Behavioral Neuroscience

Computational modeling has revealed that human research participants use both rapid working memory (WM) and incremental reinforcement learning (RL) (RL+WM) to solve a simple instrumental learning task, relying on WM when the number of stimuli is small and supplementing with RL when the number of stimuli exceeds WM capacity. Inspired by this work, we examined which learning systems and strategies are used by adolescent and adult mice when they first acquire a conditional associative learning task. In a version of the human RL+WM task translated for rodents, mice were required to associate odor stimuli (from a set of 2 or 4 odors) with a left or right port to receive reward. Using logistic regression and computational models to analyze the first 200 trials per odor, we determined that mice used both incremental RL and stimulus-insensitive, one-back strategies to solve the task. While these one-back strategies may be a simple form of short-term or working memory, they did not approximate the boost to learning performance that has been observed in human participants using WM in a comparable task. Adolescent and adult mice also showed comparable performance, with no change in learning rate or softmax beta parameters with adolescent development and task experience. However, reliance on a one-back perseverative, win-stay strategy increased with development in males in both odor set sizes. Our findings advance a simple conditional associative learning task and new models to enable the isolation and quantification of reinforcement learning alongside other strategies mice use while learning to associate stimuli with rewards within a single behavioral session. These data and methods can inform and aid comparative study of reinforcement learning across species. Author summaryHere we studied the strategies and mechanisms mice use to learn a simple two choice odor based task in a single session. Using a set size manipulation and computational models we find evidence that mice use incremental reinforcement learning as well as several short-term (one-back) strategies to earn water reward. Our data and models clarify how mice learn a simple task and establish methods by which mouse and human reinforcement learning may be isolated for cross-species comparison of learning.

Aversive associative learning paradigms such as inhibitory avoidance (IA) are frequently used to examine episodic-like memories in rodents. In IA, rodents learn to associate a context with a footshock, followed by testing for memory strength in the original training context and for memory precision in a similar yet distinct neutral context. The present work assessed the effects of different contextual exposure procedures on memory strength and precision in IA at both recent and remote time points using male and female Long-Evans rats. An initial experiment found that rats kept in the lit (non-shock) compartment of the IA apparatus for 60 s during training, as opposed to 10 s, displayed enhanced memory strength, with discrimination between both chambers at the recent retention test and generalization at the remote retention test. Subsequent experiments investigated the effects of contextual pre-exposure the day before training. The results indicate that pre-exposure to the neutral context promoted generalization without altering memory strength compared to the first experiment. In contrast, pre-exposure to the aversive chamber promoted discrimination and enhanced memory strength. Notably, the different procedures yielded similar effects in both sexes. However, the results also indicate an overall pattern of greater contextual discrimination in females compared to males. These findings provide evidence for how different contextual exposures influence the degree of encoding at the time of training and a behavioral foundation for future studies examining the neurobiological mechanisms underlying memory strength and precision in IA, while highlighting the importance of using both sexes in initial behavioral work. Significance StatementStrength and precision are two fundamental properties of memory that can be simultaneously measured using inhibitory avoidance (IA), a type of context-footshock association task. However, little is known about how different context exposures alter rats encoding of these memories, thereby influencing subsequent memory strength and precision. Here, we found that pre-exposure to the neutral IA chamber decreased memory precision, whereas pre-exposure to the aversive IA chamber promoted memory strength and precision. Additionally, females demonstrated overall enhanced memory precision compared to males. These results indicate that different types of contextual exposures influence initial IA encoding and add to a limited body of research examining memory strength and precision in IA in both sexes.

