Memory Strength Research Articles

Chinese Soft-Shelled Turtle Oil in Combination With Swimming Training Improves Spatial Memory and Sports Performance of Aging Rats.

In this study, waste fat from the Chinese soft-shelled turtle (Pelodiscus sinensis) was used as the raw material, and soft-shelled turtle oil (SSTO) was extracted by water heating. Analysis of the fatty acid composition of SSTO revealed that unsaturated fatty acids (UFAs) comprised more than 70% of the oil, of which more than 20% were omega-3 poly-UFAs. DPPH radical scavenging and cellular ROS assays confirmed the reduction of oxidative stress by SSTO. In D-galactose-induced aging rats, SSTO feeding alone or in combination with swimming training resulted in improved memory and physical strength. In addition, SSTO feeding with swimming intervention significantly increased the SOD level and maintained better blood pressure in the aged rats. The serum DHEAS and soleus muscle glycogen level were also highly correlated with SSTO feeding and swimming training. In conclusion, the results of this study demonstrated that SSTO has the potential to be developed into a health food that exerts anti-aging effects, and those effects are stronger when combined with daily swimming exercise.

Recollection and familiarity in schizophrenia:An ERP investigation using face recognition exclusion tasks

Recent studies suggest that the recollection deficit observed in schizophrenia may not be a unitary phenomenon but could depend on the information to retrieve.Here we investigated whether the nature of the perceptual information affects recollection and familiarity in schizophrenia. ERP old/new effects were explored in 20 patients with schizophrenia and 20 healthy controls during unfamiliar face exclusion tasks, with either intrinsic (expression) or extrinsic (background) information either changing or remaining the same between study and test. Schizophrenia patients rejected old faces as distractors in a greater extent than healthy controls. The FN400 old/new effect (300-500ms) was found in both groups. It was sensitive to facial expression change for healthy controls but not schizophrenia patients. In addition, the parietal old/new effect was lower for correctly excluded faces for patients, but not for controls. This points to the conclusion that schizophrenia patients discriminate between target and non-target faces on the basis of the memory strength signal corresponding to the study-test mismatch rather than the recollection of the critical information, as observed in healthy controls. This functioning can be useful when study-test perceptual mismatch must be detected but, in return, can lead to the over-exclusion of old stimuli.

Sleep and Memory Consolidation Dysfunction in Psychiatric Disorders: Evidence for the Involvement of Extracellular Matrix Molecules.

Sleep disturbances and memory dysfunction are key characteristics across psychiatric disorders. Recent advances have revealed insight into the role of sleep in memory consolidation, pointing to key overlap between memory consolidation processes and structural and molecular abnormalities in psychiatric disorders. Ongoing research regarding the molecular mechanisms involved in memory consolidation has the potential to identify therapeutic targets for memory dysfunction in psychiatric disorders and aging. Recent evidence from our group and others points to extracellular matrix molecules, including chondroitin sulfate proteoglycans and their endogenous proteases, as molecules that may underlie synaptic dysfunction in psychiatric disorders and memory consolidation during sleep. These molecules may provide a therapeutic targets for decreasing strength of reward memories in addiction and traumatic memories in PTSD, as well as restoring deficits in memory consolidation in schizophrenia and aging. We review the evidence for sleep and memory consolidation dysfunction in psychiatric disorders and aging in the context of current evidence pointing to the involvement of extracellular matrix molecules in these processes.

Augmenting Neurogenesis Rescues Memory Impairments in Alzheimer's Disease by Restoring the Engram

It is unknown whether adult-born hippocampal neurons play a role in memory deficits in Alzheimer’s disease (AD). Here we show that significantly less new granule neurons, but a similar number of mature neurons, were recruited into contextual memory engram ensemble in a mouse model of AD compared to wild type. Augmentation of neurogenesis in AD mice increased the number of new neurons recruited into the engram and restored memory. The number of new neurons in the engram significantly correlated with the strength of contextual memory. Chemogenetic inactivation of new neurons following enhanced neurogenesis in AD, reversed mouse performance and diminished memory. Collectively, these observations suggest that new neurons play an integral role in memory engram. Insufficient numbers of new neurons recruited into the engram in AD leads to memory deficits. Augmenting hippocampal neurogenesis restores memory impairments by increasing the number of new neurons incorporated in the memory circuit.

