TAAR1 and 5-HT1B receptor agonists attenuate autism-like irritability and aggression in rats prenatally exposed to valproic acid

Despite the rising prevalence of autism spectrum disorder (ASD), there remains a significant unmet need for pharmacotherapies addressing its core and associative symptoms. While some atypical antipsychotics have been approved for managing associated irritability and aggression, their use is constrained by substantial side effects. This study aimed firstly to develop behavioral measures to explore frustration, irritability and aggression phenotypes in the rat prenatal valproic acid (VPA) model of ASD. Additionally, we investigated the potential of two novel mechanisms, 5-HT1B and TAAR1 agonism, to alleviate these behaviors. Male offspring exposed to prenatal VPA were trained to achieve stable performance on a cued operant task, followed by pharmacological assessment in an operant frustration test, bottle brush test and resident intruder test. VPA exposed rats demonstrated behaviors indicative of frustration and irritability, as well as increased aggression compared to controls. The irritability-like behavior and aggression were further exacerbated in animals previously experiencing a frustrative event during the operant test. Single administration of the 5-HT1B agonist CP-94253 or TAAR1 agonist RO5263397 attenuated the frustration-like behavior compared to vehicle. Additionally, both agonists reduced irritability-like behavior under both normal and frustrative conditions. While CP-94253 reduced aggression in the resident intruder test under both conditions, RO5263397 only produced effects in rats that previously experienced a frustrative event. Our study describes previously uncharacterized phenotypes of frustration, irritability, and aggression in the rat prenatal VPA model of ASD. Administration of selective TAAR1 or 5-HT1B receptor agonists alleviated these deficits, warranting further exploration of both targets in ASD treatment.

Developmental trajectory of social reward motivation from early adolescence into adulthood in female and male Long-Evans rats

Most studies of adolescent and adult behavior involved one age group of each, whereas the dynamic changes in brain development suggest that there may be behavioral flux in adolescence. In two studies, we investigated developmental changes in social reward motivation in female and male Long-Evans rats from prepuberty to early adulthood in a social operant conditioning task. Given the earlier onset of puberty in females than in males, we predicted the course of social reward development would differ between the sexes. Overall, the pattern of results from both studies suggests that the trajectory of social motivation across adolescence is characterized by upward and downward shifts that do not depend on the sex of the rats. During training, in both studies, the mean number of social gate openings and percentage of social gate openings was higher at P30 (prepubertal, early adolescence) and P50 (late adolescence) than at P40 (mid adolescence) and P70 (adulthood) irrespective of sex. Nevertheless, the specific age comparisons that were significant depended on the study. In both studies, P30 rats had greater levels of social motivation than did adults in accessing a social reward when increased effort was required (progressive ratio tests). In an extinction test, only P30 and P50 rats continued to show more nose-pokes at the previously social gate than at the nonsocial gate, suggesting resistance to extinction. The results highlight the importance of characterizing behavior at several timepoints in adolescence to understand the neural mechanisms, many of which show similar discontinuities as they develop across adolescence.

Quantifying animals' perception of environmental predictability using anticipatory behavior

Animals under human care often experience predictable daily husbandry events, which can promote the development of anticipatory behavior. Previous research suggests even short delays in the arrival of a predictable, desired outcome can lead to negative welfare outcomes for animals. As such, providing reliable information to animals regarding the onset of important events may be a simple but useful method to support positive welfare. Here we evaluated the quantitative characteristics of anticipatory behavior of a California sea lion at the San Francisco Zoo in three situations (1) when the animal had accurate information about the occurrence of the event (temporally predictable training sessions), (2) when the information was semi-reliable (unscheduled training session), and (3) when a reliable signal was offered before unscheduled sessions. Results showed that providing a reliable cue resulted in a stronger temporal correlation of anticipation before the beginning of the unscheduled session, similar to the temporally predictable training session. However, providing a reliable cue did not reduce the intensity of the anticipatory behavior. We propose to take into account two aspects of the quantitative characteristics of anticipatory behavior: correlation with time until a desired event (correlation) and intensity, where the correlation indicates the ability of an individual animal to predict the occurrence of an event, and the intensity indicates the degree of sensitivity of the animal to reward. We discuss the implications for animal welfare and husbandry.

Failure to mate enhances investment in behaviors that may promote mating reward and impairs the ability to cope with stressors via a subpopulation of Neuropeptide F receptor neurons

Living in dynamic environments such as the social domain, where interaction with others determines the reproductive success of individuals, requires the ability to recognize opportunities to obtain natural rewards and cope with challenges that are associated with achieving them. As such, actions that promote survival and reproduction are reinforced by the brain reward system, whereas coping with the challenges associated with obtaining these rewards is mediated by stress-response pathways, the activation of which can impair health and shorten lifespan. While much research has been devoted to understanding mechanisms underlying the way by which natural rewards are processed by the reward system, less attention has been given to the consequences of failure to obtain a desirable reward. As a model system to study the impact of failure to obtain a natural reward, we used the well-established courtship suppression paradigm in Drosophila melanogaster as means to induce repeated failures to obtain sexual reward in male flies. We discovered that beyond the known reduction in courtship actions caused by interaction with non-receptive females, repeated failures to mate induce a stress response characterized by persistent motivation to obtain the sexual reward, reduced male-male social interaction, and enhanced aggression. This frustrative-like state caused by the conflict between high motivation to obtain sexual reward and the inability to fulfill their mating drive impairs the capacity of rejected males to tolerate stressors such as starvation and oxidative stress. We further show that sensitivity to starvation and enhanced social arousal is mediated by the disinhibition of a small population of neurons that express receptors for the fly homologue of neuropeptide Y. Our findings demonstrate for the first time the existence of social stress in flies and offers a framework to study mechanisms underlying the crosstalk between reward, stress, and reproduction in a simple nervous system that is highly amenable to genetic manipulation.