In monkeys, the muscarinic cholinergic receptor antagonist scopolamine is known to broadly disrupt learned behaviors, though the precise nature of the cognitive deficits has been questioned. Experimentally observable deficits in memory can be ascribed to poor attentional focusing, human interference as well as age, sex, and dosing regimen. Stress and social isolation can also play a role during behavioral testing, particularly in small nonhuman social primates like marmosets that have been used widely. In this study, we examine the effects of scopolamine in marmosets under conditions of reduced stress, attentional distraction, and human interference. Using a custom designed home-cage touchscreen-based testing system, we investigated the influence of scopolamine on the performance on a visual associative learning task. During self-paced, voluntary testing, monkeys learned to discriminate pairs of complex visual patterns through trial and error by touching the stimulus associated with reward. Using this approach, we demonstrated over 75% discrimination accuracy in the eight marmosets tested (male and female) within three days of home-cage testing. Although the averaged data revealed no impact of acute or chronic scopolamine injections on learning, modeling the choice data with trial-level analysis revealed both age- and sex-specific deficits. The results demonstrate the value of home-cage testing combined with trial-level analysis to reveal subtle behavioral changes, such as those brought about by scopolamine. Significance statementWe created a custom home cage testing system to test the effects of muscarinic cholinergic blockade on complex discrimination learning in marmoset monkeys. We found that systemic scopolamine administration disrupts visual association learning in a manner that was specific to older females. This deficit was hidden in session-averaged measures and only became evident in trial-level modeling of the choice data. Our findings demonstrate that cholinergic blockade impairs the dynamics of learning in marmosets and highlights the value of trial-level analysis for detecting nuanced pharmacological effects on primate cognition.

The frontal cortex plays a critical role in decision-making. One specific frontal area, the anterior cingulate cortex, has been identified as crucial for setting a threshold for how much evidence is needed before a choice is made (Domenech & Dreher, 2010). Threshold is a key concept in drift diffusion models, a popular framework used to understand decision-making processes. Here, we investigated the role of the prelimbic cortex, part of the rodent cingulate cortex, in decision making. Male and female rats learned to choose between stimuli associated with high and low value rewards. Females learned faster, were more selective in their responses, and integrated information about the stimuli more quickly. By contrast, males learned more slowly and showed a decrease in their decision thresholds during choice learning. Inactivating the prelimbic cortex in female and male rats sped up decision making without affecting choice accuracy. Drift diffusion modeling found selective effects of prelimbic cortex inactivation on the decision threshold, which was reduced with increasing doses of the GABA-A agonist muscimol. Stimulating the prelimbic cortex through mu opioid receptors slowed the animals choice latencies and increased the decision threshold. These findings provide the first causal evidence that the prelimbic cortex directly influences decision processes. Additionally, they suggest possible sex-based differences in early choice learning.

Our understanding of sex differences in reward learning has been limited due to the predominant study of males, yet recent studies have uncovered significant differences in the use of adaptive strategies, sensitivity to negative feedback, and impulsivity. Here, we evaluated sex differences in flexible learning in two domains: the learning of stimulus- and action-based associations and their reversals. During action-based learning, rats selected between two identical visual stimuli presented on a touchscreen, where the spatial location predicted a higher probability of reward. For stimulus-based learning, rats chose between two distinct visual stimuli presented in pseudorandom spatial locations, one of which was associated with a higher probability of reward. Reversal phases involved switching reward contingency between the two actions or stimuli. To gain a detailed understanding of diffferences across conditions, we modeled animals trial-by-trial choices using reinforcement learning (RL) models and examined their steady-state behavior to capture transitions between distinct behavioral states. We found that female rats were more likely to omit trials and take longer to initiate trials in both domains. The omissions were more frequent in late-stage action-based reversal learning, once learning had plateaued. Moreover, although the estimated parameters of the best-fitting RL model revealed some sex differences, the model that incorporated transitions between different behavioral states provided a better overall fit to the data. This model also revealed that across all reversal phases, females exhibited a higher transition-specific lapse rate than males, indicating greater task disengagement once there was no need for further learning. Together, our fine-grained analysis of behavior adds to a growing literature on sex differences in flexible reward learning.

