Effortful retrieval of semantic memories induces forgetting of related negative and neutral episodic memories

Retrieval-induced forgetting (RIF) experiments show that the act of retrieving some recently encoded items from a given conceptual category leads to greater forgetting of competing items from that same category. However, RIF studies using emotional stimuli have produced mixed results, perhaps due to the reinstatement of arousal or negative affect during retrieval practice. To induce forgetting of negative episodic memories more indirectly, we examined if retrieving neutral semantic memories leads to RIF of related negative memories. In two experiments, participants studied eight categorized lists comprised of an equal number of negative and neutral words (Experiment 1) or neutral words preceded by neutral or negative images (Experiment 2). To avoid re-exposing individuals to negative material during retrieval practice, participants then performed a semantic memory retrieval task in which they generated (i.e., completed word-stems for) new neutral words from half of the studied categories. We found that semantic retrieval, or word generation, induced forgetting of recently studied words irrespective of their emotional valence or original emotional context. Additionally, across both experiments, less successful word generation was associated with stronger RIF effects. In Experiment 2, the magnitude of RIF was also correlated with higher subjective ratings of retrieval effort during word generation. Together, these results suggest that even when retrieving neutral semantic memories, effortful retrieval may enhance inhibitory processes that lead to forgetting of both neutral and negative episodic memories.

Neural manifestation of L2 novel concept acquisition from multi-contexts via both episodic memory and semantic memory systems

This study aims to examine the process of L2 novel word learning through the combination of episodic and semantic memory, and how the process differs between the formation of thematic and taxonomic relations. The major approach adopted was observing the neural effects of word learning, which is manifested in the N400 from event-related potentials (ERPs). Eighty-eight participants were recruited for the experiment. In the learning session, L2 contextual discourses related to novel words were learned by participants. In the testing session, discourses embedded with incongruous and congruous novel words in the final position were used for participants to judge the congruency which affected the N400 neural activity. The results showed that both recurrent and new-theme discourses elicited significant N400 effects, while taxonomic sentences did not. These results confirmed the formation of episodic and semantic memory during L2 new word learning, in which semantic memory was mainly supported by thematic relations.

Extra-hippocampal contributions to pattern separation

Pattern separation, or the process by which highly similar stimuli or experiences in memory are represented by non-overlapping neural ensembles, has typically been ascribed to processes supported by the hippocampus. Converging evidence from a wide range of studies, however, suggests that pattern separation is a multistage process supported by a network of brain regions. Based on this evidence, considered together with related findings from the interference resolution literature, we propose the 'cortico-hippocampal pattern separation' (CHiPS) framework, which asserts that brain regions involved in cognitive control play a significant role in pattern separation. Particularly, these regions may contribute to pattern separation by (1) resolving interference in sensory regions that project to the hippocampus, thus regulating its cortical input, or (2) directly modulating hippocampal processes in accordance with task demands. Considering recent interest in how hippocampal operations are modulated by goal states likely represented and regulated by extra-hippocampal regions, we argue that pattern separation is similarly supported by neocortical-hippocampal interactions.

Mapping the long-term delayed recall-based cortex-hippocampus network constrained by the structural and functional connectome: a case-control multimodal MRI study

Background

Connectome mapping may reveal new treatment targets for patients with neurological and psychiatric diseases. However, the long-term delayed recall based-network with structural and functional connectome is still largely unknown. Our objectives were to (1) identify the long-term delayed recall-based cortex-hippocampus network with structural and functional connectome and (2) investigate its relationships with various cognitive functions, age, and activities of daily living.

Methods

This case-control study enrolled 131 subjects (73 amnestic mild cognitive impairment [aMCI] patients and 58 age- and education-matched healthy controls [HCs]). All subjects completed a neuropsychological battery, activities of daily living assessment, and multimodal magnetic resonance imaging. Nodes of the cortical-hippocampal network related to long-term delayed recall were identified by probabilistic fiber tracking and functional connectivity (FC) analysis. Then, the main and interaction effects of the network on cognitive functions were assessed by a generalized linear model. Finally, the moderating effects of the network on the relationships between long-term delayed recall and clinical features were analyzed by multiple regression and Hayes’ bootstrap method. All the effects of cortex-hippocampus network were analyzed at the connectivity and network levels.

Results

The result of a generalized linear model showed that the bilateral hippocampus, left dorsolateral superior frontal gyrus, right supplementary motor area, left lingual gyrus, left superior occipital gyrus, left superior parietal gyrus, left precuneus, and right temporal pole (superior temporal gyrus) are the left and right cortex-hippocampus network nodes related to long-term delayed recall (P < 0.05). Significant interaction effects were found between the Auditory Verbal Learning Test Part 5 (AVLT 5) scores and global properties of the left cortex-hippocampus network [hierarchy, clustering coefficient, characteristic path length, global efficiency, local efficiency, Sigma and synchronization (P < 0.05 Bonferroni corrected)]. Significant interaction effects were found between the general cognitive function/executive function/language and global properties of the left cortex-hippocampus network [Sigma and synchronization (P < 0.05 Bonferroni corrected)].

Conclusion

This study introduces a novel symptom-based network and describes relationships among cognitive functions, brain function, and age. The cortex–hippocampus network constrained by the structural and functional connectome is closely related to long-term delayed recall.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-023-01197-7.

Are the inhibitory and faciliatory effects during retrieval of semantically related items present in amnestic mild cognitive impairment?

Prefrontal functions subserve inhibition control for retrieval of semantically related items inducing forgetting 19 a-MCI patients and 29 controls underwent neuropsychological evaluation and retrieval-practice paradigm (RPP) to estimate baseline remember (BR), retrieval-induced facilitation (FAC) and retrieval-induced forgetting (RIF). A-MCI patients underwent also 3 T-MRI to assess relationship between regional grey matter (rGM) volumes and RPP indexes Behaviourally, RIF and FAC were both observed controls, while RIF only was observed in a-MCI patients. In patients but not in controls, RIF was associated with cognitive efficiency and FAC with memory performance. Patients showed also associations between BR and rGM volumes in the precuneus, no association was found between rGM volumes and RIF and FAC. A-MCI patients did not benefit from repeated practice during retrieval of studied items, which is likely due to their memory disorder. In contrast, patient cognitive efficiency would drive retrieval suppression of interfering stimuli.

