Source monitoring 15 years later: what have we learned from fMRI about the neural mechanisms of source memory?

Altered task-dependent functional connectivity patterns during subjective recollection experiences of episodic retrieval in postpartum women

Numerous studies have suggested that postpartum women show a decline in cognitive abilities. However, to date, no study has investigated the presence of qualitative alterations in recognition memory processes in postpartum women that may lead to a decline in cognitive ability. To address this issue, we employed the Remember/Know procedure and functional magnetic resonance imaging (fMRI). Behavioral results demonstrated that compared with the matched control (CTRL) group, the postpartum (PP) group endorsed "Remember" less and "Know" more to old items. A univariate analysis of fMRI data indicated lower neural activity of the subjective recollection network in the PP group than in the CTRL group. We also performed a large-scale functional connectivity multivariate pattern analysis (fcMVPA) using task-dependent time-series to detect differences in functional connectivity patterns and neural interactivity between the PP and CTRL groups. The fcMVPA results revealed that the PP group exhibited altered functional connectivity patterns from which machine learning algorithms could discriminate group membership with 94% accuracy. Collectively, these findings demonstrated that altered subjective recollection processes in the PP group during episodic memory decisions are associated with diminished neural activity and abnormal interactivity across the subjective recollection network. We believe that this is one of the first studies demonstrating qualitative alterations in recognition memory processes in postpartum women.

Everyday false memories in older persons with depressive disorder

Generally we tend to think that memory in daily living is complete and accurate in healthy persons. However, current memory research has revealed inconspicuous memory faults. Rarely omissions and distortions of memory are researched with tasks resembling everyday life. We investigated healthy older control subjects (HC) and patients with depressive disorder (DD). Cognitive function was assessed with a comprehensive neuropsychological test battery and mood with the Montgomery-Asberg Depression Scale (MADRS). We assessed everyday veridical and distorted memories on showing participants original news and commercials. In most aspects of attention, executive functions, and memory, patients with DD performed worse than HC. Regarding memory content on viewing news or commercials the difference between patients with DD and HC was more pronounced for false memory content than for veridical memory content. Linear regression analysis showed the extent of false memory content being associated with mental flexibility as assessed with the Trail Making Test and mood as assessed with the MADRS for both information obtained on viewing news and commercials. Increase of false memories impedes overall accuracy of memory more than decrease of veridical memories in older persons with depressive disorder. Diminished executive functions and depressive mood partly explain these memory distortions.

Can implicit measures detect source information in crime-related amnesia?

Participants who are asked to simulate amnesia for a mock crime have a weaker memory for this event when they have to give up their role as a feigner, than those who are not asked to feign memory loss. According to the source monitoring framework (SMF), this memory-undermining effect of simulating amnesia for a crime would be due to misattribution of the right source of information. However, we know that the content of self-generated information (e.g., feigned version of the crime) might be preserved and recognised over time as a result of elaborative cognitive processing. In the present study, we aimed to contrast these two explanations. We showed participants a mock crime video and we instructed them to either feign amnesia (simulators) or confess the mock crime (confessors). Next, a free recall memory test was administered. After one week, participants were asked to perform a personalised source monitoring task using the autobiographical Implicit Association Test (aIAT). As predicted, we found that simulators were able to discriminate the content of their self-generated feigned story of the crime from the original version. Moreover, simulators were quicker than confessors at the aIAT task. Practical and theoretical implications of our results are discussed.

Is Source Information Automatically Available in Working Memory?

We often remember information without its source (e.g., word or picture format). This phenomenon has been studied extensively in long-term memory but rarely in the context of short-term working memory (WM), which leaves open the question of whether source amnesia can result from a lack of memory encoding rather than forgetting. This study provided a series of striking and novel demonstrations showing participants' inability to report the source of a color representation immediately after that color was used in a task and stored in memory. These counterintuitive findings occurred when participants repeatedly judged the congruency between two color representations from one single object (i.e., color and identity of a color word) or two distinct objects (i.e., color of a square and identity of a color word) and then were unexpectedly asked to report the source of one color representation. These discoveries suggest that source information is often not stored in WM.

Facial Recall: Feature–Conjunction Effects in Source Retrieval Versus Item Recognition

Within memory processing, feature and conjunction effects refer to higher false alarms (incorrectly naming items as previously seen) for stimuli with partial/all features taken from different previously studied versus novel items. In this study, we compared feature–conjunction effects in the memory tasks of both item recognition and source retrieval, using faces as stimuli. We found greater feature–conjunction effects on source retrieval versus item recognition tasks, though participants gave slower responses on source retrieval versus item recognition. Thus, our data were consistent with dual-process memory theory in which familiarity contributes to high false alarms in compound faces even while feature–conjunction effects enhance recollection in source retrieval.

Effects of perceptual similarity but not semantic association on false recognition in aging

This study investigated semantic and perceptual influences on false recognition in older and young adults in a variant on the Deese-Roediger-McDermott paradigm. In two experiments, participants encoded intermixed sets of semantically associated words, and sets of unrelated words. Each set was presented in a shared distinctive font. Older adults were no more likely to falsely recognize semantically associated lure words compared to unrelated lures also presented in studied fonts. However, they showed an increase in false recognition of lures which were related to studied items only by a shared font. This increased false recognition was associated with recollective experience. The data show that older adults do not always rely more on prior knowledge in episodic memory tasks. They converge with other findings suggesting that older adults may also be more prone to perceptually-driven errors.

