Behavioral Neuroscience

The midsession reversal (MSR) task is frequently used to study behavioral flexibility and decision strategies in animals. In a typical version of the task, subjects complete 80 trials in which they choose between two simultaneously presented stimuli, S1 and S2. During the first 40 trials, responses to S1 are reinforced, whereas responses to S2 are not. The contingencies then reverse without warning: From trial 41 to 80, only responses to S2 are reinforced. In birds, performance in this task is often characterized by anticipatory and perseverative errors around the reversal point, suggesting a reliance on elapsed time since the session began. In contrast, rats tested in operant conditioning chambers typically show near-optimal performance with few errors, a pattern often interpreted as evidence that rats rely primarily on local reinforcement cues rather than temporal information. The present study investigated whether rats exclusively rely on local cues in the MSR task or whether temporal information also contributes to the decision process. Two groups of rats were trained with different intertrial intervals (ITIs; 5 s or 10 s) while the reversal point remained fixed at Trial 41. During acquisition, both groups diplayed similar learning rates and near-optimal steady-state performance with minimal anticipatory or perseverative errors. However, when the ITI was manipulated in probe sessions, systematic shifts in switching behavior emerged. Rats adjusted their choices according to the temporal midpoint experienced during training rather than the nominal trial number of the reversal. These results suggest that rats rely on a mixed strategy that integrates local reinforcement cues with global timing information. Temporal control may therefore be present even when it is not expressed during standard training conditions.

Signal detection theory posits that subjects in two-stimulus, two-choice discrimination tasks decide by comparing random samples of an evidence variable to a static decision criterion. While the core assumptions of the theory have received ample experimental support, it has become evident that the decision criterion is not static but subject to trial-by-trial fluctuations and can be influenced by experimental manipulations. The mechanisms governing the trial-by-trial criterion changes are however not well understood. Here, we report results from five experiments in which we subjected rats to a two-stimulus, two-choice auditory discrimination task. In the first three experiments, we investigated the effects of stimulus presentation ratios and reward ratios and provide clear evidence that the effects of changing reward ratios are more pronounced than those of stimulus presentation ratios. A model-based analysis revealed that this effect was due to more than tenfold higher learning rates when reward ratios were manipulated. In two separate experiments, we investigated the effect of reward density (i.e., global reward rate) on criterion learning but failed to find consistent effects. A systematic comparison of three different trial-by-trial criterion learning models based on detection theory, the matching law, and reinforcement learning showed that no model was able to capture the differential effects of stimulus presentation and reward ratios. We conclude that subjects explicitly represent either prior stimulus probabilities or entire stimulus distributions, and accordingly future models need to represent these factors as well.

Accurate and efficient memory processing is essential for survival. Recent work in human subjects and animal models has suggested that memory processing may differ in meaningful ways between males and females. In mice, contextual fear memory (CFM) encoding, consolidation, and recall have been well studied, and the mouse hippocampus and amygdala have been implicated in these processes. The present study addresses how the specific contribution of these brain regions to each stage CFM processing in female vs. male mice. We find that male and female mice show no differences in CFM recall, nor in sleep behavior in the hours following single-trial contextual fear conditioning (CFC), which is essential for CFM consolidation. However, females - but not males - show significantly increased expression of cFos in dorsal hippocampal CA1 and CA2 neurons during CFM encoding. On the other hand, males - but not females - show increased cFos expression among DG granule cells during CFM consolidation. These findings highlight the fact that the neurobiological underpinnings of memory processing may differ between males and females, even when recall performance is identical. Scope statementHistorically, research on the neurobiological basis of memory processing has been carried out mainly in male subjects. Thus, our understanding of these mechanisms is biased towards male brain neurophysiology. Recent studies have variously reported performance differences for episodic memory tasks, in which male subjects perform better, worse, or the same as females. Here, we find that male and female mice perform similarly on a well-studied experimental memory task but nonetheless have differences in the relative activity of different brain structures during sequential stages of memory processing. This emphasizes the importance of including both males and females in memory studies, due to potential sex differences in the neurobiological substrates of memory.