Episodic Events as Spatiotemporal Memory: The Sequence of Information in the Episodic Buffer of Working Memory for Language Comprehension

Memory and language are the two higher-order cognitive abilities intertwined for communication and other cognitive skills. Memory is the storage capacity of all the information we perceive. Where the sensory memory perceives the stimuli, the working memory actively stores the information and passes it to the long-term memory. However, there is a question that how is the continuous perception of stimuli transformed into meaningful information and organized for proper execution and retrieval from the memory? This paper focuses on the episodic memory that perceives information that is spatial and temporal based on our everyday experiences. Though the spatiotemporal information we receive is continuous; the episodic memory arranges the information as to episodes in the working memory before the information is stored for a longer period. The episodic buffer is one of the components of the working memory model which holds the episodic memory that is organized concerning time. To this point, the paper tries to understand the working of the episodic buffer in maintaining the episodic memory and also about the process of episodic events into meaningful units. Further, the paper also concentrates on the hippocampus which is considered to be the location of the episodic buffer.

Targeted memory reactivation during sleep can induce forgetting of overlapping memories

Memory reactivation during sleep can shape new memories into a long-term form. Reactivation of memories can be induced via the delivery of auditory cues during sleep. Although this targeted memory reactivation (TMR) approach can strengthen newly acquired memories, research has tended to focus on single associative memories. It is less clear how TMR affects retention for overlapping associative memories. This is critical, given that repeated retrieval of overlapping associations during wake can lead to forgetting, a phenomenon known as retrieval-induced forgetting (RIF). We asked whether a similar pattern of forgetting occurs when TMR is used to cue reactivation of overlapping pairwise associations during sleep. Participants learned overlapping pairs—learned separately, interleaved with other unrelated pairs. During sleep, we cued a subset of overlapping pairs using TMR. While TMR increased retention for the first encoded pairs, memory decreased for the second encoded pairs. This pattern of retention was only present for pairs not tested prior to sleep. The results suggest that TMR can lead to forgetting, an effect similar to RIF during wake. However, this effect did not extend to memories that had been strengthened via retrieval prior to sleep. We therefore provide evidence for a reactivation-induced forgetting effect during sleep.

Simple contextual cueing prevents retroactive interference in short-term perceptual training of orientation detection tasks

Perceptual training of multiple tasks suffers from interference between the trained tasks. Here, we conducted five psychophysical experiments with separate groups of participants to investigate the possibility of preventing the interference in short-term perceptual training. We trained the participants to detect two orientations of Gabor stimuli in two adjacent days at the same retinal location and examined the interference of training effects between the two orientations. The results showed significant retroactive interference from the second orientation to the first orientation (Experiment 1 and Experiment 2). Introducing a 6-h interval between the pre-test and training of the second orientation did not eliminate the interference effect, excluding the interpretation of disrupted reconsolidation as the pre-test of the second orientation may reactivate and destabilize the representation of the first orientation (Experiment 3). Finally, the training of the two orientations was accompanied by fixations in two colors, each serving as a contextual cue for one orientation. The results showed that the retroactive interference was not evident if the participants passively perceived contextual cues during the training and test sessions (Experiment 4). Importantly, this facilitation effect could be observed if the contextual cues appeared only during the training, demonstrating the robustness of the effect (Experiment 5). Our findings suggest that the retroactive interference effect in short-term perceptual training of orientation detection tasks was likely the result of higher-level factors such as shared contextual cues embedded in the tasks. The efficiency of multiple perceptual trainings could be facilitated by associating the trained tasks with different contextual cues.

Retrieval-induced forgetting in children and adolescents with and without obesity

BACKGROUND/OBJECTIVES

Previous research indicates that youth with obesity exhibit deficits in executive functioning (EF), which often take the form of impaired response inhibition. One aspect of EF not previously studied in obesity is the adaptive process known as retrieval-induced forgetting (RIF), the suppression/inhibition of intrusive or non-target items by the retrieval of specific items from memory. The present study investigated if child or adolescent obesity disrupts the ability to inhibit retrieval of intrusive memories.

SUBJECTS/METHODS

We compared the manifestation of RIF in children (ages 8-12) and adolescents (ages 13-18) as a function of their weight status and sex. We also evaluated the effects of these variables on simple recall of items from episodic memory under conditions where competition from intrusive items was reduced.

RESULTS

Children with obesity did not demonstrate significant RIF, whereas RIF was exhibited by preteens without obesity and by teenage participants with- and without obesity (Weight Status × Age Group interaction p = 0.028). This pattern of results did not differ as a function of sex for either age group. No differences in episodic memory were found. Additional analyses using Age as continuous covariate (and not as a nominal group) comparing participants who exhibited RIF with those who did not, found that the no RIF group consumed fast-food meals more frequently (p = 0.024) and had higher percentages of total body adiposity and android fat compared to the RIF group (p's < 0.05).

CONCLUSIONS

The findings expand what is known about the effects of childhood obesity on cognitive functioning, identify impaired RIF with specific behavioral and dietary factors and increased adiposity, and suggest the possibility that impairments in the ability to inhibit intrusive memories of food and eating may contribute to poor early-life weight control.

The Role of Executive Functions in Item Recognition and Temporal Order Memory Development

Item recognition and temporal order memory follow different developmental trajectories during middle childhood, with item recognition performance stabilizing and temporal order memory performance continuing to improve. We investigated the potential unique role of individual executive functions on item recognition and temporal order memory during this critical development period. Our results replicate and expand on previous findings, suggesting that executive functions, specifically inhibitory control and working memory, may be more crucial for successful temporal order memory than for item recognition during middle childhood.