Choice-Supportive Misremembering: A New Taxonomy and Review

Although the literature on the influence of memory on decisions is well developed, research on the effects of decision making on memory is rather sparse and scattered. Choice-supportive misremembering (i.e., misremembering choice-related information that boosts the chosen option and/or demotes the foregone options) has been observed in several studies and has the potential to affect future choices. Nonetheless, no attempt has been made to review the relevant literature, categorize the different types of choice-supportive misremembering observed, and critically appraise the existing evidence and proposed explanations. Thus, starting from a new theoretically motivated and empirically grounded taxonomy, we review the current research. Our taxonomy classifies choice-supportive misremembering into four conceptually distinct types: misattribution is when information is attributed to the wrong source, fact distortion when the facts are remembered in a distorted manner, false memory when items that were not part of the original decision scenarios are remembered as presented and, finally, selective forgetting is when information is selectively forgotten. After assessing the impact of various potentially moderating factors, we evaluate the evidence for each type of misremembering and conclude that the support for the phenomenon is solid in relation to misattribution when recognition memory is assessed, but significantly weaker for the other three types, and when other memory tests are used to assess memory. Finally, we review the cognitive and emotional explanations proposed for choice-supportive misremembering in the light of the available evidence and identify the main gaps in the current knowledge and the more promising avenues for future research.

Simultaneous Reality Filtering and Encoding of Thoughts: The Substrate for Distinguishing between Memories of Real Events and Imaginations?

Any thought, whether it refers to the present moment or reflects an imagination, is again encoded as a new memory trace. Orbitofrontal reality filtering (ORFi) denotes an on-line mechanism which verifies whether upcoming thoughts relate to ongoing reality or not. Its failure induces reality confusion with confabulations and disorientation. If the result of this process were simultaneously encoded, it would easily explain later distinction between memories relating to a past reality and memories relating to imagination, a faculty called reality monitoring. How the brain makes this distinction is unknown but much research suggests that it depends on processes active when information is encoded. Here we explored the precise timing between ORFi and encoding as well as interactions between the involved brain structures. We used high-density evoked potentials and two runs of a continuous recognition task (CRT) combining the challenges of ORFi and encoding. ORFi was measured by the ability to realize that stimuli appearing in the second run had not appeared in this run yet. Encoding was measured with immediately repeated stimuli, which has been previously shown to induce a signal emanating from the medial temporal lobe (MTL), which has a protective effect on the memory trace. We found that encoding, as measured with this task, sets in at about 210 ms after stimulus presentation, 35 ms before ORFi. Both processes end at about 330 ms. Both were characterized by increased coherence in the theta band in the MTL during encoding and in the orbitofrontal cortex (OFC) during ORFi. The study suggests a complex interaction between OFC and MTL allowing for thoughts to be re-encoded while they undergo ORFi. The combined influence of these two processes at 200-300 ms may leave a memory trace that allows for later effortless reality monitoring in most everyday situations.

Self-Referential Information Alleviates Retrieval Inhibition of Directed Forgetting Effects-An ERP Evidence of Source Memory

Directed forgetting (DF) assists in preventing outdated information from interfering with cognitive processing. Previous studies pointed that self-referential items alleviated DF effects due to the elaboration of encoding processes. However, the retrieval mechanism of this phenomenon remains unknown. Based on the dual-process framework of recognition, the retrieval of self-referential information was involved in familiarity and recollection. Using source memory tasks combined with event-related potential (ERP) recording, our research investigated the retrieval processes of alleviative DF effects elicited by self-referential information. The FN400 (frontal negativity at 400 ms) is a frontal potential at 300–500 ms related to familiarity and the late positive complex (LPC) is a later parietal potential at 500–800 ms related to recollection. The FN400 effects of source memory suggested that familiarity processes were promoted by self-referential effects without the modulation of to-be-forgotten (TBF) instruction. The ERP results of DF effects were involved with LPCs of source memory, which indexed retrieval processing of recollection. The other-referential source memory of TBF instruction caused the absence of LPC effects, while the self-referential source memory of TBF instruction still elicited the significant LPC effects. Therefore, our neural findings suggested that self-referential processing improved both familiarity and recollection. Furthermore, the self-referential processing advantage which was caused by the autobiographical retrieval alleviated retrieval inhibition of DF, supporting that the self-referential source memory alleviated DF effects.

Production on hold: delaying vocal production enhances the production effect in free recall

The Production Effect (PE) represents superior memory for produced (read aloud) relative to non-produced (silently read) items. Another method of improving memory is taking a test on the study material - the Testing Effect. We evaluated the combined influence of both effects on free recall memory, using delayed vocal production, in which study words were vocally produced only after their disappearance. Such procedure involves an initial instant test since participants had to vocally retrieve the words (rather than read them aloud). In five experiments, participants were presented with study words that they were instructed to learn by no-production (reading silently), immediate production (reading aloud), delayed reading aloud, or delayed vocal production (instant retrieval). The results showed superior recall for delayed production over all other conditions. We suggest that the source of this superiority is the desirable difficulty induced by the addition of the initial test (retrieval effort) to the vocal production. The novel delayed production condition forms a superior mnemonic.

Abnormal prefrontal and parietal activity linked to deficient active binding in working memory in schizophrenia

Working memory deficits have been widely reported in schizophrenia, and may result from inefficient binding processes. These processes, and their neural correlates, remain understudied in schizophrenia. Thus, we designed an FMRI study aimed at investigating the neural correlates of both passive and active binding in working memory in schizophrenia. Nineteen patients with schizophrenia and 23 matched controls were recruited to perform a working memory binding task, in which they were instructed to memorize three letters and three spatial locations. In the passive binding condition, letters and spatial locations were directly presented as bound. Conversely, in the active binding condition, words and spatial locations were presented as separated, and participants were instructed to intentionally create associations between them. Patients exhibited a similar performance to the controls for the passive binding condition, but a significantly lower performance for the active binding. FMRI analyses revealed that this active binding deficit was related to aberrant activity in the posterior parietal cortex and the ventrolateral prefrontal cortex. This study provides initial evidence of a specific deficit for actively binding information in schizophrenia, which is linked to dysfunctions in the neural networks underlying attention, manipulation of information, and encoding strategies. Together, our results suggest that all these dysfunctions may be targets for neuromodulation interventions known to improve cognitive deficits in schizophrenia.

