Fragile X syndrome (FXS) is a leading inherited cause of intellectual disability. FXS is caused by a trinucleotide repeat expansion in the fragile X messenger ribonucleoprotein 1 (fmr1) gene, which results in transcriptional silencing, and loss of its protein product, FMRP. One symptom of FXS is cognitive inflexibility, but there is no generally accepted way to test this in rodents. Tests of reversal learning or extinction paradigms have been used as measures of cognitive flexibility, but these are indirect, require substantial training and experimenter effort, and often yield inconsistent results. This study tests male and female Fmr1 knockout (KO) and wild-type (WT) mice in a "puzzle box" specifically designed to assess cognitive flexibility. The Puzzle Box is a two-chambered apparatus with a brightly illuminated area and an enclosed goal area. Novel obstacles block the underpass to the goal area, requiring that mice adopt new strategies. Results reveal that female, but not male, Fmr1 KO mice exhibit impaired performance compared to WT controls. Analysis of behavioral measures during novel obstacle presentation revealed a behavioral phenotype consistent with increased anxiety-like and hyperactivity behaviors, as well as altered engagement with novel obstacle conditions, in female Fmr1 KO mice compared to WT controls. Overall, the Puzzle Box test shows promise as a rapid screening test for cognitive flexibility impairments in FXS or other rodent models of neurological disorders.
Computational models and neurobehavioral data suggest that encoding variability affects forced-choice mnemonic discrimination. Here, we experimentally manipulated encoding variability on the forced-choice Mnemonic Similarity Task by varying stimulus repetitions during encoding. We first generated predictions from a global matching model. Behavioral data supported all predictions. Across most conditions, repetitions consistently enhanced mnemonic discrimination; however, when encoding variability was induced by 3-repetitions of the original version of the noncorresponding lure and 1-repetition of the target during learning, individuals exhibited increased interference. These findings provide further insight into theories of human memory, especially the effect of stimulus repetition on mnemonic discrimination.
Memory cues can be associated with both positive and negative experiences at different time points, in either a positive-to-negative or negative-to-positive order. While sleep preferentially consolidates recent experiences, its impact on emotional memory across such opposing-valence sequences remains unclear. We tested whether sleep differentially modulates delayed cue affect in positive-to-negative versus negative-to-positive conditions. One hundred twenty participants were randomly assigned to sleep or wake groups and completed both conditions in counterbalanced order. Participants learned pseudoword-picture associations where the same cues were paired with emotional pictures of opposite valence. Emotional valence ratings were collected immediately after encoding and after a 12 h interval (overnight sleep vs. daytime wakefulness). Sleep led to more positive cue ratings in the negative-to-positive condition and more negative ratings in the positive-to-negative condition, compared to wake controls. Stronger positive picture ratings predicted greater positive-valence shifts after sleep in the negative-to-positive condition. These findings indicate that sleep preferentially modulates the affective tone of memories encoded closer to sleep onset, independent of recognition accuracy. This suggests a dissociation between mnemonic and affective consolidation, where sleep selectively biases emotional value according to the temporal order of experience. This principle may inform therapeutic strategies for optimizing emotional outcomes by timing positive experiences before sleep, though clinical applications require further study.
Chronic stress is a major risk factor for psychiatric disorders. Previous work from our laboratory has demonstrated that chronic stress exposure disrupted network activity in the basolateral amygdala (BLA) and altered the activity of projection-specific neurons in the BLA to bias information processing to favor negative valence processing. Although the BLA is well established as a critical hub for fear memory encoding and retrieval, it remains unclear how chronic stress alters ensemble recruitment within the BLA and its downstream circuit dynamics to shape fear and extinction learning. To answer this question, we used retrograde tracing combined with immunohistochemistry in adult male mice to examine how chronic unpredictable stress (CUS) during adulthood alters the activity of the BLA and its projections to the nucleus accumbens (NAc) or bed nucleus of the (BNST) following fear extinction. Here we demonstrate that CUS produced a shift toward persistent threat responding and alters extinction learning, accompanied by reduced recruitment within the lateral nucleus of the BLA (LA) and in BLA-NAc projecting neurons. These findings provide circuit-level evidence for how chronic stress disrupts information flow from BLA, biasing valence processing toward extinction-resistant fear states and potentially contributing to the persistence of maladaptive fear in stress-related psychiatric disorders.