032 Sleep Consolidates Memory for Strong but not Weak Information After Incidental Encoding

Abstract Introduction Slow wave sleep (SWS) strengthens memory for studied information, but research on the effect of sleep on information that is not intentionally remembered is scarce. Previous research from our lab suggests sleep consolidates some information that has been encoded incidentally, meaning that it has been acted on but not intentionally remembered. It remains unclear what determines which information is consolidated during sleep after incidental encoding and what aspects of sleep are related to this mnemonic benefit. In two experiments, we test the hypothesis that sleep consolidates strong but not weak memory traces following incidental encoding and assess the relationship between memory performance and sleep attributes. Methods In Experiment 1, we manipulated memory strength within- and between-subjects. Participants rated words one or three times (within) in a shallow or deep incidental encoding task (between). In the shallow task, participants counted vowels in each word; in the deep task, participants rated each word on a scale from ‘concrete’ to ‘abstract’. Following a 12-hour period containing sleep or wakefulness, participants took a surprise memory test. In Experiment 2, participants rated words one or three times in the deep encoding task, received an 8-hour sleep opportunity with partial PSG, and took the surprise memory test. Results In Experiment 1, participants remembered words better after sleep than wake regardless of number of encoding trials, but only after deep encoding. There was not an effect of sleep following shallow encoding. In Experiment 2, SWS correlated negatively with response latency for correctly recognized words encoded once, but not those encoded three times. That is, participants who received more SWS showed faster performance. Conclusion Results suggest sleep consolidated information based on the depth of encoding, and this benefit was related to SWS. This work is broadly consistent with theories of memory consolidation that predict sleep is more beneficial for strong than weak memory traces, such as the synaptic downscaling hypothesis. Support (if any):

Recognition Receiver Operating Characteristic Curves: The Complex Influence of Input Statistics, Memory, and Decision-making.

Receiver operating characteristic (ROC) analysis is the standard tool for studying recognition memory. In particular, the curvilinearity and the y-offset of recognition ROC curves have been interpreted as indicative of either memory strength (single-process models) or different memory processes (dual-process model). The distinction between familiarity and recollection has been widely studied in cognitive neuroscience in a variety of conditions, including lesions of different brain regions. We develop a computational model that explicitly shows how performance in recognition memory is affected by a complex and, as yet, underappreciated interplay of various factors, such as stimulus statistics, memory processing, and decision-making. We demonstrate that (1) the factors in the model affect recognition ROC curves in unexpected ways, (2) fitting R and F parameters according to the dual-process model is not particularly useful for understanding the underlying processes, and (3) the variability of recognition ROC curves and the controversies they have caused might be due to the uncontrolled variability in the contributing factors. Although our model is abstract, its functional components can be mapped onto brain regions, which are involved in corresponding functions. This enables us to reproduce and interpret in a coherent framework the diverse effects on recognition memory that have been reported in patients with frontal and hippocampal lesions. To conclude, our work highlights the importance of the rich interplay of a variety of factors in driving recognition memory performance, which has to be taken into account when interpreting recognition ROC curves.

Glucocorticoids Promote Fear Generalization by Increasing the Size of a Dentate Gyrus Engram Cell Population

BackgroundTraumatic experiences, such as conditioned threat, are coded as enduring memories that are frequently subject to generalization, which is characterized by (re-) expression of fear in safe environments. However, the neurobiological mechanisms underlying threat generalization after a traumatic experience and the role of stress hormones in this process remain poorly understood. MethodsWe examined the influence of glucocorticoid hormones on the strength and specificity of conditioned fear memory at the level of sparsely distributed dentate gyrus (DG) engram cells in male mice. ResultsWe found that elevating glucocorticoid hormones after fear conditioning induces a generalized contextual fear response. This was accompanied by a selective and persistent increase in the excitability and number of activated DG granule cells. Selective chemogenetic suppression of these sparse cells in the DG prevented glucocorticoid-induced fear generalization and restored contextual memory specificity, while leaving expression of auditory fear memory unaffected. ConclusionsThese results implicate the sparse ensemble of DG engram cells as a critical cellular substrate underlying fear generalization induced by glucocorticoid stress hormones.

