The neuroscience of active learning and direct instruction

Throughout the educational system, students experiencing active learning pedagogy perform better and fail less than those taught through direct instruction. Can this be ascribed to differences in learning from a neuroscientific perspective? This review examines mechanistic, neuroscientific evidence that might explain differences in cognitive engagement contributing to learning outcomes between these instructional approaches. In classrooms, direct instruction comprehensively describes academic content, while active learning provides structured opportunities for learners to explore, apply, and manipulate content. Synaptic plasticity and its modulation by arousal or novelty are central to all learning and both approaches. As a form of social learning, direct instruction relies upon working memory. The reinforcement learning circuit, associated agency, curiosity, and peer-to-peer social interactions combine to enhance motivation, improve retention, and build higher-order-thinking skills in active learning environments. When working memory becomes overwhelmed, additionally engaging the reinforcement learning circuit improves retention, providing an explanation for the benefits of active learning. This analysis provides a mechanistic examination of how emerging neuroscience principles might inform pedagogical choices at all educational levels.

Effect of emotions on learning, memory, and disorders associated with the changes in expression levels: A narrative review

Emotions, in general, have no scientific definition. Emotions can be denoted as the mental state because of the neurophysiological changes. Emotions are related to mood, personality, temperament, and consciousness. People exhibit different emotions in different situations causing changes in cognitive functions. One of the major cognitive functions is the ability to learn, to store the acquired information in the parts of the brain such as the hippocampus, amygdala, cortex, and cerebellum. Learning and memory are affected by different types of emotions. Emotional responses such as fear, depression, and stress have impaired effects on cognitive functions such as learning and memory, whereas optimistic and happy emotions have positive effects on long-term memory. Certain disorders have greater effects on the regions of the brain which are also associated with synaptic plasticity and Learning and Memory(LM). Neuroimaging techniques are involved in studying the changing regions of the brain due to varied emotions and treatment strategies based on the changes observed. There are many drugs, and in advancements, nanotechnology is also utilized in the treatment of such psychiatric disorders. To improve mental health and physical health, emotional balance is most important, and effective care should be provided for people with less emotional quotient and different types of disorders to inhibit cognitive dysfunctions. In this review, emotions and their varied effects on a cognitive function named learning and memory, disorders associated with the defects of learning due to emotional instability, the areas of the brain that are in control of emotions, diagnosis, and treatment strategies for psychiatric disorders dependent on emotions are discussed.

States of epistemic curiosity interfere with memory for incidental scholastic facts

Curiosity can be a powerful motivator to learn and retain new information. Evidence shows that high states of curiosity elicited by a specific source (i.e., a trivia question) can promote memory for incidental stimuli (non-target) presented close in time. The spreading effect of curiosity states on memory for other information has potential for educational applications. Specifically, it could provide techniques to improve learning for information that did not spark a sense of curiosity on its own. Here, we investigated how high states of curiosity induced through trivia questions affect memory performance for unrelated scholastic facts (e.g., scientific, English, or historical facts) presented in close temporal proximity to the trivia question. Across three task versions, participants viewed trivia questions closely followed in time by a scholastic fact unrelated to the trivia question, either just prior to or immediately following the answer to the trivia question. Participants then completed a surprise multiple-choice memory test (akin to a pop quiz) for the scholastic material. In all three task versions, memory performance was poorer for scholastic facts presented after trivia questions that had elicited high versus low levels of curiosity. These results contradict previous findings showing curiosity-enhanced memory for incidentally presented visual stimuli and suggest that target information that generates a high-curiosity state interferes with encoding complex and unrelated scholastic facts presented close in time.

Awake ripples enhance emotional memory encoding in the human brain

Enhanced memory for emotional experiences is hypothesized to depend on amygdala-hippocampal interactions during memory consolidation. Here we show using intracranial recordings from the human amygdala and the hippocampus during an emotional memory encoding and discrimination task increased awake ripples after encoding of emotional, compared to neutrally-valenced stimuli. Further, post-encoding ripple-locked stimulus similarity is predictive of later memory discrimination. Ripple-locked stimulus similarity appears earlier in the amygdala than in hippocampus and mutual information analysis confirms amygdala influence on hippocampal activity. Finally, the joint ripple-locked stimulus similarity in the amygdala and hippocampus is predictive of correct memory discrimination. These findings provide electrophysiological evidence that post-encoding ripples enhance memory for emotional events.

In-Sensor Computing Realization Using Fully CMOS-Compatible TiN/HfOx-Based Neuristor Array

With the evolution of artificial intelligence, the explosive growth of data from sensory terminals gives rise to severe energy-efficiency bottleneck issues due to cumbersome data interactions among sensory, memory, and computing modules. Heterogeneous integration methods such as chiplet technology can significantly reduce unnecessary data movement; however, they fail to address the fundamental issue of the substantial time and energy overheads resulting from the physical separation of computing and sensory components. Brain-inspired in-sensor neuromorphic computing (ISNC) has plenty of room for such data-intensive applications. However, one key obstacle in developing ISNC systems is the lack of compatibility between material systems and manufacturing processes deployed in sensors and computing units. This study successfully addresses this challenge by implementing fully CMOS-compatible TiN/HfOx-based neuristor array. The developed ISNC system demonstrates several advantageous features, including multilevel analogue modulation, minimal dispersion, and no significant degradation in conductance (@125 °C). These characteristics enable stable and reproducible neuromorphic computing. Additionally, the device exhibits modulatable sensory and multi-store memory processes. Furthermore, the system achieves information recognition with a high accuracy rate of 93%, along with frequency selectivity and notable activity-dependent plasticity. This work provides a promising route to affordable and highly efficient sensory neuromorphic systems.

Hippocampal Mechanisms Support Cortisol-Induced Memory Enhancements

Stress can powerfully influence episodic memory, often enhancing memory encoding for emotionally salient information. These stress-induced memory enhancements stand at odds with demonstrations that stress and the stress-related hormone cortisol can negatively affect the hippocampus, a brain region important for episodic memory encoding. To resolve this apparent conflict and determine whether and how the hippocampus supports memory encoding under cortisol, we combined behavioral assays of associative memory, high-resolution fMRI, and pharmacological manipulation of cortisol in a within-participant, double-blinded procedure (in both sexes). Behaviorally, hydrocortisone promoted the encoding of subjectively arousing, positive associative memories. Neurally, hydrocortisone led to enhanced functional connectivity between hippocampal subregions, which predicted subsequent memory enhancements for emotional associations. Cortisol also modified the relationship between hippocampal representations and associative memory: whereas hippocampal signatures of distinctiveness predicted memory under placebo, relative integration predicted memory under cortisol. Together, these data provide novel evidence that the human hippocampus contains the necessary machinery to support emotional associative memory enhancements under cortisol.SIGNIFICANCE STATEMENT Our daily lives are filled with stressful events, which powerfully shape the way we form episodic memories. For example, stress and stress-related hormones can enhance our memory for emotional events. However, the mechanisms underlying these memory benefits are unclear. In the current study, we combined functional neuroimaging, behavioral tests of memory, and double-blind, placebo-controlled hydrocortisone administration to uncover the effects of the stress-related hormone cortisol on the function of the human hippocampus, a brain region important for episodic memory. We identified novel ways in which cortisol can enhance hippocampal function to promote emotional memories, highlighting the adaptive role of cortisol in shaping memory formation.