The chemotherapeutic agent paclitaxel selectively impairs reversal learning while sparing prior learning, new learning and episodic memory

Chemotherapy is widely used to treat patients with systemic cancer. The efficacy of cancer therapies is frequently undermined by adverse side effects that have a negative impact on the quality of life of cancer survivors. Cancer patients who receive chemotherapy often experience chemotherapy-induced cognitive impairment across a variety of domains including memory, learning, and attention. In the current study, the impact of paclitaxel, a taxane derived chemotherapeutic agent, on episodic memory, prior learning, new learning, and reversal learning were evaluated in rats. Neurogenesis was quantified post-treatment in the dentate gyrus of the same rats using immunostaining for 5-Bromo-2'-deoxyuridine (BrdU) and Ki67. Paclitaxel treatment selectively impaired reversal learning while sparing episodic memory, prior learning, and new learning. Furthermore, paclitaxel-treated rats showed decreases in markers of hippocampal cell proliferation, as measured by markers of cell proliferation assessed using immunostaining for Ki67 and BrdU. This work highlights the importance of using multiple measures of learning and memory to identify the pattern of impaired and spared aspects of chemotherapy-induced cognitive impairment.

Hippocampal maturity promotes memory distinctiveness in childhood and adolescence

Adaptive learning systems need to meet two complementary and partially conflicting goals: detecting regularities in the world versus remembering specific events. The hippocampus (HC) keeps a fine balance between computations that extract commonalities of incoming information (i.e., pattern completion) and computations that enable encoding of highly similar events into unique representations (i.e., pattern separation). Histological evidence from young rhesus monkeys suggests that HC development is characterized by the differential development of intrahippocampal subfields and associated networks. However, due to challenges in the in vivo investigation of such developmental organization, the ontogenetic timing of HC subfield maturation remains controversial. Delineating its course is important, as it directly influences the fine balance between pattern separation and pattern completion operations and, thus, developmental changes in learning and memory. Here, we relate in vivo, high-resolution structural magnetic resonance imaging data of HC subfields to behavioral memory performance in children aged 6-14 y and in young adults. We identify a multivariate profile of age-related differences in intrahippocampal structures and show that HC maturity as captured by this pattern is associated with age differences in the differential encoding of unique memory representations.

Autobiographical memory conjunction errors in younger and older adults: Evidence for a role of inhibitory ability

Because of its reconstructive nature, autobiographical memory (AM) is subject to a range of distortions. One distortion involves the erroneous incorporation of features from one episodic memory into another, forming what are known as memory conjunction errors. Healthy aging has been associated with an enhanced susceptibility to conjunction errors for laboratory stimuli, yet it is unclear whether these findings translate to the autobiographical domain. We investigated the impact of aging on vulnerability to AM conjunction errors, and explored potential cognitive processes underlying the formation of these errors. An imagination recombination paradigm was used to elicit AM conjunction errors in young and older adults. Participants also completed a battery of neuropsychological tests targeting relational memory and inhibition ability. Consistent with findings using laboratory stimuli, older adults were more susceptible to AM conjunction errors than younger adults. However, older adults were not differentially vulnerable to the inflating effects of imagination. Individual variation in AM conjunction error vulnerability was attributable to inhibitory capacity. An inability to suppress the cumulative familiarity of individual AM details appears to contribute to the heightened formation of AM conjunction errors with age. (PsycINFO Database Record

Dynamic Hippocampal and Prefrontal Contributions to Memory Processes and Representations Blur the Boundaries of Traditional Cognitive Domains

The hippocampus has long been known to be a critical component of the memory system involved in the formation and use of long-term declarative memory. However, recent findings have revealed that the reach of hippocampal contributions extends to a variety of domains and tasks that require the flexible use of cognitive and social behavior, including domains traditionally linked to prefrontal cortex (PFC), such as decision-making. In addition, the prefrontal cortex (PFC) has gained traction as a necessary part of the memory system. These findings challenge the conventional characterizations of hippocampus and PFC as being circumscribed to traditional cognitive domains. Here, we emphasize that the ability to parsimoniously account for the breadth of hippocampal and PFC contributions to behavior, in terms of memory function and beyond, requires theoretical advances in our understanding of their characteristic processing features and mental representations. Notably, several literatures exist that touch upon this issue, but have remained disjointed because of methodological differences that necessarily limit the scope of inquiry, as well as the somewhat artificial boundaries that have been historically imposed between domains of cognition. In particular, this article focuses on the contribution of relational memory theory as an example of a framework that describes both the representations and processes supported by the hippocampus, and further elucidates the role of the hippocampal–PFC network to a variety of behaviors.

Encoding focus alters diagnostic recollection and event-related potentials (ERPs)

The influence of encoding focus on source memory was investigated using event-related potentials (ERPs). Encoding was focused on the self (self-focus) or on the speaker (other-focus) while hearing words spoken in a male or female voice. Examination of the behavioral and ERP evidence suggests that encoding focus alters the amount of diagnostic recollection. Self-focus encoding produced more positive encoding ERPs, led to greater old/new recognition, and elicited a greater Late Positive Component (LPC; the putative neural correlate of recollection) during the source test. Other-focus encoding led to greater source memory and a smaller LPC amplitude. Collectively, the results suggest that encoding focus alters the information bound in the memory trace that leads to varying levels of source-diagnostic features. Drawing attention to the speaker facilitates binding of source-diagnostic features (i.e., voice), whereas self-focus encoding facilitates binding a host of non-diagnostic features. The results have important implications for situations that depend on encoding processes, such as false memory or classroom learning, and they provide evidence that the LPC tracks recollected details but not necessarily diagnostic recollection.