Interfering with fear memories by eye movement desensitization and reprocessing

ObjectivePharmacologic and behavioral interventions that block reconsolidation of reactivated fear memory have demonstrated only limited success in modifying stronger and long-standing fear memories. Given the efficacy of Eye Movement Desensitization and Reprocessing (EMDR) in treating PTSD, pursuit eye movements are a promising and novel intervention for studies of human memory reconsolidation. Here, we examined the efficacy of pursuit eye movements in interfering with reconsolidation of conditioned fear memories. MethodsWe conducted a 3-day differential Pavlovian fear conditioning procedure in healthy adults, using videos of biologically prepared stimuli (tarantulas), partly reinforced with electrical shocks while recording skin conductance response (SCR) as a measure of autonomic conditioned responses. Fear conditioning was performed on Day 1. On Day 2, 38 participants were randomized into groups performing pursuit eye movements either immediately after fear memory reactivation, when the fear memory was stable, or 10 min later, when the fear memory was assumed to be more labile. On Day 3, fear memory strength was assessed by SCR to both reactivated and nonreactivated fear memories. ResultsStrong differential conditioning to the spider stimuli were observed during both fear acquisition and fear memory reactivation. Reactivated fear memory conditioned responses of participants performing pursuit eye movements after a 10-min delay were significantly smaller in the reinstatement phase (0.16 μS; 95% CI [0.02, 0.31]). ConclusionsPursuit eye movements were effective in reducing fear-conditioned SCR in reinstatement. This result supports the theoretical proposition that EMDR can interfere with reactivated fear memory reconsolidation.

The use of novel measures to detect Accelerated Long-term forgetting in people with epilepsy: The Crimes Test and Four Doors Test

Most patients with memory disorders appear to forget at a relatively normal rate.Hence testing retention beyond the initial test session becomes unnecessary. However, it is now well established that a subsample of patients, most notably people with epilepsy, can show substantially increased forgetting rates even when acquisition rate is normal, raising the need for new tests focused on the assessment of long-term forgetting. Our study is part of the process of developing two such tests. Both focus on the need to test the same person several times and address the problem that each successive test may interfere with the memory of the event being tested. Depending on conditions, such effects can be substantial and may be either positive or negative. The Crimes and Four Doors Tests tackle this problem by presenting easily memorised episodes or scenes, from which a different sample of features is tested at each delay by telephone. We apply these two novel tests to assess rates of forgetting in groups of people with epilepsy and a matched control group. Both the visual and verbal tests showed clear evidence of accelerated forgetting in the epilepsy group supporting the potential value of the tests as convenient and sensitive measures of the rate of long-term forgetting.

Short-term memory reactivation of a weak CS-US association promotes long-term memory persistence in conditioned odor aversion.

In conditioned odor aversion (COA), the association of a tasteless odorized solution (the conditioned stimulus [CS]) with an intraperitoneal injection of LiCl (the unconditioned stimulus [US[), which produces visceral malaise, results in its future avoidance. The strength of this associative memory is mainly dependent on two parameters, that is, the strength of the US and the interstimuli interval (ISI). In rats, COA has been observed only with ISIs of ≤15 min and LiCl (0.15 M) doses of 2.0% of bodyweight, when tested 48 h after acquisition (long-term memory [LTM]). However, we previously reported a robust aversion in rats trained with ISIs up to 60 min when tested 4 h after acquisition (short-term memory [STM]). Since memories get reactivated during retrieval, in the current study we hypothesized that testing for STM would reactivate this COA trace, strengthening its LTM. For this, we compared the LTM of rats trained with long ISIs or low doses of LiCl initially tested for STM with that of rats tested for LTM only. Interestingly, rats conditioned under parameters sufficient to produce STM, but not LTM, showed a reliable LTM when first tested for STM. These observations suggest that under suboptimal training conditions, such as long ISIs or low US intensities, a CS–US association is established but requires reactivation in the short-term in order to persist in the long-term.

