or conceptual stage of representation. We also intended to relate patients' object unitization capacity to the integrity of their perirhinal cortex (PrC), as the PrC is thought to underlie unitization and is also one of the first affected regions in AD. We evaluated perceptual integration capacity and subsequent memory for those items that have supposedly been unitized in 23 mild AD patients and 20 controls. We systematically manipulated the level of perceptual integration during encoding by presenting object pictures that were either left intact, separated into 2 fragments, or separated into 4 fragments. Subjects were instructed to unitize the fragments into a single representation. Success of integration was assessed by a question requiring the identification of the object. Participants also underwent a structural magnetic resonance imaging examination, and measures of PrC, posterior cingulate cortex volume and thickness, and hippocampal volume, were extracted. The results showed that patients' perceptual integration performance decreased with the increased fragmentation level and that their memory for unitized representations was impaired whatever the demands in terms of perceptual integration at encoding. Both perceptual integration and memory for unitized representations were related to the integrity of the PrC, and memory for unitized representations was also related to the volume of the hippocampus. We argue that, globally, this supports representational theories of memory that hold that the role of the PrC is not only perceptual nor mnemonic but instead underlies complex object representation.

Motivated forgetting reduces veridical memories but slightly increases false memories in both young and healthy older people

The aim of the current study is to examine the effects of motivated forgetting and aging on true and false memory. Sixty young and 54 healthy older adults were instructed to study two lists of 18 words each. Each list was composed of three sets of six words associated with three non-presented critical words. After studying list 1, half of the participants received the instruction to forget List 1, whereas the other half received the instruction to remember List 1. Next, all the subjects studied list 2; finally, they were asked to remember the words studied in both lists. The results showed that when participants intended to forget the studied List 1, they were less likely to recall the studied words, but more likely to intrude the critical words. That is, we can intentionally forget something but this can also entail the intrusion of some related false memories.

Effects of Stimuli Repetition and Age in False Recognition

The aim of the current study is to examine the effects of stimuli repetition and age in false recognition using the Deese-Roediger-McDermott experimental paradigm. Two matched samples of 32 young adults and 32 healthy older adults studied 10 lists of six words associated with three non-presented critical words. On half of the lists, the words were presented once, and on the other five lists, the words were presented three times, always following a same sequential order. After each study list, participants performed a self-paced recognition test containing 12 words: the 6 studied words and 6 other non-studied words (the 3 critical words and 3 distractors). The results show that false recognition increases with age and declines in both samples with repetitions (although more in the young adults than in the older people). Results are discussed in relation to the dual-process theories of (false) memory.

Response bias and response monitoring: Evidence from healthy older adults and patients with mild Alzheimer's disease

Patients with Alzheimer's disease (AD) often exhibit an abnormally liberal response bias in recognition memory tests, responding "old" more frequently than "new." Investigations have shown patients can to shift to a more conservative response bias when given instructions. We examined if patients with mild AD could alter their response patterns when the ratio of old items is manipulated without explicit instruction. Healthy older adults and AD patients studied lists of words and then were tested in three old/new ratio conditions (30%, 50%, or 70% old items). A subset of participants provided estimates of how many old and new items they saw in the memory test. We demonstrated that both groups were able to change their response patterns without the aid of explicit instructions. Importantly, AD patients were more likely to estimate seeing greater numbers of old than new items, whereas the reverse was observed for older adults. Elevated estimates of old items in AD patients suggest their liberal response bias may be attributed to their reliance on familiarity. We conclude that the liberal response bias observed in AD patients is attributable to their believing that more of the test items are old and not due to impaired meta-memorial monitoring abilities.

fNIRS can robustly measure brain activity during memory encoding and retrieval in healthy subjects