Decision Making and Sequential Sampling from Memory

Decisions take time, and as a rule more difficult decisions take more time. But this only raises the question of what consumes the time. For decisions informed by a sequence of samples of evidence, the answer is straightforward: more samples are available with more time. Indeed, the speed and accuracy of such decisions are explained by the accumulation of evidence to a threshold or bound. However, the same framework seems to apply to decisions that are not obviously informed by sequences of evidence samples. Here, we proffer the hypothesis that the sequential character of such tasks involves retrieval of evidence from memory. We explore this hypothesis by focusing on value-based decisions and argue that mnemonic processes can account for regularities in choice and decision time. We speculate on the neural mechanisms that link sampling of evidence from memory to circuits that represent the accumulated evidence bearing on a choice. We propose that memory processes may contribute to a wider class of decisions that conform to the regularities of choice-reaction time predicted by the sequential sampling framework.

Remembering verbally-presented items as pictures: Brain activity underlying visual mental images in schizophrenia patients with visual hallucinations

BACKGROUND

Previous research suggests that visual hallucinations in schizophrenia consist of mental images mistaken for percepts due to failure of the reality-monitoring processes. However, the neural substrates that underpin such dysfunction are currently unknown. We conducted a brain imaging study to investigate the role of visual mental imagery in visual hallucinations.

METHOD

Twenty-three patients with schizophrenia and 26 healthy participants were administered a reality-monitoring task whilst undergoing an fMRI protocol. At the encoding phase, a mixture of pictures of common items and labels designating common items were presented. On the memory test, participants were requested to remember whether a picture of the item had been presented or merely its label.

RESULTS

Visual hallucination scores were associated with a liberal response bias reflecting propensity to erroneously remember pictures of the items that had in fact been presented as words. At encoding, patients with visual hallucinations differentially activated the right fusiform gyrus when processing the words they later remembered as pictures, which suggests the formation of visual mental images. On the memory test, the whole patient group activated the anterior cingulate and medial superior frontal gyrus when falsely remembering pictures. However, no differential activation was observed in patients with visual hallucinations, whereas in the healthy sample, the production of visual mental images at encoding led to greater activation of a fronto-parietal decisional network on the memory test.

CONCLUSIONS

Visual hallucinations are associated with enhanced visual imagery and possibly with a failure of the reality-monitoring processes that enable discrimination between imagined and perceived events.

Abnormal semantic knowledge in a case of developmental amnesia

An important theory holds that semantic knowledge can develop independently of episodic memory. One strong source of evidence supporting this independence comes from the observation that individuals with early hippocampal damage leading to developmental amnesia generally perform normally on standard tests of semantic memory, despite their profound impairment in episodic memory. However, one aspect of semantic memory that has not been explored is conceptual structure. We built on the theoretically important distinction between intrinsic features of object concepts (e.g., shape, colour, parts) and extrinsic features (e.g., how something is used, where it is typically located). The accrual of extrinsic feature knowledge that is important for concepts such as chair or spoon may depend on binding mechanisms in the hippocampus. We tested HC, an individual with developmental amnesia due to a well-characterized lesion of the hippocampus, on her ability to generate semantic features for object concepts. HC generated fewer extrinsic features than controls, but a similar number of intrinsic features than controls. We also tested her on typicality ratings. Her typicality ratings were abnormal for nonliving things (which more strongly depend on extrinsic features), but normal for living things (which more strongly depend on intrinsic features). In contrast, NB, who has MTL but not hippocampal damage due to surgery, showed no impairments in either task. These results suggest that episodic and semantic memory are not entirely independent, and that the hippocampus is important for learning some aspects of conceptual knowledge.

Urban Legends and Paranormal Beliefs: The Role of Reality Testing and Schizotypy

Recent research suggests that unconventional beliefs are locatable within a generic anomalous belief category. This notion derives from the observation that apparently dissimilar beliefs share fundamental, core characteristics (i.e., contradiction of orthodox scientific understanding of the universe and defiance of conventional understanding of reality). The present paper assessed the supposition that anomalous beliefs were conceptually similar and explicable via common psychological processes by comparing relationships between discrete beliefs [endorsement of urban legends (ULs) and belief in the paranormal] and cognitive-perceptual personality measures [proneness to reality testing (RT) and schizotypy]. A sample of 222 volunteers, recruited via convenience sampling, took part in the study. Participants completed a series of self-report measures (Urban Legends Questionnaire, Reality Testing subscale of the Inventory of Personality Organization, Revised Paranormal Belief Scale and the Schizotypal Personality Questionnaire Brief). Preliminary analysis revealed positive correlations between measures. Within schizotypy, the cognitive-perceptual factor was most strongly associated with anomalistic beliefs; disorganized and interpersonal produced only weak and negligible correlations respectively. Further investigation indicated complex relationships between RT, the cognitive-perceptual factor of schizotypy and anomalistic beliefs. Specifically, proneness to RT deficits explained a greater amount of variance in ULs, whilst schizotypy accounted for more variance in belief in the paranormal. Consideration of partial correlations supported these conclusions. The relationship between RT and ULs remained significant after controlling for the cognitive-perceptual factor. Contrastingly, the association between the cognitive-perceptual factor and ULs controlling for RT was non-significant. In the case of belief in the paranormal, controlling for proneness to RT reduced correlation size, but relationships remained significant. This study demonstrated that anomalistic beliefs vary in nature and composition. Findings indicated that generalized views of anomalistic beliefs provide only limited insight into the complex nature of belief.

