The effects of cocaine and mazindol on the cognitive judgement bias of rats in the ambiguous-cue interpretation paradigm

Neuropsychological Effects of Antidepressants: Translational Studies

Pharmacological treatments that improve mood were first identified serendipitously, but more than half a century later, how these drugs induce their antidepressant effects remains largely unknown. With the help of animal models, a detailed understanding of their pharmacological targets and acute and chronic effects on brain chemistry and neuronal function has been achieved, but it remains to be elucidated how these effects translate to clinical efficacy. Whilst the field has been dominated by the monoamine and neurotrophic hypotheses, the idea that the maladaptive cognitive process plays a critical role in the development and perpetuation of mood disorders has been discussed since the 1950s. Recently, studies using objective methods to quantify changes in emotional processing found acute effects with conventional antidepressants in both healthy volunteers and patients. These positive effects on emotional processing and cognition occur without a change in the subjective ratings of mood. Building from these studies, behavioural methods for animals that quantify similar cognitive affective processes have been developed. Integrating these behavioural approaches with pharmacology and targeted brain manipulations, a picture is beginning to emerge of the underlying mechanisms that may link the pharmacology of antidepressants, these neuropsychological constructs and clinical efficacy. In this chapter, we discuss findings from animal studies, experimental medicine and patients investigating the neuropsychological effects of antidepressant drugs. We discuss the possible neural circuits that contribute to these effects and discuss whether a neuropsychological model of antidepressant effects could explain the temporal differences in clinical benefits observed with conventional delayed-onset antidepressants versus rapid-acting antidepressants.

The Acute Pharmacological Manipulation of Dopamine Receptors Modulates Judgment Bias in Japanese Quail

We have studied the effects of dopamine antagonists and agonists on Japanese quail behavior in the spatial judgment task. Twenty-four Japanese quail hens were trained in the spatial discrimination task to approach the feeder placed in the rewarded location (Go response, feeder containing mealworms) and to not approach the punished location (No-Go response, empty feeder plus aversive sound). In a subsequent spatial judgment task, the proportion of Go responses as well as approach latencies to rewarded, punished, and three ambiguous locations (near-positive, middle, near-negative, all neither rewarded nor punished) were assessed in 20 quail hens that successfully mastered the discrimination task. In Experiment 1, each bird received five treatments (0.1 and 1.0 mg/kg of dopamine D1 receptor antagonist SCH 23390, 0.05 and 0.5 mg/kg of dopamine D2 receptor antagonist haloperidol, and saline control) in a different order, according to a Latin square design. All drugs were administered intramuscularly 15 min before the spatial judgment test, with 2 days break between the treatments. Both antagonists caused a significant dose-dependent increase in the approach latencies as well as a decrease in the proportion of Go responses. In Experiment 2, with the design analogous to Experiment 1, the hens received again five treatments (1.0 and 10.0 mg/kg of dopamine D1 receptor agonist SKF 38393, 1.0 and 10.0 mg/kg of dopamine D2 receptor agonist bromocriptine, and saline control), applied intramuscularly 2 h before the test. The agonists did not have any significant effect on approach latencies and the proportion of Go responses in the spatial judgment task, as compared to the saline control, except for 10.0 mg/kg SKF 38393, which caused a decrease in the proportion of Go responses. The approach latency and the proportion of Go responses were affected by the cue location in both experiments. Our data suggest that the dopamine D1 and D2 receptor blockade leads to a decrease in the reward expectation and the negative judgment of stimuli. The effect of dopamine receptor activation is less clear. The results reveal that dopamine receptor manipulation alters the evaluation of the reward and punishment in the spatial judgment task.

Neuromolecular Underpinnings of Negative Cognitive Bias in Depression

This selective review aims to summarize the recent advances in understanding the neuromolecular underpinnings of biased cognition in depressive disorder. We begin by considering the cognitive correlates of depressed mood and the key brain systems implicated in its development. We then review the core findings across two domains of biased cognitive function in depression: pessimistic judgment bias and abnormal response to negative feedback. In considering their underlying substrates, we focus on the neurochemical mechanisms identified by genetic, molecular and pharmacological challenge studies. We conclude by discussing experimental approaches to the treatment of depression, which are derived largely from an improved understanding of its cognitive substrates.

