Implicit Memory Research Articles

Long-Term Implicit Epigenetic Stress Information in the Enteric Nervous System and its Contribution to Developing and Perpetuating IBS.

Psychiatric and mood disorders may play an important role in the development and persistence of irritable bowel syndrome (IBS). Previously, we hypothesized that stress-induced implicit memories may persist throughout life via epigenetic processes in the enteric nervous system (ENS), independent of the central nervous system (CNS). These epigenetic memories in the ENS may contribute to developing and perpetuating IBS. Here, we further elaborate on our earlier hypothesis. That is, during pregnancy, maternal prenatal stresses perturb the HPA axis and increase circulating cortisol levels, which can affect the maternal gut microbiota. Maternal cortisol can cross the placental barrier and increase cortisol-circulating levels in the fetus. This leads to dysregulation of the HPA axis, affecting the gut microbiota, microbial metabolites, and intestinal permeability in the fetus. Microbial metabolites, such as short-chain fatty acids (which also regulate the development of fetal ENS), can modulate a range of diseases by inducing epigenetic changes. These mentioned processes suggest that stress-related, implicit, long-term epigenetic memories may be programmed into the fetal ENS during pregnancy. Subsequently, this implicit epigenetic stress information from the fetal ENS could be conveyed to the CNS through the bidirectional microbiota-gut-brain axis (MGBA), leading to perturbed functional connectivity among various brain networks and the dysregulation of affective and pain processes.

Implicit memory reduced selectively for negative words with aging.

Disproportionally better memory for positive versus negative information (mnemonic positivity effect, MPE) in older versus younger adults has been reported on tests of explicit memory (direct, intentional) as measured by recall and recognition. The purpose of this investigation was to examine whether the MPE would be observed for implicit memory (indirect, unintentional) under conditions where, based on previous research using single words, it was expected that the MPE for explicit memory would be absent. This study investigated the influence of age on explicit and implicit memory for positive, negative, and neutral single words as measured by yes/no recognition and word identification on 24 older adults (aged 66-85) and 24 younger adults (aged 18-37) recruited from community centers in South Boston, Massachusetts. Older adults had lower recognition memory accuracy for positive, negative, and neutral words than younger adults, and, consistent with most prior studies, did not exhibit an explicit memory MPE for single words. For both groups, recognition accuracy was greatest for negative words, and was similar for positive and neutral words. In contrast, older adults exhibited implicit repetition priming, as measured by superior identification performance for repeated words, that was similar to younger adults for positive and neutral words. In younger adults, implicit memory was significantly greater for negative words than for positive and neutral words, whereas in older adults there were no significant differences in implicit memory for negative, positive, and neutral words. Therefore, selectively reduced priming for negative words in older adults was found in the context of enhanced priming for negative words in the younger adults. These findings show that there was an implicit memory MPE in older adults for words even under conditions where there was no explicit memory MPE in the older adults. Dampening of negative valence implicit memory with aging expands the perimeter of the age-related positivity framework.

The effects of prediction representations on implicit learning: evidence from sentence reading and perceptual identification

Predicting errors can facilitate implicit learning, but the long-term consequences of prediction errors are not yet fully understood. Especially when predictions are disconfirmed, it remains unclear whether initially correct prediction representations persist or are suppressed. In this study, participants first engaged in a sentence reading task and then performed a perceptual identification task after completing an N-back task or after a 24-hour delay. The perceptual identification task presented previously expected and unexpected words and previously predicted but not presented words to measure implicit memory for the critical items. This study aims to investigate the mechanisms underlying the persistence of prediction representations and the long-term effects of prediction errors on implicit learning. Our results indicate that prediction errors can promote implicit learning and can persist for more than 24 hours. Furthermore, originally correct but not seen in reality prediction representations persist to facilitate performance on the implicit memory task after 24 hours. This may reflect long-term changes in the internal representation probabilities of prediction representations.

Are selection history effects limited to implicit forms of memory? Evidence from intertrial repetition.