Endocannabinoid (eCB) signaling is a key regulator of reward-related dopaminergic signaling, particularly in response to drugs of abuse, such as cocaine. To date, our understanding of this mechanism has primarily been limited to male subjects. Prior work establishes that female cocaine users have more adverse outcomes, and female rats show greater sensitivity to cannabinoid type 1 receptor (CB1R) regulation of cocaine self-administration. Therefore, we hypothesize that female rats exhibit enhanced eCB regulation of cocaine-evoked dopamine (DA). We used in vivo fiber photometry recording of the dopamine biosensor, dLight 1.3b, in the nucleus accumbens medial shell (NAcms) in response to cocaine in male and female rats. Rats were pretreated with cannabinoid-targeting drugs to investigate the effects of CB1R inactivation or augmentation of the eCB 2-AG on cocaine-evoked DA. Our results revealed that CB1R inactivation attenuates cocaine-evoked DA in male and female rats, but females showed enhanced sensitivity for CB1R regulation of cocaine-evoked DA. Cocaine-evoked DA was enhanced by augmenting 2-AG levels, and females again showed increased sensitivity to this manipulation. Finally, females show greater cocaine-evoked DA when in a non-estrous cycle compared to estrous, reinforcing that estrous cycle is a determinant of cocaine-evoked DA. These data indicate that females show enhanced eCB regulation of cocaine-evoked DA signaling, underscoring the importance of sex as a biological variable in our understanding of endocannabinoid regulation of drug reward. HighlightsO_LICB1R inactivation attenuates cocaine-evoked DA in NAcms, preferentially in females C_LIO_LI2-AG augmentation via MAGL inhibition enhances cocaine-evoked DA, with female bias C_LIO_LIEstrous phase modulates the dopamine response to a high dose of cocaine in females C_LIO_LIMale and female rats show similar baseline DA and locomotor responses to cocaine C_LI

Physical activity offers myriad benefits to health and well-being, in humans and other animals as well. In rodents, voluntary wheel running can attenuate the effects of both physical and social stressors on rodent social behavior. Whether wheel running affects rodent social behaviors per se remains less well understood. We conducted the current study to test whether home cage access to running wheels impacts the social behaviors of adult, group-housed C57BL/6J female mice during same-sex interactions with novel females. Group-housed females were either given continuous home cage running wheel access or a standard paper hut starting at weaning, and as adults, social behaviors were measured during interactions with novel females. In two cohorts, we found that 5 weeks of running wheel access during adolescence reduced the time that subject females spent investigating a novel female and also tended to reduce total ultrasonic vocalizations produced during interactions. These effects were not reversed by a 2-week period of running wheel removal but were recapitulated in a different cohort by 2 weeks of running wheel access in adulthood. Unexpectedly, we found that these effects on female social behavior were not due to wheel running per se, because females raised from weaning with immobile running wheels also showed low rates of social behaviors during same-sex interactions in adulthood. Overall, we find that the presence of a running wheel in the home cage has an enduring inhibitory influence on female social behavior during same-sex interactions, a finding that has implications for the design of studies that include same-sex interactions between female mice.

RationaleRecent research on habits and skills has produced a wave of new theories regarding the shift in control from medial to lateral regions of the dorsal striatum, and how these regions are implicated in the selected and executed of action sequences. ObjectivesTo examine the comparative effects of muscimol/baclofen inactivation and dopamine D1 and D2 receptor agents in the dorsomedial (DMS) and dorsolateral (DLS) striatum on the performance of skilled action sequences. MethodsInfusions were made in well-trained rats using the five-step nose poke task to isolate the effects on initiation, execution and termination components of skilled action sequences. ResultsDLS inactivation produced sequencing deficits like those observed with pre-training lesions, indicating that the DLS is critical for both the acquisition and performance of sequences. Behaviour was unchanged following DMS inactivation, consistent with models of DMS disengagement following training. Infusions of D1 and D2 antagonists did not alter behaviour, however the D2 receptor agonist quinpirole increased sequence errors at a low dose and reduced sequences at the high dose in the DLS. DLS manipulations impaired sequence initiation and termination as well as reward transitions, while the chunking ballistic response pattern was largely unaltered, indicating that between-but not within-sequence actions rely on the DLS. ConclusionsSkilled action sequencing, including chunk transitions was dependent on DLS and its modulation by D2 receptors, but not on DMS function. Using a novel sequencing task, these results support the dissociable and dopamine-dependent role of the dorsal striatum subregions in performing skilled motor actions.