Short telomeres drive pessimistic judgement bias in zebrafish

The role of telomerase reverse transcriptase has been widely investigated in the contexts of ageing and age-related diseases. Interestingly, decreased telomerase activities (and accelerated telomere shortening) have also been reported in patients with emotion-related disorders, opening the possibility for subjective appraisal of stressful stimuli playing a key role in stress-driven telomere shortening. In fact, patients showing a pessimistic judgement bias have shorter telomeres. However, in humans the evidence for this is correlational and the causal directionality between pessimism and telomere shortening has not been established experimentally yet. We have developed and validated a judgement bias experimental paradigm to measure subjective evaluations of ambiguous stimuli in zebrafish. This behavioural assay allows classification of individuals in an optimistic-pessimistic dimension (i.e. from individuals that consistently evaluate ambiguous stimuli as negative to others that perceive them as positive). Using this behavioural paradigm we found that telomerase-deficient zebrafish (tert-/-) were more pessimistic in response to ambiguous stimuli than wild-type zebrafish. The fact that individuals with constitutive shorter telomeres have pessimistic behaviours demonstrates for the first time in a vertebrate model a genetic basis of judgement bias.

The neuroscience of positive emotions and affect: Implications for cultivating happiness and wellbeing

This review paper provides an integrative account regarding neurophysiological correlates of positive emotions and affect that cumulatively contribute to the scaffolding for happiness and wellbeing in humans and other animals. This paper reviews the associations among neurotransmitters, hormones, brain networks, and cognitive functions in the context of positive emotions and affect. Consideration of lifespan developmental perspectives are incorporated, and we also examine the impact of healthy social relationships and environmental contexts on the modulation of positive emotions and affect. The neurophysiological processes that implement positive emotions are dynamic and modifiable, and meditative practices as well as flow states that change patterns of brain function and ultimately support wellbeing are also discussed. This review is part of "The Human Affectome Project" (http://neuroqualia.org/background.php), and in order to advance a primary aim of the Human Affectome Project, we also reviewed relevant linguistic dimensions and terminology that characterizes positive emotions and wellbeing. These linguistic dimensions are discussed within the context of the neuroscience literature with the overarching goal of generating novel recommendations for advancing neuroscience research on positive emotions and wellbeing.

Use of cognitive bias as a welfare tool in poultry

In human psychology, the link between cognition and emotions is broadly accepted. However, the idea of using the interaction between cognition and emotions as a tool for a better understanding of animal emotions or for welfare assessment is relatively new. The first avian species used in cognitive bias tests was the European starling followed by the domestic chicken and other species. The most frequently used paradigm is the affect-induced judgment bias. There are many variations of the judgment bias tests in birds. The test itself is preceded by discrimination training. Discrimination tasks vary from visual cue discrimination, discrimination of time intervals to spatial location discrimination. During the discrimination training, birds flip or do not flip the lids of the food dishes, and their latency to approach the cues in a straight alley maze, in a two-choice arena, or different locations in spatial judgment task arena are measured. Alternately, the birds fulfill operant tasks in a Skinner box. Before or after the discrimination training phase, birds are subjected to manipulations that are hypothesized to induce positive or negative emotional states. In the last stage, birds are subjected to judgment bias tests. The assumption is that animals in a negative affective state would more likely respond to ambiguous cues, as if they predict the negative event, than animals in a more positive state. However, the results of some avian studies are inconsistent, particularly those studying the effect of environmental enrichment. In starlings, each of the three studies has supplied conflicting results. In poultry, none of the four studies demonstrated a positive effect of environmental enrichment on emotional states. Only the study using unpredictable stressors in combination with environmental complexity showed that animals kept in a more complex environment are more optimistic. Manipulation of the social environment seems to be more effective in judgment bias induction. Conflicting results could be attributable to the design of the tests, the manner of affect induction, or the data analysis. Further optimization and validation of avian cognitive bias tests could help to avoid problems such as the loss of ambiguity. New methods of attention and memory bias testing are promising. However, regardless of the abovementioned complications, a cognitive bias paradigm is a valuable tool, which can help us better understand avian emotions and assess poultry welfare.