Environmental exposures co-occurring during early life have a profound influence on neurodevelopment. Our previous work in rats suggests that postnatal maternal care modulates the effects of prenatal exposure to bisphenols, an estrogenic endocrine disrupting chemical, on offspring neurodevelopment. Elevated postnatal maternal licking/grooming and prenatal bisphenol exposure have known opposing effects on estrogen receptor alpha (Esr1) expression in the medial preoptic area (MPOA) of the hypothalamus, which could impact expression of estrogen-responsive genes. Based on this previous work, we hypothesized that postnatal maternal licking/grooming would mitigate the effects of prenatal bisphenol exposure on Esr1 expression and estrogen-responsive genes in the developing MPOA. In addition, we hypothesized that there would be interactive effects of prenatal bisphenol exposure and postnatal maternal licking/grooming on DNA methylation, particularly nearby estrogen responsive elements. Our results suggest that maternal postnatal licking/grooming normalized prenatal bisphenol-induced upregulation of estrogen-related receptor gamma (Esrrg) expression in female pups. These mitigating impacts were also evident in co-expression gene profiles in female pups; the majority of which were enriched for estrogen-responsive genes. Finally, DNA methylation analyses indicated that adding postnatal maternal licking/grooming as a covariate influenced the number of differentially methylated regions for prenatal bisphenol-exposed male and female pups. These differentially methylated regions were enriched for binding sites for transcription factors that are known to interact with estrogen receptors, suggesting some secondary effects on postnatal gene regulation. These results suggest a novel biological mechanism in which postnatal maternal care can mitigate the negative neurodevelopmental impacts of prenatal bisphenol exposure. These results also suggest that postnatal tactile stimulation might be a potential intervention strategy to mitigate the neurodevelopmental risks from prenatal endocrine disrupting chemical exposure. Author SummaryNeurodevelopment can be shaped by both aversive and positive experiences early in life, in part due to epigenetic mechanisms such as DNA methylation. Here, we follow up on our previous studies that suggest high levels of postnatal maternal care could mitigate the negative impacts of prenatal bisphenol exposure, an estrogenic endocrine disrupting chemical. We focused on gene expression and DNA methylation changes in the developing medial preoptic area, a brain area that is enriched in estrogen receptors and important for sex-specific social behaviors. We found that maternal postnatal licking/grooming normalized prenatal bisphenol-induced upregulation of estrogen-related receptor gamma (Esrrg) expression in female pups only. We find similar patterns in multiple co-expressed gene networks that are enriched in estrogen-responsive genes. Finally, postnatal maternal licking/grooming influenced DNA methylation patterns for prenatal bisphenol-exposed male and female pups. These results suggest a novel biological mechanism in which postnatal maternal care can mitigate the negative neurodevelopmental impacts of prenatal bisphenol exposure. This is important because it suggests that postnatal tactile stimulation could be an effective intervention against the negative neurodevelopmental impacts from prenatal endocrine disrupting chemical exposure.

RationaleLearning the association between rewards and predictive cues is critical for appetitive behavioral responding. The mesolimbic dopamine system is thought to play an integral role in establishing these cue-reward associations. The dopamine response to cues can signal differences in reward value, though this emerges only after significant training. This suggests that the dopamine system may differentially regulate behavioral responding depending on the phase of training. ObjectivesThe purpose of this study was to determine whether antagonizing dopamine receptors elicited different effects on behavior depending on the phase of training or the type of Pavlovian task. MethodsSeparate groups of male rats were trained on Pavlovian tasks in which distinct audio cues signaled either differences in reward size or differences in reward rate. The dopamine receptor antagonist flupenthixol was systemically administered prior to either the first ten sessions of training (acquisition phase) or the second ten sessions of training (expression phase) and we monitored the effect of these manipulations for an additional ten training sessions. ResultsWe identified acute effects of dopamine receptor antagonism on conditioned responding, the latency to respond, and post-reward head entries in both Pavlovian tasks. Interestingly, dopamine receptor antagonism during the expression phase produced persistent deficits in behavioral responding only in rats trained on the reward size Pavlovian task. ConclusionsTogether, our results illustrate that dopamines control over behavior in Pavlovian tasks depends upon ones prior training experience and the information signaled by the cues.