Memory updating requires detecting changes between similar events and preserving information about their relative order. Two experiments examined whether memory-based rejection of similar lures in the Mnemonic Similarity Task supports subsequent temporal memory. Participants studied objects, completed a modified recognition test including repeated targets, similar lures, and novel foils, and then performed a relative recency test in which they selected which of two versions of the same object appeared during the previous recognition test. Recency judgments for lures were most accurate when they were correctly rejected as “similar,” suggesting that retrieval-based comparison processes during recognition supported subsequent memory updating. Conditional analyses showed that this benefit was enhanced when participants also reported the subjective experience of remembering that both objects had appeared in the experiment, indexing memory for change. Subjective reports of retrieving studied objects before seeing lures were associated with more accurate lure decisions, and clearer subjective retrieval was associated with more frequent reports indicating memory for change. Together, these findings suggest that retrieval and comparison processes engaged during mnemonic discrimination encode information that supports distinguishing earlier and later events. This study provides a step toward integrating cognitive accounts of temporal memory with complementary neural accounts of episodic memory updating.
Strong evidence has emerged over the last two decades implicating proteasome-dependent and independent protein polyubiquitination in the memory consolidation process. Recently, it was shown that multiple forms of polyubiquitination, including proteasome-dependent K48 and proteasome-independent M1 polyubiquitination, regulate fear memory formation in a sex-dependent manner in the amygdala. However, prior work focused on single time points during the postlearning period, leaving questions about whether these are true sex differences in polyubiquitin modifications that persist throughout the extended consolidation process. Here, using unbiased polyubiquitin-type specific proteomics, we identified the protein targets of K48 and M1 polyubiquitination in the amygdala 2 and 4 h after contextual fear conditioning. Notably, we found that while the sex differences in the targeting of proteins with these polyubiquitin modifications persist for several hours after fear conditioning, the temporal dynamics of these changes vary across males and females. Further, while target protein pathways vary significantly across sexes at every time point examined, there are several notable overlaps between males and females. Together, these data provide the first comprehensive analysis of sex differences in proteasome-dependent and independent protein polyubiquitination in fear memory formation and significantly advance our understanding of the potential sex-specific roles of diverse polyubiquitin modifications in the memory consolidation process.
Flexible strategy use relies on the concerted effort of multiple cognitive processes. Originally appreciated for its role in aversive conditioning (for review, see Mondoloni et al., Transl Psychiatry 12: 86 [2022]), the lateral habenula (LHb) has recently been linked to flexible behavior more broadly (Baker et al., Front Behav Neurosci 9: 1-22 [2015]; Baker et al., Front Mol Neurosci 12: 1-15 [2019]; Mizumori and Baker, Trends Neurosci 40: 481-493 [2017]; Hones and Mizumori, Front Behav Neurosci 16: 852235 [2022]; Ahmadlou et al., Nature 641: 151-161 [2025]), prompting the question as to whether its encoding of negative outcomes contributes specifically to adaptive strategy switching. To address this gap in knowledge, the present study investigated how LHb inactivation with muscimol affects distinct aspects of flexible decision-making that depend on an understanding of negative outcomes when using a spatial set-shifting task. LHb inactivation resulted in a decreased ability to efficiently acquire new strategies after changes in reward contingencies but did not affect the exploitation of adopted strategies. A measure of choice flexibility confirmed that, without an intact LHb, rats fail to appropriately adapt to new strategies following errors. This effect suggests that the LHb contributes to the appropriate use of negative choice outcomes to inform future decisions. Therefore, aversive signaling in the LHb may play a broad role beyond purely aversive contexts, such as in guiding behavioral adaptation.
Memory generalization allows individuals to extract and apply information from prior experiences to novel situations, supporting flexible learning and efficient decision-making. Theoretical models suggest that sleep should facilitate generalization, yet the literature examining its role in promoting generalization is mixed. We recruited 137 participants via Prolific to complete an image-location memory task over two sessions spaced 12 h apart. Participants were randomly assigned to the Wake group (learning in the morning) or the Sleep group (learning in the evening). In Session 1, participants learned the location of stimuli on the screen and were tested on their memory 5 min later. Twelve hours later, in Session 2, they were tested on their memory again. Stimuli consisted of 160 images from eight semantic categories and were strategically positioned on-screen to test the effects of generalization on retrieval (i.e., category-based memory distortions and biases). After the delay, retrieval was less accurate and demonstrated more generalization. However, these effects were mostly independent of Group, with some evidence for enhanced generalization following a period of wakefulness over sleep. Generalization was also driven by time of day, with more generalization in the evening relative to the morning. Taken together, our results, based on a large online sample, do not support a role for sleep in promoting memory generalization.
It is not yet clear how dorsal hippocampal rhythms contribute specific information that impacts future behavior. Using a spatial set-shifting task that requires animals to behave flexibly and continuously adapt to different spatial strategies, we found that beta power increased after incorrect choices. Higher beta and gamma power after reward feedback was linked with greater accuracy on the next trial, scaling with rhythm power. These results highlight the importance of relating hippocampal rhythms to multiple within-trial segments to better understand how individual rhythms may differentially support future behaviors.