Selection history effects in visual attention are typically considered implicit memory effects. In three experiments, we investigated if a key selection history effect, intertrial priming, could be based on the incidental application of explicit memory. In the basic search task (Experiment 1), participants searched for real-world objects from different categories. We examined nonpredictive, intertrial repetition at two levels: (1) the repetition of target location from trial N-1 to trial N and (2) the repetition of target location and color within a category. Reliable repetition advantages were observed at both levels. In Experiments 2-4, we examined whether participants had explicit access to the target values driving the selection history effects here. In Experiments 2 and 3, participants could reliably report the properties of the immediately preceding search target. In Experiment 4, participants could reliably report the properties of the last target exemplar they had found in each of the 36 categories. These data indicate that guidance by selection history was based on the nonstrategic application of memory representations that could be explicitly retrieved and reported. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Influence of sleep on motor skill acquisition in children: a systematic review.

Effects of sleep on procedural (implicit) memory consolidation in children remain controversial. The aim of this systematic review was to synthesise the evidence on the influence of sleep on motor skills acquisition in children. Four electronic databases were searched: PubMed, Cochrane Central Register of Controlled Trials (CENTRAL), Excerpta Medica Database (Embase), and Biblioteca Virtual em Saúde (BVS). Original studies, published until October 17, 2023, on motor skill acquisition in children aged ≤12 years, in which the intervention group slept after motor skill training, while the control group remained awake, were considered for inclusion. Risk of bias was evaluated using the Cochrane's Risk of Bias 2 tool. The review protocol was pre-registered at the International Prospective Register of Systematic Reviews (PROSPERO protocol number: CRD42022363868) and all reported items followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Of the 7241 articles initially retrieved, nine met the primary criteria and were included in this review. Of these, six studies reported that daytime or night-time sleep intervention improved motor skill acquisition, as compared to wakefulness. All studies presented a high risk of bias. In conclusion, the evidence summarised suggests that sleep may enhance motor skills acquisition and could be important for motor development in childhood. However, due to the high risk of bias in the included studies, future randomised controlled trials with high methodological quality are necessary to better clarify this topic.

Emotional memory bias in adolescents with chronic pain: examining the relationship with neural, stress, and psychological factors.

Memory biases for pain-related information may contribute to the development and maintenance of chronic pain; however, evidence for when (and for whom) these biases occur is mixed. Therefore, we examined neural, stress, and psychological factors that could influence memory bias, focusing on memories that motivate disabling behaviors: pain perception, conditioned responses to threat-and-safety cues, and responses to aversive nonnoxious stimuli. Two studies were conducted with adolescents with and without chronic pain. Data from 58 participants were included in study 1 (chronic pain n = 34, pain free n = 24, mean age = 16 years), and 39 participants were included in study 2 (chronic pain n = 26, pain free n = 13, mean age = 16 years). Both studies used a threat-safety learning paradigm with memory recall (≈1 month later). Participants completed structural and functional (resting-state) magnetic resonance imaging, salivary cortisol measurements, and self-report measures. Adolescents with pain and pain-free peers consistently recalled being more afraid of safety cues (CS-) and, during heightened stress at encoding (higher cortisol levels), also reported being more afraid of threat cues (CS+). However, no memory bias was present for the emotional response to an aversive stimulus (US; loud scream) or for the recall of pain intensity. Functional connectivity of the amygdala and hippocampus with memory circuits related to the degree of memory bias, but the specific connections varied between the studies, and we observed no relationship between memory bias and brain morphology. Our findings highlight the value of considering the interaction between implicit and explicit memory systems, contributing to a more comprehensive understanding of emotional memory biases in the context of chronic pain.

Sensitive periods in language development: Do children outperform adults on auditory word-form segmentation?