Learning can occur in markedly different ways: in some cases, it unfolds as a gradual process, with behavior improving slowly toward an asymptotic level of performance; in others, it appears as an abrupt process that sharply separates behavior before and after a change point. Under-standing the behavioral and neural processes underlying these distinct acquisition patterns may be critical for elucidating the basic principles of learning. We investigated this question experimentally using naive rats performing a differential reinforcement of response duration (DRRD) task, in which animals were required to remain inside a nosepoke for a minimum duration of 1.5 seconds to get a sugar pellet as a reward. All rats learned to wait longer in the nosepoke when comparing behavior at the beginning and at the end of the experiment. We tested several continuous models against a single change point (CP) model, in which behavior changes at a specific moment and remains stable thereafter. Instead of the traditional approach based on trial-segmented behavior, we used the real time elapsed since the beginning of the experiment as a continuous, uncontrolled variable. We fitted all models to data from individual rats and compared model fit quality across alternatives. Our results provide strong evidence in favor of an abrupt change, as captured by the CP model, over all other models. Moreover, the residuals of the CP model exhibited a Gaussian distribution, suggesting that no additional systematic dynamics remained unexplained and that the behavioral dynamics were fully captured by a single change point.

Pavlovian fear conditioning is a widely used behavioral paradigm for studying associative learning in rodents. Despite early recognition that subjects may engage in a variety of both conditioned and unconditioned responses, the last several decades have seen the field narrow its focus to measure freezing as the sole indicator of conditioned fear. We previously reported that female rats were more likely than males to engage in darting, an escape-like conditioned response that is associated with heightened shock reactivity. To determine how experimental parameters contribute to the frequency of darting in both males and females, we manipulated factors such as chamber size, shock intensity, and number of trials. To better capture fear-related behavioral repertoires in our animals, we developed ScaredyRat, an open-source custom Python tool that analyzes Noldus Ethovision-generated raw data files to identify Darters and quantify both conditioned and unconditioned responses. We find that like freezing, conditioned darting occurrences scale with experimental alterations. While most darting occurs in females, we find that with an extended training protocol, darting can emerge in males as well. Collectively, our data suggest that darting reflects a behavioral switch in conditioned responding that is a product of both an individual animals sex, shock reactivity, and experimental parameters, underscoring the need for careful consideration of sex as a biological variable in classic learning paradigms.

Inferential reasoning is a vital cognitive ability that enables animals to navigate novel situations by leveraging existing relational knowledge of memory schema, with hypothesized roles of prefrontal cortical - hippocampal circuits. Transitive inference (TI) tasks test the ability of subjects to infer relationships within a value hierarchy (e.g., A>B>C>D>E) after being trained only on adjacent premise pairs (e.g., A-B, B-C, etc.). In rodents, current TI paradigms are primarily based on odor-cues and have several limitations that preclude investigation of physiological mechanisms underlying schemas and deliberation. To address these challenges, we developed a novel, automated spatial TI task for rats using a radial maze with maze arms as premise elements and a dedicated deliberation zone. Most rats successfully learned the premise pairs over training. Further, animals demonstrated rapid, successful inference (test pair B>D and control pair A>E) within a single test session, with higher initial accuracy than comparable premise pairs, indicating the use of schema-based inference. We also investigated vicarious trial and errors (VTE), a behavioral correlate of spatial deliberation. VTE behavior was elevated on choice trajectories early in learning, when novel premise pairs were introduced, and generally for incorrect trials, corresponding to the hypothesized association of VTEs with uncertainty. Further, rats also exhibited elevated VTE behavior with high variability during inference testing, with individual variability suggestive of varying strengths of schema usage. Our findings demonstrate the feasibility of a rodent spatial TI task that provides new insights into the behavioral correlates of schemas and deliberation for inferential reasoning.