Indirect modulation of human visual memory

Conditions in which memories become maladaptive have inspired extensive research geared to modulate memory by targeting it directly and explicitly. Given limitations of direct memory modulation, we asked the following: can the target memories be modulated indirectly? To address this question, we uniquely targeted visual memories, and leveraged a paradigm utilizing instructions to either forget or remember newly encoded memories. We used a multi-domain approach, and applied the instructions to embedded verbal information presented during encoding (words), with the intention to indirectly modulate recognition of the target visual context memory itself (pictures). Accordingly, participants were presented with two lists of words, where each word was preceded and followed by pictures. Participants were instructed to either remember or forget the first list of words. As expected, the instruction to either remember or forget the words differentially influenced word memory strength. Importantly, the instruction regarding the words, indirectly modulated picture memory strength. Better memory for words resulted in reduced picture memory strength and vice versa, with the instruction to remember the words reducing picture memory strength. Together with a negative correlation between word and picture memory strength, the results suggest a competition for shared resources between memory for content and context. These findings may open new avenues to indirectly modulate maladaptive memories.

Validity of mock-witness measures for assessing lineup fairness

ABSTRACT Although eyewitness researchers have used mock-witness measures to assess aspects of lineup fairness, they have paid little attention to their validity. The current study tested predictive validity, convergent validity, and discriminant validity of mock-witness measures from a meta-analytic perspective. Overall, mock-witness measures had predictive validity, particularly in target-absent (TA) lineups – the lineup fairness estimated by the measures reliably predicted eyewitnesses’ choosing behaviors and discriminability of a suspect from fillers in TA lineups. However, correlations between lineup fairness estimated by mock-witnesses and eyewitness performance were significant in target-present (TP) lineups only when eyewitnesses had a moderate memory for the perpetrator. Multitrait-multimethod correlations demonstrated significant intradomain correlations between mock-witness measures and other lineup fairness indices and nonsignificant interdomain correlations between the mock-witness measures and indices reflecting memory strength for the perpetrator, which supported convergent validity and discriminant validity, respectively. The implications for research and practice are discussed.

Cognitive profiles in perimenopause: hormonal and menopausal symptom correlates

Objective Perimenopause is associated with declines in attention, working memory and verbal memory; however, there are significant individual differences. Further, the contributions of hormones and menopausal symptoms to domain-specific cognitive functions remain unknown. This longitudinal study aimed to determine whether there were distinct cognitive profiles in perimenopause and to identify factors associated with each profile. Design In a sample of 85 women evaluated over 400 bi-annual visits, we administered a comprehensive neuropsychological battery, assessed menopausal symptoms and measured 17β-estradiol and follicle stimulating hormone. Multilevel latent profile analysis was used to identify cognitive profiles. Regressions were conducted to determine differences in hormones and symptoms by profile after adjusting for Stages of Reproductive Aging Workshop + 10 (STRAW + 10) stage and demographic factors. Results Perimenopausal cognitive profiles consisted of cognitively normal (Profile 1; n = 162), weaknesses in verbal learning and memory (Profile 2; n = 94), strengths in verbal learning and memory (Profile 3; n = 98) and strengths in attention and executive function (Profile 4; n = 61). Profile 2 was differentiated by less hormonal variability and more sleep disturbance than Profile 1 (p < 0.05). Conclusions There is significant heterogeneity in cognition during perimenopause. While most women do not develop impairments, a significant minority experience weaknesses in verbal learning and memory. Profile analysis may identify at-risk populations and inform interventions.

