Age differences in priming as a function of processing at encoding.

It is unclear whether implicit memory (priming) is affected by aging. Some studies have reported no difference between young and older adults, while others have uncovered reliable reductions. An important factor that may explain these discrepancies is the manner of encoding. Processing requirements (perceptual/conceptual) have varied considerably between studies, yet processing abilities are not equally affected by aging. This study examined whether processing during encoding moderates age effects on priming. Young and older participants studied object-word pairs and made natural/manufactured (conceptual) and left/right rotation (perceptual) judgements in relation to the word or object. Objects served as targets on a subsequent continuous identification with recognition task to assess priming and recognition. Priming and recognition were greater in young than older adults for attended items, with a larger effect size in the conceptual than the perceptual condition. Findings suggest that age differences in priming may be a function of processing at encoding.

The influence of classical music on learning and memory in rats: a systematic review and meta-analysis.

During the learning process, music can activate important neural areas in the brain, promoting the retention of information and memory formation. However, studies testing music effects on memory had found different improvements, which could be due to the methodological differences across studies. Thus, the purpose of this article was to systematically review the literature and meta-analyze the effects of music on Rattus norvegicus' explicit memory (Maze tests) only in controlled investigations. The seven studies included led to a very homogeneous analysis (I2 = 0%), confirming the consistency of the significant standardized mean difference (SMD) between the memory of animals exposed and not exposed to music (SMD 0.60 (95% CI 0.38; 0.83, p < 0.001)). Exploratory analysis suggests music benefits on memory can be acquired when begun at any age, when tested with the three types of mazes evaluated, with exposure lasting from 8 to 83 days and when the age on test day was either under 30 days or over 30 days. To expand the actual understanding of music effects on memory, future studies should investigate different types of music and animal species, with different sex and health conditions, at different time points.

Plasma concentrations of anti-inflammatory cytokine TGF-ß are associated with hippocampal structure related to explicit memory performance in older adults.

Human cognitive abilities, and particularly hippocampus-dependent memory performance typically decline with increasing age. Immunosenescence, the age-related disintegration of the immune system, is increasingly coming into the focus of research as a considerable factor contributing to cognitive decline. In the present study, we investigated potential associations between plasma levels of pro- and anti-inflammatory cytokines and learning and memory performance as well as hippocampal anatomy in young and older adults. Plasma concentrations of the inflammation marker CRP as well as the pro-inflammatory cytokines IL-6 and TNF-α and the anti-inflammatory cytokine TGF-ß1 were measured in 142 healthy adults (57 young, 24.47 ± 4.48 years; 85 older, 63.66 ± 7.32 years) who performed tests of explicit memory (Verbal Learning and Memory Test, VLMT; Wechsler Memory Scale, Logical Memory, WMS) with an additional delayed recall test after 24 h. Hippocampal volumetry and hippocampal subfield segmentation were performed using FreeSurfer, based on T1-weighted and high-resolution T2-weighted MR images. When investigating the relationship between memory performance, hippocampal structure, and plasma cytokine levels, we found that TGF-ß1 concentrations were positively correlated with the volumes of the hippocampal CA4-dentate gyrus region in older adults. These volumes were in turn positively associated with better performance in the WMS, particularly in the delayed memory test. Our results support the notion that endogenous anti-inflammatory mechanisms may act as protective factors in neurocognitive aging.

Learning strategy differentially impacts memory connections in children and adults.