Adolescence shapes adaptive adult behaviors. Most studies compare single adolescent and adult age groups using only one type of reward, limiting insight into developmental trajectories underlying behavioral change. Here, we investigated how social, cocaine, and palatable food rewards become associated with environmental contexts in female and male C57BL/6 mice across early- (pubertal onset), mid- (peripubertal phase), and late- (sexual maturity) adolescence, compared to adults. Using the conditioned place preference (CPP) task, we found that generally all rewards induced place preference for the reward-associated context, with only minor effects of sex. In contrast, age significantly influenced CPP expression. Adolescent mice exhibited a significantly reduced CPP compared to adults in palatable food and social CPP paradigms, evident in both decreased mean conditioned context preference and lower proportion of animals that developed a preference after conditioning. Cocaine CPP was not significantly affected by age. Direct comparisons across CPP task outcomes further confirmed that age, rather than reward type or sex, was the primary factor influencing the magnitude of CPP. Specifically, mid- and late-adolescent mice showed reduced mean reward CPP, and mid-adolescents were less likely to express a reward preference relative to adults. Based on the behavioral analyses, we conclude that the lower expression of preference for a conditioned context in adolescent animals is due to developmental changes in reward sensitivity, rather than deficits in learning or higher novelty-seeking behavior.

Knowing what factors affect the acquisition of a behavioural task is central to understanding the mechanisms of learning and memory. It also has practical implications, as animal behavioural experiments used to probe cognitive functions often require long training durations. Delayed Match (or Non-Match)-to-Sample (DMS/DNMS) tasks are relatively complex tasks used to study working memory and sensory perception, but their use in the mouse remains hampered by the lengthy training involved. In this study, we assessed two aspects of stimulus timing on the acquisition of an olfactory DNMS task: how the sample-test odour delay durations and the reward timing affect the acquisition rate. We demonstrate that head-fixed mice learn to perform an olfactory DNMS task more quickly when the initial training uses a shorter sample-test odour delay without detectable loss of generalisability. Unexpectedly, we observed a slower task acquisition when the odour-reward interval was shorter. This effect was accompanied by a shortening of reaction times and more frequent sporadic licking. Analysis of this result using a drift-diffusion model indicated that a primary consequence of early reward delivery is a lower decision bound. Since an accurate performance with a lower decision bound requires greater discriminability in the sensory representations, this may underlie the slower learning rate with early reward arrival. Together, our results reflect the possible effects of stimulus timing on stimulus encoding and its consequence on the acquisition of a complex task.

Avoidance learning involves associating a behavioral response with the omission of an expected threat, but the neural mechanisms that drive this learning remain unclear. Research on fear extinction points to a critical role for opioid receptors in the ventrolateral periaqueductal gray (vlPAG) in computing the aversive prediction error signal that is generated when there is a difference between expected and actual aversive events. Based on these fear extinction findings, we hypothesized that vlPAG opioid signaling might also support the early stages of avoidance learning. To test this, 15 Wistar rats (7 females, 8 males) received intra-vlPAG infusions of either naloxone hydrochloride (n = 7, 2.5 {micro}g/0.5 {micro}l), a non-selective opioid receptor antagonist, or vehicle (n = 8, 0.5 {micro}l), immediately before the first and second session of two-way active avoidance training. No infusions were given before the third session, to examine avoidance performance under continued, drug-free acquisition. For the fourth and final session, drug conditions were reversed to examine the acute effect of naloxone on already established avoidance performance. Our results indicated that intra-vlPAG naloxone did not impair avoidance acquisition, nor its performance. These findings suggest that opioid signaling in the vlPAG may not be essential for the initial learning or expression of two-way active avoidance.