Declining locus coeruleus-dopaminergic and noradrenergic modulation of long-term memory in aging and Alzheimer's disease

Memory is essential in defining our identity by guiding behavior based on past experiences. However, aging leads to declining memory, disrupting older adult's lives. Memories are encoded through experience-dependent modifications of synaptic strength, which are regulated by the catecholamines dopamine and noradrenaline. While cognitive aging research demonstrates how dopaminergic neuromodulation from the substantia nigra-ventral tegmental area regulates hippocampal synaptic plasticity and memory, recent findings indicate that the noradrenergic locus coeruleus sends denser inputs to the hippocampus. The locus coeruleus produces dopamine as biosynthetic precursor of noradrenaline, and releases both to modulate hippocampal plasticity and memory. Crucially, the locus coeruleus is also the first site to accumulate Alzheimer's-related abnormal tau and severely degenerates with disease development. New in-vivo assessments of locus coeruleus integrity reveal associations with Alzheimer's markers and late-life memory impairments, which likely stem from impaired dopaminergic and noradrenergic neurotransmission. Bridging research across species, the reviewed findings suggest that degeneration of the locus coeruleus results in deficient dopaminergic and noradrenergic modulation of hippocampal plasticity and thus memory decline.

The ubiquitin-proteasome system and learning-dependent synaptic plasticity - A 10 year update

Over 25 years ago, a seminal paper demonstrated that the ubiquitin-proteasome system (UPS) was involved in activity-dependent synaptic plasticity. Interest in this topic began to expand around 2008 following another seminal paper showing that UPS-mediated protein degradation controlled the "destabilization" of memories following retrieval, though we remained with only a basic understanding of how the UPS regulated activity- and learning-dependent synaptic plasticity. However, over the last 10 years there has been an explosion of papers on this topic that has significantly changed our understanding of how ubiquitin-proteasome signaling regulates synaptic plasticity and memory formation. Importantly, we now know that the UPS controls much more than protein degradation, is involved in plasticity underlying drugs of abuse and that there are significant sex differences in how ubiquitin-proteasome signaling is used for memory storage processes. Here, we aim to provide a critical 10-year update on the role of ubiquitin-proteasome signaling in synaptic plasticity and memory formation, including updated cellular models of how ubiquitin-proteasome activity could be regulating learning-dependent synaptic plasticity in the brain.

Characterization of deconditioning-update on fear memory attenuation

Fear memory expression can be attenuated by updating the footshock perception during the plastic state induced by retrieval, from a strong unconditioned stimulus to a very weak one through deconditioning. In this process, the original fear association of the conditioned stimulus with the footshock is substituted by an innocuous stimulus and the animals no longer express a fear response. In the present study, we explore the boundaries of this deconditioning-update strategy by the characterization of this phenomenon. We found that there is an optimal mismatch between the footshock intensity delivered in the training and in the reactivation. Likewise, we characterized the temporal window that the protocol is efficient in hindering fear response. Our findings contribute to a better understanding of the limits in which deconditioning acts in attenuating fear memory, so that an optimized protocol using this strategy can be planned in order to deal with emotional disorders.

Control of working memory maintenance by theta-gamma phase amplitude coupling of human hippocampal neurons

Retaining information in working memory (WM) is a demanding process that relies on cognitive control to protect memoranda-specific persistent activity from interference. How cognitive control regulates WM storage, however, remains unknown. We hypothesized that interactions of frontal control and hippocampal persistent activity are coordinated by theta-gamma phase amplitude coupling (TG-PAC). We recorded single neurons in the human medial temporal and frontal lobe while patients maintained multiple items in WM. In the hippocampus, TG-PAC was indicative of WM load and quality. We identified cells that selectively spiked during nonlinear interactions of theta phase and gamma amplitude. These PAC neurons were more strongly coordinated with frontal theta activity when cognitive control demand was high, and they introduced information-enhancing and behaviorally relevant noise correlations with persistently active neurons in the hippocampus. We show that TG-PAC integrates cognitive control and WM storage to improve the fidelity of WM representations and facilitate behavior.

The Illusion of Pure Reason in Science: A Cautionary Note

Introspection tells people that their behavior is both consciously reasoned and functional (i.e., rational), at least based on the evidence available to them. In contrast, research has found that much human behavior reported to be consciously determined, is strongly influenced by heuristics and the mechanistic principles of associative learning that usually function unconsciously and are sometimes sub-optimal. Scientists are trained to base their conclusions on a rational analysis of evidence, which enhances the scientific validity of their conclusions. But scientific training appears to do little to constrain the role of unconscious heuristics. The present point is that scientists are humans and, as such, they are subject to the influence of heuristics in their scientific conclusions just as laypeople are in their everyday behavior. As an example, the availability heuristic and how it seemingly feeds the repetition-induced truth effect are described. One consequence of this is that failures to replicate frequently cited papers do little to devalue the irreplicable reports. Although unconscious heuristics influence the scientific thinking of researchers, scientists are typically unaware of the role of these heuristics due to their operating below the horizon of introspection. This appears to explain the persistence, in light of overwhelming evidence to the contrary, of the views by many researchers that 'a prediction error is necessary for learning' and that 'reactivated memories have to be reconsolidated to be retained for future access.'

Hippocampal mechanisms support cortisol-induced memory enhancements

Stress can powerfully influence episodic memory, often enhancing memory encoding for emotionally salient information. These stress-induced memory enhancements stand at odds with demonstrations that stress and the stress-related hormone cortisol can negatively affect the hippocampus, a brain region important for episodic memory encoding. To resolve this apparent conflict and determine whether and how the hippocampus supports memory encoding under cortisol, we combined behavioral assays of associative memory, high-resolution functional magnetic resonance imaging (fMRI), and pharmacological manipulation of cortisol in a within-participant, double-blinded procedure. Hydrocortisone led to enhanced functional connectivity between hippocampal subregions, which predicted subsequent memory enhancements for emotional information. Cortisol also modified the relationship between hippocampal representations and memory: whereas hippocampal signatures of distinctiveness predicted memory under placebo, relative integration predicted memory under cortisol. Together, these data provide novel evidence that the human hippocampus contains the necessary machinery to support emotional memory enhancements under stress.