Children are more successful language learners than adults, yet the nature and cause of this phenomenon are still not well understood. Auditory statistical learning from speech has been a prominent focus of research in the field of language development because it is regarded as a fundamental learning mechanism underlying word segmentation in early language acquisition. However, a handful of studies that investigated developmental trajectories for auditory statistical learning found no clear child advantages. The degree to which the learning task measures explicit rather than implicit mechanisms might obscure a potential advantage for younger learners, as suggested by recent findings. In the present study, we compared children aged 7–12 years and young adults on an adapted version of the task that disentangles explicit and implicit contributions to learning. They were exposed to a continuous stream of speech sounds comprising four repeating trisyllabic pseudowords. Learning of the hidden words was tested (a) online through a target-detection task and (b) offline via a forced-choice word recognition test that included a memory judgement procedure. Both measures revealed comparable learning abilities. However, children's performance on the recognition task showed evidence for both explicit and implicit word knowledge while adults appeared primarily sensitive to explicit memory. Since implicit memory is more stable in time than explicit memory, we suggest that future work should focus more on developmental differences in the nature of the memory that is formed, rather than the strength of learning, when trying to understand child advantages in language acquisition.

Implicit Selective Attention: The Role of the Mesencephalic-basal Ganglia System.

The ability of the brain to recognize and orient attention to relevant stimuli appearing in the visual field is highlighted by a tuning process, which involves modulating the early visual system by both cortical and subcortical brain areas. Selective attention is coordinated not only by the output of stimulus-based saliency maps but is also influenced by top-down cognitive factors, such as internal states, goals, or previous experiences. The basal ganglia system plays a key role in implicitly modulating the underlying mechanisms of selective attention, favouring the formation and maintenance of implicit sensory-motor memories that are capable of automatically modifying the output of priority maps in sensory-motor structures of the midbrain, such as the superior colliculus. The article presents an overview of the recent literature outlining the crucial contribution of several subcortical structures to the processing of different sources of salient stimuli. In detail, we will focus on how the mesencephalic- basal ganglia closed loops contribute to implicitly addressing and modulating selective attention to prioritized stimuli. We conclude by discussing implicit behavioural responses observed in clinical populations in which awareness is compromised at some level. Implicit (emergent) awareness in clinical conditions that can be accompanied by manifest anosognosic symptomatology (i.e., hemiplegia) or involving abnormal conscious processing of visual information (i.e., unilateral spatial neglect and blindsight) represents interesting neurocognitive "test cases" for inferences about mesencephalicbasal ganglia closed-loops involvement in the formation of implicit sensory-motor memories.

Repertoires of action and collective memory: the re-emergence of feminist self-managed health centers in Italy

ABSTRACT This article analyzes the relationship between repertoires of action and collective memory by exploring the re-emergence of feminist self-managed health centers in Italy. These were a key form of action of 1970s feminism in the country, which rapidly disappeared after the institution of state-based Family Health Centers. In the last decades, feminist and transfeminist self-managed health centers have resurfaced in several Italian cities. The present article investigates the mnemonic dynamics underpinning the re-adoption of a form of action from the past in subsequent cycles of mobilization. Social movement scholars have stressed the relatively stable and repetitive character of the repertoire of collective action over time, considering it as part of an implicit memory. The article examines a case in which the discontinuous adoption of a form of action makes its retrieval by subsequent activists the result of active memory work. While the study of social movements and collective memory has grown considerably in the last decades, the study of repertoires remains largely under-researched in this field. Filling this gap, this study shows how, by adopting a symbolically and historically meaningful repertoire, activists re-elaborate their collective identity in the present and establish a relationship with previous cycles. It suggests that further research should investigate the relationship between collective memory and repertoires of action.

Visual fidelity in the metaverse matters for memory performance

The metaverse offers unlimited opportunities for interaction, training, business and pleasure across industries. While research is still in its infancy, the concept has been around for more than a decade, experiencing vast technological innovation in recent years. Headsets to experience metaverses via virtual reality (VR) provide increasing visual fidelity, which can alter the metaverse experience for the individual. Visual fidelity refers to the degree to which visual features in the metaverse imitate visual features in the equivalent real-world setting. We use a VR supermarket setting to study consumers' memory processes, dependent on the visual fidelity of the headset as well as task demands. Based on a 2 × 2 between-subjects design, we find that generally a higher visual fidelity improves explicit memory of features in the visual scene. Only for the case of a more abstract task, lower visual fidelity improves implicit memory. Additionally, higher explicit memory is associated with lower spending. We attribute these findings to the level of detail needed to perform the task adequately. We provide recommendations for designing metaverse experiences and research practice. We contribute to the literature on information processing by demonstrating the effect of visual fidelity on memory performance, depending on task demands.