Translational new approaches for investigating mood disorders in rodents and what they may reveal about the underlying neurobiology of major depressive disorder

Mood disorders represent one of society's most costly and challenging health burdens. The drug treatments used today were initially discovered serendipitously in the 1950s. Animal models were then developed based on the ability of these drugs to alter specific behaviours. These models have played a major role in the development of the second generation of antidepressants. However, their use has been heavily criticized, particularly in relation to whether they recapitulate similar underlying biology to the psychiatric disorder they are proposed to represent. This article considers our work in the field of affective bias and the development of a translational research programme to try to develop and validate better animal models. We discuss whether the new data that have arisen from these studies support an alternative perspective on the underlying neurobiological processes that lead to major depressive disorder (MDD). Specifically, this article will consider whether a neuropsychological mechanism involving affective biases plays a causal role in the development of MDD and its associated emotional and behavioural symptoms. These animal studies also raise the possibility that neuropsychological mechanisms involving affective biases are a precursor to, rather than a consequence of, the neurotrophic changes linked to MDD.

This article is part of a discussion meeting issue ‘Of mice and mental health: facilitating dialogue between basic and clinical neuroscientists’.

Rat models of reward deficits in psychiatric disorders

Loss of interest in rewarding activities is a hallmark of many psychiatric disorders and may be relevant for neurodegenerative disorders and patients suffering from brain injury. There is increasing evidence that deficits in reward-related behaviour are more complex than previously described. The traditional view of anhedonia as 'the inability to experience pleasure' may be too limited to fully encompass the types of reward deficit observed in these patients. Developments in methods to measure different aspects of reward processing in humans and animals are starting to provide insights into the complexity of this behaviour. In this article we consider the rodent models which have traditionally been used to study reward deficits in psychiatric disorders and consider their limitations relative to clinical findings. We then discuss work where methods derived from human neuropsychological tests are providing insights into the complexity of reward-related behaviour. Specifically, we consider tasks which investigate different aspects of reward-related behaviour focusing on learning and memory as well as decision-making and consider what these may mean in terms of how we model reward deficits in rodents.

The effects of pessimism on cell-mediated immunity in rats

We used a recently developed ambiguous-cue interpretation (ACI) paradigm to investigate whether 'optimism' and 'pessimism' as behavioural traits may be interrelated with immune functions in rodents. To this aim, in a series of ACI tests (cognitive bias screening, CBS), we identified rats that displayed 'pessimistic' and 'optimistic' traits. We found significant differences in immune biomarkers between 'optimistic' and 'pessimistic' animals. Moreover 'pessimism' was associated with significantly lower relative weight of the spleen and thymus, significantly decreased proliferative activity of splenocytes. Pessimism was associated with an increased production of interleukin-(IL)1β and IL-4, activin A, l-selectin, interferon (IFN)-γ and some chemokines and receptors for advanced glycation endproducts. The findings indicate an inflammatory profile in "pessimistic" animals.

Translational Shifts in Preclinical Models of Depression: Implications for Biomarkers for Improved Treatments

Understanding the neurobiology of major depressive disorder (MDD) remains one of the major challenges in neuroscience. The disease is heterogeneous in nature, and patients present with a varied symptom profile. Studies seeking to identify biomarkers for MDD diagnosis and treatment have not yet found any one candidate which achieves sufficient sensitivity and specificity. In this article, we consider whether neuropsychological impairments, specifically affective biases, could provide a behavioural biomarker. Affective biases are observed when emotional states influence cognitive function. These biases have been shown to influence a number of different cognitive domains with some specific deficits observed in MDD. It has also been possible to use these neuropsychological tests to inform the development of translational tasks for non-human species. The results from studies in rodents suggest that quantification of affective biases is feasible and may provide a reliable method to predict antidepressant efficacy as well as pro-depressant risk. Animal studies suggest that affective state-induced biases in learning and memory operate over a different time course to biases influencing decision-making. The implications for these differences in terms of task validity and future ideas relating to affective biases and MDD are discussed. We also describe our most recent studies which have shown that depression-like phenotypes share a common deficit in reward-related learning and memory which we refer to as a reward-induced positive bias. This deficit is dissociable from more typical measures of hedonic behaviour and motivation for reward and may represent an important and distinct form of reward deficit linked to MDD.