Hippocampal cholinergic receptors and the mTOR participation in fear-motivated inhibitory avoidance extinction memory

Evidence has demonstrated the hippocampal cholinergic system and the mammalian target of rapamycin (mTOR) participation during the memory formation of aversive events. This study assessed the role of these systems in the hippocampus for the extinction memory process by submitting male Wistar rats to fear-motivated step-down inhibitory avoidance (IA). The post-extinction session administration of the nicotinic and muscarinic cholinergic receptor antagonists, mecamylamine and scopolamine, respectively, both at doses of 2 µg/µl/side, and rapamycin, an mTOR inhibitor (0.02 µg/µl/side), into the CA1 region of the dorsal hippocampus, impaired the IA extinction memory. Furthermore, the nicotinic and muscarinic cholinergic receptor agonists, nicotine and muscarine, respectively, had a dose-dependent effect on the IA extinction memory when administered intra-CA1, immediately after the extinction session. Nicotine (0.6 µg/µl/side) and muscarine (0.02 µg/µl/side), respectively, had no effect, while the higher doses (6 and 2 µg/µl/side, respectively) impaired the IA extinction memory. Interestingly, the co-administration of muscarine at the lower dose blocked the impairment that was induced by rapamycin. This effect was not observed when nicotine at the lower dose was co-administered. These results have demonstrated the participation of the cholinergic receptors and mTOR in the hippocampus for IA extinction, and that the cholinergic agonists had a dose-dependent effect on the IA extinction memory. This study provides insights related to the behavioural aspects and the neurobiological properties underlying the early stage of fear-motivated IA extinction memory consolidation and suggests that there is hippocampal muscarinic receptor participation independent of mTOR in this memory process.

PDZD8-deficient mice manifest behavioral abnormalities related to emotion, cognition, and adaptation due to dyslipidemia in the brain

Although dyslipidemia in the brain has been implicated in neurodegenerative disorders, the molecular mechanisms underlying its pathogenesis have been largely unclear. PDZD8 is a lipid transfer protein and mice deficient in PDZD8 (PDZD8-KO mice) manifest abnormal accumulation of cholesteryl esters (CEs) in the brain due to impaired lipophagy, the degradation system of lipid droplets. Here we show the detailed mechanism of PDZD8-dependent lipophagy. PDZD8 transports cholesterol to lipid droplets (LDs), and eventually promotes fusion of LDs and lysosomes. In addition, PDZD8-KO mice exhibit growth retardation, hyperactivity, reduced anxiety and fear, increased sensorimotor gating, and impaired cued fear conditioned memory and working memory. These results indicate that abnormal CE accumulation in the brain caused by PDZD8 deficiency affects emotion, cognition and adaptive behavior, and that PDZD8 plays an important role in the maintenance of brain function through lipid metabolism.

Effect of Cannabis on Memory Consolidation, Learning and Retrieval and Its Current Legal Status in India: A Review

Cannabis is one of the oldest crops grown, traditionally held religious attachments in various cultures for its medicinal use much before its introduction to Western medicine. Multiple preclinical and clinical investigations have explored the beneficial effects of cannabis in various neurocognitive and neurodegenerative diseases affecting the cognitive domains. Tetrahydrocannabinol (THC), the major psychoactive component, is responsible for cognition-related deficits, while cannabidiol (CBD), a non-psychoactive phytocannabinoid, has been shown to elicit neuroprotective activity. In the present integrative review, the authors focus on the effects of cannabis on the different cognitive domains, including learning, consolidation, and retrieval. The present study is the first attempt in which significant focus has been imparted on all three aspects of cognition, thus linking to its usage. Furthermore, the investigators have also depicted the current legal position of cannabis in India and the requirement for reforms.

The effects of physical activity timing and complexity on episodic memory: A randomized controlled trial

The role of two types of acute physical activity (PA) bouts were assessed on young adults' free-recall and recognition memory in two experiments, which differed in the temporal relation of PA and word encoding. Before or following training on the Rey Auditory Verbal Learning Task, participants performed a simple two-step dance, a complex four-step dance, or remained seated. Hypotheses proposed that PA prior to encoding and complex PA would enhance PA's mnemonic benefits. Memory assessed post-PA, 24 h, and 7 days after training indicated that timing and complexity of PA did not impact free-recall or recognition memory. Findings differ from a previous study showing complex PA benefited motor learning more than simple PA (Tomporowski & Pendleton, 2018). The inconsistency may be due to different working memory processes underlying consolidation and retrieval of procedural or episodic information. Theory-based explanations regarding memory storage and retrieval are proposed to elucidate this selective process.

Reappraisal enhances memory formation for a stressful episode

Emotion regulation strategies have been shown to modify the physiological response to stress, yet whether these strategies can modulate also cognitive responses to stress is largely unknown. A prominent cognitive response to stress is the enhanced memory formation for the stressful event, which is an adaptive mechanism to prepare for similar events in the future. Thus, the present study aimed to investigate whether emotion regulation strategies impact the memory formation for a stressful episode. In a two-day study, participants (n = 124) underwent an enriched stressful episode or a control episode. Critically, before the exposure to the stressor, they were instructed to use a suppression or reappraisal strategy during the stressful episode. One week later, participants completed a memory test for central and peripheral details of this episode. Our results show that reappraisal enhanced not only the cortisol response to the stressor but also the memory formation for central features of the stressful episode. This reappraisal-related boost of memory for the stressor was particularly pronounced in participants' with high working memory capacity. These findings show that reappraisal may not only impact the physiological response to a stressful event but also the cognitive representation of this event in memory.

Wakeful Rest Benefits Recall, but Not Recognition, of Incidentally Encoded Memory Stimuli in Younger and Older Adults

Older adults exhibit deficits in episodic memory tasks, which have often been attributed to encoding or retrieval deficits, with little attention to consolidation mechanisms. More recently, researchers have attempted to measure consolidation in the context of a behavioral experiment using the wakeful rest paradigm (i.e., a brief, quiet period of minimal stimulation, which facilitates memory performance, compared to a distractor task). Critically, older adults might not produce this effect, given established age differences in other episodic memory processes and mind-wandering. In three experiments, we directly compared younger and older adults in modified versions of the wakeful rest paradigm. Critically, we utilized incidental encoding procedures (all experiments) and abstract shape stimuli (in Experiment 3) to limit the possibility of retrieval practice or maintenance rehearsal as potential confounding mechanisms in producing the wakeful rest effect. Wakeful rest reliably and equally benefited recall of incidentally encoded words in both younger and older adults. In contrast, wakeful rest had no benefit for standard accuracy measures of recognition performance in verbal stimuli, although there was an effect in response latencies for non-verbal stimuli. Overall, these results suggest that the benefits of wakeful rest on episodic retrieval are preserved across age groups, and hence support age-independence in potential consolidation mechanisms as measured by wakeful rest. Further, these benefits do not appear to be dependent on the intentionality of encoding or variations in distractor task types. Finally, the lack of wakeful rest benefits on recognition performance might be driven by theoretical constraints on the effect or methodological limitations of recognition memory testing in the current paradigm.