Sex differences in responses to chronic stress are implicated in the higher prevalence of major depression and PTSD in females. Evidence of sex differences in endocannabinoid (eCB) physiology suggests that eCB signaling contributes to sexual disparities in fear conditioning and extinction. In adolescent male Sprague-Dawley rats, exposure to chronic-mild-unpredictable stress (CMS) resulted in enhanced trace-fear conditioning that was reversed by CB1 activation (Reich et al, 2013). In the present study, we assessed the effects of CMS and CB1 activation on hippocampal-dependent trace and contextual fear conditioning in adolescent female Sprague-Dawley rats. CMS exposure enhanced trace freezing behavior during memory recall compared to non-stress controls. This effect was not observed in contextually conditioned females. The CB1 receptor agonist, ACEA (0.1 mg/kg), administered prior to trace memory recall, but not prior to acquisition, significantly decreased freezing in both stress and non-stress females. ACEA significantly reduced baseline freezing behavior during trace memory recall in both stress and non-stress rats, however ACEA either 1) did not affect or 2) impaired short and long-term extinction in stress and non-stress females. In contextually conditioned females, ACEA decreased freezing during memory recall, although the effect was more robust in stress rats. ACEA impaired long-term contextual extinction in stress females while facilitating this in non-stress controls. However, ACEA had no effect or impaired short-term contextual extinction in both stress and non-stress groups. The results demonstrate that CMS enhances hippocampal-dependent episodic fear memories but has limited effects on contextual fear conditioning in female rats. These findings have implications in the use of medical cannabinoid treatment of disorders such as PTSD, as well as recreational cannabis use in adolescent/young adult females.

Sexual motivation is a complex concept involving both the initial drive to begin mating and the motivation to sustain copulation. Disruptions in sexual motivation are often observed in psychiatric disorders. This study proposes that sexual motivation can be divided into two distinct components: sexual incentive motivation and the drive to sustain copulation. To investigate this, we utilized the Motivation to Continue Copulation (MCC) test, which measures effort (nose pokes) to gain access to a sexual reward, and compared it with the Sexual Incentive Motivation (SIM) test and standard copulation tests. Male and female rats were trained on a fixed ratio (FR) 1 schedule using cheese rewards before transitioning to sexual rewards. After six FR1 sessions, the effort required increased to FR5 and progressive ratio (PR) schedules. Results revealed that sexual incentive motivation, measured by the SIM test, was higher in males after sexual experience, while females maintained consistent levels. In the MCC test, both males and females exhibited increased motivation to continue copulation with experience, but the motivation declined in the 2nd ejaculatory series. These findings demonstrate that sexual motivation comprises distinct components. The MCC test effectively measures the drive to sustain copulation, while the SIM test assesses incentive motivation. This distinction is crucial for advancing behavioral neuroscience and understanding sexual dysfunction in psychiatric conditions.

By relying on the observation of others experiences, humans learn about threat while avoiding harmful experiences. Yet, previous neuroscience research has focused on observational threats that are predictable. While the neurobiological distinction between temporally predictable (cued) and unpredictable (contextual) threats has been well-characterized in firsthand learning. In this study, we developed a novel observational paradigm in which participants learned from predictable (P) and unpredictable (U) observational threats, as well as a no-threat (N) condition and encountered the same conditions during an expression phase based on the NPU paradigm to investigate how the brain encodes predictable and unpredictable threat cues observed in others. Participants in Experiment 1 (n=20, male and female) and Experiment 2 (n=23, male and female) successfully learned threat contingencies, showing heightened threat expectations for predictable cues and unpredictable contexts. This converged with neural (fMRI, Experiment 2) responses in the anterior insula during the expression phase. Reflecting the dynamic process of learning, the amygdala responded to predictable threat cues with a linear decrease across trials. Interestingly, we found that responses to others pain was enhanced within the amygdala, insula and hippocampus, when participant could learn to predict threats, as compared to unpredictable conditions. Our findings suggest that humans learn to resolve temporal uncertainty, relying solely on observation, which thereby lays a foundation to the concept of fear and anxiety in social groups.