Rapid neural reorganization during retrieval practice predicts subsequent long-term retention and false memory

Active retrieval can alter the strength and content of a memory, yielding either enhanced or distorted subsequent recall. However, how consolidation influences these retrieval-induced seemingly contradictory outcomes remains unknown. Here we show that rapid neural reorganization over an eight-run retrieval practice predicted subsequent recall. Retrieval practice boosted memory retention following a 24-hour (long-term) but not 30-minute delay, and increased false memory at both delays. Long-term retention gains were predicted by multi-voxel representation distinctiveness in the posterior parietal cortex (PPC) that increased progressively over retrieval practice. False memory was predicted by unstable representation distinctiveness in the medial temporal lobe (MTL). Retrieval practice enhanced the efficiency of memory-related brain networks, through building up PPC and MTL connections with the ventrolateral and dorsolateral prefrontal cortex that predicted long-term retention gains and false memory, respectively. Our findings indicate that retrieval-induced rapid neural reorganization together with consecutive consolidation fosters long-term retention and false memories via distinct pathways.

Intrinsic connectivity of left ventrolateral prefrontal cortex predicts individual differences in controlled semantic retrieval

Control processes allow us to constrain the retrieval of semantic information from long-term memory so that it is appropriate for the task or context. Control demands are influenced by the strength of the target information itself and by the circumstances in which it is retrieved, with more control needed when relatively weak aspects of knowledge are required and after the sustained retrieval of related concepts. To investigate the neurocognitive basis of individual differences in these aspects of semantic control, we used resting-state fMRI to characterise the intrinsic connectivity of left ventrolateral prefrontal cortex (VLPFC), implicated in controlled retrieval, and examined associations on a paced serial semantic task, in which participants were asked to detect category members amongst distractors. This task manipulated both the strength of target associations and the requirement to sustain retrieval within a narrow semantic category over time. We found that individuals with stronger connectivity between VLPFC and medial prefrontal cortex within the default mode network (DMN) showed better retrieval of strong associations (which are thought to be recalled more automatically). Stronger connectivity between the same VLPFC seed and another DMN region in medial parietal cortex was associated with larger declines in retrieval over the course of the category. In contrast, participants with stronger connectivity between VLPFC and cognitive control regions within the ventral attention network (VAN) had better controlled retrieval of weak associations and were better able to sustain their comprehension throughout the category. These effects overlapped in left insular cortex within the VAN, indicating that a common pattern of connectivity is associated with different aspects of controlled semantic retrieval induced by both the structure of long-term knowledge and the sustained retrieval of related information.

The Mechanisms Underlying Interference and Inhibition: A Review of Current Behavioral and Neuroimaging Research

The memory literature has identified interference and inhibition as two major sources of forgetting. While interference is generally considered to be a passive cause of forgetting arising from exposure to additional information that impedes subsequent recall of target information, inhibition concerns a more active and goal-directed cause of forgetting that can be achieved intentionally. Over the past 25 years, our knowledge of the neural mechanisms underlying both interference-induced and inhibition-induced forgetting has expanded substantially. The present paper gives a critical overview of this research, pointing out empirical gaps in the current work and providing suggestions for future studies.

Support for an inhibitory model of word retrieval

Word retrieval may involve an inhibitory process in which a target word is activated and related words are suppressed. In the current functional magnetic resonance imaging (fMRI) study, we examined the inhibition of language processing cortex by the left dorsolateral prefrontal cortex (DLPFC) during word retrieval using an anagram-solving paradigm. Participants were presented with a distractor that was read aloud followed by a to-be-solved anagram. Distractor types were defined relative to orthographic overlap with the subsequent anagram solution and included related words with one letter different (e.g., "gripe" for the anagram of "price"), related pseudo-words, and unrelated words (i.e., all five letters were different). The anagram solution reaction time was slower in both the related word and related pseudo-word distractor conditions as compared to the unrelated word distractor condition, which can be attributed to greater inhibition following related distractors. The contrast of related words and unrelated words produced one activation in the left DLPFC, a region that has been associated with memory inhibition. To identify the regions that were negatively correlated with activity in the left DLPFC for related distractors, we conducted a functional connectivity analysis between this left DLPFC region and the rest of the brain. We found negatively correlated activity between the DLPFC and language processing cortex for the related word distractor condition (and the related pseudo-word distractor condition at a relaxed threshold). These findings suggest that that the left DLPFC may inhibit related word (and pseudo-word) representations in language processing cortex.

A Lifespan Model of Interference Resolution and Inhibitory Control: Risk for Depression and Changes with Illness Progression

The cognitive processes involved in inhibitory control accuracy (IC) and interference resolution speed (IR) or broadly - inhibition - are discussed in this review, and both are described within the context of a lifespan model of mood disorders. Inhibitory control (IC) is a binary outcome (success or no for response selection and inhibition of unwanted responses) for any given event that is influenced to an extent by IR. IR refers to the process of inhibition, which can be manipulated by task design in earlier and later stages through use of distractors and timing, and manipulation of individual differences in response proclivity. We describe the development of these two processes across the lifespan, noting factors that influence this development (e.g., environment, adversity and stress) as well as inherent difficulties in assessing IC/IR prior to adulthood (e.g., cross-informant reports). We use mood disorders as an illustrative example of how this multidimensional construct can be informative to state, trait, vulnerability and neuroprogression of disease. We present aggregated data across numerous studies and methodologies to examine the lifelong development and degradation of this subconstruct of executive function, particularly in mood disorders. We highlight the challenges in identifying and measuring IC/IR in late life, including specificity to complex, comorbid disease processes. Finally, we discuss some potential avenues for treatment and accommodation of these difficulties across the lifespan, including newer treatments using cognitive remediation training and neuromodulation.