Even once children can accurately remember their experiences, they nevertheless struggle to use those memories in flexible new ways-as in when drawing inferences. However, it remains an open question as to whether the developmental differences observed during both memory formation and inference itself represent a fundamental limitation on children's learning mechanisms, or rather their deployment of suboptimal strategy. Here, 7-9-year-old children (N = 154) and young adults (N = 130) first formed strong memories for initial (AB) associations and then engaged in one of three learning strategies as they viewed overlapping (BC) pairs. We found that being told to integrate-combine ABC during learning-both significantly improved children's ability to explicitly relate the indirectly associated A and C items during inference and protected the underlying pair memories from forgetting. However, this finding contrasted with implicit evidence for memory-to-memory connections: Adults and children both formed A-C links prior to any knowledge of an inference test-yet for children, such links were most apparent when they were told to simply encode BC, not integrate. Moreover, the accessibility of such implicit links differed between children and adults, with adults using them to make explicit inferences but children only doing so for well-established direct AB pairs. These results suggest that while a lack of integration strategy may explain a large share of the developmental differences in explicit inference, children and adults nevertheless differ in both the circumstances under which they connect interrelated memories and their ability to later leverage those links to inform flexible behaviours. RESEARCH HIGHLIGHTS: Children and adults view AB and BC pairs related through a shared item, B. This provides an opportunity for learners to connect A-C in memory. Being encouraged to integrate ABC during learning boosted performance on an explicit test of A-C connections (children and adults) and protected from forgetting (children). Children and adults differed in when implicit A-C connections were formed-occurring primarily when told to separately encode BC (children) versus integrate (adults), respectively. Adults used implicit A-C connections to facilitate explicit judgments, while children did not. Our results suggest developmental differences in the learning conditions promoting memory-to-memory connections.

Cognitive Impairments, Neuroinflammation and Blood-Brain Barrier Permeability in Mice Exposed to Chronic Sleep Fragmentation during the Daylight Period.

Obstructive sleep apnea (OSA) is a chronic condition characterized by intermittent hypoxia (IH) and sleep fragmentation (SF). In murine models, chronic SF can impair endothelial function and induce cognitive declines. These deficits are likely mediated, at least in part, by alterations in Blood-brain barrier (BBB) integrity. Male C57Bl/6J mice were randomly assigned to SF or sleep control (SC) conditions for 4 or 9 weeks and in a subset 2 or 6 weeks of normal sleep recovery. The presence of inflammation and microglia activation were evaluated. Explicit memory function was assessed with the novel object recognition (NOR) test, while BBB permeability was determined by systemic dextran-4kDA-FITC injection and Claudin 5 expression. SF exposures resulted in decreased NOR performance and in increased inflammatory markers and microglial activation, as well as enhanced BBB permeability. Explicit memory and BBB permeability were significantly associated. BBB permeability remained elevated after 2 weeks of sleep recovery (p < 0.01) and returned to baseline values only after 6 weeks. Chronic SF exposures mimicking the fragmentation of sleep that characterizes patients with OSA elicits evidence of inflammation in brain regions and explicit memory impairments in mice. Similarly, SF is also associated with increased BBB permeability, the magnitude of which is closely associated with cognitive functional losses. Despite the normalization of sleep patterns, BBB functional recovery is a protracted process that merits further investigation.

Behavioral evidence for two distinct memory systems in rats.

Serial reaction time tasks, in which subjects have to match a target to a cue, are used to explore whether non-human animals have multiple memory systems. Predictable sub-sequences embedded in the sequence of cues are responded to faster, demonstrating incidental learning, often considered implicit. Here, we used the serial implicit learning task (SILT) to determine whether rats' memory shows similar effects. In SILT, subjects must nose-poke into a sequence of two lit apertures, S1 and S2. Some S1 are always followed by the same S2, creating predictable sequences (PS). Across groups, we varied the proportion of PS trials, from 10 to 80%, and show that rats with more PS experience do better on them than on unpredictable sequences, and better than rats with less experience. We then introduced test trials in which no S2 was cued. Rats with more PS experience did better on test trials. Finally, we reversed some sequences (from predictable to unpredictable and vice versa) and changed others. We find that rats with more PS experience perseverate on old (now incorrect) responses more than those with less PS experience. Overall, we find a discontinuity in performance as the proportion of PS increases, suggesting a switch in behavioral strategies or memory systems, which we confirm using a Process Dissociation Procedure analysis. Our data suggest that rats have at least two distinct memory systems, one of which appears to be analogous to human implicit memory and is differentially activated by varying the proportion of PS in our task.

Predicting explicit memory for meaningful cartoons from visual paired comparison in infants and toddlers.