BackgroundPavlovian responding is a core component of behavior and can be measured via Pavlovian-instrumental transfer (PIT), where Pavlovian responses bias instrumental actions. Standard single-lever PIT paradigms, which assess responses using a single-choice option, cannot dissociate the contribution of model-free versus model-based reinforcement learning. While indirect evidence suggests a role for model-free responding in single-lever PIT, the contribution of model-based strategies is unclear. It also remains unknown whether internal cognitive states, such as mind wandering, impair specifically model-based but not model-free PIT, as is theoretically expected. MethodsWe developed a novel, trial-by-trial two-stage PIT paradigm designed to computationally dissociate model-free and model-based Pavlovian responding by leveraging probabilistic state transitions and trial-wise outcome predictions. After each two-stage Pavlovian learning trial, participants performed a single-lever PIT trial as well as a query trial of explicit value judgment. Detailed task instructions were provided to support potential model-based strategies. Computational modeling was used to quantify individual learning strategies. We assessed mind-wandering questionnaires and thought probes. ResultsAnalysis of query and PIT trials revealed trial-by-trial updating of outcome expectations based on probabilistic task structure, consistent with model-based Pavlovian responding. Behavioral responses during PIT were best explained by a computational model-based reinforcement learning model. In contrast, we found little evidence for model-free Pavlovian responding. Higher levels of mind wandering were associated with reduced model-based control but did not impact model-free indices. ConclusionWe introduce a novel single-lever PIT paradigm that enables fine-grained dissociation of model-free versus model-based Pavlovian response systems. Our findings provide evidence that single-lever PIT can operate through model-based mechanisms, challenging the assumption that single-lever PIT is predominantly model-free. Our findings also indicate that internal attentional states selectively modulate model-based PIT. Given the involvement of Pavlovian responding in numerous psychiatric conditions, our paradigm offers new avenues for understanding maladaptive behavior. Author SummaryOur daily actions are often influenced by cues like the smell of food or the sound of phone notifications that signal potential rewards or losses. These Pavlovian cues can shape our instrumental behavior even though their outcomes do not depend on what we do - a process known as Pavlovian-instrumental transfer (PIT). Here we study the computational learning mechanisms that underlie such PIT effects. While it is often assumed that Pavlovian responding follows simple, automatic rules without a cognitive model of cue consequences (i.e., model-free), evidence also shows a role for cognitive anticipations in Pavlovian responding (i.e., model-based). In this study, we extend this evidence by showing that PIT responding can be driven by flexible model-based learning. We designed a task to test whether participants use model-free versus model-based strategies to guide PIT, providing detailed task instructions. Using reinforcement learning models, we found that most participants used model-based learning when forming cue-outcome associations. Importantly, peoples attention mattered: when they were more distracted and doing mind wandering, they relied less on model-based strategies. Our findings suggest that Pavlovian learning is complex, flexible, and influenced by internal mental states, opening new windows to understand decision-making problems in mental health conditions like addiction.

Approach and avoidance behavior towards sensory stimuli serve as powerful behavioral readouts of our mental representations of the external world and our expectations and motivations in navigating it. In the olfactory system, approach or avoidance of odors statistically associated with people, places, and things relate to ecologically critical functions like feeding, fear, and reproduction. However, experimental methods for quantifying approach/avoidance behavior in relative terms across odors have been limited. Here we present a novel method for quantifying mouse approach/avoidance in an open field arena scented with up to four odors simultaneously. In lieu of traditional inferential statistics (which greatly limit the information that can be learned in this multivariate experiment), we demonstrate the a priori definition of quantitative hypotheses for the distribution of time among scented corners and the use of information theory-derived statistical metrics to quantify the relative likelihood of each competing hypothesis given the data collected. Finally, we use data from a fear conditioning experiment to demonstrate the application of this method to conclude that fear conditioned mice exhibit a fear generalization gradient that decreases as odorants become more different from the threat-predictive odorant, as opposed to competing hypotheses that mice are specifically avoiding the threat-predictive odorant or have overgeneralized their fear and avoid all test odors regardless of similarity. Critically, this method takes only a few minutes per animal with no prior behavioral training required, and it can be performed easily without automated apparatus.