Retrieval intentionality and forgetting: How retention time and cue distinctiveness affect involuntary and voluntary retrieval of episodic memories

Forgetting, understood as a measurable reduction in memory accessibility over time, has been studied extensively in episodic memory for more than 130 years. However, this research has typically focused on voluntary memory-that is, information retrieved intentionally. Few studies have examined forgetting in relation to involuntary memories-that is, memories coming to mind spontaneously with no preceding attempt at retrieval. The purpose of the present studies was to investigate the effects of cue distinctiveness and the passage of time on the accessibility of involuntary and voluntary memories for pictures of scenes. For both types of retrieval, we examined the frequency of correct memories after a few minutes, one day, and seven days; in Study 2, we also examined frequency after three days. Across both studies and both types of retrieval, distinct cues yielded better memory access than nondistinct cues, and memory frequency dropped systematically with increased retention time. At the shortest retention interval, voluntary retrieval led to greater memory access than involuntary retrieval, but after one week, this advantage had disappeared. The findings suggest that memories for events become more cue-dependent over time, which limits the beneficial effects of strategic search associated with voluntary retrieval at longer delays.

Consistently inconsistent: Multimodal episodic deficits in semantic aphasia

Semantic Aphasia (SA) patients have difficulty accessing semantic knowledge in both verbal and non-verbal tasks appropriately for the current context. Automatically activated semantic knowledge overwhelms the system, because it is no longer able to inhibit interference from dominant meanings in order to select weaker alternatives. Episodic memory, like semantic memory, requires control to select relevant memories amongst competing episodes. For example, our memory for what we ate for breakfast last Saturday is affected by competition from numerous other breakfast meals eaten on other days. Where one is unable to guide retrieval, we may rely on automatically activated knowledge about "breakfast foods", and therefore experience false memories. Brain systems that support semantic control are also implicated in episodic control, and therefore deficits in semantic control are likely to cause more widespread problems. Despite this, nearly all research to date focuses on semantic performance alone. This study explored the impact of this semantic impairment on episodic recall. We used a verbal and non-verbal episodic memory task: participants remembered nursery rhymes in the verbal condition and logos and their associated products in the visual condition (e.g. bowl of cereal and coco-pops). For both tasks, we manipulated a) congruency with pre-existing knowledge (e.g. expectancy of trials: baa baa blackbuild - instead of sheep) and b) whether these trial types were blocked by congruency or mixed, as well as (c) distractor strength. If SA patients experience overwhelming automatic activation, they should find incongruent items more difficult to suppress, particularly when presented in an unpredictable task format. A total of 13 SA patients were compared to 33 controls across three experiments. In line with our predictions, SA patients found it more difficult to retrieve episodic memories which were in conflict with pre-existing semantic knowledge. This was true across modalities. Moreover, these deficits were accentuated when the congruency was presented in a mixed fashion, and so unpredictable across trials. Evidence of these episodic control impairments in SA cases supports the idea of a shared mechanism for semantic and episodic memory control.

Does retrieving a memory insulate it against memory inhibition? A retroactive interference study

Several recent studies suggest that an initial retrieval attempt imbues retrieved memories with special resilience against future interference and other forgetting mechanisms. Here we report two experiments examining whether memories established through initial retrieval remain subject to retrieval-induced forgetting. Using a version of a classical retroactive interference design, we trained participants on a list of A-B pairs via anticipation - constituting a form of retrieval practice. After next training participants on interfering A-C pairs, they performed 0-12 additional A-C anticipation trials. Because these trials required retrieval of A-C pairs, they should function similarly to retrieval practice in paradigms establishing retrieval-induced forgetting. We observed robust evidence that retroactive interference generalises to final memory tests involving novel, independent memory probes. Moreover, in contrast to practising retrieval of A-C items, their extra study failed to induce cue-independent forgetting of the original B items. Together, these findings substantiate the role of retrieval-related inhibitory processes in a traditional retroactive interference design. Importantly, they indicate that an initial retrieval attempt on a competitor does not abolish retrieval-induced forgetting, at least not in the context of this classic design. Although such an attempt may protect against inhibition in some circumstances, the nature of those circumstances remains to be understood.

Theta oscillations show impaired interference detection in older adults during selective memory retrieval

Seemingly effortless tasks, such as recognizing faces and retrieving names, become harder as we age. Such difficulties may be due to the competition generated in memory by irrelevant information that comes to mind when trying to recall a specific face or name. It is unknown, however, whether age-related struggles in retrieving these representations stem from an inability to detect competition in the first place, or from being unable to suppress competing information once interference is detected. To investigate this, we used the retrieval practice paradigm, shown to elicit memory interference, while recording electrophysiological activity in young and older adults. In two experiments, young participants showed Retrieval-Induced Forgetting (RIF), reflecting the suppression of competing information, whereas older adults did not. Neurally, mid-frontal theta power (~4-8 Hz) during the first retrieval cycle, a proxy for interference detection, increased in young compared to older adults, indicating older adults were less capable of detecting interference. Moreover, while theta power was reduced across practice cycles in younger adults, a measure of interference resolution, older adults did not show such a reduction. Thus, in contrast with younger adults, the lack of an early interference detection signal rendered older adults unable to recruit memory selection mechanisms, eliminating RIF.

Efficacy and mechanisms of non-invasive brain stimulation to enhance exposure therapy: A review

Though cognitive behavioral techniques are generally effective in the treatment of anxiety disorders, some people fail to benefit from exposure therapy or experience a return of fear after terminating exposure therapy. The burgeoning field of non-invasive brain stimulation provides a potential method of augmenting exposure therapy so that it is more effective. Successful exposure therapy is hypothesized to occur due to inhibition, and research suggests that brain stimulation can alter inhibitory learning and related processes. As such, one can reasonably posit that brain stimulation could be used to test the inhibitory learning theory of exposure therapy and to increase the efficacy of exposure therapy by inducing stronger inhibitory learning during exposures. Four known studies that pair brain stimulation with exposure therapy have yielded promising preliminary evidence in support of the therapeutic use of brain stimulation. In this review we describe research illustrating the mechanisms and efficacy of non-invasive brain stimulation to enhance the understanding of and outcomes produced by exposure therapy.