Transcutaneous auricular vagus nerve stimulation in poststroke cognitive impairment: protocol for a randomised controlled trial

BACKGROUND

As one of the most common stroke sequelae, poststroke cognitive impairment significantly impacts 17.6%-83% of survivors, affecting their rehabilitation, daily living and quality of life. Improving cognitive abilities among patients in stroke recovery is therefore critical and urgent. Transcutaneous auricular vagus nerve stimulation (TAVNS) is a non-invasive, safe, cost-effective treatment with great potential for improving the cognitive function of poststroke patients. This clinical research will evaluate the effectiveness, and help elucidate the possible underlying mechanisms, of TAVNS for improving poststroke cognitive function.

METHODS AND ANALYSIS

A single-centre, parallel-group, allocation concealment, assessor-blinded randomised controlled clinical trial. We will allocate 88 recruited participants to the TAVNS or sham group for an intervention that will run for 8 weeks, 5 days per week with twice daily sessions lasting 30 min each. Blood tests will be performed and questionnaires issued at baseline and 8-week and 12 week follow-ups. Primary outcomes will be changes in cognitive function scores. Secondary outcomes will be changes in activities of daily living, quality of life and serum oxidative stress indicators.

ETHICS AND DISSEMINATION

The Ethics Committee of the First Affiliated Hospital of Hunan University of Chinese Medicine has approved the protocol (No. HN-LL-YJSLW-2022200). Findings will be published in peer-reviewed academic journals and presented at scientific conferences.

TRIAL REGISTRATION NUMBER

ChiCTR2200057808.

Wakeful resting and listening to music contrast their effects on verbal long-term memory in dependence on word concreteness

Wakeful resting and listening to music are powerful means to modulate memory. How these activities affect memory when directly compared has not been tested so far. In two experiments, participants encoded and immediately recalled two word lists followed by either 6 min wakefully resting or 6 min listening to music. The results of Experiment 1 show that both post-encoding conditions have a similar effect on memory after 1 day. In Experiment 2, we explored the possibility that less concrete words, i.e. lower in imageability than in Experiment 1, are differently affected by the two post-encoding conditions. The results of Experiment 2 show that, when words are less concrete, more words are retained after 1 day when encoding is followed by wakeful resting rather than listening to music. These findings indicate that the effects of wakeful resting and listening to music on memory consolidation are moderated by the concreteness of the encoded material.

Tag and capture: how salient experiences target and rescue nearby events in memory

The long-term fate of a memory is not exclusively determined by the events occurring at the moment of encoding. Research at the cellular, circuit, and behavioral levels is beginning to reveal how neurochemical activations in the moments surrounding an event can retroactively and proactively rescue weak memory for seemingly mundane experiences. We review emerging evidence showing enhancement of weakly formed memories encoded minutes to hours before or after a related motivationally relevant experience. We discuss proposed neurobiological mechanisms for strengthening weak memories formed in temporal proximity to a strong event, and how this knowledge could be leveraged to improve memory for information that is prone to forgetting.

Distinct stress-related changes in intrinsic amygdala connectivity predict subsequent positive and negative memory performance

Experiencing stress before an event can influence how that event is later remembered. In the current study, we examine how individual differences in one's physiological response to a stressor are related to changes to underlying brain states and memory performance. Specifically, we examined how changes in intrinsic amygdala connectivity relate to positive and negative memory performance as a function of stress response, defined as a change in cortisol. Twenty-five participants underwent a social stressor before an incidental emotional memory encoding task. Cortisol samples were obtained before and after the stressor to measure individual differences in stress response. Three resting state scans (pre-stressor, post-stressor/pre-encoding and post-encoding) were conducted to evaluate pre- to post-stressor and pre- to post-encoding changes to intrinsic amygdala connectivity. Analyses examined relations between greater cortisol changes and connectivity changes. Greater cortisol increases were associated with a greater decrease in prefrontal-amygdala connectivity following the stressor and a reversal in the relation between prefrontal-amygdala connectivity and negative vs. positive memory performance. Greater cortisol increases were also associated with a greater increase in amygdala connectivity with a number of posterior sensory regions following encoding. Consistent with prior findings in non-stressed individuals, pre- to post-encoding increases in amygdala-posterior connectivity were associated with greater negative relative to positive memory performance, although this was specific to lateral rather than medial posterior regions and to participants with the greatest cortisol changes. These findings suggest that stress response is associated with changes in intrinsic connectivity that have downstream effects on the valence of remembered emotional content.

Dopamine activity on the perceptual salience for recognition memory

To survive, animals must recognize relevant stimuli and distinguish them from inconspicuous information. Usually, the properties of the stimuli, such as intensity, duration, frequency, and novelty, among others, determine the salience of the stimulus. However, previously learned experiences also facilitate the perception and processing of information to establish their salience. Here, we propose “perceptual salience” to define how memory mediates the integration of inconspicuous stimuli into a relevant memory trace without apparently altering the recognition of the physical attributes or valence, enabling the detection of stimuli changes in future encounters. The sense of familiarity is essential for successful recognition memory; in general, familiarization allows the transition of labeling a stimulus from the novel (salient) to the familiar (non-salient). The novel object recognition (NOR) and object location recognition (OLRM) memory paradigms represent experimental models of recognition memory that allow us to study the neurobiological mechanisms involved in episodic memory. The catecholaminergic system has been of vital interest due to its role in several aspects of recognition memory. This review will discuss the evidence that indicates changes in dopaminergic activity during exposure to novel objects or places, promoting the consolidation and persistence of memory. We will discuss the relationship between dopaminergic activity and perceptual salience of stimuli enabling learning and consolidation processes necessary for the novel-familiar transition. Finally, we will describe the effect of dopaminergic deregulation observed in some pathologies and its impact on recognition memory.

Artificial Neural Pathway Based on a Memristor Synapse for Optically Mediated Motion Learning

Animals execute intelligent and efficient interactions with their surroundings through neural pathways, exhibiting learning, memory, and cognition. Artificial autonomous devices that generate self-optimizing feedback mimicking biological systems are essential in pursuing future intelligent robots. Here, we report an artificial neural pathway (ANP) based on a memristor synapse to emulate neuromorphic learning behaviors. In our ANP, optical stimulations are detected and converted into electrical signals through a flexible perovskite photoreceptor. The acquired electrical signals are further processed in a zeolitic imidazolate frameworks-8 (ZIF-8)-based memristor device. By controlling the growth of the ZIF-8 nanoparticles, the conductance of the memristor can be finely modulated with electrical stimulations to mimic the modulation of synaptic plasticity. The device is employed in the ANP to implement synaptic functions of learning and memory. Subsequently, the synaptic feedbacks are used to direct a robotic arm to perform responding motions. Upon repeatedly "reviewing" the optical stimulation, the ANP is able to learn, memorize, and complete the specific motions. This work provides a promising strategy toward the design of intelligent autonomous devices and bioinspired robots through memristor-based systems.