Dopamine (DA) has been implicated in exploration-exploitation behaviour, i.e., exploring novel, potentially better options vs. exploiting known, previously rewarding options. Impairments in this trade-off occur in psychiatric disorders involving DAergic dysfunction, including addiction and schizophrenia. Pharmacological studies revealed a contribution of DA to exploration, but inconsistent findings suggest that interindividual variability in baseline DA may modulate effects. To address this, we investigated the effects of the DA precursor L-DOPA on exploration-exploitation during reinforcement learning in a sample of N = 75 healthy participants (n = 32 women), following a randomised, double-blind, placebo-controlled, pre-registered design (https://osf.io/p2r7u). We assessed whether putative baseline DA markers, including spontaneous eye blink rate, working memory (WM) capacity, and impulsivity, modulated drug effects and probed visual fixation patterns and pupil dilation as markers of exploration. L-DOPA had no overall effect on computational model parameters of random exploration, directed exploration or choice perseveration. WM capacity moderated drug effects on random exploration, with stronger effects at higher WM capacity. Remaining DA proxies showed no credible effects. Pooling the data from male participants with that from an earlier male-only study (Chakroun et al., 2020; total N = 74), L-DOPA increased uncertainty-dependent value weighting and perseveration strength, while decreasing habit updating, indicating a stronger tendency to repeat previous choices and slower decay of their influence over time. No credible drug effects were observed in female participants. Pupil dilation was tonically increased under L-DOPA and scaled with exploration behaviour and prediction error, confirming that pupillometry can index exploration-exploitation dynamics. Visual exploration patterns reflected uncertainty-driven sampling, but were unaffected by L-DOPA. Taken together, results suggest that DAergic modulation of exploration and perseveration behaviour may be contingent on cognitive capacity and sex, rather than exerting uniform effects across individuals.

BackgroundThe three-chamber test (3CT) is widely used to assess social behaviour in mice, based on the assumption that time spent near a conspecific reflects motivation for social contact. However, the design of the task constrains interpretation, as behaviour may reflect exploration, novelty seeking, or territorial investigation rather than affiliative social motivation. In addition, key biological factors such as sex differences and social hierarchy are often overlooked. AimsWe hypothesised that the 3CT overestimates sociability and used a direct-interaction phase to investigate motivation for affiliative social contact. We also integrated social status to determine if this modulated behavioural patterns and interacted with sex. MethodsAdult male and female C57BL/6 mice (n = 32) were tested in a standard 3CT, followed by removal of the cage barrier to permit direct contact. Behavioural parameters were quantified, and social status was determined using the tube test. ResultsMales exhibited higher social interest index scores than females. Once the barrier was removed, both sexes displayed a negative direct sociability index, indicating greater environmental exploration than social engagement. Correlation analysis revealed no association between indirect and direct measures. Sex differences emerged primarily among submissive mice, with submissive males showing greater social investigation than submissive females. ConclusionThese findings suggest that standard 3CT indices reflect exploratory rather than affiliative social motivation. The modified paradigm incorporating direct interaction provides a more realistic assessment of social behaviour and challenges assumptions about intrinsic sociability in mice.