Study questionAre there differences in operant learning and memory between mice born through intracytoplasmic sperm injection (ICSI) and naturally-conceived control (CTL) mice? Summary answerICSI females exhibited deficits in acquisition learning relative to CTL females, whereas ICSI males exhibited deficiency in discrimination learning and memory relative to CTL males during initial assessments. ICSI and CTL groups exhibited equally poor long-term retention of learned discrimination and memory performances at old age. What is known alreadySome human outcome studies have suggested that ICSI might be associated with an increased risk of certain cognitive disorders, but only one of two behavioral studies with ICSI mouse models have reported differences between ICSI and CTL females. No studies to date have investigated associative learning in ICSI mice. Study design, size, duration36 ICSI mice (18 male, 18 female) and 37 CTL mice (19 male, 18 female) aged 3-6 months were compared in a series of operant learning procedures that assessed acquisition of a new behavior, discrimination learning, and memory. 16 ICSI mice (9 male, 7 female) and 17 CTL mice (10 males, 7 females) received follow-up discrimination learning and memory assessments at 12 months of age (six months after the end of initial training) to evaluate retention and reacquisition of learned performances. Participants/materials, setting, methodsMice received daily operant learning sessions in experimental chambers in which all stimulus events and the recording of responses were automated. Food rewards were delivered for responding under different conditions of reinforcement, which varied by procedure. Subjects received a successive series of sessions of nose poke acquisition training, discrimination training, and the delayed non-matching-to-position (DNTMP) memory procedure. Mixed repeated measures ANOVAs in which the between-subjects factor was group (ICSI vs. CTL) and the within-subjects factor was repeated exposures to learning procedures (i.e., sessions) were used to analyze data. Main results and the role of chanceIn comparisons between all mice (i.e., males and females combined), CTL mice exhibited superior performance relative to ICSI in response acquisition (p = 0.03), discrimination (p = 0.001), and memory (p = 0.007). Sex-specific comparisons between the groups yielded evidence of sexual dimorphism. ICSI females exhibited a deficit in acquisition learning relative to CTL females (p < 0.001) but there was not a significant difference between CTL and ICSI males. In the discrimination and memory tasks, ICSI males exhibited deficits relative to CTL males (p = 0.002 and p = 0.02, respectively) but the differences between females in these tasks were not significant. There was no difference in discrimination or memory retention/re-acquisition assessments conducted with mice at 12 months of age. ICSI males and females weighed significantly more than CTL counterparts at all points during the experiment. Limitations, reasons for cautionThe study was not blinded. All learning assessments utilized food reward; other assessments of operant, Pavlovian, and nonassociative learning are needed to fully characterize learning in ICSI mice and speculate regarding the implications for cognitive function in humans conceived via ICSI. Wider implications of the findingsStudying learning and memory processes in mouse models has the potential to shed light on ICSI outcomes at the level of cognitive function. Future research should use multiple learning paradigms, assess both males and females, and investigate the effects of variables related to the ICSI procedure. Studying cognitive function in ICSI is an interdisciplinary endeavor and requires coordination between researchers at the genetic and psychological levels of analysis. Study funding/competing interest(s)This work was supported, in part, by grants from NIH (P30GM110767, HD071736 and HD085506 to WY), the Templeton Foundation (Grant ID: 61174 to WY), and a New Scholarly Endeavor Grant from the University of Nevada, Reno Office of Research and Innovation (to ML, YW, HZ, LH, and WY). The authors declare no competing interests.

Decision-making circuits are modulated across life stages (e.g. juvenile, adolescent, or adult)--as well as on the shorter timescale of reproductive cycles in females--to meet changing environmental and physiological demands. Ovarian hormonal modulation of relevant neural circuits is a potential mechanism by which behavioral flexibility is regulated in females. Here we examined the influence of prepubertal ovariectomy (pOVX) versus sham surgery on performance in an odor-based multiple choice reversal task. We observed that pOVX females made different types of errors during reversal learning compared to sham surgery controls. Using reinforcement learning models fit to trial-by-trial behavior, we found that pOVX females exhibited lower inverse temperature parameter ({beta}) compared to sham females. These findings suggest that OVX females solve the reversal task using a more exploratory choice policy, whereas sham females use a more exploitative policy prioritizing estimated high value options. To seek a neural correlate of this behavioral difference, we performed whole-cell patch clamp recordings within the dorsomedial striatum (DMS), a region implicated in regulating action selection and explore/exploit choice policy. We found that the intrinsic excitability of dopamine receptor type 2 (D2R) expressing indirect pathway spiny projection neurons (iSPNs) was significantly higher in pOVX females compared to both unmanipulated and sham surgery females. Finally, to test whether mimicking this increase in iSPN excitability could recapitulate the pattern of reversal task behavior observed in pOVX females, we chemogenetically activated DMS D2R(+) neurons within intact female mice. We found that chemogenetic activation increased exploratory choice during reversal, similar to the pattern we observed in pOVX females. Together, these data suggest that pubertal status may influence explore/exploit balance in females via the modulation of iSPN intrinsic excitability within the DMS.