Early intervention in Alzheimer’s Disease (AD) requires novel biomarkers that can capture changes in brain activity at an early stage. Current AD biomarkers are expensive and/or invasive and therefore unsuitable for use as screening tools, but a non-invasive, inexpensive, easily accessible screening method could be useful in both clinical and research settings. Prior studies suggest that especially paired-associate learning tasks may be useful in detecting the earliest memory impairment in AD. Here, we investigated the utility of functional Near Infrared Spectroscopy in measuring brain activity from prefrontal, parietal and temporal cortices of healthy adults (n = 19) during memory encoding and retrieval under a face-name paired-associate learning task. Our findings demonstrate that encoding of novel face-name pairs compared to baseline as well as compared to repeated face-name pairs resulted in significant activation in left dorsolateral prefrontal cortex while recalling resulted in activation in dorsolateral prefrontal cortex bilaterally. Moreover, brain response to recalling was significantly higher than encoding in medial, superior and middle frontal cortices for novel faces. Overall, this study shows that fNIRS can reliably measure cortical brain activation during a face-name paired-associate learning task. Future work will include similar measurements in populations with progressing memory deficits.

The Age Effects on the Cognitive Processes of Intention-Based and Stimulus-Based Actions: An ERP Study

The functional decline in action among older adults is caused not only by physical weakness but also by cognitive decline. In this study, we aimed to compare the cognitive effects of age between intention-based and stimulus-based action modes electrophysiologically. Because age-related declines in cognitive function might proceed distinctly according to specific action modes and processes, four specific cognitive processes, action-effect binding, stimulus-response linkage, action-effect feedback control, and effect-action retrieval, were investigated. We recorded event-related potentials (ERPs) during a modified acquisition-test paradigm in young (mean age = 21, SD = 2) and old (mean age = 69, SD = 5) groups. A temporal bisection task and a movement pre-cuing task were used during the acquisition and test phases, respectively. Using ERP indices including readiness potential (RP), P3, N2 and contingent negative variation (CNV) to identify these four specific processes for the two action modes, we revealed the effects of age on each ERP index. The results showed similar patterns of waveforms but consistently decreasing amplitudes of all four ERP indices in the old age group compared with the young age group, which indicates not only generally declining functions of action preparation in older adults but also age effects specific to the action modes and processes that might otherwise be mixed together under confounding experimental conditions. Particularly, an interference effect indexed by the differences in the amplitudes of CNV between congruent and incongruent tasks was observed in the young age group, which is consistent with previous behavioral reports. However, this effect was absent in the old age group, indicating a specific age-related deficit in the effect-action retrieval process of intention-based action, which might be caused by an age-related deficit in associative memory. In sum, this study investigated the cognitive processes of two action modes from a developmental perspective and suggests the importance of adding associative memory training to interventions for older adults with the aim of improving intention-based action.

Neuropsychological Testing and Machine Learning Distinguish Alzheimer's Disease from Other Causes for Cognitive Impairment

With promising results in recent treatment trials for Alzheimer’s disease (AD), it becomes increasingly important to distinguish AD at early stages from other causes for cognitive impairment. However, existing diagnostic methods are either invasive (lumbar punctures, PET) or inaccurate Magnetic Resonance Imaging (MRI). This study investigates the potential of neuropsychological testing (NPT) to specifically identify those patients with possible AD among a sample of 158 patients with Mild Cognitive Impairment (MCI) or dementia for various causes. Patients were divided into an early stage and a late stage group according to their Mini Mental State Examination (MMSE) score and labeled as AD or non-AD patients based on a post-mortem validated threshold of the ratio between total tau and beta amyloid in the cerebrospinal fluid (CSF; Total tau/Aβ(1–42) ratio, TB ratio). All patients completed the established Consortium to Establish a Registry for Alzheimer’s Disease—Neuropsychological Assessment Battery (CERAD-NAB) test battery and two additional newly-developed neuropsychological tests (recollection and verbal comprehension) that aimed at carving out specific Alzheimer-typical deficits. Based on these test results, an underlying AD (pathologically increased TB ratio) was predicted with a machine learning algorithm. To this end, the algorithm was trained in each case on all patients except the one to predict (leave-one-out validation). In the total group, 82% of the patients could be correctly identified as AD or non-AD. In the early group with small general cognitive impairment, classification accuracy was increased to 89%. NPT thus seems to be capable of discriminating between AD patients and patients with cognitive impairment due to other neurodegenerative or vascular causes with a high accuracy, and may be used for screening in clinical routine and drug studies, especially in the early course of this disease.