Still-face effect in domestic dogs: comparing untrained with trained and animal assisted interventions dogs

The still-face effect has been extensively studied in human infants and comprises the reduction in affiliative behaviors and increased stress that occurs after a sudden interruption of social interaction with a caregiver. Domestic dogs (Canis familiaris) are model candidates for showing this effect, as they form deep bonds with their owners and interspecific social interaction is reinforcing to them. The aim of these studies was to assess if companion dogs exhibit the still-face effect and whether prior experiences during ontogeny modulate this effect. To this end, Study 1 compared dogs with different levels of training (untrained, intermediate, and advanced), while Study 2 assessed dogs that participated in Animal Assisted Interventions (AAIs) and companion dogs (CDs). The procedure was carried out virtually and comprised three phases lasting 1 min: interaction, still-face (the owner turned suddenly indifferent), and reunion (the interaction was resumed). Dogs exhibited a decrease in proximity to and contact with the owner, as well as an increase in begging and stress behaviors during the still-face phase. Moreover, this was not observed in a control condition in which the interaction continued in the same way during all three phases, discarding alternative explanations for these changes. These results show that dogs experience a still-face effect in a similar way to infants, highlighting the value interspecific social interaction has for dogs. Nevertheless, the absence of differences according to their training level or participation in AAIs suggests this is a robust phenomenon, which appears to be less susceptible to the influences of ontogenetic experiences.

Environmental enrichment accelerates the acquisition of schedule-induced drinking in rats

Environmental enrichment (EE) provides an improvement in the housing conditions of experimental animals, such as laboratory rats, with greater physical and social stimulation through toys and company in the home cages. Its use is known to influence performance of experimental protocols, but these effects have not been well determined in the schedule-induced drinking (SID) procedure. The main goal of this study was to investigate the effects of EE on the acquisition of SID in 24 12-week-old male Wistar rats, divided into two groups, a group with EE housed with toys and companions, and a group without enrichment in individual housing conditions without toys (social isolation and no environmental enrichment, INEE). A total of 25 sessions, under a fixed time 30 s food reinforcement schedule and with access to water in the experimental chambers were carried out. Sessions lasted 30 min. The results showed that the EE group developed faster the excessive drinking pattern of SID, and drank to higher levels, than the INEE group. The greater development of SID in the EE group contradicts the view of schedule-induced behavior as linked to stress reduction and better suits with the conception of induction related to positive reinforcement.

Affective trajectories: Are hens influenced by positive and negative changes in their living conditions?

Most studies of the effects of housing and husbandry on animals' affective states and welfare investigate the impact of stable living conditions, comparing for example, animals living in enriched environments with those living in non-enriched ones. Changes in living conditions, including from more to less enriched environments, have also been found to have effects on measures of affective state and welfare in some species. But these studies have not investigated whether it is the trajectory of change that has affected the animals (e.g., worsening conditions), or simply the nature of their final environment (e.g., non-enriched). Here, we hypothesised that laying hens living in worsening conditions across a six-week period (gradually moving from preferred to non-preferred living conditions; "Trajectory to Non-Preferred", TNP, n = 30), would show evidence of more negative affective states and poorer welfare than those living continuously in non-preferred conditions for the same duration ("Stable Non-Preferred", SNP, n = 30). We also hypothesised that hens living in improving conditions (gradually moving from non-preferred to preferred living conditions; "Trajectory to Preferred", TP, n = 30), would show evidence of more positive affective states and better welfare than those living continuously in preferred conditions ("Stable Preferred", SP, n = 30). The preferred living condition provided extensive resources and intermittent rewarding events (such as the delivery of food treats) known to be valued and preferred by most hens, while the non-preferred living condition provided just basic resources and intermittent aversive events (e.g., loud noises). The hens' affective states and welfare were measured using home-pen behavioural observations, body condition assessments, physiological stress measures (e.g., blood corticosterone, glucose, etc.), physical challenge tests, and judgement bias tests. A number of differences between hens in the trajectory and stable living conditions were found: TP hens were lighter, showed more foraging behaviour and less standing alert and head-shaking than SP hens, while TNP hens showed more head-shaking, mild feather pecking and aggressive attacking of pen mates than SNP hens. However, some of these differences failed to reach significance following Benjamini adjustments for multiple testing. The groups also did not differ in their judgement biases (measured in a sub-sample of 12 hens per experimental group), response to physical challenges, or measures of physiological stress. We conclude that the hens in the present study showed some evidence of responsiveness to 'affective trajectories' in their living conditions, but no definitive effects on their affective states and welfare.

Dopamine error signal to actively cope with lack of expected reward

To obtain more of a particular uncertain reward, animals must learn to actively overcome the lack of reward and adjust behavior to obtain it again. The neural mechanisms underlying such coping with reward omission remain unclear. Here, we developed a task in rats to monitor active behavioral switch toward the next reward after no reward. We found that some dopamine neurons in the ventral tegmental area exhibited increased responses to unexpected reward omission and decreased responses to unexpected reward, following the opposite responses of the well-known dopamine neurons that signal reward prediction error (RPE). The dopamine increase reflected in the nucleus accumbens correlated with behavioral adjustment to actively overcome unexpected no reward. We propose that these responses signal error to actively cope with lack of expected reward. The dopamine error signal thus cooperates with the RPE signal, enabling adaptive and robust pursuit of uncertain reward to ultimately obtain more reward.