We tested the memory of 18-, 33-, and 39-month-olds (N = 120) for dynamic stimulus material (simple cartoons) after 6 months in a visual paired comparison (VPC) task. We also tested the explicit recognition memory (ERM) for the same material. Only the oldest age group (39-month-olds) showed a significant visual (familiarity) preference at the test. Similarly, only the oldest group reliably chose the correct cartoon in the ERM test. Data from the VPC and ERM tasks did not correlate in any age group. However, we suggested a novel score (coined ΔVPC) measuring how much visual preference changes during the test phase in the VPC task. We found that this ΔVPC score (and vocabulary) predicted children's performance in the ERM task, whereas other potential predictors such as age and conventional novelty preference did not. We discuss the impact of these findings in relation to the development of implicit and explicit memory. Furthermore, we propose that VPC measures are associated with explicit memory only when the participants processed the stimuli conceptually. In such cases, we suggest that the ΔVPC score is an approximation of how demanding it is to construct the mental representation of the familiar stimulus during the test phase.

Modulating Long Term Memory at Late-Encoding Phase: An rTMS Study.

Despite a huge effort of the scientific community, the functioning of Long-Term Memory (LTM) processes is still debated and far from being elucidated. Functional and neurophysiological data point to an involvement of Dorsolateral Prefrontal Cortex (DLPFC) in both encoding and retrieval phases. However, the recently proposed Explicit/Implicit Memory Encoding and Retrieval (EIMER) model proposes that LTM at the encoding phase consists of anatomically and chronologically different sub-phases. On this basis, we aimed to investigate the role of right DLPFC during a late-encoding phase by means of low-frequency rTMS. Thirty right-handed healthy subjects were divided into three experimental groups. Inhibitory rTMS was applied over right-DLPFC immediately after the encoding phase (Late-Encoding Group) or before recognition phase (Pre-Recognition Group), 24 h after, of an LTM task. Both groups also received sham stimulation during the non-target phase, while the third group (Sham Group) received only sham stimulation in both phases. The Late-Encoding Group collected a lower number of correct responses compared with Sham Group (p = 0.00), while Pre-Retrieval Group increased accuracy as compared to the Sham Group (p = 0.0). rTMS-inhibition of the right DLPFC seems able to interfere with LTM memory performances when delivered at a late stage of the encoding phase, with opposite effects at the pre-retrieval phase.

Order, please! Explicit sequence learning in hybrid search in younger and older age.

Sequence learning effects in simple perceptual and motor tasks are largely unaffected by normal aging. However, less is known about sequence learning in more complex cognitive tasks that involve attention and memory processes and how this changes with age. In this study, we examined whether incidental and intentional sequence learning would facilitate hybrid visual and memory search in younger and older adults. Observers performed a hybrid search task, in which they memorized four or 16 target objects and searched for any of those target objects in displays with four or 16 objects. The memorized targets appeared either in a repeating sequential order or in random order. In the first experiment, observers were not told about the sequence before the experiment. Only a subset of younger adults and none of the older adults incidentally learned the sequence. The "learners" acquired explicit knowledge about the sequence and searched faster in the sequence compared to random condition. In the second experiment, observers were told about the sequence before the search task. Both younger and older adults searched faster in sequence blocks than random blocks. Older adults, however, showed this sequence-learning effect only in blocks with smaller target sets. Our findings indicate that explicit sequence knowledge can facilitate hybrid search, as it allows observers to predict the next target and restrict their visual and memory search. In older age, the sequence-learning effect is constrained by load, presumably due to age-related decline in executive functions.

Aging Predicts Decline in Explicit and Implicit Memory: A Life-Span Study.

Explicit memory declines with age, but age effects on implicit memory are debated. This issue is important because if implicit memory is age invariant, it may support effective interventions in individuals experiencing memory decline. In this study, we overcame several methodological issues in past research to clarify age effects on implicit memory (priming) and their relationship to explicit memory (recognition, source memory). We (a) recruited a large life-span sample of participants (N = 1,072) during a residency at the Science Museum in London, (b) employed an implicit task that was unaffected by explicit contamination, and (c) systematically manipulated attention and depth of processing to assess their contribution to age effects. Participants witnessed a succession of overlapping colored objects, attending to one color stream and ignoring the other, and identified masked objects at test before judging whether they were previously attended, unattended, or new. Age significantly predicted decline in both explicit and implicit memory for attended items.