Episodic memory helps facilitate navigation of the social world. Yet, whether social content is prioritized in episodic memory is unclear. Testing whether social elements are prioritized when retrieving multielement episodes used for social and nonsocial inferences, online volunteers encoded episode triplets comprising a location, activity, and a clique (i.e., social group) that related to a cue that was either a person or an object. Subsequent associative memory tests in all tasks revealed some form of enhanced retrieval for activity pairings with cliques. Additionally, social cover task contexts further boosted retrieval of social event content linked to the same cue. Computational modeling of retrieval response times revealed that these effects were consistent with more holistic retrieval of event triplets when retrieving social content. These results imply that social content can hold a privileged role over other event details in episodic memory, while offering a putative mechanism for social prioritization in episodic memory processes.
Fast mapping is an incidental learning paradigm that presents a novel word and new item alongside a familiar "supporting foil," allowing the learner to infer (and possibly learn) the meaning of the new word. While fast mapping is well studied in children, its role in adult learning remains debated, with studies reporting robust effects and null results. This paper reports a meta-analysis of behavioral fast mapping studies in healthy adults. Across 28 experiments, fast mapping produced a significant overall medium effect (Hedges' g = 0.39) on memory outcomes. This was observed to a similar extent across three theoretically motivated categories: (1) interaction with existing memory traces, (2) stability over time, and (3) moderation by semantic features. The meta-analytic findings converge on the conclusion that fast mapping can facilitate integration into memory, likely through schema-based mechanisms, with a need to clarify boundary conditions through further experimentation.
Food-associated memories are fundamental to our survival. Learned food cues guide food-seeking and eating behaviors. How long these memories persist varies across individuals. In some people, enduring food memories become maladaptive and cause sustained cravings and disordered eating. Women are more susceptible than men to obesity, eating disorders, and addiction, and yet, memory and extinction of food cues have not been systematically examined in both sexes. Here, we compared adult male and female rats during cue-food acquisition, extinction, and renewal or reacquisition in three experiments with Pavlovian conditioning. Extinction is context-specific, and there are sex differences in context-dependent renewal of responding after extinction. The first two experiments tested whether pretraining habituation to the learning and extinction contexts (with or without food reward) would improve renewal in both sexes. Habituation did not improve renewal in either experiment. Unexpectedly, females showed impaired extinction. The third experiment utilized a test of extinction resistance: the partial reinforcement extinction effect. In this task, females showed pronounced resistance to extinction compared to males, especially when learning and extinction occurred in the same context. These findings point to differences in extinction as the potential cause of individual differences in persistent cue-driven food cravings and the inability to alter eating behaviors.
This study examined how agentic decisions in the absence of explicit rewards influence memory organization. Participants studied lists of items to assign as gifts to two characters-either choosing freely (Choice group) or following instructions (Fixed group). During free recall, participants in the Choice group showed reduced temporal clustering and instead organized their memories around the choices they made. Specifically, they were more likely to recall together items that were assigned to the same character. These findings suggest that agency shifts memory organization away from temporal proximity and toward meaningful associations, highlighting how agency can shape the organization of memory.
The basolateral amygdala (BLA) is critical for Pavlovian and instrumental emotional association learning. Pavlovian fear conditioning is accompanied by increased excitability of BLA neurons. Here we tested whether instrumental learning similarly enhances BLA excitability. Electrophysiological recordings were taken from BLA neurons in brain slices prepared from instrumentally trained Long-Evans rats. Both reward and punishment training increased intrinsic excitability. Moreover, excitability positively correlated with performance on the punishment task, suggesting a functional link between neuronal excitability and learning. These findings support the idea that enhanced excitability facilitates synaptic plasticity and circuit integration during instrumental learning.
Murine studies show that the gut microbiota - the collection of the microbes residing in the large intestine - affects memory performance in the host. However, whether commensal gut bacteria are linked to human episodic memory remains unknown. Here, we investigated whether individual differences in episodic memory performance were associated with differences in the indigenous gut microbiota composition between individuals. We show that greater gut microbiota alpha diversity was associated with better item recognition and that gut microbiota dissimilarity index (beta diversity) between participants was associated with differences in their performance. Finally, our results suggest that Prevotella copri might play a role in the relationship between gut microbiota and human item recognition in healthy individuals. In a sample size larger than previous human studies and examining unmanipulated gut microbiota, we provide evidence that episodic memory in healthy humans is linked to their gut microbiota composition.