Kisspeptin neurons in the rostral hypothalamus are hypothesized to initiate preovulatory gonadotropin-releasing hormone (GnRH) surges by causing estradiol-dependent activation of GnRH neuron action potential firing and subsequent GnRH release. To determine if estradiol or ovarian cycle stage modulates functional connectivity in this circuit, we used optogenetics to photostimulate anteroventral-periventricular (AVPV) area kisspeptin neurons while recording electrical activity and/or evoked synaptic currents from preoptic area GnRH neurons in acutely-prepared mouse brain slices. Slices were prepared from mice in multiple hormonal states, including 2-days post ovariectomy (OVX) and OVX plus estradiol during the morning or afternoon, diestrus, proestrus and 1-week post OVX, and 6-weeks post OVX with or without 1 week of estradiol replacement. Photostimulation induced a sustained, frequency-dependent increase in GnRH neuron firing rate. This neuromodulatory-typical response was not different in diestrous vs proestrous mice but was blunted in 1-week OVX mice, suggesting ovarian steroids amplify this response. Neuromodulatory responses were infrequent in 6-week OVX mice even with 1-week of estradiol treatment. A minority of GnRH neurons exhibited a substantial and near-immediate increase in firing rate typical of fast synaptic transmission. Monosynaptic connectivity was low and stable across the hormone states tested and mediated by GABA. Interestingly, evidence of a monosynaptic connection was not a requirement for GnRH neurons to exhibit a sustained increase in firing rate, suggesting non-synaptic or volume transmission occurs in this system. Synaptic connectivity did, however, amplify the increase in firing rate observed in GnRH neurons from proestrous mice, indicating proestrous hormonal conditions can amplify this response. Significance statementOvulation is initiated by central positive feedback effects of estradiol stimulating a surge of gonadotropin-releasing hormone (GnRH) release. Estradiol feedback is conveyed to GnRH neurons by afferents expressing estrogen receptor alpha, including kisspeptin-expressing neurons in the anteroventral periventricular (AVPV) area. To determine if endocrine milieu modulates functional interactions between AVPV kisspeptin and GnRH neurons, optogenetics was used to stimulate AVPV kisspeptin neurons while recording GnRH neuron spiking activity or synaptic currents in brain slices from ovariectomized, estradiol-treated, and ovary-intact mice. Stimulation (20Hz) increased GnRH neuron firing rate in all hormone conditions. This effect was stronger during proestrus and was further increased in GnRH neurons receiving fast-synaptic transmission. A synaptic connection was not required, however, suggesting volume transmission occurs.

Early life adverse (ELA) experiences such as child maltreatment (MALT) are associated with physical and mental illness, including substance use disorders (SUDs), but underlying neurobiological mechanisms remain unclear. This study examined long-term effects of infant MALT on adult brain serotonin (5HT) and dopamine (DA) receptors in corticolimbic regions involved in reward and emotional control, using positron emission tomography (PET) imaging, a translational infant MALT macaque model of cocaine use disorder (CUD) risk and a COC self-administration (SA) paradigm. The study focused on regional serotonin 5HT1A, 5HT2A, and dopamine D2/D3 receptor availability (BP) differences between MALT and Control animals using PET, both at baseline (pre-COC SA) and following chronic COC SA (once they reached a total of 100 mg/kg intake). We also examined whether levels of these neurochemical receptors predicted COC SA measures, including reinforcing effects and potency using fixed-ratio (FR) peak response rates and progressive-ratio (PR) peak breakpoint. Our findings showed long-term effects of infant MALT on 5HT, but not DA, receptors in corticolimbic circuits. Specifically, MALT animals showed lower 5HT1A BP in the anterior cingulate cortex (ACC), medial prefrontal cortex (mPFC), and hippocampus compared to Controls. A MALT by Sex interaction effect was detected in 5HT2A BP in the OFC, with lower levels in MALT than Control males, but not in females. In addition, upregulation of 5HT1A and 5HT2A receptors was detected following chronic COC SA in most PFC subregions, hippocampus, and NAcc, particularly in the Control group. These findings suggest long-term effects of ELA on adult 5HT, but not DA, receptors in corticolimbic regions involved in emotional and reward processes. We also found associations between PET baseline (pre-COC SA) receptor BP data and COC SA measures. In particular, a positive correlation between 5HT1A receptor BP in caudate and peak FR Response Rates, whereas amygdala 5HT1A receptor levels were positively correlated with peak PR breakpoint and negatively correlated with peak FR Response Rates. Overall, these findings suggest an important role of 5HT1A and 5HT2A PFC receptors in early COC-related changes in reward circuitry and of amygdala 5HT receptors on cocaine-maintained behaviors. The dynamic change of these 5HT1A and 5HT2A receptors following chronic COC exposure was blunted in animals with ELA. It would be important to understand the biological consequences of these dynamic changes in 5HT receptors and whether they are associated with other stages of the addiction cycle, for example COC relapse, which could inform future pharmacological interventions that target 5HT receptors for treatment of CUD. Simple SummaryWe studied the long-term effects of early life adversity (ELA) on adult brain dopamine (DA) and serotonin (5HT) signaling in corticolimbic regions involved in emotional and reward regulation. We used specific PET radioligands that bind to the DA D2/D3, 5HT1A and 5HT2A receptors, finding lower levels of 5HT, but not DA, receptors binding potential (BP) in animals that experienced ELA. We also found associations between PET receptor BP measures and reinforcing effects of cocaine in i.v. self-administration paradigms using fixed- and progressive-ratio reinforcement schedules. In addition, a strong upregulation of 5HT, but not DA, receptors was identified following chronic cocaine exposure in prefrontal cortex (PFC). Our findings suggest long-term effects of ELA on adult PFC 5HT1A and 5HT2A receptors. The findings also suggest an important role of 5HT1A and 5HT2A, more so than D2/D3, receptors in early cocaine-related changes in reward circuitry. The early dynamic changes of these 5HT receptors could serve as biomarkers for cocaine use disorder (CUD) and inform future pharmacological interventions.