Using EEG microstates to examine post-encoding quiet rest and subsequent word-pair memory

Evidence suggests that the brain preferentially consolidates memories during “offline” periods, in which an individual is not performing a task and their attention is otherwise undirected, including spans of quiet, resting wakefulness. Moreover, research has demonstrated that factors such as the initial encoding strength of information influence which memories receive the greatest benefit. Recent studies have begun to investigate these periods of post-learning quiet rest using EEG microstate analysis to observe the electrical dynamics of the brain during these stretches of memory consolidation, specifically finding an increase in the amount of the canonical microstate D during a post-encoding rest period. Here, we implement an exploratory analysis to probe the activity of EEG microstates during a post-encoding session of quiet rest in order to scrutinize the impact of learning on microstate dynamics and to further understand the role these microstates play in the consolidation of memories. We examined 54 subjects (41 female) as they completed a word-pair memory task designed to use repetition to vary the initial encoding strength of the word-pair memories. In this study, we were able to replicate previous research in which there was a significant increase (p < .05) in the amount of microstate D (often associated with the dorsal attention network) during post-encoding rest. This change was accompanied by a significant decrease (p < .05) in the amount of microstate C (often associated with the default mode network). We also found preliminary evidence indicating a positive relationship between the amount of microstate D and improved memory for weakly encoded memories, which merits further exploration.

Individual differences in experienced and observational decision-making illuminate interactions between reinforcement learning and declarative memory

Decision making can be shaped both by trial-and-error experiences and by memory of unique contextual information. Moreover, these types of information can be acquired either by means of active experience or by observing others behave in similar situations. The interactions between reinforcement learning parameters that inform decision updating and memory formation of declarative information in experienced and observational learning settings are, however, unknown. In the current study, participants took part in a probabilistic decision-making task involving situations that either yielded similar outcomes to those of an observed player or opposed them. By fitting alternative reinforcement learning models to each subject, we discerned participants who learned similarly from experience and observation from those who assigned different weights to learning signals from these two sources. Participants who assigned different weights to their own experience versus those of others displayed enhanced memory performance as well as subjective memory strength for episodes involving significant reward prospects. Conversely, memory performance of participants who did not prioritize their own experience over others did not seem to be influenced by reinforcement learning parameters. These findings demonstrate that interactions between implicit and explicit learning systems depend on the means by which individuals weigh relevant information conveyed via experience and observation.

Design and Implementation of Memory Assistant Based on Ebbinghaus Forgetting Curve

In view of the single stereotype of memorizing knowledge points with the help of traditional books and easy to distract attention in the process of memorizing with the help of mobile phones and computers, a mobile handheld device, memory assistant, is designed and developed based on Ebbinghaus forgetting law curve, embedded software and hardware development technology, and memory list cycle pushing intelligent algorithm designed by forgetting curve law as the core. The experiment shows that the device is convenient and flexible like electronic devices such as mobile phones and computers, and also has the characteristics of high efficiency and concentration of book memorizing, at the same time, scientific and reasonable learning plan can effectively improve the efficiency of users’ Recitation and memory.

Effects of Tyrosine and Tryptophan in Rats with Diet-Induced Obesity.

Amino acids tyrosine (Tyr) and tryptophan (Trp) play a significant role in the regulation of energy metabolism, locomotor activity, and eating behavior. We studied the possibility of modulating these processes in obesity by increasing the pool of Tyr and Trp in the experimental diet. As a model of obesity, we used Wistar rats fed a diet with an excess specific energy value (HFCD) for 64 days. Trp led to a normalization of the rats’ body weight almost to the control level, but increased anxiety-like behavior and decreased long-term memory. The consumption of amino acids resulted in increased grip strength and impairment of short-term memory. The locomotor activity of animals decreased with age as a result of Tyr consumption, while Trp, on the contrary, prevented this. The Tyr supplementation led to the normalization of triglycerides and LDL. In the spleen cell lysates, amino acids suppressed the production of proinflammatory cytokines. The liver tissue morphology showed that the consumption of Tyr noticeably weakened the signs of fatty degeneration. The addition of Trp, on the contrary, led to an unfavorable effect, consisting of the appearance of a high number of large rounded fatty vacuoles. The data obtained indicate a more pronounced anti-inflammatory effect of Tyr as compared to Trp.

Temporally coherent perturbation of neural dynamics during retention alters human multi-item working memory.