The use of metacognitive strategies to decrease false memories in source monitoring in patients with mild cognitive impairment

Patients with amnestic mild cognitive impairment (MCI) and Alzheimer's disease (AD) often demonstrate high rates of false memories, leading to stressful and frustrating situations for both patients and caregivers in everyday life. Sometimes these false memories are due to failures in monitoring the source of the information. In the current study, we examined interventions aimed to enhance the use of the metacognitive "recall-to-reject" memory strategy. Such interventions could improve source memory and decrease false memory in patients with MCI. Because the picture superiority effect (better memory for pictures compared to words) has been shown to be present in both patients with MCI and healthy older controls, we investigated whether pictures could help patients with MCI use a recall-to-reject strategy in a simulation of real-world source memory task. In this experiment, patients with MCI and healthy older adults were asked to simulate preparing for and then taking a trip to the market. Subjects first studied 30 pictures of items in their "cupboard," followed by a list of 30 words of items on their "shopping list." At test, participants saw 90 pictures (30 cupboard, 30 list, 30 new) organized as they would be if walking down the market aisles, and are provided with either standard or metacognitive instructions. With standard instructions, they were asked if they needed to buy the item. With the metacognitive instructions, they were asked a series of questions to help guide them through a recall-to-reject strategy to highlight the different sources of memories. Results showed that the metacognitive instructions did significantly reduce the false memory rates for patients with MCI. Further studies need to investigate how to best implement these practical strategies into the everyday lives of patients.

The influence of strategic encoding on false memory in patients with mild cognitive impairment and Alzheimer's disease dementia

Patients with Alzheimer's disease (AD) dementia exhibit high rates of memory distortions in addition to their impairments in episodic memory. Several investigations have demonstrated that when healthy individuals (young and old) engaged in an encoding strategy that emphasized the uniqueness of study items (an item-specific encoding strategy), they were able to improve their discrimination between old items and unstudied critical lure items in a false memory task. In the present study we examined if patients with AD could also improve their memory discrimination when engaging in an item-specific encoding strategy. Healthy older adult controls, patients with mild cognitive impairment (MCI) due to AD, and patients with mild AD dementia were asked to study lists of categorized words. In the Item-Specific condition, participants were asked to provide a unique detail or personal experience with each study item. In the Relational condition, they were asked to determine how each item in the list was related to the others. To assess the influence of both strategies, recall and recognition memory tests were administered. Overall, both patient groups exhibited poorer memory in both recall and recognition tests compared to controls. In terms of recognition, healthy older controls and patients with MCI due to AD exhibited improved memory discrimination in the Item-Specific condition compared to the Relational condition, whereas patients with AD dementia did not. We speculate that patients with MCI due to AD use intact frontal networks to effectively engage in this strategy.

The ERP Effects of Combined Cognitive Training on Intention-Based and Stimulus-Based Actions in Older Chinese Adults