Interfering With Contextual Fear Memories by Post-reactivation Administration of Propranolol in Mice: A Series of Null Findings

Post-reactivation amnesia of contextual fear memories by blockade of noradrenergic signaling has been shown to have limited replicability in rodents. This is usually attributed to several boundary conditions that gate the destabilization of memory during its retrieval. How these boundary conditions can be overcome, and what neural mechanisms underlie post-reactivation changes in contextual fear memories remain largely unknown. Here, we report a series of experiments in a contextual fear-conditioning paradigm in mice, that were aimed at solving these issues. We first attempted to obtain a training paradigm that would consistently result in contextual fear memory that could be destabilized upon reactivation, enabling post-retrieval amnesia by the administration of propranolol. Unexpectedly, our attempts were unsuccessful to this end. Specifically, over a series of experiments in which we varied different parameters of the fear acquisition procedure, at best small and inconsistent effects were observed. Additionally, we found that propranolol did not alter retrieval-induced neural activity, as measured by the number of c-Fos⁺ cells in the hippocampal dentate gyrus. To determine whether propranolol was perhaps ineffective in interfering with reactivated contextual fear memories, we also included anisomycin (i.e., a potent and well-known amnesic drug) in several experiments, and measures of synaptic glutamate receptor subunit GluA2 (i.e., a marker of memory destabilization). No post-retrieval amnesia by anisomycin and no altered GluA2 expression by reactivation was observed, suggesting that the memories did not undergo destabilization. The null findings are surprising, given that the training paradigms we implemented were previously shown to result in memories that could be modified upon reactivation. Together, our observations illustrate the elusive nature of reactivation-dependent changes in non-human fear memory.

Alpha-2 Adrenoreceptor Antagonist Yohimbine Potentiates Consolidation of Conditioned Fear

BACKGROUND

Hyperconsolidation of aversive associations and poor extinction learning have been hypothesized to be crucial in the acquisition of pathological fear. Previous animal and human research points to the potential role of the catecholaminergic system, particularly noradrenaline and dopamine, in acquiring emotional memories. Here, we investigated in a between-participants design with 3 groups whether the noradrenergic alpha-2 adrenoreceptor antagonist yohimbine and the dopaminergic D2-receptor antagonist sulpiride modulate long-term fear conditioning and extinction in humans.

METHODS

Fifty-five healthy male students were recruited. The final sample consisted of n = 51 participants who were explicitly aware of the contingencies between conditioned stimuli (CS) and unconditioned stimuli after fear acquisition. The participants were then randomly assigned to 1 of the 3 groups and received either yohimbine (10 mg, n = 17), sulpiride (200 mg, n = 16), or placebo (n = 18) between fear acquisition and extinction. Recall of conditioned (non-extinguished CS+ vs CS-) and extinguished fear (extinguished CS+ vs CS-) was assessed 1 day later, and a 64-channel electroencephalogram was recorded.

RESULTS

The yohimbine group showed increased salivary alpha-amylase activity, confirming a successful manipulation of central noradrenergic release. Elevated fear-conditioned bradycardia and larger differential amplitudes of the N170 and late positive potential components in the event-related brain potential indicated that yohimbine treatment (compared with a placebo and sulpiride) enhanced fear recall during day 2.

CONCLUSIONS

These results suggest that yohimbine potentiates cardiac and central electrophysiological signatures of fear memory consolidation. They thereby elucidate the key role of noradrenaline in strengthening the consolidation of conditioned fear associations, which may be a key mechanism in the etiology of fear-related disorders.

Revisiting Preclinical Observations of Several Histamine H3 Receptor Antagonists/Inverse Agonists in Cognitive Impairment, Anxiety, Depression, and Sleep-Wake Cycle Disorder

A relationship appears to exist between dysfunction of brain histamine (HA) and various neuropsychiatric brain disorders. The possible involvement of brain HA in neuropathology has gained attention recently, and its role in many (patho)physiological brain functions including memory, cognition, and sleep-wake cycle paved the way for further research on the etiology of several brain disorders. Histamine H3 receptor (H3R) evidenced in the brains of rodents and humans remains of special interest, given its unique position as a pre- and postsynaptic receptor, controlling the synthesis and release of HA as well as different other neurotransmitters in different brain regions, respectively. Despite several disappointing outcomes for several H3R antagonists/inverse agonists in clinical studies addressing their effectiveness in Alzheimer's disease (AD), Parkinson's disease (PD), and schizophrenia (SCH), numerous H3R antagonists/inverse agonists showed great potentials in modulating memory and cognition, mood, and sleep-wake cycle, thus suggesting its potential role in neurocognitive and neurodegenerative diseases such as AD, PD, SCH, narcolepsy, and major depression in preclinical rodent models. In this review, we present preclinical applications of selected H3R antagonists/inverse agonists and their pharmacological effects on cognitive impairment, anxiety, depression, and sleep-wake cycle disorders. Collectively, the current review highlights the behavioral impact of developments of H3R antagonists/inverse agonists, aiming to further encourage researchers in the preclinical drug development field to profile the potential therapeutic role of novel antagonists/inverse agonists targeting histamine H3Rs.

Laboratory models of post-traumatic stress disorder: The elusive bridge to translation

Post-traumatic stress disorder (PTSD) is a debilitating mental illness composed of a heterogeneous collection of symptom clusters. The unique nature of PTSD as arising from a precipitating traumatic event helps simplify cross-species translational research modeling the neurobehavioral effects of stress and fear. However, the neurobiological progress on these complex neural circuits informed by animal models has yet to produce novel, evidence-based clinical treatment for PTSD. Here, we provide a comprehensive overview of popular laboratory models of PTSD and provide concrete ideas for improving the validity and clinical translational value of basic research efforts in humans. We detail modifications to simplified animal paradigms to account for myriad cognitive factors affected in PTSD, which may contribute to abnormalities in regulating fear. We further describe new avenues for integrating different areas of psychological research underserved by animal models of PTSD. This includes incorporating emerging trends in the cognitive neuroscience of episodic memory, emotion regulation, social-emotional processes, and PTSD subtyping to provide a more comprehensive recapitulation of the human experience to trauma in laboratory research.

Unrelenting Fear Under Stress: Neural Circuits and Mechanisms for the Immediate Extinction Deficit

Therapeutic interventions for disorders of fear and anxiety rely on behavioral approaches that reduce pathological fear memories. For example, learning that threat-predictive stimuli are no longer associated with aversive outcomes is central to the extinction of conditioned fear responses. Unfortunately, fear memories are durable, long-lasting, and resistant to extinction, particularly under high levels of stress. This is illustrated by the “immediate extinction deficit,” which is characterized by a poor long-term reduction of conditioned fear when extinction procedures are attempted within hours of fear conditioning. Here, I will review recent work that has provided new insight into the neural mechanisms underlying resistance to fear extinction. Emerging studies reveal that locus coeruleus norepinephrine modulates amygdala-prefrontal cortical circuits that are critical for extinction learning. These data suggest that stress-induced activation of brain neuromodulatory systems biases fear memory at the expense of extinction learning. Behavioral and pharmacological strategies to reduce stress in patients undergoing exposure therapy might improve therapeutic outcomes.