Shared processes resolve competition within and between episodic and semantic memory: Evidence from patients with LIFG lesions

Semantic cognition is supported by two interactive components: semantic representations and mechanisms that regulate retrieval (cf. 'semantic control'). Neuropsychological studies have revealed a clear dissociation between semantic and episodic memory. This study explores if the same dissociation holds for control processes that act on episodic and semantic memory, or whether both types of long-term memory are supported by the same executive mechanisms. We addressed this question in a case-series of semantic aphasic patients who had difficulty retrieving both verbal and non-verbal conceptual information in an appropriate fashion following infarcts to left inferior frontal gyrus (LIFG). We observed parallel deficits in semantic and episodic memory: (i) the patients' difficulties extended beyond verbal materials to include picture tasks in both domains; (ii) both types of retrieval benefitted from cues designed to reduce the need for internal constraint; (iii) there was little impairment of both semantic and episodic tasks when control demands were minimised; (iv) there were similar effects of distractors across tasks. Episodic retrieval was highly susceptible to false memories elicited by semantically-related distractors, and confidence was inappropriately high in these circumstances. Semantic judgements were also prone to contamination from recent events. These findings demonstrate that patients with deregulated semantic cognition have comparable deficits in episodic retrieval. The results are consistent with a role for LIFG in resolving competition within both episodic and semantic memory, and also in biasing cognition towards task-relevant memory stores when episodic and semantic representations do not promote the same response.

Long-Term Visual Memory and Its Role in Learning Suppression

Long-term memory is a core aspect of human learning that permits a wide range of skills and behaviors often important for survival. While this core ability has been broadly observed for procedural and declarative memory, whether similar mechanisms subserve basic sensory or perceptual processes remains unclear. Here, we use a visual learning paradigm to show that training humans to search for common visual features in the environment leads to a persistent improvement in performance over consecutive days but, surprisingly, suppresses the subsequent ability to learn similar visual features. This suppression is reversed if the memory is prevented from consolidating, while still permitting the ability to learn multiple visual features simultaneously. These findings reveal a memory mechanism that may enable salient sensory patterns to persist in memory over prolonged durations, but which also functions to prevent false-positive detection by proactively suppressing new learning.

Single-Neuron Representation of Memory Strength and Recognition Confidence in Left Human Posterior Parietal Cortex

The human posterior parietal cortex (PPC) is thought to contribute to memory retrieval, but little is known about its specific role. We recorded single PPC neurons of two human tetraplegic subjects implanted with microelectrode arrays, who performed a recognition memory task. We found two groups of neurons that signaled memory-based choices. Memory-selective neurons preferred either novel or familiar stimuli, scaled their response as a function of confidence, and signaled subjective choices regardless of truth. Confidence-selective neurons signaled confidence regardless of stimulus familiarity. Memory-selective signals appeared 553 ms after stimulus onset, but before action onset. Neurons also encoded spoken numbers, but these number-tuned neurons did not carry recognition signals. Together, this functional separation reveals action-independent coding of declarative memory-based familiarity and confidence of choices in human PPC. These data suggest that, in addition to sensory-motor integration, a function of human PPC is to utilize memory signals to make choices.

Comparing the testing effect under blocked and mixed practice: The mnemonic benefits of retrieval practice are not affected by practice format

The act of retrieving information modifies memory in critical ways. In particular, testing-effect studies have demonstrated that retrieval practice (compared to restudy or to no testing) benefits long-term retention and protects from retroactive interference. Although such testing effects have previously been demonstrated in both between- and within-subjects manipulations of retrieval practice, it is less clear whether one or the other testing format is most beneficial on a final test. In two paired-associate learning experiments conducted under typical testing-effect conditions, we manipulated restudy and test trials using either blocked or mixed practice conditions while equating other factors. Retrieval-practice and restudy trials were presented either separately in different blocks (blocked practice) or randomly intermixed (mixed practice). In Experiment 1, recall was assessed after short and long delay intervals; in Experiment 2, the final memory test occurred after a short delay, but with or without an interfering activity before the final test. In both experiments, typical testing effects emerged, and critically, they were found to be unaffected by practice format. These results support the conclusion that testing effects are robust and emerge to equal extents in both blocked and mixed designs. The generality of testing effects further encourages the application of retrieval practice as a memory enhancer in a variety of contexts, including education.

Reversing the testing effect by feedback: Behavioral and electrophysiological evidence

The testing effect refers to the finding that retrieval practice of previously studied information enhances its long-term retention more than restudy practice does. Recent work showed that the testing effect can be dramatically reversed when feedback is provided to participants during final recall testing (Storm, Friedman, Murayama, & Bjork, 2014). Following this prior work, in this study, we examined the reversal of the testing effect by investigating oscillatory brain activity during final recall testing. Twenty-six healthy participants learned cue-target word pairs and underwent a practice phase in which half of the items were retrieval practiced and half were restudy practiced. Two days later, two cued recall tests were administered, and immediate feedback was provided to participants in Test 1. Behavioral results replicated the prior work by showing a testing effect in Test 1, but a reversed testing effect in Test 2. Extending the prior work, EEG results revealed a feedback-related effect in alpha/lower-beta and retrieval-related effects in slow and fast theta power, with practice condition modulating the fast theta power effect for items that were not recalled in Test 1. The results indicate that the reversed testing effect can arise without differential strengthening of restudied and retrieval-practiced items via feedback learning. Theoretical implications of the findings, in particular with respect to the distribution-based bifurcation model of testing effects (Kornell, Bjork, & Garcia, 2011), are discussed.

Control over interfering memories in eating disorders

INTRODUCTION

Recent studies have suggested that patients suffering from either anorexia nervosa (AN) or bulimia nervosa (BN) exhibit abnormal performance in the ability to control cognitive interference in response selection.