Age-related decreases in action are caused by neuromuscular weakness and cognitive decline. Although physical interventions have been reported to have beneficial effects on cognitive function in older adults, whether cognitive training improves action-related function remains unclear. In this study, we investigated the effects of combined cognitive training on intention-based and stimulus-based actions in older adults using event-related potentials (ERPs). A total of 26 healthy older adults (16 in the training group and 10 in the control group) participated in the study. The training group received 16 sessions of cognitive training, including eight sessions of executive function training and eight sessions of memory strategy training. Before and after training, both groups of participants underwent cognitive assessments and ERP recordings during both the acquisition and test phases with a motor cognitive paradigm. During the acquisition phase, subjects were asked to press one of two keys, either using a self-selected (intention-based) method or based on the preceding stimulus (stimulus-based). During the test phase, subjects were asked to respond to the pre-cues with either congruent or incongruent tasks. Using ERP indices—including readiness potential, P3 and contingent negative variation to identify motor preparation, stimulus processing and interference effect, respectively—we revealed the effects of training on both intention-based and stimulus-based actions. The correlations were also computed between the improved cognitive performance and the ERP amplitudes. It was shown that the improved executive function might extend substantial benefits to both actions, whereas associative memory may be specifically related to the bidirectional action-effect association of intention-based action, although the training effect of memory was absent during the insufficient training hours. In sum, the present study provided empirical evidence demonstrating that action could benefit from cognitive training. Clinical Trial Registration: www.chictr.org.cn, identifier: ChiCTR-OON-16007793.

Increasing the salience of fluency cues does not reduce the recognition memory impairment in Alzheimer's disease!

In Alzheimer's disease (AD), it is now well established that recollection is impaired from the beginning of the disease, whereas findings are less clear concerning familiarity. One of the most important mechanisms underlying familiarity is the sense of familiarity driven by processing fluency. In this study, we attempted to attenuate recognition memory deficits in AD by maximizing the salience of fluency cues in two conditions of a recognition memory task. In one condition, targets and foils have been created from the same pool of letters (Overlap condition). In a second condition, targets and foils have been derived from two separate pools of letters (No-Overlap condition), promoting the use of letter-driven visual and phonetic fluency. Targets and foils were low-frequency words. The memory tasks were performed by 15 patients with AD and 16 healthy controls. Both groups improved their memory performance in the No-Overlap condition compared to the Overlap condition. Patients with AD were able to use fluency cues during recognition memory as older adults did, but this did not allow to compensate for dysfunction of recognition memory processes.

From Cognitive Science to Dementia Assessment

Alzheimer’s disease is a degenerative disease of the brain that impairs mental skills and abilities and undermines independent living. It is estimated to affect over 44 million people worldwide, and 5.3 million people in the United States at an estimated cost of US$226 billion. The numbers of people affected are expected to increase dramatically over the next few decades along with increased life expectancy, and costs are expected to be over US$1 trillion by 2050. There is currently no cure, and accurate diagnosis in primary care is hampered by a lack of widely available, reliable, and specific forms of assessment. Accurate diagnosis is essential to avoid inappropriate and expensive clinical follow-up, to evaluate new treatments when these become available, to avoid underestimating or overestimating prevalence of the disease, and to inform policy priorities on resource allocation for health care and for research. We argue that the cognitive and behavioral sciences offer an important route to developing widely available, inexpensive, reliable, and specific assessment tools for the disease.

Medial temporal lobe activity associated with the successful retrieval of destination memory

Destination memory is the process of remembering to whom we tell particular things. Although recent behavioral studies have clarified the cognitive nature of destination memory, the neural mechanisms underlying destination memory retrieval remain unclear. We used functional magnetic resonance imaging (fMRI) to determine whether the medial temporal lobe (MTL), a structure that has been implicated in recollection-based memory, is activated during the successful retrieval of destination information. During a study phase before fMRI scanning, the subjects told a series of facts to either a woman or a man. During fMRI scanning, the subjects were asked to judge whether each fact presented was old or new, and if they judged it as old, to indicate, including a confidence rating (high or low), whether the subjects had told that fact to either a man or a woman. We found that successful destination retrieval, when compared to failed destination retrieval, was associated with increased activity in the parahippocampal gyrus. We also found that the confidence level (high vs. low) for destination memory retrieval was associated with increased activity in another (posterior) region of the parahippocampal gyrus. The present study suggests that the successful retrieval of destination information depends highly on MTL-mediated recollection processes.