Determinants of memory development in childhood and adolescence.

Research on the development of memory has a long history and constitutes one of the most active research areas in the field of cognitive development. In this article, we first describe major historical developments in the literature on children's memory, focusing on systematic research that began in the late 1960s. We then examine new developments in the field, describing four important lines of inquiry: (a) the development of implicit memory, (b) short- and long-term memory development in infancy, (c) longitudinal research on memory strategies and metamemory, and (d) developmental cognitive neuroscience of memory. Finally, promising lines of future research on memory development are briefly discussed.

Reduced recognition and priming in older relative to young adults for incidental and intentional information.

Older adults often show greater implicit/unconscious memory than young adults for incidental information that was task-irrelevant during its acquisition. Shallow/perceptual encoding by older adults may boost performance on implicit tasks that reinstate this type of processing, whereas deeper/conceptual encoding by young adults may support greater explicit/conscious memory. To test this, young and older participants were exposed to incidental words in a text color identification task before the trial-by-trial capture of priming and recognition. In Experiments 1-3 priming and recognition were significantly greater in young than older adults, providing evidence against age differences in encoding style. In Experiments 2-3 older adults were more liberal than young adults in making positive recognition judgments to incidental relative to intentional items, even though source memory was poor in both groups. Findings pinpoint age differences in the utilization of previously incidental versus intentional information on different types of task.

The effect of encoding duration on implicit and explicit eyewitness memory.

The present study investigated the effect of encoding duration on implicit and explicit eyewitness memory. Participants (N = 227) viewed a mock crime (brief, 15-s vs. long, 30-s vs. irrelevant/control) and were then tested with both implicit and explicit memory prompts or with explicit memory prompts only. Brief-encoding participants revealed more critical details implicitly than long-encoding or control participants. Further, the number and percentage of accurate details recalled explicitly were higher for long-encoding than for brief-encoding participants. Implicit testing prior to explicit recall-as compared to completing a filler task-was detrimental to free recall performance. Interestingly, brief-encoding participants were significantly more likely to remember critical details implicitly but not explicitly than long-encoding participants. This is the first study to investigate implicit eyewitness memory for a multimodal mock crime. Findings are theoretically consistent with prior research on cognition while expanding upon the extant eyewitness memory and investigative interviewing literature.

Rats know when they remember: transfer of metacognitive responding across odor-based delayed match-to-sample tests.

Metamemory entails cognitively assessing the strength of one's memories. We tested the ability of nine Long-Evans rats to distinguish between remembering and forgetting by presenting a decline option that allowed a four-choice odor-based delayed match to sample (DMTS) tests to be by-passed. Rats performed significantly better on tests they chose to take than on tests they were forced to take, indicating metacognitive responding. However, rather than control by internal mnemonic cues, one alternative explanation is that decline use is based on external test-specific cues that become associated with increased rewards overtime. To examine this possibility, we tested rats on three generalization tests in which external contingencies were inconsistent and therefore could not serve as discriminative cues. Rats transferred adaptive use of the decline response in tests that eliminated memory by presenting no sample, increased memory by presenting multiple samples, and both weakened and strengthened memory by varying the retention interval. Further, subjects chose to take or decline the test before encountering the memory test, providing evidence that rats based their metacognitive responding on internal cues rather than external ones. To our knowledge, this is the first robust evidence for metamemory in rats using the DMTS decline-test paradigm in which several possible sources of external stimulus control can be ruled out.

Memory effects of sleep, emotional valence, arousal and novelty in children.