Early-Stage Alzheimer's Disease Affects Fast But Not Slow Adaptive Processes in Motor Learning.

Alzheimer's disease (AD) is characterized by an initial decline in declarative memory, while nondeclarative memory processing remains relatively intact. Error-based motor adaptation is traditionally seen as a form of nondeclarative memory, but recent findings suggest that it involves both fast, declarative, and slow, nondeclarative adaptive processes. If the declarative memory system shares resources with the fast process in motor adaptation, it can be hypothesized that the fast, but not the slow, process is disturbed in AD patients. To test this, we studied 20 early-stage AD patients and 21 age-matched controls of both sexes using a reach adaptation paradigm that relies on spontaneous recovery after sequential exposure to opposing force fields. Adaptation was measured using error clamps and expressed as an adaptation index (AI). Although patients with AD showed slightly lower adaptation to the force field than the controls, both groups demonstrated effects of spontaneous recovery. The time course of the AI was fitted by a hierarchical Bayesian two-state model in which each dynamic state is characterized by a retention and learning rate. Compared to controls, the retention rate of the fast process was the only parameter that was significantly different (lower) in the AD patients, confirming that the memory of the declarative, fast process is disturbed by AD. The slow adaptive process was virtually unaffected. Since the slow process learns only weakly from an error, our results provide neurocomputational evidence for the clinical practice of errorless learning of everyday tasks in people with dementia.

Dreams, memories, and the psychoanalytic process

Freud believed the dreamer’s wish amounted to the most powerful motive underlying all dreaming processes. Ángel Garma suggested traumatic memories might play a similar or even greater role. In the present paper, I extend Garma’s suggestion and propose that unconscious memories of interpersonal interactions are the basic components of dream narratives. Within this perspective, latent dream content includes a wealth of information about the unconscious experience of the transference situation. Through a clinical vignette, I show the reader how appropriate transference interpretations allow the identification of such transferential emotions and their reintegration within the psychoanalytic field.

Acting out as criminal impulse. History, Definitions, Forensic aspects

The present article aims to conduct a comprehensive review of the existing scientific literature on this human behavioral modality, impulsive and transient, which escapes the conscious control of the subject, from a psychopathological and forensic approach. To achieve this, historical points about the different nuances of the topic will be made, supplying a panoramic and critical overview of it. It can be said that these are implicit memories about past traumatic situations that, because of a present reenactment of the unpleasant event through a dissociative mechanism, generate in the individual an impulsive aggressive reaction, over which the person has no control or awareness. This type of behavior opens the debate, within the framework of Forensic Psychology and Psychiatry, about the defendants' ability, under these circumstances, to understand the criminality of the act and direct their actions, posing a controversial challenge to the criteria of different courts. Similarly, it is necessary to understand these behaviors, develop more proper prevention strategies, propose new therapeutic approaches to psychological trauma, and intervene in these criminal behaviors that endanger society's safety and well-being.

The hippocampus and implicit memory

ABSTRACT The traditional memory-systems view is that explicit (conscious) long-term memory is associated with the hippocampus and implicit (nonconscious) memory is associated with non-hippocampal brain regions. This special issue of Cognitive Neuroscience focuses on whether the hippocampus is associated with implicit memory. An empirical fMRI paper by Miller, Kennard, Gowland, Antoniades, and Rosenthal (this issue) evaluated recognition memory performance of autobiographical amnesia patients with bilateral damage to hippocampal sub-region CA3 and found they had greater than chance recognition memory performance for spatial sequence learning, spatial item learning-same location, and non-spatial item learning, but chance performance for non-spatial sequence learning and spatial item learning-different location. These results are at odds with the view that the hippocampus is generally involved in sequence learning and complex event recognition. A discussion paper by Steinkrauss and Slotnick (this issue) considered whether fMRI studies have provided evidence that the hippocampus is associated with implicit memory. It was argued that all previous studies have been confounded by explicit memory, attentional states, stimuli, or novelty. This discussion paper is followed by commentaries from Hannula (this issue), Henke and Ruch (this issue), Rosenthal (this issue), Spaak (this issue), Thakral et al. (this issue), and Züst (this issue). The articles in this special issue illustrate that the association between the hippocampus and implicit memory is under active investigation and debate. It is hoped that the evidence and discourse in this issue will provide directions for future research.