False memories in Lewy-body disease

Recently, de Boysson, Belleville, Phillips et al. (2011) found that patients with Lewy-body disease (LBD) showed significantly lower rates of false memories than healthy controls, using the Deese-Roediger-McDermott (DRM) experimental procedure. Given that this result could be explained by the practically null rate of true recognition in the LBD group (0.09), we decided to replicate the study by de Boysson et al. (2011), but including a new condition that would maximize the true recognition rate (and analyze its effect on the rate of false memories). Specifically, in a DRM experiment, we manipulated (within subjects) two study and recognition conditions: in the "immediate" condition, both the LBD patients and the control group of healthy older people received a different recognition test after each study list (containing twelve words associated with a non-presented critical word), while in the "delayed" condition (similar to the one in de Boysson et al., 2011), the participants received the entire series of study lists and then took only one recognition test. The results showed that, in both samples, the "immediate" condition produced higher corrected rates of both true and false recognition than the "delayed" condition, although they were both lower in the LBD patients, which shows that these patients are capable of encoding and recognizing the general similitude underlying information (gist memory) in the right conditions.

Electrophysiological evidence for the effects of unitization on associative recognition memory in older adults

Normal aging is associated with greater decline in associative memory relative to item memory due to impaired recollection. Familiarity may also contribute to associative recognition when stimuli are perceived as a 'unitized' representation. Given that familiarity is relatively preserved in older adults, we explored whether age-related associative memory deficits could be attenuated when associations were unitized (i.e., compounds) compared with those non-unitized (i.e., unrelated word pairs). Young and older adults performed an associative recognition task while electroencephalogram (EEG) was recorded. Behavioral results showed that age differences were smaller for recognition of compounds than for unrelated word pairs. ERP results indicated that only compounds evoked an early frontal old/new effect in older adults. Moreover, the early frontal old/new effect was positively correlated with associative discrimination accuracy. These findings suggest that reduced age-related associative deficits under unitized condition may be associated with the presence of familiarity-based retrieval of compounds in older adults.

The imagination inflation effect in healthy older adults and patients with mild Alzheimer's disease

OBJECTIVE

The imagination inflation effect is a type of memory distortion defined as an increased tendency to falsely remember that an item has been seen, or an action has been performed, when it has only been imagined. For patients with very mild Alzheimer's disease (AD), susceptibility to the imagination inflation effect could have significant functional consequences in daily life.

METHOD

We assessed whether patients with very mild AD were more or less susceptible to the imagination inflation effect when compared with healthy older adults. In the first session, participants were read an action statement such as "fill the pillbox" and engaged in 1 of 3 activities: listened to the statement being read, performed the action, or imagined performing the action. During the second session, participants imagined action statements from the first session, as well as new action statements. During the recognition test, participants were asked to determine whether action statements were or were not performed during the first session.

RESULTS

We found that imagining performing actions increased the tendency of patients with very mild AD to falsely recall the action as having been performed to an extent similar to that of healthy older adults.

CONCLUSION

We concluded that, similar to healthy older adults, patients with very mild AD were susceptible to the imagination inflation effect, which we attributed to difficulties with source monitoring and reliance on familiarity.

The effects of unitization on the contribution of familiarity and recollection processes to associative recognition memory: evidence from event-related potentials

Familiarity and recollection are two independent cognitive processes involved in recognition memory. It is traditionally believed that both familiarity and recollection can support item recognition, whereas only recollection can support associative recognition. Here, using a standard associative recognition task, we examined whether associative retrieval of unitized associations involved differential patterns of familiarity and recollection processes relative to non-unitized associations. The extent of engagement of familiarity and recollection processes during associative retrieval was estimated by using event-related potentials (ERPs). Twenty participants studied compound words and unrelated word pairs during encoding. Subsequently, they were asked to decide whether a presented word pair was intact, rearranged, or a new pair while electroencephalogram (EEG) was recorded. ERP results showed that compound words evoked a significant early frontal old/new effect (associated with familiarity) between ERPs to intact and rearranged word pairs, whereas this effect disappeared for the unrelated word pairs. In addition, the left parietal old/new effect (associated with recollection) between ERPs to intact and rearranged word pairs was greater for compounds than for unrelated word pairs. These findings suggest that unitization enhances the contribution of both familiarity and recollection processes to associative recognition.