Effectiveness of memory consolidation is determined by multiple factors, including sleep after learning, emotional valence, arousal and novelty. Few studies investigated how the effect of sleep compares with (and interacts with) these other factors, of which virtually none are in children. The present study did so by repeated assessment of declarative memory in 386 children (45% boys) aged 9-11 years through an online word-pair task. Children were randomly assigned to either a morning or evening learning session of 30 unrelated word-pairs with positive, neutral or negative valenced cues and neutral targets. After immediately assessing baseline recognition, delayed recognition was recorded either 12 or 24 h later, resulting in four different assessment schedules. One week later, the procedure was repeated with exactly the same word-pairs to evaluate whether effects differed for relearning versus original novel learning. Mixed-effect logistic regression models were used to evaluate how the probability of correct recognition was affected by sleep, valence, arousal, novelty and their interactions. Both immediate and delayed recognition were worse for pairs with negatively valenced or less arousing cue words. Relearning improved immediate and delayed word-pair recognition. In contrast to these effects, sleep did not affect recognition, nor did sleep moderate the effects of arousal, valence and novelty. The findings suggest a robust inclination of children to specifically forget the pairing of words to negatively valenced cue words. In agreement with a recent meta-analysis, children seem to depend less on sleep for the consolidation of information than has been reported for adults, irrespective of the emotional valence, arousal and novelty of word-pairs.

Functional neuroanatomy associated with the interaction between emotion and cognition in explicit memory tasks in patients with generalized anxiety disorder.

BACKGROUND: The functional neuroanatomy for explicit memory in conjunction with the major anxiety symptoms in patients with generalized anxiety disorder (GAD) has not yet been clearly identified. PURPOSE: To investigate the brain activation patterns on the interaction between emotional and cognitive function during the explicit memory tasks, as well as its correlation with clinical characteristics in GAD. MATERIAL AND METHODS: The participants comprised GAD patients and age-matched healthy controls. The fMR images were obtained while the participants performed an explicit memory task with neutral and anxiety-inducing words. RESULTS: Patients showed significantly decreased functional activities in the putamen, head of the caudate nucleus, hippocampus, and middle cingulate gyrus during the memory tasks with the neutral and anxiety-inducing words, whereas the precentral gyrus and ventrolateral prefrontal cortex were significantly increased only in the memory tasks with the anxiety-inducing words. Also, the blood oxygenation level-dependent (BOLD) signal changes in the hippocampus were positively correlated with the recognition accuracy for both neutral and anxiety-inducing words. CONCLUSION: This study identified the brain areas associated with the interaction between emotional regulation and cognitive function in the explicit memory tasks in patients with GAD. These findings would be helpful to understand the neural mechanism on the explicit memory-related cognitive deficits and emotional dysfunction with GAD symptoms.

Abnormalities in gray and white matter volumes associated with explicit memory dysfunction in patients with generalized anxiety disorder.

Background The neuroanatomical abnormalities associated with behavioral dysfunction on explicit memory in patients generalized anxiety disorder (GAD) have not yet been clearly identified. Purpose To investigate the regional gray matter (GM) and white matter (WM) volume alterations over the whole brain in patients with GAD, as well as the correlation between the brain structural abnormality and explicit memory dysfunction. Material and Methods Twenty patients with GAD and 20 healthy controls matched for age, sex, and education level underwent high-resolution T1-weighted magnetic resonance imaging (MRI). The participants performed the explicit memory tasks with the neutral and anxiety-inducing words. Results Patients with GAD showed significantly reduced GM volumes in the midbrain (MB), thalamus, hippocampus (Hip), insula, and superior temporal gyrus (STG); and reduced WM volumes in the MB, anterior limb of the internal capsule (ALIC), dorsolateral prefrontal cortex (DLPFC), and precentral gyrus (PrG). It is important to note that the GM volume of the Hip and the WM volume of the DLPFC were positively correlated with the recognition accuracy (%) in the explicit memory tasks with neutral and anxiety-inducing words, respectively. On the other hand, the WM volume of the PrG was negatively correlated with the reaction time in the same memory tasks. Conclusion This study demonstrated the regional volume changes on whole-brain GM and WM and the correlation between the brain structural alteration and explicit memory dysfunction in GAD patients. These findings would be helpful to understand the association between the brain structure abnormality and the functional deficit in the explicit memory in GAD.