Effects of acute exercise on emotional memory

Research has demonstrated beneficial effects of acute exercise on memory for neutral materials, such as word lists of neutral valence/low arousal. However, the impacts of exercise on emotional memory is less understood. Across three laboratory experiments in college students, we tested if acute exercise could enhance both neutral and emotional memory performance, anticipating a greater effect for emotional memory. We examined effects of exercise at varying intensities (Experiment 1: high-intensity; Experiment 2: low- and high-intensity; Experiment 3: moderate-intensity), of diverse modalities (Experiment 1: treadmill jogging; Experiment 2: cycling; Experiment 3: open-skill (racquetball) and closed-skill (treadmill jogging) exercise), and on emotional memory performance assessed at increasing levels of hippocampal dependency (Experiment 1: Y/N recognition task; Experiment 2: paired-associative recognition task; Experiment 3: cued-recall task). We found that, in all experiments, acute exercise did not significantly influence emotional or neutral memory performance relative to sedentary control conditions. However, we observed several noteworthy outcomes indicating that acute exercise may be linked to improvements in memory confidence and accuracy for central aspects of emotional memory stimuli, and that select exercise modalities (e.g. treadmill exercise) may also be associated with increased frequency of memory intrusions.

Mechanisms of memory under stress

It is well established that stress has a major impact on memory, driven by the concerted action of various stress mediators on the brain. Recent years, however, have seen considerable advances in our understanding of the cellular, neural network, and cognitive mechanisms through which stress alters memory. These novel insights highlight the intricate interplay of multiple stress mediators, including-beyond corticosteroids, catecholamines, and peptides-for instance, endocannabinoids, which results in time-dependent shifts in large-scale neural networks. Such stress-induced network shifts enable highly specific memories of the stressful experience in the long run at the cost of transient impairments in mnemonic flexibility during and shortly after a stressful event. Based on these recent discoveries, we provide a new integrative framework that links the cellular, systems, and cognitive mechanisms underlying acute stress effects on memory processes and points to potential targets for treating aberrant memory in stress-related mental disorders.

Extended amygdala, conditioned withdrawal and memory consolidation

Opioid withdrawal can be associated to environmental cues through classical conditioning. Exposure to these cues can precipitate a state of conditioned withdrawal in abstinent subjects, and there are suggestions that conditioned withdrawal can perpetuate the addiction cycle in part by promoting the storage of memories. This review discusses evidence supporting the hypothesis that conditioned withdrawal facilitates memory consolidation by activating a neurocircuitry that involves the extended amygdala. Specifically, the central amygdala, the bed nucleus of the stria terminalis, and the nucleus accumbens shell interact functionally during withdrawal, mediate expression of conditioned responses, and are implicated in memory consolidation. From this perspective, the extended amygdala could be a neural pathway by which drug-seeking behaviour performed during a state of conditioned withdrawal is more likely to become habitual and persistent.

The potential of invasive and non-invasive vagus nerve stimulation to improve verbal memory performance in epilepsy patients

It has been demonstrated that acute vagus nerve stimulation (VNS) improves word recognition memory in epilepsy patients. Transcutaneous auricular vagus nerve stimulation (taVNS) has gained interest as a non-invasive alternative to improve cognition. In this prospective randomized cross-over study, we investigated the effect of both invasive VNS and taVNS on verbal memory performance in 15 patients with drug-resistant epilepsy. All patients conducted a word recognition memory paradigm in 3 conditions: VNS ON, VNS OFF and taVNS (3-period 3-treatment cross-over study design). For each condition, patients memorized 21 highlighted words from text paragraphs. Afterwards, the intervention was delivered for 30 s. Immediate recall and delayed recognition scores were obtained for each condition. This memory paradigm was repeated after 6 weeks of VNS therapy in 2 conditions: VNS ON and VNS OFF (2-period 2-treatment cross-over study design). Acute VNS and taVNS did not improve verbal memory performance. Immediate recall and delayed recognition scores were significantly improved after 6 weeks of VNS treatment irrespective of the acute intervention. We can conclude that the previously described positive effects of invasive VNS on verbal memory performance could not be replicated with invasive VNS and taVNS. An improved verbal memory performance was seen after 6 weeks of VNS treatment, suggesting that longer and more repetitive stimulation of the vagal pathway is required to modulate verbal memory performance.Clinical trial registration number: NCT05031208.

Distinct medial-tempora lobe mechanisms of encoding and amygdala-mediated memory reinstatement for disgust and fear

Current models of episodic memory posit that retrieval involves the reenactment of encoding processes. Recent evidence has shown that this reinstatement process - indexed by subsequent encoding-retrieval similarity of brain activity patterns - is related to the activity in the hippocampus during encoding. However, we tend to re-experience emotional events in memory more richly than dull events. The role of amygdala - a critical hub of emotion processing - in reinstatement of emotional events was poorly understood. To investigate it, we leveraged a previously overlooked divergence in the role of amygdala in memory modulation by distinct emotions - disgust and fear. Here we used a novel paradigm in which participants encoded complex events (word pairs) and their memory was tested after 3 weeks, both phases during fMRI scanning. Using representational similarity analysis and univariate analyses, we show that the strength of amygdala activation during encoding was correlated with memory reinstatement of individual event representations in emotion-specific regions. Critically, amygdala modulated reinstatement more for disgust than fear. This was in line with other differences observed at the level of memory performance and neural mechanisms of encoding. Specifically, amygdala and perirhinal cortex were more involved during encoding of disgust-related events, whereas hippocampus and parahippocampal gyrus during encoding of fear-related events. Together, these findings shed a new light on the role of the amygdala and medial temporal lobe regions in encoding and reinstatement of specific emotional memories.

Sex hormones and cortisol during experimental trauma memory consolidation: Prospective association with intrusive memories

Background Trauma- and stress-related disorders, such as post-traumatic stress disorder (PTSD), are more common in females than in males. Sex hormones affect learning and emotional memory formation and may be associated with the development of PTSD. Most previous studies have indexed these hormones in isolation. Objectives: To investigate associations of sex hormones and cortisol during memory consolidation on the development of intrusive memories. Methods: We employed an experimental trauma film paradigm in 61 healthy women and indexed salivary testosterone, progesterone, estradiol, and cortisol on day one and day two post experimental trauma exposure and their effects on intrusion frequency, distress, and vividness. Intrusive trauma memories were indexed by means of a diary in which participants documented intrusion frequency, distress, and vividness. Results and conclusion: Participants reported an average of 5.3 intrusions over the course of seven days (SD = 4.6, range 0-26). Progesterone, and estradiol indexed on day one predicted intrusion frequency, with higher progesterone and lower estradiol predicting more intrusive memories (p-values AUC progesterone 0.01 and estradiol 0.02). There was no evidence for associations between hormone concentration indices on day two and intrusion outcomes. Further research on the roles of gonadal and adrenal hormones in trauma memory formation is needed to advance our efforts to understand their influence on PTSD development.