Recognizing What Matters: Value Improves Recognition by Selectively Enhancing Recollection

We examined the effects of value on recognition by assessing its contribution to recollection and familiarity. In three experiments, participants studied English words, each associated with a point-value they would earn for correct recognition, with the goal of maximizing their score. In Experiment 1, participants provided Remember/Know judgments. In Experiment 2 participants indicated whether items were recollected or if not, their degree of familiarity along a 6-point scale. In Experiment 3, recognition of words was accompanied by a test of memory for incidental details. Across all experiments, participants were more likely to recognize items with higher point-value. Furthermore, value appeared to primarily enhance recollection, as effects on familiarity were small and not consistent across experiments. Recollection of high-value items appears to be accompanied by fewer incidental details, suggesting that value increases focus on items at the expense of irrelevant information.

Fractionating controlled memory processes and recall of context in recognition memory: a case report

Recollection has been described as both a recognition memory judgment requiring cognitive control and the ability to retrieve contextual information about a prior occurrence. At the core of this article is the question whether or not these two subcomponents of recollection are dissociable in amnesia. In three experiments, we explored the influence of exclusion task instructions on performance in a single case (CJ), with the view to understand the relative contributions of control and source memory to recognition memory decisions. First, contrasting findings were obtained between tasks requiring strategic control or source reports. Second, even though CJ displayed some residual source memory relative to the ability to strategically control this information, his source memory capacity was time-limited. Our findings resonate with the novel proposal that recollection draws heavily upon working memory resources, and provide an example of how amnesic patients might utilize residual working memory capacity to solve episodic memory tasks.

Assumptions behind scoring source versus item memory: Effects of age, hippocampal lesions and mild memory problems

Source monitoring paradigms have been used to separate: 1) the probability of recognising an item (Item memory) and 2) the probability of remembering the context in which that item was previously encountered (Source memory), conditional on it being recognised. Multinomial Processing Tree (MPT) models are an effective way to estimate these conditional probabilities. Moreover, MPTs make explicit the assumptions behind different ways to parameterise Item and Source memory. Using data from six independent groups across two different paradigms, we show that one would draw different conclusions about the effects of age, age-related memory problems and hippocampal lesions on Item and Source memory, depending on the use of: 1) standard accuracy calculation vs MPT analysis, and 2) two different MPT models. The MPT results were more consistent than standard accuracy calculations, and furnished additional parameters that can be interpreted in terms of, for example, false recollection or missed encoding. Moreover, a new MPT structure that allowed for separate memory representations (one for item information and one for item-plus-source information; the Source-Item model) fit the data better, and provided a different pattern of significant differences in parameters, than the more conventional MPT structure in which source information is a subset of item information (the Item-Source model). Nonetheless, there is no theory-neutral way of scoring data, and thus proper examination of the assumptions underlying the scoring of source monitoring paradigms is necessary before theoretical conclusions can be drawn.

Working memory predicts presence of auditory verbal hallucinations in schizophrenia and bipolar disorder with psychosis

OBJECTIVE

The recent dramatic increase in research investigating auditory verbal hallucinations (AVHs) has broadened the former narrow focus on schizophrenia to incorporate additional populations that experience these symptoms. However, an understanding of potential shared mechanisms remains elusive. Based on theories suggesting a failure of top-down cognitive control, we aimed to compare the relationship between AVHs and cognition in two categorical diagnoses of psychosis, schizophrenia and psychotic bipolar disorder.

METHOD

A total of 124 adults aged 21-60 participated, of whom 76 had present-state psychosis (schizophrenia, n = 53; bipolar disorder with psychosis, n = 23), and 48 were non-clinical controls. Diagnosis and hallucination presence was determined using the Structured Clinical Diagnostic Interview for DSM-IV TR. AVHs severity was assessed using the Positive and Negative Syndrome Scale. Participants also completed the MATRICS cognitive battery.

RESULTS

The bipolar disorder with psychosis group performed better than the schizophrenia group for cognitive domains of Processing speed, Attention, Working memory (WM), and Visual memory. Hierarchical binary logistic regression found that WM significantly predicted presence of AVHs in both psychotic groups, but diagnosis did not significantly increase the predictive value of the model. A hierarchical multiple linear regression found that schizophrenia diagnosis was the only significant predictor of hallucination severity.

CONCLUSIONS

The findings of this study-the first, to our knowledge, to compare the relationship between AVHs and MATRICS domains across schizophrenia and bipolar disorder with psychosis-support theories that deficits in WM underly the genesis of AVHs. WM potentially represents a shared mechanism of AVHs across diagnoses, supporting dimensional classifications of these psychotic disorders. However, non-cognitive factors predictive of hallucination severity may be specific to schizophrenia.