Frustrative nonreward and the basal ganglia: Chemogenetic inhibition and excitation of the nucleus accumbens and globus pallidus externus during reward downshift

Frustrative nonreward contributes to anxiety disorders and addiction, and is included in the Research Domain Criteria initiative as a relevant endophenotype. These experiments explored the role of the basal ganglia in consummatory reward downshift (cRD) using inhibitory and excitatory DREADDs (designer receptors exclusively activated by designer drugs) infused in either the nucleus accumbens (NAc) or one of its downstream targets, the globus pallidus externus (GPe). NAc inhibition did not disrupt consummatory suppression during a 32-to-2% (Experiment 1) or 8-to-2% sucrose downshift (Experiment 2). However, NAc excitation enhanced consummatory suppression during a 32-to-2% sucrose downshift (Experiment 1). GPe inhibition caused a trend toward increased consummatory suppression after a 32-to-2% sucrose downshift, whereas GPe excitation eliminated consummatory suppression after an 8-to-2% sucrose downshift (Experiment 3). Chemogenetic manipulations of NAc and GPe had no detectable effects on open field activity. The effects of DREADD activation via clozapine N-oxide (CNO) administration were compared to controls that carried the DREADDs, but received vehicle injections. There was no evidence that CNO or vehicle injections in virus vector control (VVC) animals affected cRD or OF activity after either CNO or vehicle injections. NAc and GPe excitation led to opposite results in the cRD task, providing evidence that the basal ganglia circuit has a function in frustrative nonreward in the absence of detectable motor effects.

Long-Lasting Chews Elicit Positive Emotional States in Dogs during Short Periods of Social Isolation

Dogs may experience negative emotional states when isolated from human caregivers and conspecifics. This study aimed to evaluate how dogs interact with different enrichments during a short period of social isolation, as a first step towards identifying methods for improving their emotional wellbeing. Using a cross-over design, dogs (n = 20) at the Waltham Petcare Science Institute were exposed to four different food-based enrichments while left alone in a familiar room for 20 min: long-lasting chew (Chew), kibble in a treat-dispensing toy (Toy), and kibble dispensed through a smart treat-dispensing device with (Device + Voice) and without (Device) a person talking to the dog. Time spent engaging with each enrichment item and emotional valence and arousal (7-point scale collected every 5-min) were scored from videos. The results of linear mixed models indicated Chew was the most successful enrichment, with dogs having lower arousal scores (p < 0.05 vs. Device and Toy) during the first five minutes of isolation, higher positive valence scores (p < 0.05 vs. all) during the second five minutes of isolation, and spending the most total time engaged (p < 0.01 vs. all). Based on these findings, long-lasting chews should be further explored to assess their impact on dog emotional wellbeing.

Tonic activity in lateral habenula neurons acts as a neutral valence brake on reward-seeking behavior

Survival requires both the ability to persistently pursue goals and the ability to determine when it is time to stop, an adaptive balance of perseverance and disengagement. Neural activity in the lateral habenula (LHb) has been linked to negative valence, but its role in regulating the balance between engaged reward seeking and disengaged behavioral states remains unclear. Here, we show that LHb neural activity is tonically elevated during minutes-long periods of disengagement from reward-seeking behavior, both when due to repeated reward omission (negative valence) and when sufficient reward has been consumed (positive valence). Furthermore, we show that LHb inhibition extends ongoing reward-seeking behavioral states but does not prompt task re-engagement. We find no evidence for similar tonic activity changes in ventral tegmental area dopamine neurons. Our findings support a framework in which tonic activity in LHb neurons suppresses engagement in reward-seeking behavior in response to both negatively and positively valenced factors.

A Theory of the Extinction Burst

A preliminary theory of a temporary increase in the rate of an operant response with the transition to extinction (i.e., the extinction burst) is proposed. The theory assumes reinforcers are events permitting access to some valuable activity, and that such activity can compete for allocation with the target response under some conditions (e.g., very high reinforcement rates). With the transition to extinction, elimination of this competition for allocation can produce an increase in the the target response, but the increase is transient because the value of the target response decreases with exposure to extinction. The theory provides a way to understand why the extinction burst is not ubiquitous, seems more common following very small ratio schedules, occurs for a short period of time following the transition to extinction, and may be eliminated with the availability of alternative reinforcement. It appears to provide a reasonable starting point for a theory of the extinction burst that does not necessarily require inclusion of invigorating effects of frustration, and it is closely aligned with Resurgence as Choice theory. Additional research on factors modulating reinforcement-related activities and how they affect the extinction burst could help to further evaluate the theory.