Temporarily storing a list of items in working memory (WM), a fundamental ability in cognition, has been posited to rely on the temporal dynamics of multi-item neural representations during retention. However, the causal evidence, particularly in human subjects, is still lacking, let alone WM manipulation. Here, we develop a novel "dynamic perturbation" approach to manipulate the relative memory strength of WM items held in human brain, by presenting temporally correlated luminance sequences during retention to interfere with the multi-item neural dynamics. Six experiments on more than 150 subjects confirm the effectiveness of this WM manipulation approach. A computational model combining continuous attractor neural network (CANN) and short-term synaptic plasticity (STP) principles further reproduces all the empirical findings. The model reveals that the "dynamic perturbation" modifies the synaptic efficacies of WM items through STP principles, eventually leading to changes in their relative memory strengths. Our results support the causal role of temporal dynamics of neural network in mediating multi-item WM, and offer a promising, purely bottom-up approach to manipulate WM.

Encoding-linked pupil response is modulated by expected and unexpected novelty: Implications for memory formation and neurotransmission

Whether a novel stimulus is expected or unexpected may have implications for the kind of ensuing encoding and the type of subsequent memory. Pupil response was used in the present study to explore the way expected and unexpected stimuli are encoded and whether encoding-linked pupil response is modulated by expectation. Participants first established a contingency relationship between a series of symbols and the type of stimulus (man-made or natural) that followed each one. At encoding, some of the target stimuli violated the previously established relationship (i.e., unexpected), while the majority conformed to this relationship (i.e., expected). Expectation at encoding had opposite effects on familiarity and recollection, the two types of memory that support recognition, and modulated differently the way pupil response predicted subsequent memory. Encoding of unexpected novel stimuli was associated with increased pupil dilation as a predictor of subsequent memory type and strength. In contrast, encoding of expected novel stimuli was associated with decreased pupil response (constriction), which was predictive of subsequent memory type and strength. The findings support the close link between pupil response and memory formation, but critically indicate that this is modulated by the type of novelty as defined by expectation. These novel findings have important implications for the encoding mechanisms involved when different types of novelty are detected and is proposed to indicate the operation of different neurotransmitters during memory formation.

Distinguishing between high-confidence true and false memories: evidence from eye movements

ABSTRACT Objective: Memory confidence tends to be positively related to accuracy. However, false memory that fits well with the theme of an experience can also produce high-confidence responses. How to distinguish between high-confidence true and false recognition is unknown. The current study used eye movements to measure the retrieval processes of retrieval cues (i.e., item and theme) on recognition confidence and accuracy. Method: Participants (N = 30, Mage = 21.13 ± 2.06, 15 males) studied four visual thematic scenes, and after a filler task, took an item-theme recognition test in which their eye movements were recorded. Results: The gaze behaviour could distinguish between high-confidence true and false recognition. High-confidence false recognition was associated with longer fixation duration on item and theme, and more regression counts on theme as compared to high-confidence true recognition. Conclusion: High-confidence false recognition, compared to high-confidence true recognition, may have a weaker memory strength, such that more time-consuming and effortful retrieval-related monitoring processes were required before making a decision. The gaze behaviour based on both item and theme implied these processes. Thus, tracking eye movements during the identification may help evaluate whether a high-confidence recognition is true or false. KEY POINTS What is already known about this topic? False memories occur when people rely on the theme of an experience. The unexperienced item (e.g., “beach ball”) which is contextually associated with the theme (e.g., “beach scene”) of the experience can be recognized as “old”. Memory confidence tends to be positively related to accuracy. However, false memory that fits well with the theme of an experience can also produce high-confidence responses. Gaze behaviour recorded at retrieval can serve as indices of memory-related processing: previously viewed items had shorter fixation duration relative to high-interference novel items. What does this paper add? This study is the first to provide evidence suggesting that eye movements on either item cue or theme cue can differentiate between high-confidence true and false recognition. Compared to high-confidence true recognition, high-confidence false recognition was associated with longer fixation duration on item and theme. These results suggest that the time-consuming retrieval-related processes are based on both item and theme retrieval. High-confidence false recognition was related to more regression counts on theme than high-confidence true recognition, suggesting that inflated confidence of false recognition may be associated with more effortful retrieval-related monitoring processes.