Visual integration enhances associative memory equally for young and older adults without reducing hippocampal encoding activation

The ability to remember associations between previously unrelated pieces of information is often impaired in older adults (Naveh-Benjamin, 2000). Unitization, the process of creating a perceptually or semantically integrated representation that includes both items in an associative pair, attenuates age-related associative deficits (Bastin et al., 2013; Ahmad et al., 2015; Zheng et al., 2015). Compared to non-unitized pairs, unitized pairs may rely less on hippocampally-mediated binding associated with recollection, and more on familiarity-based processes mediated by perirhinal cortex (PRC) and parahippocampal cortex (PHC). While unitization of verbal materials improves associative memory in older adults, less is known about the impact of visual integration. The present study determined whether visual integration improves associative memory in older adults by minimizing the need for hippocampal (HC) recruitment and shifting encoding to non-hippocampal medial temporal structures, such as the PRC and PHC. Young and older adults were presented with a series of objects paired with naturalistic scenes while undergoing fMRI scanning, and were later given an associative memory test. Visual integration was varied by presenting the object either next to the scene (Separated condition) or visually integrated within the scene (Combined condition). Visual integration improved associative memory among young and older adults to a similar degree by increasing the hit rate for intact pairs, but without increasing false alarms for recombined pairs, suggesting enhanced recollection rather than increased reliance on familiarity. Also contrary to expectations, visual integration resulted in increased hippocampal activation in both age groups, along with increases in PRC and PHC activation. Activation in all three MTL regions predicted discrimination performance during the Separated condition in young adults, while only a marginal relationship between PRC activation and performance was observed during the Combined condition. Older adults showed less overall activation in MTL regions compared to young adults, and associative memory performance was most strongly predicted by prefrontal, rather than MTL, activation. We suggest that visual integration benefits both young and older adults similarly, and provides a special case of unitization that may be mediated by recollective, rather than familiarity-based encoding processes.

Brain Mechanisms of Reality Monitoring

Reality monitoring processes are necessary for discriminating between internally generated information and information that originated in the outside world. They help us to identify our thoughts, feelings, and imaginations, and to distinguish them from events we may have experienced or have been told about by someone else. Reality monitoring errors range from confusions between real and imagined experiences, that are byproducts of normal cognition, to symptoms of mental illness such as hallucinations. Recent advances support an emerging neurocognitive characterization of reality monitoring that provides insights into its underlying operating principles and neural mechanisms, the differing ways in which impairment may occur in health and disease, and the potential for rehabilitation strategies to be devised that might help those who experience clinically significant reality monitoring disruption.

From hippocampus to whole-brain: The role of integrative processing in episodic memory retrieval

Multivariate functional connectivity analyses of neuroimaging data have revealed the importance of complex, distributed interactions between disparate yet interdependent brain regions. Recent work has shown that topological properties of functional brain networks are associated with individual and group differences in cognitive performance, including in episodic memory. After constructing functional whole-brain networks derived from an event-related fMRI study of memory retrieval, we examined differences in functional brain network architecture between forgotten and remembered words. This study yielded three main findings. First, graph theory analyses showed that successfully remembering compared to forgetting was associated with significant changes in the connectivity profile of the left hippocampus and a corresponding increase in efficient communication with the rest of the brain. Second, bivariate functional connectivity analyses indicated stronger interactions between the left hippocampus and a retrieval assembly for remembered versus forgotten items. This assembly included the left precuneus, left caudate, bilateral supramarginal gyrus, and the bilateral dorsolateral superior frontal gyrus. Integrative properties of the retrieval assembly were greater for remembered than forgotten items. Third, whole-brain modularity analyses revealed that successful memory retrieval was marginally significantly associated with a less segregated modular architecture in the network. The magnitude of the decreases in modularity between remembered and forgotten conditions was related to memory performance. These findings indicate that increases in integrative properties at the nodal, retrieval assembly, and whole-brain topological levels facilitate memory retrieval, while also underscoring the potential of multivariate brain connectivity approaches for providing valuable new insights into the neural bases of memory processes. Hum Brain Mapp 38:2242-2259, 2017. © 2017 Wiley Periodicals, Inc.

Predictive Processing, Source Monitoring, and Psychosis

A comprehensive understanding of psychosis requires models that link multiple levels of explanation: the neurobiological, the cognitive, the subjective, and the social. Until we can bridge several explanatory gaps, it is difficult to explain how neurobiological perturbations can manifest in bizarre beliefs or hallucinations, or how trauma or social adversity can perturb lower-level brain processes. We propose that the predictive processing framework has much to offer in this respect. We show how this framework may underpin and complement source monitoring theories of delusions and hallucinations and how, when considered in terms of a dynamic and hierarchical system, it may provide a compelling model of several key clinical features of psychosis. We see little conflict between source monitoring theories and predictive coding. The former act as a higher-level description of a set of capacities, and the latter aims to provide a deeper account of how these and other capacities may emerge.

Sex Matters: Hippocampal Volume Predicts Individual Differences in Associative Memory in Cognitively Normal Older Women but Not Men

The hippocampus plays a prominent role in associative memory by supporting relational binding and recollection processes. Structural atrophy in the hippocampus is likely to induce associative memory deficits in older adults. Previous studies have primarily focused on average age-related differences in hippocampal structure and memory performance. To date, however, it remains unclear whether individual differences in hippocampal morphometry underlie differential associative memory performance, and whether there are sex differences in the structural correlates of associative memory in healthy older adults. Here, we used voxel-based morphometry (VBM) to examine the extent to which gray matter volume (GMV) of the hippocampus predicts associative memory performance in cognitively normal older adults. Seventy-one participants completed a cued recall paired-associative learning test (PALT), which consists of novel associations and semantically related associations, and underwent magnetic resonance imaging (MRI). We observed worse associative memory performance and larger variability for novel associations than for semantically related associations. The VBM results revealed that higher scores on associative memory for novel associations were related to greater hippocampal GMV across all older adults. When considering men and women separately, the correlation between hippocampal GMV and associative memory performance for novel associations reached significance only in older women. These findings suggest that hippocampal structural volumes may predict individual differences in novel associative memory in older women but not men.

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.