Frustrative nonreward and emotional self-medication:Factors modulating alcohol consumption following reward downshift in rats

Life experience involving unexpected incentive loss (e.g., loss of job or a significant other) may result in negative emotional reactions (frustration) and promote alcohol drinking. Similarly, animals exposed to a frustrative 32-to-4% sucrose downshift increase their preference for alcohol (2%) vs. water. This result was interpreted as reflecting emotional self-medication-the consumption of substances that reduce negative emotions. We conducted three experiments examining parametric manipulations of the animal model: (1) effects of a severe reward downshift (32-to-4% sucrose) on consumption of various alcohol concentrations (Experiment 1); (2) effects of different magnitudes of reward downshifts on consumption of 32% alcohol (Experiment 2); and (3) effects of partial reinforcement (an intervention that increases resistance to frustration) on 2% alcohol intake induced by a 32-to-4% sucrose downshift (Experiment 3). The results show that (1) a 32-to-4% sucrose downshift leads to an increase in alcohol intake over a wide range of alcohol concentrations; (2) the greater the reward downshift, the higher the relative increase in alcohol consumption; and (3) a treatment that increases resistance to frustration (partial reinforcement) also attenuates alcohol consumption after a sucrose downshift. These data are discussed in relation to the role of frustrative nonreward in alcohol consumption.

Jays are sensitive to cognitive illusions

Jays hide food caches, steal them from conspecifics and use tactics to minimize cache theft. Jays are sensitive to the content of their own caches, retrieving items depending on their preferences and the perishability of the cached item. Whether jays impose the same content sensitivity when they steal caches is less clear. We adapted the 'cups-and-balls' magic routine, creating a cognitive illusion to test whether jays are sensitive to the (i) content of hidden items and (ii) type of displacement. Subjects were presented with two conditions in which hidden food was consistent with their expectations; and two conditions in which food was manipulated to violate their expectations by switching their second preferred food for their preferred food (up-value) or vice versa (de-value). Subjects readily accepted food when it was consistent with their expectations but were more likely to re-inspect the baited cup and alternative cup when their expectations were violated. In the de-value condition, jays exhibited longer latencies to consume the food and often rejected it. Dominant subjects were more likely to reject the food, suggesting that social factors influence their responses to cognitive illusions. Using cognitive illusions offers innovative avenues for investigating the psychological constraints in diverse animal minds.

Still-face Effect in Dogs (Canis familiaris). A Pilot Study

The Still-face Paradigm has been widely used for the assessment of emotion regulation in infants, as well as for the study of the mother-child relationship. Given the close bond that dogs have with humans, the purpose of this research was to evaluate, through an exploratory descriptive study, the presence of the Still-face effect in dogs. To this end, a group of Beagle dogs were exposed to three one-minute phases in which first, an unknown experimenter interacted actively and positively with each dog (Interaction). Then, suddenly, she interrupted the interaction and remained passive, with a non-expressive face and without speaking or petting the dog (Still-face). Finally, the experimenter reestablished the interaction (Reunion). Our results showed a decrease in affiliative behaviors in dogs during the Still-face phase according to changes in the human's behavior, a pattern similar to the one previously found in infants. Contrary to expectations, no stress-related behaviors were shown during that phase. A carry-over effect was also observed in the Reunion phase. This study provides information about the human-dog interaction and the effects of its disruption on dogs' behaviors.

Converging vulnerability factors for compulsive food and drug use

Highly palatable foods and substance of abuse have intersecting neurobiological, metabolic and behavioral effects relevant for understanding vulnerability to conditions related to food (e.g., obesity, binge eating disorder) and drug (e.g., substance use disorder) misuse. Here, we review data from animal models, clinical populations and epidemiological evidence in behavioral, genetic, pathophysiologic and therapeutic domains. Results suggest that consumption of highly palatable food and drugs of abuse both impact and conversely are regulated by metabolic hormones and metabolic status. Palatable foods high in fat and/or sugar can elicit adaptation in brain reward and withdrawal circuitry akin to substances of abuse. Intake of or withdrawal from palatable food can impact behavioral sensitivity to drugs of abuse and vice versa. A robust literature suggests common substrates and roles for negative reinforcement, negative affect, negative urgency, and impulse control deficits, with both highly palatable foods and substances of abuse. Candidate genetic risk loci shared by obesity and alcohol use disorders have been identified in molecules classically associated with both metabolic and motivational functions. Finally, certain drugs may have overlapping therapeutic potential to treat obesity, diabetes, binge-related eating disorders and substance use disorders. Taken together, data are consistent with the hypotheses that compulsive food and substance use share overlapping, interacting substrates at neurobiological and metabolic levels and that motivated behavior associated with feeding or substance use might constitute vulnerability factors for one another. This article is part of the special issue on 'Vulnerabilities to Substance Abuse'.

Emotion in animal contests

Emotions encompass cognitive and behavioural responses to reward and punishment. Using contests as a case-study, we propose that short-term emotions underpin animals' assessments, decision-making and behaviour. Equating contest assessments to emotional 'appraisals', we describe how contestants appraise more than resource value and outcome probability. These appraisals elicit the cognition, drive and neurophysiology that governs aggressive behaviour. We discuss how recent contest outcomes induce long-term moods, which impact subsequent contest behaviour. Finally, we distinguish between integral (objectively relevant) and incidental (objectively irrelevant) emotions and moods (affective states). Unlike existing ecological models, our approach predicts that incidental events influence contest dynamics, and that contests become incidental influences themselves, potentially causing maladaptive decision-making. As affective states cross contexts, a more holistic ethology (incorporating emotions and moods) would illuminate animal cognition and behaviour.