Empathy reduces susceptibility to false memory

Psychological and physiological evidence has demonstrated that the underlying mechanisms for empathy and for autobiographical memories were related to a great extent. However, whether the facilitative effect of empathy on memory also applied to misinformation was unknown. To test this, we used a misinformation paradigm on a sample of 51 participants aged 20–27. The participants viewed videos that evoked different degrees of empathy, and then were fed misleading information. The participants’ susceptibility to misleading information was lower for the videos that provoked a high degree of empathy compared to the videos that provoked a low degree of empathy. Based on our data, we conclude that empathy can prevent people from being misled by false information.

Role of Wnt signaling in synaptic plasticity and memory

Ever since their discoveries, the Wnt pathways have been consistently associated with key features of cellular development, including metabolism, structure and cell fate. The three known pathways (the canonical Wnt/β-catenin and the two non-canonical Wnt/Ca⁺⁺ and Wnt/JNK/PCP pathways) participate in complex networks of interaction with a wide range of regulators of cell function, such as GSK-3β, AKT, PKC and mTOR, among others. These proteins are known to be involved in the formation and maintenance of memory. Currently, studies with Wnt and memory have shown that the canonical and non-canonical pathways play key roles in different processes associated with memory. So, in this review we briefly summarize the different roles that Wnt signaling can play in neurons and in memory, as well as in Alzheimer's disease, focusing towards animal studies. We start with the molecular characterization of the family and its receptors, as well as the most commonly used drugs for pharmacological manipulations. Next, we describe its role in synaptic plasticity and memory, and how the regulations of these pathways affect crucial features of neuronal function. Furthermore, we succinctly present the current knowledge on how the Wnt pathways are implicated in Alzheimer's disease, and how studies are seeing them as a potential candidate for effective treatments. Lastly, we point toward challenges of Wnt research, and how knowledge on these pathways can lead towards a better understanding of neurobiological and pathological processes.

Short-Term Exposure to Nature and Benefits for Students’ Cognitive Performance: a Review

There is growing interest recently in the outdoor environment surrounding schools where students spent time during breaks, in-school activities, and after-school programs. Several reviews have examined the impact of long-term exposures to nearby nature on students’ academic achievement, but none has focused on the effects of short-term contacts with nature on students’ cognitive performance. The aim of this review is to understand the context in which short-term passive exposures to greenness occur, how cognitive performance is measured, and the conditions under which cognitive benefits emerge at various educational levels. We reviewed 14 studies in the extant literature that report investigations involving students at different educational levels, from elementary school to university, in a short exposure to nature lasting from 10 to 90 min during a study day. The review shows that in 12 out of the 14 studies, across educational levels, cognitive benefits emerge in terms of directed attention restoration from mental fatigue due to contact with nature. A no-cost opportunity to sustain students’ cognition is a break in a green environment after mentally demanding activities.

Noradrenergic arousal after encoding reverses the course of systems consolidation in humans

It is commonly assumed that episodic memories undergo a time-dependent systems consolidation process, during which hippocampus-dependent memories eventually become reliant on neocortical areas. Here we show that systems consolidation dynamics can be experimentally manipulated and even reversed. We combined a single pharmacological elevation of post-encoding noradrenergic activity through the α2-adrenoceptor antagonist yohimbine with fMRI scanning both during encoding and recognition testing either 1 or 28 days later. We show that yohimbine administration, in contrast to placebo, leads to a time-dependent increase in hippocampal activity and multivariate encoding-retrieval pattern similarity, an indicator of episodic reinstatement, between 1 and 28 days. This is accompanied by a time-dependent decrease in neocortical activity. Behaviorally, these neural changes are linked to a reduced memory decline over time after yohimbine intake. These findings indicate that noradrenergic activity shortly after encoding may alter and even reverse systems consolidation in humans, thus maintaining vividness of memories over time.

Relearning can eliminate the effect of retrieval-induced forgetting

The retrieval of a subset of items can cause the forgetting of other, non-retrieved items, a phenomenon known as retrieval-induced forgetting. Initial work suggested that giving people the opportunity to restudy non-retrieved items following retrieval practice is sufficient to eliminate the effect of retrieval-induced forgetting, but more recent work has suggested otherwise. If retrieval-induced forgetting is not eliminated by restudy, then such a finding would have important implications for understanding the theoretical nature of retrieval-induced forgetting. It would suggest, for example, that retrieval-induced forgetting reflects more than the temporary reduction in the accessibility of non-retrieved items in memory. The two experiments reported here sought to clarify this issue, with the results suggesting that retrieval-induced forgetting can be eliminated by restudy. Indeed, retrieval-induced forgetting was eliminated by restudy even when the forgetting effect was produced by three rounds of retrieval practice instead of one round of retrieval practice. These findings are consistent with the idea that retrieval-induced forgetting, at least under the conditions of the current experiments, reflects a temporary reduction in the accessibility of non-retrieved items in memory.

Interactions of Noradrenergic, Glucocorticoid and Endocannabinoid Systems Intensify and Generalize Fear Memory Traces

Systemic administration of drugs that activate the noradrenergic or glucocorticoid system potentiates aversive memory consolidation and reconsolidation. The opposite happens with the stimulation of endocannabinoid signaling under certain conditions. An unbalance of these interacting neurotransmitters can lead to the formation and maintenance of traumatic memories, whose strength and specificity attributes are often maladaptive. Here we aimed to investigate whether originally low-intensity and precise contextual fear memories would turn similar to traumatic ones in rats systemically administered with adrenaline, corticosterone, and/or the cannabinoid type-1 receptor antagonist/inverse agonist AM251 during consolidation or reconsolidation. The high dose of each pharmacological agent evaluated significantly increased freezing times at test in the conditioning context one and nine days later when given alone post-acquisition or post-retrieval. Their respective low dose produced no relative changes when given separately, but co-treatment of adrenaline with corticosterone or AM251 and the three drugs combined, but not corticosterone with AM251, produced results equivalent to those mentioned initially. Neither the high nor the low dose of adrenaline, corticosterone, or AM251 altered freezing times at test in a novel, neutral context two and ten days later. In contrast, animals receiving the association of their low dose exhibited significantly higher freezing times than controls. Together, the results indicate that newly acquired and destabilized threat memory traces become more intense and generalized after a combined interference acting synergistically and mimicking that reported in patients presenting stress-related psychiatric conditions.