Reality Monitoring and Metamemory in Adults with Autism Spectrum Conditions

Studies of reality monitoring (RM) often implicate medial prefrontal cortex (mPFC) in distinguishing internal and external information, a region linked to autism-related deficits in social and self-referential information processing, executive function, and memory. This study used two RM conditions (self-other; perceived-imagined) to investigate RM and metamemory in adults with autism. The autism group showed a deficit in RM, which did not differ across source conditions, and both groups exhibited a self-encoding benefit on recognition and source memory. Metamemory for perceived-imagined information, but not for self-other information, was significantly lower in the autism group. Therefore, reality monitoring and metamemory, sensitive to mPFC function, appear impaired in autism, highlighting a difficulty in remembering and monitoring internal and external details of past events.

Age-related changes in neural oscillations supporting context memory retrieval

Recent evidence suggests that directing attention toward single item-context associations during encoding improves young and older adults' context memory performance and reduces demands on executive functions during retrieval. In everyday situations, there are many event features competing for our attention, and our ability to successfully recover those details may depend on our ability to ignore others. Failures of selective attention may contribute to older adults' context memory impairments. In the current electroencephalogram (EEG) study, we assessed the effects of age on processes supporting successful context memory retrieval of selectively attended features as indexed by neural oscillations. During encoding, young and older adults were directed to attend to a picture of an object and its relationship to one of two concurrently presented contextual details: a color or scene. At retrieval, we tested their memory for the object, its attended and unattended context features, and their confidence for both the attended and unattended features. Both groups showed greater memory for attended than unattended contextual features. However, older adults showed evidence of hyper-binding between attended and unattended context features while the young adults did not. EEG results in the theta band suggest that young and older adults recollect similar amounts of information but brain-behavior correlations suggest that this information was supportive of contextual memory performance, particularly for young adults. By contrast, sustained beta desynchronization, indicative of sensory reactivation and episodic reconstruction, was correlated with contextual memory performance for older adults only. We conclude that older adults' inhibition deficits during encoding reduced the selectivity of their contextual memories, which led to reliance on executive functions like episodic reconstruction to support successful memory retrieval.

Destination memory in schizophrenia: "Did I told Elvis Presley about the thief?"

Destination memory refers to the ability to remember to whom a piece of information was previously transmitted. Our paper assessed this ability in schizophrenia. Twenty-five patients with schizophrenia and 25 control participants told proverbs (e.g., "send a thief to catch a thief") to pictures of celebrities (e.g., Elvis Presley). Afterward, participants had to indicate to which celebrity they had previously said the proverbs. Participants also completed a binding task in which they were required to associate letters with their corresponding context (i.e., location). Analysis revealed worse destination memory and binding in patients with schizophrenia than in controls. In both populations, destination memory was significantly correlated with performances on the binding task. Our findings suggest difficulty in the ability to attribute information to its appropriate destination in schizophrenia. This difficulty may be related to compromise in binding separate cues together to form a coherent representation of an event in memory.

The Anterior Prefrontal Cortex and the Hippocampus Are Negatively Correlated during False Memories

False memories commonly activate the anterior/dorsolateral prefrontal cortex (A/DLPFC) and the hippocampus. These regions are assumed to work in concert during false memories, which would predict a positive correlation between the magnitudes of activity in these regions across participants. However, the A/DLPFC may also inhibit the hippocampus, which would predict a negative correlation between the magnitudes of activity in these regions. In the present functional magnetic resonance imaging (fMRI) study, during encoding, participants viewed abstract shapes in the left or right visual field. During retrieval, participants classified each old shape as previously in the "left" or "right" visual field followed by an "unsure"-"sure"-"very sure" confidence rating. The contrast of left-hits and left-misses produced two activations in the hippocampus and three activations in the left A/DLPFC. For each participant, activity associated with false memories (right-"left"-"very sure" responses) from the two hippocampal regions was plotted as a function of activity in each A/DLPFC region. Across participants, for one region in the left anterior prefrontal cortex, there was a negative correlation between the magnitudes of activity in this region and the hippocampus. This suggests that the anterior prefrontal cortex might inhibit the hippocampus during false memories and that participants engage either the anterior prefrontal cortex or the hippocampus during false memories.

Neural mechanisms of mood-induced modulation of reality monitoring in schizophrenia

Reality monitoring is the ability to accurately distinguish the source of self-generated information from externally-presented information. Although people with schizophrenia (SZ) show impaired reality monitoring, nothing is known about how mood state influences this higher-order cognitive process. Accordingly, we induced positive, neutral and negative mood states to test how different mood states modulate subsequent reality monitoring performance. Our findings indicate that mood affected reality monitoring performance in HC and SZ participants in both similar and dissociable ways. Only a positive mood facilitated task performance in Healthy Control (HC) subjects, whereas a negative mood facilitated task performance in SZ subjects. Yet, when both HC and SZ participants were in a positive mood, they recruited medial prefrontal cortex (mPFC) to bias better subsequent self-generated item identification, despite the fact that mPFC signal was reduced in SZ participants. Additionally, in SZ subjects, negative mood states also modulated left and right dorsal mPFC signal to bias better externally-presented item identification. Together our findings reveal that although the mPFC is hypoactive in SZ participants, mPFC signal plays a functional role in mood-cognition interactions during both positive and negative mood states to facilitate subsequent reality monitoring decision-making.