METHOD

We assessed the status of cognitive control in episodic memory by addressing the ability to inhibit interfering memories. To this end, we used the retrieval-practice paradigm, which allows for measuring both the beneficial and the detrimental effects of memory practice. The latter phenomenon, known as retrieval-induced forgetting (RIF), is thought to reflect an adaptive inhibitory mechanism aimed at reducing competition in memory retrieval. Twenty-seven healthy controls and 27 patients suffering from eating disorders (either AN or BN) performed a retrieval-practice paradigm and a control task addressing general reactivity and filled a self-report questionnaire on impulsivity.

RESULTS

No differences between patients and healthy controls were observed for the beneficial effects of practice. The same pattern also emerged for RIF. However, when patients with AN and BN were analyzed separately, a clear dissociation emerged: patients with AN displayed no hint of RIF, whereas patients with BN showed an intact memory suppression performance. No group differences emerged in the control task.

CONCLUSIONS

Our findings suggest a specific impairment in the ability to suppress interfering memories in patients with AN, thus extending current evidence of cognitive control deficits in AN to episodic memory.

Retrieval-induced versus context-induced forgetting: Does retrieval-induced forgetting depend on context shifts?

Retrieval-induced forgetting (RIF) is the observation that retrieval of target information causes forgetting of related nontarget information. A number of accounts of this phenomenon have been proposed, including a context-shift-based account (Jonker, Seli, & Macleod, 2013). This account proposes that RIF occurs as a result of the context shift from study to retrieval practice, provided there is little context shift between retrieval practice and test phases. We tested both claims put forth by this context account. In Experiment 1, we degraded the context shift between study and retrieval practice by implementing a generative study condition that was highly similar to retrieval practice. We observed no degradation of RIF for these generated exemplars relative to a conventional study control. In Experiment 2, we conceptually replicated the finding of RIF following generative study, and tested whether context differences between each of the three phases affected the size of RIF. Our findings were again contrary to the predictions of the context account. Conjointly, the 2 experiments refute arguments about the potential inadequacy of our context shifts that could be used to explain either result alone. Overall, our results are most consistent with an inhibitory account of RIF (e.g., Anderson, 2003).

Retrieval-practice task affects relationship between working memory capacity and retrieval-induced forgetting

Retrieving a subset of items from memory can cause forgetting of other items in memory, a phenomenon referred to as retrieval-induced forgetting (RIF). Individuals who exhibit greater amounts of RIF have been shown to also exhibit superior working memory capacity (WMC) and faster stop-signal reaction times (SSRTs), results which have been interpreted as suggesting that RIF reflects an inhibitory process that is mediated by the processes of executive control. Across four experiments, we sought to further elucidate this issue by manipulating the way in which participants retrieved items during retrieval practice and examining how the resulting effects of forgetting correlated with WMC (Experiments 1-3) and SSRT (Experiment 4). Significant correlations were observed when participants retrieved items from an earlier study phase (within-list retrieval practice), but not when participants generated items from semantic memory (extra-list retrieval practice). These results provide important new insight into the role of executive-control processes in RIF.

Face naming and retrieval inhibition in old and very old age

BACKGROUND/STUDY CONTEXT: Aging has traditionally been related to impairments in proper name retrieval. This study analyzed the possible role of the Inhibitory Deficit Hypothesis in explaining face naming impairments during aging. The dynamics of inhibition have been thoroughly studied by the retrieval-practice paradigm (Anderson, Bjork, & Bjork, 1994, Journal of Experimental Psychology: Learning, Memory, and Cognition, 20, 1063-1087) and its aftereffect, the retrieval-induced forgetting effect.

METHODS

A version of the retrieval-practice paradigm was employed: younger-old (YO; mean age = 66.40, SD = 3.94) and older-old (OO; mean age = 80.94, SD = 4.53) adults were asked to repeatedly name faces of categorically related famous people.

RESULTS

Retrieval-induced forgetting for names was observed in the YO group but not in the OO group.

CONCLUSION

These findings indicate that whereas the YO adults had enough resources to inhibit intrusive names, OO adults were not able to suppress competing names, supporting the proposal of the Inhibitory Deficit Hypothesis at older ages.

Retrieval induces adaptive forgetting of competing memories via cortical pattern suppression

Remembering a past experience can, surprisingly, cause forgetting. Forgetting arises when other competing traces interfere with retrieval, and inhibitory control mechanisms are engaged to suppress the distraction they cause. This form of forgetting is considered adaptive because it reduces future interference. The impact of this proposed inhibition process on competing memories has, however, never been observed both because behavioural methods are “blind” to retrieval dynamics and because neuroimaging methods have not isolated retrieval of individual memories. Here we introduce a canonical template tracking method to quantify the activation state of individual target memories and competitors during retrieval. This method revealed that repeatedly retrieving target memories suppressed cortical patterns unique to competitors. Pattern suppression was related to engagement of prefrontal regions implicated in resolving retrieval competition, and, critically, predicted later forgetting. We thus demonstrate a cortical pattern suppression mechanism through which remembering adaptively shapes which aspects of our past remain accessible.

Interference resolution in face perception and name retrieval

Selective retrieval is a rather difficult task, and especially so when one attempts to retrieve personal representations such as faces or names. Retrieval of memories under strong competition conditions is pervasive in human memory and some have suggested that inhibitory control is used to overcome interference between competing stimuli. In the present study, we used the retrieval practice paradigm to investigate if competition among personal representations (such as facial features and names) is also resolved by inhibitory mechanisms. This question is theoretically relevant, since personal representations have been said to have a special status on cognition. Moreover, some models of face recognition assume that interference can arise between different representations, but that this interference would be automatically and rapidly solved, with no need for a controlled inhibitory mechanism to act. In two experiments we showed RIF for facial features and familiar names, but only when participants had to actively retrieve some information. This suggests that personal information is subject to mechanisms of inhibitory control, which could help explain everyday life difficulties in processes such as face feature recognition or name retrieval.