Dopaminergic signaling of uncertainty and the aetiology of gambling addiction

Although there is increasing clinical recognition of behavioral addictions, of which gambling disorder is the prototype example, there is a limited understanding of the psychological properties of (non-substance-related) behaviors that enable them to become 'addictive' in a way that is comparable to drugs of abuse. According to an influential application of reinforcement learning to substance addictions, the direct effects of drugs to release dopamine can create a perpetual escalation of incentive salience. This article focusses on reward uncertainty, which is proposed to be the core feature of gambling that creates the capacity for addiction. We describe the neuro-dynamics of the dopamine response to uncertainty that may allow a similar escalation of incentive salience, and its relevance to behavioral addictions. We review translational evidence from both preclinical animal models and human clinical research, including studies in people with gambling disorder. Further, we describe the evidence for 1) the effects of the omission of expected reward as a stressor and to promote sensitization, 2) the effect of the resolution of reward uncertainty as a source of value, 3) structural characteristics of modern Electronic Gaming Machines (EGMs) in leveraging these mechanisms, 4) analogies to the aberrant salience hypothesis of psychosis for creating and maintaining gambling-related cognitive distortions. This neurobiologically-inspired model has implications for harm profiling of other putative behavioral addictions, as well as offering avenues for enhancing neurological, pharmacological and psychological treatments for gambling disorder, and harm reduction strategies for EGM design.

Reinforcement omission effects in rats with bilateral lesions in the substantia nigra pars compacta and ventral tegmental area

Reinforcement omission effects (ROEs) are characterized by higher response rates after reinforcement omission than after reinforcement delivery. This pattern of behavior is interpreted in terms of motivational and attentional processes. Recent studies from our laboratory have shown that the amygdala, nucleus accumbens, and medial prefrontal cortex are involved in ROE modulation. Also, the literature has demonstrated a role of other areas such as substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA) in processes related to surprising events, such as prediction error and presentation or omission of an event (exteroceptive stimulus and reinforcement). Since these structures send projections to areas related to ROE modulation such as the amygdala, nucleus accumbens, and prefrontal cortex, the objective of the present study was to determine whether the SNc and VTA also integrate the circuit involved in ROE modulation. Rats were trained on a fixed-interval 12 s with limited-hold 6 s signaled schedule of reinforcement (Pre-lesion training). After acquisition of stable performance, the rats received bilateral neurotoxic lesions of the SNc (Experiment 1) and VTA (Experiment 2). Following postoperative recovery, the rats were submitted to two refresher sessions (Post-lesion training). Subsequently, the training was changed from a 100 to a 50% schedule of reinforcement (Post-lesion testing). In both experiments, the results showed that there was no difference in performance between sham rats and rats with bilateral lesions of the SNc or the VTA.

Assessing the External Validity of Successive Negative Contrast - Implications for Animal Welfare

When unexpectedly switched from a preferred to a less-preferred food reward, non-human animals may decrease consumption below that when only receiving the less-preferred reward - a successive negative contrast (SNC) effect. SNC has been proposed as an animal welfare indicator, however, to be effective it should show external validity; being demonstrable outside of highly standardized laboratory settings. We therefore investigated whether the SNC effect typically shown in laboratory rats was observed in owned (pet) rats from heterogeneous non-laboratory environments. Subjects (N = 14) were tested in a consummatory SNC paradigm with solid food rewards. "Shifted" rats received a high-value reward for 10 days (pre-shift), a low-value reward for six days (post-shift), then one additional day of high-value reward (re-shift). "Unshifted" rats always received the same low-value reward. "Shifted" rats consumed more food during pre-shift and re-shift trials, but ate less of the low-value food than "unshifted" animals in the post-shift trials - a SNC effect. This confirms the external validity of the SNC paradigm, extending reproducibility to outside the laboratory, indicating translatability across contexts, thus enhancing its potential use as a welfare indicator.

Do dogs experience frustration? New contributions on successive negative contrast in domestic dogs (Canis familiaris)

An unexpected change in reward quantity or quality frequently elicits a sharp decrease of responses as well as a negative emotional state. This phenomenon is called successive negative contrast (SNC) and, although it has been observed in numerous mammals, results in dogs have been inconsistent. The aim of this study was to evaluate SNC in dogs, comparing the effects of rewards of different qualities in a non-social task carried out in the dogs' usual environment. Dogs were separated into two experimental groups that experienced a downshift from a high quality reward (liver or sausage) to a low quality one (dry food), as well as a control group that always received dry food. The task involved a dog toy with bone shaped pieces that had to be removed to get the food hidden underneath. When the reward changed from liver to dry food, dogs picked up significantly fewer bones than the control group. However, this effect was not observed with sausage. Results show SNC in dogs in a non-social task carried out in their home environment. Additionally, the importance of the discrepancy in the hedonic value of the rewards is highlighted.

Avian Emotions: Comparative Perspectives on Fear and Frustration

Emotions are complex reactions that allow individuals to cope with significant positive and negative events. Research on emotion was pioneered by Darwin’s work on emotional expressions in humans and animals. But Darwin was concerned mainly with facial and bodily expressions of significance for humans, citing mainly examples from mammals (e.g., apes, dogs, and cats). In birds, emotional expressions are less evident for a human observer, so a different approach is needed. Understanding avian emotions will provide key evolutionary information on the evolution of related behaviors and brain circuitry. Birds and mammals are thought to have evolved from different groups of Mesozoic reptiles, theropod dinosaurs and therapsids, respectively, and therefore, their common ancestor is likely to be a basal reptile living about 300 million years ago, during the Carboniferous or Permian period. Yet, birds and mammals exhibit extensive convergence in terms of relative brain size, high levels of activity, sleep/wakefulness cycles, endothermy, and social behavior, among others. This article focuses on two basic emotions with negative valence: fear and frustration. Fear is related to the anticipation of dangerous or threatening stimuli (e.g., predators or aggressive conspecifics). Frustration is related to unexpected reward omissions or devaluations (e.g., loss of food or sexual resources). These results have implications for an understanding of the conditions that promote fear and frustration and for the evolution of supporting brain circuitry.