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.

Associative memory and its cerebral correlates in Alzheimer׳s disease: evidence for distinct deficits of relational and conjunctive memory

This study investigated the impact of Alzheimer׳s disease (AD) on conjunctive and relational binding in episodic memory. Mild AD patients and controls had to remember item-color associations by imagining color either as a contextual association (relational memory) or as a feature of the item to be encoded (conjunctive memory). Patients׳ performance in each condition was correlated with cerebral metabolism measured by FDG-PET. The results showed that AD patients had an impaired capacity to remember item-color associations, with deficits in both relational and conjunctive memory. However, performance in the two kinds of associative memory varied independently across patients. Partial Least Square analyses revealed that poor conjunctive memory was related to hypometabolism in an anterior temporal-posterior fusiform brain network, whereas relational memory correlated with metabolism in regions of the default mode network. These findings support the hypothesis of distinct neural systems specialized in different types of associative memory and point to heterogeneous profiles of memory alteration in Alzheimer׳s disease as a function of damage to the respective neural networks.

Using pictures and words to understand recognition memory deterioration in amnestic mild cognitive impairment and Alzheimer's disease: a review

Difficulty recognizing previously encountered stimuli is one of the earliest signs of incipient Alzheimer's disease (AD). Work over the last 10 years has focused on how patients with AD and those in the prodromal stage of amnestic mild cognitive impairment make recognition decisions for visual and verbal stimuli. Interestingly, both groups of patients demonstrate markedly better memory for pictures over words, to a degree that is significantly greater in magnitude than their healthy older counterparts. Understanding this phenomenon not only helps to conceptualize how memory breaks down in AD, but also potentially provides the basis for future interventions. This review critically examines recent recognition memory work using pictures and words in the context of the dual-process theory of recognition and current hypotheses of cognitive breakdown in the course of very early AD.

Item familiarity and controlled associative retrieval in Alzheimer's disease: an fMRI study

Typical Alzheimer's disease (AD) is characterized by an impaired form of associative memory, recollection, that includes the controlled retrieval of associations. In contrast, familiarity-based memory for individual items may sometimes be preserved in the early stages of the disease. This is the first study that directly examines whole-brain regional activity during one core aspect of the recollection function: associative controlled episodic retrieval (CER), contrasted to item familiarity in AD patients. Cerebral activity related to associative CER and item familiarity in AD patients and healthy controls (HCs) was measured with functional magnetic resonance imaging during a word-pair recognition task to which the process dissociation procedure was applied. Some patients had null CER estimates (AD-), whereas others did show some CER abilities (AD+), although significantly less than HC. In contrast, familiarity estimates were equivalent in the three groups. In AD+, as in controls, associative CER activated the inferior precuneus/posterior cingulate cortex (PCC). When performing group comparisons, no region was found to be significantly more activated during CER in HC than AD+ and vice versa. However, during associative CER, functional connectivity between this region and the hippocampus, the inferior parietal and dorsolateral prefrontal cortex (DLPFC) was significantly higher in HC than in AD+. In all three groups, item familiarity was related to activation along the intraparietal sulcus (IPS). In conclusion, whereas the preserved automatic detection of an old item (without retrieval of accurate word association) is related to parietal activation centred on the IPS, the inferior precuneus/PCC supports associative CER ability in AD patients, as in HC. However, AD patients have deficient functional connectivity during associative CER, suggesting that the residual recollection function in these patients might be impoverished by the lack of some recollection-related aspects such as autonoetic quality, episodic details and verification.