Age differences in the neural correlates of novelty processing: The effects of item-relatedness

Past research finds that age-related increases in false recognitions are a key contributor to age-related memory decline, suggesting that older adults have difficulty in correctly distinguishing between new and old information, particularly when new items at retrieval are semantically or perceptually related to items from encoding. However, little work has examined the neural mechanisms older adults engage to avoid false recognitions and successfully identify information as novel. In the present study, young and older adults were scanned during a retrieval task in which new items were exemplars from studied categories (related lures) or unstudied categories (unrelated lures) in order to detect age-related differences in the neural correlates of related and unrelated novelty processing. Results showed that, unlike young adults, older adults did not differentially recruit regions such as the anterior cingulate and bilateral middle/inferior temporal gyrus to capitalize on the salient categorical differences in unrelated items. Likewise, older adults did not differentially recruit regions of early visual cortex or anterior hippocampus, suggesting that older adults have difficulty using item-specific details to make successful related novelty decisions. Instead, older adults recruited bilateral ventrolateral prefrontal cortex differentially for successful novelty processing and particularly for related novelty processing. Overall, results suggest that age deficits in novelty processing may arise because older adults process related and unrelated lures similarly and do not capitalize on categorical or item-specific properties of novel items. Similar to aging patterns in memory retrieval, results also showed that older adults have the strongest novelty success activity in lateral PFC regions associated with control and monitoring processes. This article is part of a Special Issue entitled SI: Memory & Aging.

Obsessed not to forget: lack of retrieval-induced suppression effect in obsessive-compulsive disorder

The aim of the present study was to investigate the role of executive functions in resolving memory interference in a clinical sample of patients with obsessive-compulsive disorder (OCD). Retrieval of memories has been shown to involve some form of executive act that diminishes the accessibility of rival memory traces, leading to retrieval-induced forgetting (RIF). These executive control processes might suppress unwanted thoughts and irrelevant memories during competitive retrieval. We assessed RIF with the retrieval practice paradigm among 25 OCD patients and 25 healthy controls matched for age and education. Retrieval of target memories led to enhancement of target memory recall in both groups, but suppression of related memories (RIF) occurred only among controls. Our results suggest that suppression of irrelevant, interfering memories during competitive recall is impaired in OCD.

Human memory retrieval and inhibitory control in the brain: beyond correlational evidence

Retrieving information from long-term memory can result in the episodic forgetting of related material. One influential account states that this retrieval-induced forgetting (RIF) phenomenon reflects inhibitory mechanisms called into play to decrease retrieval competition. Recent neuroimaging studies suggested that the prefrontal cortex, which is critically engaged in inhibitory processing, is also involved in retrieval competition situations. Here, we used transcranial direct current stimulation (tDCS) to address whether inhibitory processes could be causally linked to RIF. tDCS was administered over the right dorsolateral prefrontal cortex during the retrieval-practice phase in a standard retrieval-practice paradigm. Sixty human participants were randomly assigned to anodal, cathodal, or sham-control groups. The groups showed comparable benefits for practiced items. In contrast, unlike both the sham and anodal groups, the cathodal group exhibited no RIF. This pattern is interpreted as evidence for a causal role of inhibitory mechanisms in episodic retrieval and forgetting.

Interference resolution in retrieval-induced forgetting: behavioral evidence for a nonmonotonic relationship between interference and forgetting

Retrieving memories renders related memories less accessible. This phenomenon, termed retrieval-induced forgetting (RIF), is thought to be the result of processes that resolve interference during competitive retrieval. In several studies, researchers have manipulated the level of interference to test different theoretical accounts of RIF (e.g., inhibitory vs. noninhibitory). However, the nature of how interference and RIF are related has not been systematically investigated. Here, we introduce a design that allows for assessing interference during competitive retrieval by measuring the recall RTs associated with target recall. Using such a design, we found that RIF occurred only when interference during competitive retrieval reached moderate levels, but not when it was too low or too high. This finding might indicate that low levels of interference do not trigger interference resolution, whereas interference resolution might fail when the interference reaches extremely high levels.

Retrieval-induced forgetting: dynamic effects between retrieval and restudy trials when practice is mixed

Results from numerous previous studies suggest that when subjects study items from different categories and then repeatedly retrieve, or restudy, some of the items from some of the categories, repeated retrieval, but not repeated study, induces forgetting of related unpracticed items. We investigated in two experiments whether such effects of pure retrieval and pure study practice generalize to mixed practice-that is, when retrieval and restudy trials are randomly interleaved within a single experimental block. Experiment 1 employed cued recall; Experiment 2 employed item recognition testing. In both experiments, pure repeated retrieval, but not pure repeated study, caused forgetting of related unpracticed items, which is consistent with the prior work. In contrast, with mixed practice, both retrieval and restudy induced forgetting. Thus, whereas retrieval caused forgetting regardless of practice mode, restudy caused forgetting with mixed practice, but not with pure practice. The finding provides first evidence for dynamic effects between retrieval and restudy trials when practice is mixed. It is consistent with the view that, with mixed practice, subjects engage in more retrieval during restudy trials, so that restudy trials may trigger similar processes as retrieval trials and, thus, induce forgetting of related, not restudied, items.

Medial Prefrontal Theta Oscillations Track the Time Course of Interference during Selective Memory Retrieval

Memory retrieval is often challenged by other irrelevant competing memories that cause interference. This phenomenon is typically studied with the retrieval practice paradigm in which a category cue (e.g., Fruits) is presented together with an item-specific cue (e.g., Or::). Presentation of the category cue usually induces interference by reactivating competing memories (e.g., Banana, Apple, etc.), which is thought to be solved by means of inhibition, leading to retrieval-induced forgetting of these competing memories. Previous studies associated interference with an increase in medial prefrontal theta band (4–8 Hz) oscillations, but these studies could not disentangle the interference from the inhibition processes. We here used a retrieval practice procedure in which the category cue was presented before the item-specific cue to disentangle the interference from the inhibition signal. Furthermore, a competitive retrieval condition was contrasted with a noncompetitive condition. At a behavioral level, retrieval-induced forgetting was found in the competitive but not in the noncompetitive condition. At a neural level, presentation of the category cue elicited higher levels of theta power in the competitive condition, when compared with the noncompetitive retrieval condition. Importantly, this difference was localized to the ACC, which has been associated with the detection and mediation of interference. Additionally, theta power decreased upon presentation of the item-specific cue, and this difference was related to later forgetting. Our results therefore disentangle, for the first time, interference and inhibition in episodic memory retrieval and suggest that theta oscillations track the fine-grained temporal dynamics of interference during competitive memory retrieval.