Cerebellar communication with the prefrontal cortex (PFC) may play a significant role in cognitive functions. Our previous studies found that rule-based (RB) category learning depends on the PFC in humans and rats. The PFC is also crucial for behavioral flexibility following rule-changes in various tasks. Very little is known regarding the role of the cerebellum in RB category learning. The current study was designed to determine whether the cerebellum plays a role in RB category learning, and in categorization following a rule switch. Female and male rats were given bilateral lesions of the lateral cerebellar nuclei (LCN) or a control surgery and trained on an RB category learning task followed by a category rule switch. A subset of rats was trained on a control discrimination task with the same trial procedures as the categorization task. Rats with LCN lesions took significantly longer to learn both the first and second category rules but were not impaired on the control task. Computational modeling revealed less task engagement and increased switching between engaged and non-engaged states in the LCN lesion group. Several measures of task performance indicated that the category learning deficit was not caused by a motor impairment, response bias, or an inability to discriminate the stimuli. The category learning deficits with LCN lesions were related to reduced accuracy of stimulus classification, an inability to maintain task engagement, and loss of flexibility. The results show, for the first time, that the cerebellum plays a crucial role in category learning and category rule-switching.

In rats, cue-induced opioid craving intensifies (incubates) during abstinence from opioid self-administration and then remains high for a prolonged period. The prolonged plateau models persistent vulnerability to cue-induced craving and relapse in humans recovering from opioid use disorder. However, a very significant contributor to relapse vulnerability in these individuals is the presence of negative affective states that can persist for months to years, far beyond physical dependence. The goal of this study was to determine if the incubation of craving model recapitulates this aspect of relapse vulnerability. We began by comparing rats trained to self-administer oxycodone using a regimen leading to persistent elevation of cue-induced craving (6 h/d x 10 d) and rats trained to self-administer saline. We assessed somatic withdrawal signs in early abstinence and conducted behavioral tests modeling negative affect (open field, social preference, sucrose preference, and elevated plus maze) in late abstinence. Some somatic withdrawal signs were greater in oxycodone rats on abstinence day (AD)1, but cumulative scores did not differ between groups on AD1-3. On AD41-46, no group differences were found in behavioral tests modeling negative affect. To compare early and late abstinenceperiods, a second cohort of rats self-administered saline and oxycodoneand then received two cue-induced seeking tests (AD1 and AD40; oxycodone rats exhibited incubation of craving) and two series of negative affect tests (AD2-7 and AD41-48). While some time-dependent changes in affect were observed within each group, they were suggestive of reduced anxiety-like behavior in oxycodone rats. Finally, because rats are single-housed during our incubation studies, we compared drug-naive rats after 8-9 weeks of single vs pair housing and found no difference in behavioral tests modeling negative affect. We conclude that the persistence of elevated cue-induced craving observed after a standard opioid incubation regimen is not accompanied by negative affective states, probably due to lower drug intake during the intravenous regimen compared to non-contingent escalating dose regimens typically used to study withdrawal signs. This does not negate the utility of the incubation model for studying cue-induced opioid craving and its neurobiological basis.