An attention account of neural priming.

Repetition priming of familiar stimuli (e.g., objects) produces a decrease in visual cortical activity for repeated versus novel items, which has been attributed to more fluent processing for repeated items. By contrast, priming of unfamiliar stimuli (e.g., abstract shapes) produces an increase in visual cortical activity. The mechanism for priming-related increases in activity for repeated unfamiliar stimuli is unknown. We hypothesised that such increases in activity may reflect attentional allocation to these items. We tested this hypothesis using a priming-spatial attention paradigm. During Phase 1 of Experiment 1, participants viewed unfamiliar abstract shapes and familiar objects. During Phase 2, participants identified target letters (S or H). Each target letter was preceded by a non-informative shape or object cue that was repeated (from Phase 1) or novel in the same (valid) or opposite (invalid) hemifield. In Experiment 2, we manipulated shape familiarity by presenting shapes once or six times during Phase 1. For both experiments, at valid locations, target identification accuracy was higher following repeated versus novel unfamiliar item cues and lower following repeated versus novel familiar item cues. These findings support our hypothesis that priming-related increases in visual cortical activity for repeated unfamiliar items may, in part, reflect attentional allocation.

Increased gamma band power during movement planning coincides with motor memory retrieval.

The retrieval of motor memory requires a previous memory encoding and subsequent consolidation of the specific motor memory. Previous work showed that motor memory seems to rely on different memory components (e.g., implicit, explicit). However, it is still unknown if explicit components contribute to the retrieval of motor memories formed by dynamic adaptation tasks and which neural correlates are linked to memory retrieval. We investigated the lower and higher gamma bands of subjects' electroencephalography during encoding and retrieval of a dynamic adaptation task. A total of 24 subjects were randomly assigned to a treatment and control group. Both groups adapted to a force field A on day 1 and were re-exposed to the same force field A on day 3 of the experiment. On day 2, treatment group learned an interfering force field B whereas control group had a day rest. Kinematic analyses showed that control group improved their initial motor performance from day 1 to day 3 but treatment group did not. This behavioral result coincided with an increased higher gamma band power in the electrodes over prefrontal areas on the initial trials of day 3 for control but not treatment group. Intriguingly, this effect vanished with the subsequent re-adaptation on day 3. We suggest that improved re-test performance in a dynamic motor adaptation task is contributed by explicit memory and that gamma bands in the electrodes over the prefrontal cortex are linked to these explicit components. Furthermore, we suggest that the contribution of explicit memory vanishes with the subsequent re-adaptation while task automaticity increases.

Distinct contributions of explicit and implicit memory processes to weight prediction when lifting objects and judging their weights: an aging study.

Weight predictions used to scale lifting forces adapt quickly when repeatedly lifting unusually weighted objects and are readily updated by explicit information provided about weight. In contrast, weight predictions used when making perceptual judgments about weight are more resistant to change and are largely unaffected by explicit information about weight. These observations suggest that distinct memory systems underlie weight prediction when lifting objects and judging their weights. Here we examined whether these weight predictions differ in their reliance on declarative and nondeclarative memory resources by comparing the adaptability of these predictions in older adults, who exhibit relatively impaired declarative memory processes, to those in younger adults. In the size condition, we measured lift forces as participants repeatedly lifted a pair of size-weight inverted objects in alternation. To assess weight judgments, we measured the size-weight illusion every 10 lifts. The material condition was similar, except that we used material-weight inverted objects and measured the material-weight illusion. The strengths of these illusions prior to lifting, and the attenuation of the illusions that arise when lifting inverted objects, were similar for both groups. The magnitude of the change in the illusions was positively correlated with implicit memory performance in both groups, suggesting that predictions used when judging weight rely on nondeclarative memory resources. Updating of lifting forces also did not differ between groups. However, within the older group the success with which lifting forces were updated was positively correlated with working memory performance, suggesting that weight predictions used when lifting rely on declarative memory resources.