Behavioural responses to unexpected changes in reward quality

Successive negative contrast (SNC) effects are changes in anticipatory or consummatory behaviour when animals unexpectedly receive a lower value reward than they have received previously. SNC effects are often assumed to reflect frustration and appear to be influenced by background affective state. However, alternative explanations of SNC, such as the functional-search hypothesis, do not necessarily imply an aversive affective state. We tested 18 dogs in a SNC paradigm using a patch foraging task. Dogs were tested in two conditions, once with the low value reward in all of five trials (unshifted) and once when reward value was altered between high and low (shifted). Following a reward downshift, subjects showed a SNC effect by switching significantly more often between patches compared to the unshifted condition. However, approach latency, foraging time and quantity consumed did not differ between conditions, suggesting non-affective functional search behaviour rather than frustration. There was no relationship between strength of SNC and anxiety-related behaviours as measured in a novel object test and a personality questionnaire (C-BARQ). However, associations with the C-BARQ scores for Trainability and Stranger directed aggression suggest a possible link with behavioural flexibility and coping style. While reward quality clearly affects incentive motivation, the relationship between SNC, frustration and background affective state requires further exploration.

A cross-species judgement bias task: integrating active trial initiation into a spatial Go/No-go task

Judgement bias tasks are promising tools to assess emotional valence in animals, however current designs are often time-consuming and lack aspects of validity. This study aimed to establish an improved design that addresses these issues and can be used across species. Horses, rats, and mice were trained on a spatial Go/No-go task where animals could initiate each trial. The location of an open goal-box, at either end of a row of five goal-boxes, signalled either reward (positive trial) or non-reward (negative trial). Animals first learned to approach the goal-box in positive trials (Go) and to re-initiate/not approach in negative trials (No-go). Animals were then tested for responses to ambiguous trials where goal-boxes at intermediate locations were opened. The Go:No-go response ratio was used as a measure of judgement bias. Most animals quickly learned the Go/No-go discrimination and performed trials at a high rate compared to previous studies. Subjects of all species reliably discriminated between reference cues and ambiguous cues, demonstrating a monotonic graded response across the different cue locations, with no evidence of learning about the outcome of ambiguous trials. This novel test protocol is an important step towards a practical task for comparative studies on judgement biases in animals.

Reward devaluation disrupts latent inhibition in fear conditioning

Three experiments explored the link between reward shifts and latent inhibition (LI). Using consummatory procedures, rewards were either downshifted from 32% to 4% sucrose (Experiments 1-2), or upshifted from 4% to 32% sucrose (Experiment 3). In both cases, appropriate unshifted controls were also included. LI was implemented in terms of fear conditioning involving a single tone-shock pairing after extensive tone-only preexposure. Nonpreexposed controls were also included. Experiment 1 demonstrated a typical LI effect (i.e., disruption of fear conditioning after preexposure to the tone) in animals previously exposed only to 4% sucrose. However, the LI effect was eliminated by preexposure to a 32%-to-4% sucrose devaluation. Experiment 2 replicated this effect when the LI protocol was administered immediately after the reward devaluation event. However, LI was restored when preexposure was administered after a 60-min retention interval. Finally, Experiment 3 showed that a reward upshift did not affect LI. These results point to a significant role of negative emotion related to reward devaluation in the enhancement of stimulus processing despite extensive nonreinforced preexposure experience.

Open-field exposure facilitates consummatory extinction

During extinction, the organism learns that a conditioned stimulus or a conditioned response is no longer associated with an unconditioned stimulus, and as a consequence, a decrement in the response is presented. The exposure to novel situations (e.g. exploration of a novel open field) has been used widely to modulate (i.e. either enhance or deteriorate) learning and memory. The aim of the present study was to test whether open-field exposure could modulate consummatory extinction. The results indicated that open-field exposure accelerated the extinction response (i.e. experimental animals provided novelty exposure had lower consummatory behavior than control animals) when applied before - but not after - the first extinction trial, or when applied before the second extinction trial. The results suggest that environmental treatments such as novelty exposure provide a valuable, nonpharmacological alternative to potentially modulate extinction processes.

Chronic corticosterone treatment enhances extinction-induced depression in aged rats

Withdrawal and avoidance behavior are common symptoms of depression and can appear as a consequence of absence of reward, i.e. extinction-induced depression (EID). This is particularly relevant for the aged organism subjected to pronounced loss of former rewards. Avoidance of the former site of reward and increased withdrawal into a distant compartment accompany extinction of food-rewarded behavior in rodent models. During extinction, behavioral markers for re-learning dissociate from indicators of extinction-induced depression. Here we examined the effect of a chronic treatment with corticosterone (CORT), a well-known inducer of depression-related behavior, on EID in adult and aged rats. Adult (3-4months) and aged (18months) male rats were treated with CORT via drinking water for 3weeks prior to extinction of a cued food-reward task. CORT treatment increased the distance from the site of reward and decreased goal tracking behavior during extinction, especially in the aged rats. Plasma hormone levels measured before and after restraint stress showed a decline in basal ACTH- and CORT-levels after chronic CORT treatment in aged animals. The treatment significantly impaired the HPA-axis activation after acute stress in both, adult and aged animals, alike. Altogether, these findings show an enhancement of EID after chronic CORT treatment in the aged organism, which may be mediated by an impaired HPA-axis sensitivity. These findings may have special relevance for the investigation of human geriatric depression.