Finding the imposter: brain connectivity of lesions causing delusional misidentifications

SEE MCKAY AND FURL DOI101093/AWW323 FOR A SCIENTIFIC COMMENTARY ON THIS ARTICLE: Focal brain injury can sometimes lead to bizarre symptoms, such as the delusion that a family member has been replaced by an imposter (Capgras syndrome). How a single brain lesion could cause such a complex disorder is unclear, leading many to speculate that concurrent delirium, psychiatric disease, dementia, or a second lesion is required. Here we instead propose that Capgras and other delusional misidentification syndromes arise from single lesions at unique locations within the human brain connectome. This hypothesis is motivated by evidence that symptoms emerge from sites functionally connected to a lesion location, not just the lesion location itself. First, 17 cases of lesion-induced delusional misidentifications were identified and lesion locations were mapped to a common brain atlas. Second, lesion network mapping was used to identify brain regions functionally connected to the lesion locations. Third, regions involved in familiarity perception and belief evaluation, two processes thought to be abnormal in delusional misidentifications, were identified using meta-analyses of previous functional magnetic resonance imaging studies. We found that all 17 lesion locations were functionally connected to the left retrosplenial cortex, the region most activated in functional magnetic resonance imaging studies of familiarity. Similarly, 16 of 17 lesion locations were functionally connected to the right frontal cortex, the region most activated in functional magnetic resonance imaging studies of expectation violation, a component of belief evaluation. This connectivity pattern was highly specific for delusional misidentifications compared to four other lesion-induced neurological syndromes (P < 0.0001). Finally, 15 lesions causing other types of delusions were connected to expectation violation (P < 0.0001) but not familiarity regions, demonstrating specificity for delusion content. Our results provide potential neuroanatomical correlates for impaired familiarity perception and belief evaluation in patients with delusional misidentifications. More generally, we demonstrate a mechanism by which a single lesion can cause a complex neuropsychiatric syndrome based on that lesion's unique pattern of functional connectivity, without the need for pre-existing or hidden pathology.

FMRI activity during associative encoding is correlated with cardiorespiratory fitness and source memory performance in older adults

Older adults (OA), relative to young adults (YA), exhibit age-related alterations in functional Magnetic Resonance Imaging (fMRI) activity during associative encoding, which contributes to deficits in source memory. Yet, there are remarkable individual differences in brain health and memory performance among OA. Cardiorespiratory fitness (CRF) is one individual difference factor that may attenuate brain aging, and thereby contribute to enhanced source memory in OA. To examine this possibility, 26 OA and 31 YA completed a treadmill-based exercise test to evaluate CRF (peak VO₂) and fMRI to examine brain activation during a face-name associative encoding task. Our results indicated that in OA, peak VO₂ was positively associated with fMRI activity during associative encoding in multiple regions including bilateral prefrontal cortex, medial frontal cortex, bilateral thalamus and left hippocampus. Next, a conjunction analysis was conducted to assess whether CRF influenced age-related differences in fMRI activation. We classified OA as high or low CRF and compared their activation to YA. High fit OA (HFOA) showed fMRI activation more similar to YA than low fit OA (LFOA) (i.e., reduced age-related differences) in multiple regions including thalamus, posterior and prefrontal cortex. Conversely, in other regions, primarily in prefrontal cortex, HFOA, but not LFOA, demonstrated greater activation than YA (i.e., increased age-related differences). Further, fMRI activity in these brain regions was positively associated with source memory among OA, with a mediation model demonstrating that associative encoding activation in medial frontal cortex indirectly influenced the relationship between peak VO₂ and subsequent source memory performance. These results indicate that CRF may contribute to neuroplasticity among OA, reducing age-related differences in some brain regions, consistent with the brain maintenance hypothesis, but accentuating age-differences in other regions, consistent with the brain compensation hypothesis.

Visual Imagery and False Memory for Pictures: A Functional Magnetic Resonance Imaging Study in Healthy Participants

Background

Visual mental imagery might be critical in the ability to discriminate imagined from perceived pictures. Our aim was to investigate the neural bases of this specific type of reality-monitoring process in individuals with high visual imagery abilities.

Methods

A reality-monitoring task was administered to twenty-six healthy participants using functional magnetic resonance imaging. During the encoding phase, 45 words designating common items, and 45 pictures of other common items, were presented in random order. During the recall phase, participants were required to remember whether a picture of the item had been presented, or only a word. Two subgroups of participants with a propensity for high vs. low visual imagery were contrasted.

Results

Activation of the amygdala, left inferior occipital gyrus, insula, and precuneus were observed when high visual imagers encoded words later remembered as pictures. At the recall phase, these same participants activated the middle frontal gyrus and inferior and superior parietal lobes when erroneously remembering pictures.

Conclusions

The formation of visual mental images might activate visual brain areas as well as structures involved in emotional processing. High visual imagers demonstrate increased activation of a fronto-parietal source-monitoring network that enables distinction between imagined and perceived pictures.

The impact of level of education on age-related deficits in associative memory: Behavioral and neuropsychological perspectives

Older adults have difficulty forming associations and binding distinct item components despite mostly preserved item memory potentially because they rely on more automatic, rather than strategic, processing when attempting to form, store, and retrieve associations from memory. An intriguing possibility is that older adults with greater access to strategic processes (e.g., those with a high level of education) may be less susceptible to age-related associative memory deficits. Two experiments assessed the degree to which a high level of education provides an effective dose of cognitive reserve (CR), potentially preserving associative memory. Standard younger and older adults' item and associative memory performance was compared to older adults who had attained a high level of education (mostly doctoral degrees). In both experiments (Experiment 1: person-action pairs; Experiment 2: unrelated word pairs), consistent evidence was found that older adults, regardless of the level of education, exhibited an age-related associative memory deficit relative to younger adults. Interestingly, neuropsychological assessment of both older adult groups revealed greater frontal lobe, but not enhanced medial temporal lobe, functioning in the highly educated. As such, although the highly educated older adults exhibited greater frontal lobe functioning than the standard older adults, this did not aid in the reduction of the age-related associative memory deficit.