Animals exposed to pairings of a neutral stimulus with reward acquire a conditioned response to the neutral stimulus. A prominent hypothesis, formalized in the Temporal Difference (TD) learning algorithm, is that animals learn to predict the future reward associated with the neutral stimulus ("value"). Though the TD algorithm does not explicitly specify what drives conditioned responding, a typical assumption is that it reflects the animals estimate of value. In TD learning, value estimates are updated using reward prediction error (RPE, the discrepancy between observed and predicted reward), and are thought to be signaled by the phasic activity of midbrain dopamine neurons. This hypothesis posits that dopamines effects on conditioned responding are mediated entirely by its effects on learning. However, recent experimental and theoretical evidence suggests that dopamine may play a more direct role in modulating conditioned responding. We use a combination of data analysis and computational modeling to probe the relationship between dopamine and conditioned responding. Our results suggest that dopamine directly modulates conditioned responding, in addition to its role in learning. These findings can be captured by a model in which dopamine RPE acts both indirectly (via learning) and directly on conditioned responding.

Predictions can alter working memory (WM) representations. However, its effects may have been mischaracterized due to the use of precise predictions in previous experiments, where exact properties of upcoming memory items are cued in advance. Here we investigated a more ecologically valid scenario, in which we assessed the impact of diffuse predictions, where advance cues provided only partial knowledge about the targets. To investigate the resultant nature of the target representations in WM, we performed a series of multivariate analyses of EEG data. Forty participants judged whether a probe grating was rotated clockwise or counterclockwise relative to a memorized orientation, which was either predictable or unpredictable. Each memory item was preceded by a central color cue (red, green, or blue). In half of the trials, two of these (predictive) colors cued two non-overlapping 90{degrees} segments of orientations that the grating was sampled from. Thus, participants knew the range of possible orientations of these items, but not their exact orientation. In the other half of the trials, a third (non-predictive) color was presented, signaling that the item could have any possible orientation. Behavioral results revealed higher accuracy for predictable items, with systematic biases toward the center of the cued segment. EEG results revealed equally successful decoding of orientation for both predictable and unpredictable items during memory encoding. However, cross-condition decoding was significantly weaker than within-condition decoding, suggesting that the encoding format changed between conditions. Representational similarity analysis showed higher similarity between predictable items, with a representational bias towards the cued segment. Covariance matrices showed lower variance for predictable items while the representational space of predictable items was shrunk. These effects were absent during the maintenance phase. Together, our findings suggest that diffuse predictions alter the geometric layout of the neural representations and stabilize the neural code during WM encoding.

In sex-role reversed species, females are socially polyandrous and compete for multiple mates, whereas males conduct the majority of parental care. To understand the extent to which physiological differences between females and males are shaped by sex roles, we examined sex differences in gene expression in sex-role reversed northern jacanas (Jacana spinosa). Given that females compete for mating opportunities, and males cycle between courtship and parental care, we predicted that transcriptomic profiles would be more similar between females and courting males, in contrast to female and parenting males. Leveraging a high quality de novo genome assembly, we conducted RNA-seq on two brain regions associated with the regulation of social behavior: the preoptic area of the hypothalamus and the nucleus taeniae. The majority of genes differentially expressed between the sexes were male-biased. Of these male-biased genes, the majority were located on the Z-chromosome. Contrary to our prediction, the greatest difference in autosomal gene expression was between females and courting males, in the preoptic area of the hypothalamus. Several differentially expressed genes related to elements of hormone signaling that are likely to be behaviorally salient, including higher expression of androgen receptor in females relative to parenting males, and higher expression of prolactin receptor in males, regardless of breeding stage. Some sex-associated gene networks were also associated with competitive traits, whereas others were associated with aggressive behaviors, regardless of sex. Few genes were differentially expressed between courting and parenting males, yet some nonetheless had connections to behavioral endocrinology, including prolactin, thyroid and insulin-like growth factor pathways. Our investigation of sex differences in gene expression can help to reveal the molecular mechanisms underlying female competition and male parental care in socially polyandrous species. We conclude that social polyandry is not a simple reversal in the direction of sex-biased gene expression in the brain, but rather a result of complex genetic and hormonal interactions that warrants further study.