A System Computational Model of Implicit Emotional Learning

Nowadays, the experimental study of emotional learning is commonly based on classical conditioning paradigms and models, which have been thoroughly investigated in the last century. Unluckily, models based on classical conditioning are unable to explain or predict important psychophysiological phenomena, such as the failure of the extinction of emotional responses in certain circumstances (for instance, those observed in evaluative conditioning, in post-traumatic stress disorders and in panic attacks). In this manuscript, starting from the experimental results available from the literature, a computational model of implicit emotional learning based both on prediction errors computation and on statistical inference is developed. The model quantitatively predicts (a) the occurrence of evaluative conditioning, (b) the dynamics and the resistance-to-extinction of the traumatic emotional responses, (c) the mathematical relation between classical conditioning and unconditioned stimulus revaluation. Moreover, we discuss how the derived computational model can lead to the development of new animal models for resistant-to-extinction emotional reactions and novel methodologies of emotions modulation.

A sphingolipid mechanism for behavioral extinction

Reward-dependent instrumental behavior must continuously be re-adjusted according to environmental conditions. Failure to adapt to changes in reward contingencies may incur psychiatric disorders like anxiety and depression. When an expected reward is omitted, behavior undergoes extinction. While extinction involves active re-learning, it is also accompanied by emotional behaviors indicative of frustration, anxiety, and despair (extinction-induced depression). Here, we report evidence for a sphingolipid mechanism in the extinction of behavior. Rapid extinction, indicating efficient re-learning, coincided with a decrease in the activity of the enzyme acid sphingomyelinase (ASM), which catalyzes turnover of sphingomyelin to ceramide, in the dorsal hippocampus of rats. The stronger the decline in ASM activity, the more rapid was the extinction. Sphingolipid-focused lipidomic analysis showed that this results in a decline of local ceramide species in the dorsal hippocampus. Ceramides shape the fluidity of lipid rafts in synaptic membranes and by that way can control neural plasticity. We also found that aging modifies activity of enzymes and ceramide levels in selective brain regions. Aging also changed how the chronic treatment with corticosterone (stress) or intranasal dopamine modified regional enzyme activity and ceramide levels, coinciding with rate of extinction. These data provide first evidence for a functional ASM-ceramide pathway in the brain involved in the extinction of learned behavior. This finding extends the known cellular mechanisms underlying behavioral plasticity to a new class of membrane-located molecules, the sphingolipids, and their regulatory enzymes, and may offer new treatment targets for extinction- and learning-related psychopathological conditions. Sphingolipids are common lipids in the brain which form lipid domains at pre- and postsynaptic membrane compartments. Here we show a decline in dorsal hippocampus ceramide species together with a reduction of acid sphingomyelinase activity during extinction of conditioned behavior in rats. This reduction was associated with expression of re-learning-related behavior, but not with emotional behaviors. Read the Editorial Highlight for this article on page 485.

A reappraisal of successive negative contrast in two populations of domestic dogs

When an anticipated food reward is unexpectedly reduced in quality or quantity, many mammals show a successive negative contrast (SNC) effect, i.e. a reduction in instrumental or consummatory responses below the level shown by control animals that have only ever received the lower-value reward. SNC effects are believed to reflect an aversive emotional state, caused by the discrepancy between the expected and the actual reward. Furthermore, how animals respond to such discrepancy has been suggested to be a sign of animals’ background mood state. However, the occurrence and interpretation of SNC effects are not unequivocal, and there is a relative lack of studies conducted outside of laboratory conditions. Here, we tested two populations of domestic dogs (24 owned pet dogs and 21 dogs from rescue kennels) in a SNC paradigm following the methodology by Bentosela et al. (J Comp Psychol 123:125–130, 2009), using a design that allowed a within-, as well as a between-, subjects analysis. We found no evidence of a SNC effect in either population using a within- or between-subjects design. Indeed, the within-subjects analysis revealed a reverse SNC effect, with subjects in the shifted condition showing a significantly higher level of response, even after they received an unexpected reduction in reward quality. Using a within-, rather than a between-, subjects design may be beneficial in studies of SNC due to higher sensitivity and statistical power; however, order effects on subject performance need to be considered. These results suggest that this particular SNC paradigm may not be sufficiently robust to replicate easily in a range of environmental contexts and populations.