Changes in response bias with different study-test delays: evidence from young adults, older adults, and patients with Alzheimer's disease

OBJECTIVE

Along with impaired discrimination, patients with Alzheimer's disease (AD) often show an abnormally liberal response bias (greater tendency to respond "old"). Previously we matched discrimination by varying study-test list length and found that participants' usual bias is maintained, such that patients with AD were more liberal than healthy controls. However, this pattern could be a result of the way in which discrimination was matched. In this experiment, we examined whether matching discrimination with the use of a delay would lead to a liberal response bias in healthy younger and older adults as it might lead to the use of more similar memorial processing to the patients with AD.

METHOD

Younger adults, older adults, and patients with AD were run in 2 study-test sessions, with study and recognition test separated by either a 1-min or 1-day delay.

RESULTS

With the 1-min delay, both younger adults and healthy older adults showed a conservative response bias, while patients with AD showed a liberal response bias. When discrimination was matched between patients with AD and controls by the use of a delay, response bias was also matched, with all participants showing a more liberal response bias.

CONCLUSIONS

The current study suggests that how discrimination is matched between patients with AD and controls matters greatly. Potentially, this liberal bias is a result of healthy younger and older adults relying primarily on familiarity at the longer delay, thus using more similar memorial processes to patients with AD who are dependent on familiarity at any delay.

Memory distortion in Alzheimer's disease: deficient monitoring of short- and long-term memory

OBJECTIVE

This study measured distortions of memory during short-term memory (STM) and long-term memory (LTM) versions of a semantically associated word list learning paradigm. Performance of patients with mild-to-moderate Alzheimer's disease (AD; MMSE ≥16) was compared with performance of age-matched, healthy older adult participants.

METHOD

In a STM version of the Deese-Roediger-McDermott (DRM) task, participants viewed four-word lists and were prompted for recall after a brief interval. The LTM task tested recall memory for 12-word lists.

RESULTS

Compared with the healthy group, the AD participants show greater impairment on the LTM task than on the STM task, although veridical recall is significantly reduced on both tasks. Furthermore, on both memory tasks, (1) participants with AD generate more nonsemantic intrusions than healthy older adult participants, and (2) semantic intrusion rate, when computed as a proportion of total recall, does not differ between groups. Notably, nonsemantic intrusions are consistently high for AD participants across both STM and LTM despite a marked difference in recall accuracy (65% and 23%, respectively).

CONCLUSIONS

STM impairment with some preserved semantic processing is evident in AD. The extent and variety of intrusions reported by AD participants indicates a breakdown in their ability to monitor and constrain their recall responses, even within seconds of initial learning.

Alzheimer's disease can spare local metacognition despite global anosognosia: revisiting the confidence-accuracy relationship in episodic memory

Alzheimer's disease (AD) can impair metacognition in addition to more basic cognitive functions like memory. However, while global metacognitive inaccuracies are well documented (i.e., low deficit awareness, or anosognosia), the evidence is mixed regarding the effects of AD on local or task-based metacognitive judgments. Here we investigated local metacognition with respect to the confidence-accuracy relationship in episodic memory (i.e., metamemory). AD and control participants studied pictures of common objects and their verbal labels, and then took forced-choice picture recollection tests using the verbal labels as retrieval cues. We found that item-based confidence judgments discriminated between accurate and inaccurate recollection responses in both groups, implicating relatively spared metamemory in AD. By contrast, there was evidence for global metacognitive deficiencies, as AD participants underestimated the severity of their everyday problems compared to an informant's assessment. Within the AD group, individual differences in global metacognition were related to recollection accuracy, and global metacognition for everyday memory problems was related to task-based metacognitive accuracy. These findings suggest that AD can spare the confidence-accuracy relationship in recollection tasks, and that global and local metacognition measures tap overlapping neuropsychological processes.

Gist-based conceptual processing of pictures remains intact in patients with amnestic mild cognitive impairment

OBJECTIVE

The picture superiority effect, better memory for pictures compared to words, has been found in young adults, healthy older adults, and, most recently, in patients with Alzheimer's disease and mild cognitive impairment. Although the picture superiority effect is widely found, there is still debate over what drives this effect. One main question is whether it is enhanced perceptual or conceptual information that leads to the advantage for pictures over words. In this experiment, we examined the picture superiority effect in healthy older adults and patients with amnestic mild cognitive impairment (MCI) to better understand the role of gist-based conceptual processing.