Noninvasive brain stimulations modulated brain modular interactions to ameliorate working memory in community-dwelling older adults.

Non-invasive brain stimulations have drawn attention in remediating memory decline in older adults. However, it remains unclear regarding the cognitive and neural mechanisms underpinning the neurostimulation effects on memory rehabilitation. We evaluated the intervention effects of 2-weeks of neurostimulations (high-definition transcranial direct current stimulation, HD-tDCS, and electroacupuncture, EA versus controls, CN) on brain activities and functional connectivity during a working memory task in normally cognitive older adults (age 60+, n = 60). Results showed that HD-tDCS and EA significantly improved the cognitive performance, potentiated the brain activities of overlapping neural substrates (i.e. hippocampus, dlPFC, and lingual gyrus) associated with explicit and implicit memory, and modulated the nodal topological properties and brain modular interactions manifesting as increased intramodular connection of the limbic-system dominated network, decreased intramodular connection of default-mode-like network, as well as stronger intermodular connection between frontal-dominated network and limbic-system-dominated network. Predictive model further identified the neuro-behavioral association between modular connections and working memory. This preliminary study provides evidence that noninvasive neurostimulations can improve older adults' working memory through potentiating the brain activity of working memory-related areas and mediating the modular interactions of related brain networks. These findings have important implication for remediating older adults' working memory and cognitive declines.

Neural correlates of musical familiarity: a functional magnetic resonance study.

Existing neuroimaging studies on neural correlates of musical familiarity often employ a familiar vs. unfamiliar contrast analysis. This singular analytical approach reveals associations between explicit musical memory and musical familiarity. However, is the neural activity associated with musical familiarity solely related to explicit musical memory, or could it also be related to implicit musical memory? To address this, we presented 130 song excerpts of varying familiarity to 21 participants. While acquiring their brain activity using functional magnetic resonance imaging (fMRI), we asked the participants to rate the familiarity of each song on a five-point scale. To comprehensively analyze the neural correlates of musical familiarity, we examined it from four perspectives: the intensity of local neural activity, patterns of local neural activity, global neural activity patterns, and functional connectivity. The results from these four approaches were consistent and revealed that musical familiarity is related to the activity of both explicit and implicit musical memory networks. Our findings suggest that: (1) musical familiarity is also associated with implicit musical memory, and (2) there is a cooperative and competitive interaction between the two types of musical memory in the perception of music.

Awakening the Proto‐Lexicon: A Proto‐Lexicon Gives Learning Advantages for Intentionally Learning a Language

AbstractPrevious studies report that exposure to the Māori language on a regular basis allows New Zealand adults who cannot speak Māori to build a proto‐lexicon of Māori—an implicit memory of word forms without detailed knowledge of meaning. How might this knowledge feed into explicit language learning? Is it possible to “awaken” the proto‐lexicon in the context of overt language learning? We investigate whether implicit linguistic knowledge represented in a proto‐lexicon gives any advantages for intentional language learning in a tertiary educational environment. We conducted a three‐task experiment which: (a) assessed participants’ Māori proto‐lexicon, (b) assessed their phonotactic knowledge, and (c) tested them on Māori vocabulary that they had been exposed to during the course at two time points. The results show that students with larger Māori proto‐lexicons learn more words in a classroom setting. This study shows that proto‐lexicon acquired from ambient exposure can lead to significant benefits in language learning.

Performance Differences of a Touch-Based Serial Reaction Time Task in Healthy Older Participants and Older Participants With Cognitive Impairment on a Tablet: Experimental Study.