Effect of reward downshift on the behaviour and physiology of chickens

When a reward is downgraded in quantity or quality from that which is expected, one of two possible outcomes can result. Acquisition responses may decline gradually, owing to a strong stimulus-response reinforcement history, and thus follow the Thorndikian law of effect. Alternatively, there may be an exaggerated reaction to a downgraded reward when it is initially altered, compared to the behaviour of individuals that have always been trained to receive the lower magnitude reward; this is known as successive negative contrast (SNC). While behavioural SNC effects have been commonly demonstrated in mammals, evidence that they occur in other taxa is more equivocal. Additionally, studies demonstrating immediate physiological reactions during reward downshifts are limited. We investigated the reaction of chickens, Gallus gallus domesticus, to a downshift in the quality of a food reward that they had been trained to expect in a runway apparatus. During a preshift phase, 16 chickens (control) were given food that was flavoured to make it less preferred, while the other 16 (contrast) were fed the same food but without flavouring. During trial 7, unflavoured food was substituted by flavoured food for contrast hens and all birds were fed the flavoured food during a postshift phase. In the contrast group, food consumption immediately decreased and heart rate increased when the reward was downshifted from unflavoured to flavoured food, but there was no evidence of SNC effects, which could stem from methodological or taxonomic differences from previous studies. The latency to reach the food appeared to follow the Thorndikian law of effect, gradually increasing following the downshift. We suggest that the disparity between the pattern shown by the latency results and other measures could relate to the time period in which measures were taken, as acquisition responses are more likely to follow the law of effect.

Challenges of animal models in SCI research: Effects of pre-injury task-specific training in adult rats before lesion

A rarely explored subject in animal research is the effect of pre-injury variables on behavioral outcome post-SCI. Low reporting of such variables may underlie some discrepancies in findings between laboratories. Particularly, intensive task-specific training before a SCI might be important, considering that sports injuries are one of the leading causes of SCI. Thus, individuals with SCI often underwent rigorous training before their injuries. In the present study, we asked whether training before SCI on a grasping task or a swimming task would influence motor recovery in rats. Swim pre-training impaired recovery of swimming 2 and 4 weeks post-injury. This result fits with the idea of motor learning interference, which posits that learning something new may disrupt learning of a new task; in this case, learning strategies to compensate for functional loss after SCI. In contrast to swimming, grasp pre-training did not influence grasping ability after SCI at any time point. However, grasp pre-trained rats attempted to grasp more times than untrained rats in the first 4 weeks post-injury. Also, lesion volume of grasp pre-trained rats was greater than that of untrained rats, a finding which may be related to stress or activity. The increased participation in rehabilitative training of the pre-trained rats in the early weeks post-injury may have potentiated spontaneous plasticity in the spinal cord and counteracted the deleterious effect of interference and bigger lesions. Thus, our findings suggest that pre-training plays a significant role in recovery after CNS damage and needs to be carefully controlled for.

How absent negativity relates to affect and motivation: an integrative relief model

The present paper concerns the motivational underpinnings and behavioral correlates of the prevention or stopping of negative stimulation – a situation referred to as relief. Relief is of great theoretical and applied interest. Theoretically, it is tied to theories linking affect, emotion, and motivational systems. Importantly, these theories make different predictions regarding the association between relief and motivational systems. Moreover, relief is a prototypical antecedent of counterfactual emotions, which involve specific cognitive processes compared to factual or mere anticipatory emotions. Practically, relief may be an important motivator of addictive and phobic behaviors, self destructive behaviors, and social influence. In the present paper, we will first provide a review of conflicting conceptualizations of relief. We will then present an integrative relief model (IRMO) that aims at resolving existing theoretical conflicts. We then review evidence relevant to distinctive predictions regarding the moderating role of various procedural features of relief situations. We conclude that our integrated model results in a better understanding of existing evidence on the affective and motivational underpinnings of relief, but that further evidence is needed to come to a more comprehensive evaluation of the viability of IRMO.

Stimuli associated with the cancellation of food and its cues enhance eating but display negative incentive value

Initially neutral conditioned stimuli paired with food often acquire motivating properties, including serving as secondary reinforcers, enhancing instrumental responding in Pavlovian-instrumental transfer procedures, and potentiating food consumption under conditions of food satiation. Interestingly, cues associated with the cancellation of food and food cues may also potentiate food consumption (e.g., Galarce and Holland, 2009), despite their apparent negative correlations with food delivery. In three experiments with rats, we investigated conditions under which potentiation of feeding by such "interruption stimuIi" (ISs) develops, and some aspects of the content of that learning. Although in all three experiments ISs enhanced food consumption beyond control levels, they were found to act as conditioned inhibitors for anticipatory food cup entry (Experiment 1), to serve as conditioned punishers of instrumental responding (Experiment 2), and to suppress instrumental lever press responding in a Pavlovian instrumental transfer procedure (Experiment 3). Furthermore, when given concurrent choice between different foods, an IS enhanced consumption of the food whose interruption it had previously signaled, but when given a choice between performing two instrumental responses, the IS shifted rats' choice away from the response that had previously yielded the food whose interruption had been signaled by IS (Experiment 3). Thus, the effects of an IS on appetitive responses were opposite to its effects on consummatory responding. Implications for our understanding of learned incentive motivation and the control of overeating are discussed.

Behavioral neuroscience of psychological pain

Pain is a common word used to refer to a wide range of physical and mental states sharing hedonic aversive value. Three types of pain are distinguished in this article: Physical pain, an aversive state related to actual or potential injury and disease; social pain, an aversive emotion associated to social exclusion; and psychological pain, a negative emotion induced by incentive loss. This review centers on psychological pain as studied in nonhuman animals. After covering issues of terminology, the article briefly discusses the daily-life significance of psychological pain and then centers on a discussion of the results originating from two procedures involving incentive loss: successive negative contrast-the unexpected devaluation of a reward-and appetitive extinction-the unexpected omission of a reward. The evidence reviewed points to substantial commonalities, but also some differences and interactions between physical and psychological pains. This evidence is discussed in relation to behavioral, pharmacological, neurobiological, and genetic factors that contribute to the multidimensional experience of psychological pain.