Facing stress: No effect of acute stress at encoding or retrieval on face recognition memory

Eyewitnesses may experience stress during a crime and when attempting to identify the perpetrator subsequently. Laboratory studies can provide insight into how acute stress at encoding and retrieval affects memory performance. However, previous findings exploring this issue have been mixed. Across two preregistered experiments, we examined the effects of stress during encoding and retrieval on face and word recognition performance. We used the Maastricht Acute Stress Test (MAST) to induce stress and verified the success of the stress manipulation with blood pressure measures, salivary cortisol levels, and negative affect scores. To examine differences in stressor timing, participants encoded target faces or words both when confronted with the stressor and during the subsequent cortisol peak and retrieved these stimuli 24 h later. We found neither effects of acute stress on face recognition memory during encoding or retrieval (Experiments 1 and 2), nor effects of encoding stress on word recognition memory (Experiment 2). Bayesian analyses largely provided substantial or strong evidence for the null hypotheses. We emphasize the need for well-powered experiments using contemporary methodology for a more complete understanding of the effect of acute stress on face recognition memory.

Memory consolidation as an adaptive process

We rely on our long-term memories to guide future behaviors, making it adaptive to prioritize the retention of goal-relevant, salient information in memory. In this review, we discuss findings from rodent and human research to demonstrate that active processes during post-encoding consolidation support the selective stabilization of recent experience into adaptive, long-term memories. Building upon literatures focused on dynamics at the cellular level, we highlight that consolidation also transforms memories at the systems level to support future goal-relevant behavior, resulting in more generalized memory traces in the brain and behavior. We synthesize previous literatures spanning animal research, human cognitive neuroscience, and cognitive psychology to propose an integrative framework for adaptive consolidation by which goal-relevant memoranda are "tagged" for subsequent consolidation, resulting in selective transformations to the structure of memories that support flexible, goal-relevant behaviors.

Emotional learning retroactively enhances item memory but distorts source attribution

An adaptive memory system should prioritize information surrounding a powerful learning event that may prove useful for predicting future meaningful events. The behavioral tagging hypothesis provides a mechanistic framework to interpret how weak experiences persist as durable memories through temporal association with a strong experience. Memories are composed of multiple elements, and different mnemonic aspects of the same experience may be uniquely affected by mechanisms that retroactively modulate a weakly encoded memory. Here, we investigated how emotional learning affects item and source memory for related events encoded close in time. Participants encoded trial-unique category exemplars before, during, and after Pavlovian fear conditioning. Selective retroactive enhancements in 24-h item memory were accompanied by a bias to misattribute items to the temporal context of fear conditioning. The strength of this source memory bias correlated with participants' retroactive item memory enhancement, and source misattribution to the emotional context predicted whether items were remembered overall. In the framework of behavioral tagging: Memory attribution was biased to the temporal context of the stronger event that provided the putative source of memory stabilization for the weaker event. We additionally found that fear conditioning selectively and retroactively enhanced stimulus typicality ratings for related items, and that stimulus typicality also predicted overall item memory. Collectively, these results provide new evidence that items related to emotional learning are misattributed to the temporal context of the emotional event and judged to be more representative of their semantic category. Both processes may facilitate memory retrieval for related events encoded close in time.

Hypothalamic-Pituitary-Adrenal Axis Activity in Childhood Predicts Emotional Memory Effects and Related Neural Circuitry in Adolescent Girls

Negative emotional experiences can be more difficult to forget than neutral ones, a phenomenon termed the "emotional memory effect." Individual differences in the strength of the emotional memory effect are associated with emotional health. Thus, understanding the neurobiological underpinnings of the emotional memory effect has important implications, especially for individuals at risk for emotional health problems. Although the neural basis of emotional memory effects has been relatively well defined, less is known about how hormonal factors that can modulate emotional memory, such as glucocorticoids, relate to that neural basis. Importantly, probing the role of glucocorticoids in the stress- and emotion-sensitive period of late childhood to adolescence could provide actionable points of intervention. We addressed this gap by testing whether hypothalamic-pituitary-adrenal (HPA) axis activity during a parent-child conflict task at 11 years of age predicted emotional memory and its primary neural circuitry (i.e., amygdala-hippocampus functional connectivity) at 16 years of age in a longitudinal study of 147 girls (104 with complete data). Results showed that lower HPA axis activity predicted stronger emotional memory effects, r(124) = -.236, p < .01, and higher emotional memory-related functional connectivity between the right hippocampus and the right amygdala, β = -.385, p < .001. These findings suggest that late childhood HPA axis activity may modulate the neural circuitry of emotional memory effects in adolescence, which may confer a potential risk trajectory for emotional health among girls.

Recruitment of neurons in basolateral amygdala after intense training produces a stronger memory trace

Typical amnestic treatments are ineffective when administered to subjects trained in aversively-motivated tasks using relatively high foot-shock intensities. This effect has been found when treatments that disrupt neuronal activity are administered to different regions of the brain, including the amygdala. However, the molecular mechanisms induced by this intense training are unknown. We made a detailed mapping of c-Fos-expressing neurons in four regions of the amygdala after moderate and intense one-trial inhibitory avoidance training. Rats were sacrificed 90 min after training or after appropriate control procedures, and their brains were prepared for immunohistochemical c-Fos protein detection in the central, lateral, and in the anterior and posterior parts of the basolateral amygdaloid nucleus. We found a high percentage of neurons expressing c-Fos in the anterior part of the basolateral nucleus after moderate training, and this percentage increased further after intense training. Moderate and intense training did not induce changes in c-Fos expression in the other explored amygdaloid regions. These results show that inhibitory avoidance training produces a localized expression of c-Fos in the basolateral anterior nucleus of the amygdala, which is dependent upon the intensity of training, and indicate that synaptic plastic changes in this region may be required for the formation of memory of moderate and intense aversive learning.

Failures of memory and the fate of forgotten memories

This review is intended primarily to provide cognitive benchmarks and perhaps a new mindset for behavioral neuroscientists who study memory. Forgetting, defined here broadly as all types of decreases in acquired responding to stimulus-specific eliciting cues, is commonly attributed to one or more of the following families of mechanisms: (1) (4) associative interference by information similar to, but different from the target information, (2) spontaneous decay of memory with increasing retention intervals, (3) displacement from short-term memory by irrelevant information, and (4) inadequate retrieval cues at test. I briefly review each of these families and discuss data suggesting that many apparent instances of spontaneous forgetting and displacement from short-term memory can be viewed as variants of inadequate retrieval cues and associative interference. The potential for recovery of target information from each of these families of forgetting without further relevant training is then reviewed, with a conclusion that most forgetting is due to retrieval failure as opposed to irreversible erasure of memory. The more general point is made that there are logical problems with ever talking about attenuating or erasing a memory as a consequence of conventional forgetting or disrupted consolidation/reconsolidation. Consideration is then given to the frequently overlooked but highly beneficial consequences of most forgetting. Lastly, the major variables that moderate forgetting are summarized, including (a) the similarities of the target information including training context to the explicit retrieval cues and context present at test, (b) the similarities of potentially interfering acquired information to the retrieval cues and context present at test, and (c) the retention interval for the target information relative to that for the potentially interfering information. Appropriate manipulation of these variables can reduce forgetting, and increase forgetting when desired.