Dopaminergic transmission within the nucleus accumbens is broadly implicated in risk/reward decision making and impulse control, and the rat gambling task (rGT) measures both behaviours concurrently. While the resulting indices of risky choice and impulsivity correlate at the population level, dopaminergic manipulations rarely impact both behaviours uniformly, with changes in choice more likely when dopaminergic transmission is altered during task acquisition. Although the task structure of the rGT remains constant, the importance of accumbal dopamine signals relevant for reward prediction versus impulse control may vary over time; the former should dominate while learning which option maximises sugar pellet profits, while the suppression of premature responses becomes more valuable once a decision-making strategy is set and can be exploited. Cholinergic interneurons (CINs) critically control dopamine release within the striatum, and can also encode latent task states deciphered by the frontal cortex. We theorised that aCINs may set the dopaminergic tone of the accumbens to maximise reward learning or impulse control during task acquisition or performance, respectively. Using chemogenetics, we found some support for this hypothesis: activation and inhibition of aCINs once behaviour was stable increased and decreased motor impulsivity in both sexes but had no effect on choice patterns. In contrast, activating and inhibiting aCINs throughout task acquisition did not alter motor impulsivity, but decreased and increased risky choice respectively. However, the former effect was only seen in males and the latter in females. We conclude by proposing a set of testable predictions regarding interactions between acetylcholine and dopamine that could explain these sex differences.

Cognitive flexibility can be defined as the ability to adaptively shift between choices or strategies based on environmental feedback and it is disrupted in numerous neuropsychiatric conditions. Individual differences in the computations supporting cognitive flexibility are poised to reveal mechanisms of neuropsychiatric risk and resilience. One critical variable well known to influence individual differences in neuropsychiatric risk is sex. While previous research has identified sex differences in value based decision making in mice, whether sex reflects a major source of variation in cognitive flexibility remains unknown. To directly assess sex-biased individual differences in cognitive flexibility, we developed a novel touchscreen Set Shift task that permits robust and continuous testing in mice. Using this task, we discovered that female mice completed significantly more rule shifts with fewer errors than males. We next employed a suite of computational models that revealed sex-biased individual differences in the computations underlying cognitive flexibility. Overall, our results suggest that following rule shifts, female mice learn the new rule faster and commit to exploiting rule choices sooner compared to males - sometimes because they commit to multiple rules simultaneously. This suggests that increased choice stability in female rodents enhances commitment to a strategy during periods of uncertainty and directly contributes to increased rule shifting. This supports the counterintuitive conclusion that a high degree of stable choice is a strong requirement for enhanced cognitive flexibility in the Set Shift task, one of the gold standard cognitive flexibility tasks.