Digital neuropsychological tools for diagnosing neurodegenerative diseases in the older population are becoming more relevant and widely adopted because of their diagnostic capabilities. In this context, explicit memory is mainly examined. The assessment of implicit memory occurs to a lesser extent. A common measure for this assessment is the serial reaction time task (SRTT). This study aims to develop and empirically test a digital tablet-based SRTT in older participants with cognitive impairment (CoI) and healthy control (HC) participants. On the basis of the parameters of response accuracy, reaction time, and learning curve, we measure implicit learning and compare the HC and CoI groups. A total of 45 individuals (n=27, 60% HCs and n=18, 40% participants with CoI-diagnosed by an interdisciplinary team) completed a tablet-based SRTT. They were presented with 4 blocks of stimuli in sequence and a fifth block that consisted of stimuli appearing in random order. Statistical and machine learning modeling approaches were used to investigate how healthy individuals and individuals with CoI differed in their task performance and implicit learning. Linear mixed-effects models showed that individuals with CoI had significantly higher error rates (b=-3.64, SE 0.86; z=-4.25; P<.001); higher reaction times (F1,41=22.32; P<.001); and lower implicit learning, measured via the response increase between sequence blocks and the random block (β=-0.34; SE 0.12; t=-2.81; P=.007). Furthermore, machine learning models based on these findings were able to reliably and accurately predict whether an individual was in the HC or CoI group, with an average prediction accuracy of 77.13% (95% CI 74.67%-81.33%). Our results showed that the HC and CoI groups differed substantially in their performance in the SRTT. This highlights the promising potential of implicit learning paradigms in the detection of CoI. The short testing paradigm based on these results is easy to use in clinical practice.

“I have not a word about my own sensations”: Intoxication, Trauma and Imperialism in The Moonstone

ABSTRACT This article examines the relationship between intoxication, trauma, and imperialism in Wilkie Collins’s The Moonstone, exploring how altered states of consciousness recuperate and repress the shameful secrets of colonial history. Throughout the novel, the characters attempt to explicate the violence of empire by retracing the past through textual fragments, such as journals, letters, and diary-entries. However, in doing so, they succumb to quasi-narcotic states of unconscious cerebration, psychic repression, and automatic action. As such, the process of detection becomes a painful, and even traumatic, experience in which psychical information is forgotten, yet never erased. Thus, while the novel attempts to formulate a critique of the British Empire, its critical voice remains regulated by the psychosomatic logic at work, simultaneously concealing and revealing the traumas of colonial dispossession. Drawing upon the work of Judith Herman, Cathy Caruth, Jill Matus, and other contemporary trauma theorists, as well as Victorian theories of addiction, unconscious memory, and psychic shock, this article suggests that while Collins frames the imperial project as both “trauma” and “intoxication,” demonstrating how political violence creates a disturbance in memory and consciousness, the novel occupies an ideologically ambivalent space, unable to assimilate fully the horrors of British imperialism.

Reinforcement Learning during Locomotion.

When learning a new motor skill, people often must use trial and error to discover which movement is best. In the reinforcement learning framework, this concept is known as exploration and has been linked to increased movement variability in motor tasks. For locomotor tasks, however, increased variability decreases upright stability. As such, exploration during gait may jeopardize balance and safety, making reinforcement learning less effective. Therefore, we set out to determine if humans could acquire and retain a novel locomotor pattern using reinforcement learning alone. Young healthy male and female participants walked on a treadmill and were provided with binary reward feedback (indicated by a green checkmark on the screen) that was tied to a fixed monetary bonus, to learn a novel stepping pattern. We also recruited a comparison group who walked with the same novel stepping pattern but did so by correcting for target error, induced by providing real-time veridical visual feedback of steps and a target. In two experiments, we compared learning, motor variability, and two forms of motor memories between the groups. We found that individuals in the binary reward group did, in fact, acquire the new walking pattern by exploring (increasing motor variability). Additionally, while reinforcement learning did not increase implicit motor memories, it resulted in more accurate explicit motor memories compared with the target error group. Overall, these results demonstrate that humans can acquire new walking patterns with reinforcement learning and retain much of the learning over 24 h.