METHOD

We had participants study three exemplars of categories as either words or pictures. In the test phase, participants were again shown pictures or words and were asked to determine whether the item was in the same category as something they had studied earlier or whether it was from a new category.

RESULTS

We found that all participants demonstrated a robust picture superiority effect, better performance for pictures than for words.

CONCLUSIONS

These results suggest that the gist-based conceptual processing of pictures is preserved in patients with MCI. While in healthy older adults preserved recollection for pictures could lead to the picture superiority effect, in patients with MCI it is most likely that the picture superiority effect is a result of spared conceptually based familiarity for pictures, perhaps combined with their intact ability to extract and use gist information.

Characterizing episodic memory retrieval: electrophysiological evidence for diminished familiarity following unitization

Episodic memory relies on both recollection and familiarity; why these processes are differentially engaged during retrieval remains unclear. Traditionally, recollection has been considered necessary for tasks requiring associative retrieval, whereas familiarity supports recognition of items. Recently, however, familiarity has been shown to contribute to associative recognition if stimuli are "unitized" at encoding (a single representation is created from multiple elements)-the "benefit" of unitization. Here, we ask if there is also a "cost" of unitization; are the elements of unitized representations less accessible via familiarity? We manipulated unitization during encoding and used ERPs to index familiarity and recollection at retrieval. The data revealed a selective reduction in the neural correlate of familiarity for individual words originally encoded in unitized compared with nonunitized word pairs. This finding reveals a measurable cost of unitization, suggesting that the nature of to-be-remembered stimuli is critical in determining whether familiarity contributes to episodic memory.

The effects of aging and Alzheimer's disease on associative recognition memory

We investigated the effects of aging and Alzheimer's disease (AD) on item and associative recognition memory. Three groups of participants (younger adults, elderly adults, and AD patients) studied photographs of common objects that were located on either the left or the right side of a black computer screen inside either a red or a blue square. In a subsequent old/new recognition memory test, the participants were presented with four kinds of stimuli: "intact" stimuli, which were presented as they were during the study phase; "location-altered" stimuli, which were presented in a different location; "color-altered" stimuli, which were presented with a different surrounding color; and "new" stimuli, which consisted of photographs that had not been presented during the study phase. Compared with younger adults, the older adults showed equivalent performance in simple item recognition but worse performance in discriminating location-altered and color-altered stimuli. Compared with older adults, the AD patients showed equivalent performance in discriminating color-altered stimuli but worse performance in simple item recognition and the discrimination of location-altered stimuli. We speculate that distinct structural and functional changes in specific brain regions that are caused by aging and AD are responsible for the different patterns of memory impairment.

Alzheimer's disease and memory-monitoring impairment: Alzheimer's patients show a monitoring deficit that is greater than their accuracy deficit

We assessed the ability of two groups of patients with mild Alzheimer's disease (AD) and two groups of older adults to monitor the likely accuracy of recognition judgments and source identification judgments about who spoke something earlier. Alzheimer's patients showed worse performance on both memory judgments and were less able to monitor with confidence ratings the likely accuracy of both kinds of memory judgments, as compared to a group of older adults who experienced the identical study and test conditions. Critically, however, when memory performance was made comparable between the AD patients and the older adults (e.g., by giving AD patients extra exposures to the study materials), AD patients were still greatly impaired at monitoring the likely accuracy of their recognition and source judgments. This result indicates that the monitoring impairment in AD patients is actually worse than their memory impairment, as otherwise there would have been no differences between the two groups in monitoring performance when there were no differences in accuracy. We discuss the brain correlates of this memory-monitoring deficit and also propose a Remembrance-Evaluation model of memory-monitoring.