Associations can be learned incrementally, via reinforcement learning (RL), or stored instantly in working memory (WM). While WM is fast, it is also capacity-limited and effortful. Striatal dopamine may promote RL plasticity, and WM, by facilitating updating and effort exertion. Yet, prior studies have failed to distinguish between dopamines effects on RL versus WM. N = 100 participants completed a paradigm isolating these systems in a double-blind study measuring dopamine synthesis with [18F]-FDOPA imaging and manipulating dopamine with methylphenidate and sulpiride. Learning is enhanced among high synthesis capacity individuals and by methylphenidate, but impaired by sulpiride. Methylphenidate also blunts effort cost learning. Computational modeling reveals that individuals with high dopamine synthesis rely more on WM, while methylphenidate boosts their RL rates. The D2 antagonist sulpiride reduces accuracy due to diminished WM involvement and faster WM decay. We conclude that dopamine enhances both slow RL, and fast WM, by promoting plasticity and reducing effort sensitivity. These results also highlight the need to control for dopamines effects on WM when testing its effects on RL.

Delay discounting refers to the behavioral tendency to devalue rewards as a function of their delay in receipt. Heightened delay discounting has been associated with substance use disorders, as well as multiple co-occurring psychopathologies. Genetic studies in humans and animal models have established that delay discounting is a heritable trait, but only a few specific genes have been associated with delay discounting. Here, we aimed to identify novel genetic loci associated with delay discounting through a genome-wide association study (GWAS) using Heterogenous Stock rats, a genetically diverse outbred population derived from eight inbred founder strains. We assessed delay discounting in 650 male and female rats using an adjusting amount procedure in which rats chose between smaller immediate sucrose rewards or a larger reward at variable delays. Preference switch points were calculated for each rat and both exponential and hyperbolic functions were fitted to these indifference points. Area under the curve (AUC) and the discounting parameter k of both functions were used as delay discounting measures. GWAS for AUC, exponential k, and indifference points for a short delay identified significant loci on chromosomes 20 and 14. The gene Slc35f1, which encodes a member of the solute carrier family of nucleoside sugar transporters, was the only gene within the chromosome 20 locus. That locus also contained an eQTL for Slc35f1, suggesting that heritable differences in the expression of that gene might be responsible for the association with behavior. The gene Adgrl3, which encodes a member of the latrophilin family of G-protein coupled receptors, was the only gene within the chromosome 14 locus. These findings implicate novel genes in delay discounting and highlight the need for further exploration.

Simple behavioral tests like the forced swim test (FST) and tail suspension test (TST) are widely used to assess depression-like behaviors in rodents, primarily measuring immobility time. However, this approach oversimplifies behavioral readouts and overlooks the cognitive processes driving behavior, leaving the relationship between increased immobility and cognitive biases unclear. Here, we developed the SwimStruggleTracker (SST) to extract fine-grained behavioral trajectories and integrate computational modeling to methodically analyze behavior. Our findings reveal that behavior in the FST and TST follows reinforcement learning principles involving learning, consequence perception, and decision-making. Notably, the cognitive processes underlying behavior differ between the two tests, challenging the assumption that they are interchangeable for cross-validation. Regression analyses identify distinct behavior phases: early behavior is primarily influenced by learning-related factors, while later stages are more affected by consequence sensitivity. These findings suggest traditional analyses focusing final minutes may underestimate the role of learning and overemphasize consequence sensitivity. MotivationThe forced swim test (FST) and tail suspension test (TST) are among the most widely used paradigms for assessing depression-like behaviors in rodents. Yet, traditional analyses typically quantify only immobility during the final minutes, discarding rich temporal structure in the data and hindering efforts to uncover the cognitive mechanisms underlying these behaviors. To address this gap, we developed an automated tool that captures behavioral trajectories with fine temporal resolution and integrates computational modeling to dissect the cognitive processes driving behavior. Using this approach, we demonstrate that the FST and TST engage overlapping but partially distinct cognitive processes, and that the dominant cognitive components shift across different stages of the tests. HighlightsO_LISwimStruggleTracker (SST) accurately rejects passive movements, such as pendulum-like motion. C_LIO_LIReinforcement learning models capture the behavioral dynamics of mice in the FST and TST. C_LIO_LIDistinct winning models indicate that the FST and TST engage partially dissociable cognitive processes. C_LIO_LILearning factors dominate early stages, whereas consequence-sensitivity factors dominate later stages. C_LI