Learning is associated with activation of multiple protein kinases, but few details are known about the activation dynamics in response to different learning protocols. We addressed this issue by examining the long-term dynamics of kinases critical for long-term synaptic facilitation (LTF) of the Aplysia sensorimotor synapse. Three serotonin (5-HT) protocols have been found to induce LTF with distinct effectiveness: the five-pulse regular-spaced Standard protocol; the five-pulse irregular-spaced Enhanced protocol; and the two-pulse protocol with an interval of 45 min. We previously compared long-term dynamics of the mitogen-activated protein kinase (MAPK) isoform ERK after these protocols. Here we examined the long-term dynamics of additional kinases critical for LTF: p38 MAPK, protein kinase A (PKA), and p90 ribosomal S6 kinase (RSK). All four kinases showed complex dynamics of activity during 24 h, with a first wave of increase occurring shortly after 5-HT treatment and ending within 5 h, and a second wave from ∼5 to 18 h. After the standard and two-pulse protocols, all kinase activities returned toward basal at 24 h, but after the Enhanced protocol, some remained elevated at 24 h. Interactions and multiple feedback loops among the kinase pathways, and with the growth factors Aplysia neurotrophin (NT) and transforming growth factor-β (TGF-β), contribute to development of molecular clocks underlying these complex dynamics. These results help to delineate the molecular mechanisms underlying the induction of LTF and provide insights that may help design improved training protocols for induction and maintenance of LTF and long-term memory.
The ability to remember the relationship between unrelated events is a powerful cognitive function. When two unrelated stimuli are encoded in a condition of high level of unitization (LOU), the associative memory could be acquired with a strong familiarity contribution. This provides a promising way for brain lesioned patients to obtain a new associative memory. However, recent studies are inconsistent on the extent to which the recollection process is involved in unitized associative memory. To clarify this issue, two groups of participants learned unrelated word pairs once or twice in the high- and low-LOU conditions and were tested at 10 min and 24 h. The recollection and familiarity processes were estimated by dual-process models. Results showed that both recollection and familiarity were stronger for the high- than for the low-LOU condition. However, when memory strength was controlled, recollection was comparable for high- and low-LOU conditions, while familiarity still showed a significant effect of LOU. In addition, the effect of LOU for familiarity increased after repetition learning. The results suggest that the recollection contribution to unitized association is related to memory strength, but the familiarity contribution is stably observed and increases after repetition learning when unrelated word pairs are used. These findings are also significant for memory rehabilitation in aging and brain lesioned patients.
Long-term activity-dependent modifications of synaptic strength are a cellular substrate of learning and memory, but how long-lasting memory could be based on synaptic proteins that rapidly degrade and diffuse is unknown. Most current theories depend on molecular positive-feedback loops. Recent experiments, however, reveal that interactions between kidney brain protein (KIBRA) and PKMζ downregulate the proteins' degradation and maintains late-phase long-term synaptic plasticity (LTP) and long-term memory, motivating an alternative model based on negative feedback at the level of protein elimination. Here we compare positive- and negative-feedback models generally and explore biophysical models based specifically on KIBRA-PKMζ interaction. The biophysical theory predicts LTP/memory maintenance by complexes of cooperative KIBRA-PKMζ heteromers.
Monkeys sometimes accurately predict their memory accuracy, a form of metamemory. The memory signals that support this ability may differ between memory systems and depend on when memory judgments are made. Working memory requires active maintenance through the delay interval. Familiarity allows recognition without active maintenance and is triggered by representation of memoranda at test. We measured metamemory prospectively, during delay intervals, and concurrently, at the time of tests, while six male rhesus monkeys performed tasks that favored working memory or familiarity. Metamemory was accurate at both times in both tasks, and highest for concurrent judgments in the familiarity task.
Recognizing threats is crucial for animals to adopt appropriate behaviors. The orbitofrontal cortex (OFC) is essential for emotional regulation and cognitive flexibility. This study investigated the effect of medial OFC (mOFC) manipulation on discrimination ability in male rats in a fear differential conditioning paradigm. The rats were conditioned to two different types of conditioned stimuli (CS+ and CS-); the CS+ was paired with an electric footshock to increase its threat significance, whereas the CS- was made to be less threatening by not pairing with a footshock. The mOFC was manipulated during either the acquisition or retrieval stage. Inactivation of the mOFC during either stage did not significantly change the differential fear responses to CS+ and CS- or the fear discrimination index. However, mOFC activation during both the acquisition and retrieval stages of the fear differential conditioning paradigm reduced the fear discrimination index by enhancing fear expression to the less threatening signal. These results suggest that mOFC activation impairs the discrimination of environmental information and plays a critical role in modulating fear responses. This research provides insights into the neural mechanisms involved in cognitive flexibility and emotional regulation by clarifying the role of the mOFC in fear discrimination.