A perfusion fMRI investigation of thematic and categorical context effects in the spoken production of object names

The context in which objects are presented influences the speed at which they are named. We employed the blocked cyclic naming paradigm and perfusion functional magnetic resonance imaging (fMRI) to investigate the mechanisms responsible for interference effects reported for thematically and categorically related compared to unrelated contexts. Naming objects in categorically homogeneous contexts induced a significant interference effect that accumulated from the second cycle onwards. This interference effect was associated with significant perfusion signal decreases in left middle and posterior lateral temporal cortex and the hippocampus. By contrast, thematically homogeneous contexts facilitated naming latencies significantly in the first cycle and did not differ from heterogeneous contexts thereafter, nor were they associated with any perfusion signal changes compared to heterogeneous contexts. These results are interpreted as being consistent with an account in which the interference effect both originates and has its locus at the lexical level, with an incremental learning mechanism adapting the activation levels of target lexical representations following access. We discuss the implications of these findings for accounts that assume thematic relations can be active lexical competitors or assume mandatory involvement of top-down control mechanisms in interference effects during naming.

Retrieval-induced forgetting under psychosocial stress: no reduction by delayed stress and beta-adrenergic blockade

Retrieval-induced forgetting (RIF) is the phenomenon that 'retrieval-practice', the repeated retrieval of a subset of initially learned material, can impair the recall of episodically related memories. Previous studies showed that RIF is eliminated when retrieval-practice is carried out under psycho-social stress, anxiety, or in negative mood. However, pharmacological manipulation by hydrocortisone did not eliminate the effect. This study investigated the effect of beta-adrenergic blockade on stress-induced modulations of RIF, addressing possible interactive effects of the glucocorticoid and sympatho-adrenomedullary systems. Participants learned categorized word lists and then received either 60 mg propranolol or a placebo. After 90 min they were exposed to the TSST. A third group did not receive any medication and performed a non-stressful control task with the same timing as the other two groups. Finally, all participants underwent retrieval-practice and final recall. Both TSST groups exhibited a stress-induced increase in cortisol-levels, and the placebo group also exhibited large increases in markers of sympathetic nervous system activity and more psychological distress at the time of retrieval-practice. Although, overall recall was poorer under stress, an overall RIF effect emerged irrespective of group and showed no clear modulation by stress with or without beta-adrenergic blockade. In previous demonstrations of RIF elimination by negative emotion, state induction and retrieval-practice followed very briefly after initial learning. Given that both the previous study of hydrocortisone effects on RIF and the present study used longer delays between learning and retrieval-practice, the possibility that stress effects on retrieval-practice eliminate RIF only relatively briefly after learning is discussed.

Neural correlates of retrieval-based memory enhancement: an fMRI study of the testing effect

Restudying material is a common method for learning new information, but not necessarily an effective one. Research on the testing effect shows that practice involving retrieval from memory can facilitate later memory in contrast to passive restudy. Despite extensive behavioral work, the brain processes that make retrieval an effective learning strategy remain unclear. In the present experiment, we explored how initially retrieving items affected memory a day later as compared to a condition involving traditional restudy. In contrast to restudy, initial testing that contributed to future memory success was associated with engagement of several regions including the anterior hippocampus, lateral temporal cortices, and medial prefrontal cortex (PFC). Additionally, testing enhanced hippocampal connectivity with ventrolateral PFC and midline regions. These findings indicate that the testing effect may be contingent on processes that are typically thought to support memory success at encoding (e.g. relational binding, selection and elaboration of semantically-related information) in addition to those more often associated with retrieval (e.g. memory search).

Forgetting in context: the effects of age, emotion, and social factors on retrieval-induced forgetting

Retrieval-induced forgetting (RIF) refers to the finding that selectively retrieving some information impairs subsequent memory for related but nonretrieved information. This occurs both for the individual doing the remembering (i.e., within-individual retrieval-induced forgetting: WI-RIF), as well as for individuals merely listening to those recollections (i.e., socially shared retrieval-induced forgetting: SS-RIF). In the present study, we examined how the contextual factors of age and emotion independently and interactively affect both WI-RIF and SS-RIF. The results indicated that both WI-RIF and SS-RIF occurred at equivalent levels, both for younger and older adults and for neutral and emotional information. However, we identified a boundary condition to this effect: People only exhibited SS-RIF when the speaker that they were listening to was of the same sex as themselves. Given that participants reported feeling closer to same-sex speakers, this suggests that people co-retrieve more, and therefore exhibit increased SS-RIF, with close others. In everyday life, these RIF effects should influence what information is remembered versus forgotten in individual and collective memories.

Stress eliminates retrieval-induced forgetting--does the oral application of cortisol?

It is well established that stress and glucocorticoids can affect memory. Psychosocial stress has been reported to eliminate retrieval-induced forgetting (RIF), the phenomenon that repeated retrieval of a subset of previously learned material impairs later recall of related, but non-retrieved information. The stress-related reduction of RIF has been found correlated with an increase in salivary cortisol levels. Based on these findings, the current placebo-controlled study examined the effect of an oral dose of 25mg hydrocortisone on the RIF effect in 37 healthy men. Even though participants in the hydrocortisone group showed a marked increase in salivary cortisol, retrieval-induced forgetting was not affected by the pharmacological treatment. Thus, cortisol administration alone in contrast to stress experience does not impair the RIF effect. However, participants with high state anxiety during retrieval practice did not show RIF, whereas participants with low state anxiety did. This finding suggests a role for state anxiety in stress-related elimination of retrieval-induced forgetting, perhaps indicative of a memory-modulating sympathetic nervous system effect.