Selective effects of 5-HT2C receptor modulation on performance of a novel valence-probe visual discrimination task and probabilistic reversal learning in mice

RATIONALE

Dysregulation of the serotonin (5-HT) system is a pathophysiological component in major depressive disorder (MDD), a condition closely associated with abnormal emotional responsivity to positive and negative feedback. However, the precise mechanism through which 5-HT tone biases feedback responsivity remains unclear. 5-HT2C receptors (5-HT2CRs) are closely linked with aspects of depressive symptomatology, including abnormalities in reinforcement processes and response to stress. Thus, we aimed to determine the impact of 5-HT2CR function on response to feedback in biased reinforcement learning.

METHODS

We used two touchscreen assays designed to assess the impact of positive and negative feedback on probabilistic reinforcement in mice, including a novel valence-probe visual discrimination (VPVD) and a probabilistic reversal learning procedure (PRL). Systemic administration of a 5-HT2CR agonist and antagonist resulted in selective changes in the balance of feedback sensitivity bias on these tasks.

RESULTS

Specifically, on VPVD, SB 242084, the 5-HT2CR antagonist, impaired acquisition of a discrimination dependent on appropriate integration of positive and negative feedback. On PRL, SB 242084 at 1 mg/kg resulted in changes in behaviour consistent with reduced sensitivity to positive feedback. In contrast, WAY 163909, the 5-HT2CR agonist, resulted in changes associated with increased sensitivity to positive feedback and decreased sensitivity to negative feedback.

CONCLUSIONS

These results suggest that 5-HT2CRs tightly regulate feedback sensitivity bias in mice with consequent effects on learning and cognitive flexibility and specify a framework for the influence of 5-HT2CRs on sensitivity to reinforcement.

Behavioural and computational methods reveal differential effects for how delayed and rapid onset antidepressants effect decision making in rats

Major depressive disorder (MDD) is one of the most prevalent psychiatric disorders. Until the recent discovery of the rapid onset antidepressant action of ketamine, pharmacological treatments for MDD were limited to conventional antidepressant drugs with delayed clinical efficacy. Using a judgement bias task, this study has investigated whether the temporal differences observed in patients would be reflected in affective biases and decision making behaviour in rodents. The diffusion model was also used to investigate the underlying decision making processes. Positive biases were induced in this task over timeframes that mirror the rapid versus delayed antidepressant efficacy of the drugs in clinical populations. Diffusion modelling revealed that the antidepressants tested also have different effects on decision making processes, suggesting they may act through different neurobiological substrates. This combination of behaviour and computational modelling may provide a useful approach to further investigate the mechanisms underlying rapid antidepressant effect and assess potential new treatments.

Lesions of the Orbitofrontal but Not Medial Prefrontal Cortex Affect Cognitive Judgment Bias in Rats

Neuroimaging studies in humans have recently shown that the prefrontal cortex (PFC) and orbitofrontal cortex (OFC) mediate bias in the judgment of forthcoming events. In the present study, we sought to determine whether cognitive judgment bias (CJB) is also dependent on these prefrontal regions in non-human animals. For this, we trained a cohort of rats in the ambiguous-cue interpretation (ACI) paradigm, subjected them to excitotoxic lesions in the medial PFC (mPFC) and OFC, and tested the effects of neuronal loss within these regions on CJB. Comparison of the lesions' behavioral effects in the ACI paradigm revealed that neuronal loss within the OFC but not within the mPFC influences the interpretation of ambiguous cues by animals. Our findings demonstrate the specific involvement of the OFC in CJB in rats.

Measuring Cognitive Judgement Bias in Rats Using the Ambiguous-Cue Interpretation Test

An active-choice, operant, ambiguous-cue interpretation (ACI) paradigm is described that can be used for measuring cognitive judgement bias in rats. In this behavioral test, animals in an operant conditioning chamber are trained to press a lever to receive a food reward when a specific tone is presented, and to press another lever in response to a different tone to avoid punishment by an electric foot-shock. The tones, which serve as discriminative stimuli, acquire a positive or negative valence, and the training continues until the rats demonstrate a stable, correct discrimination between these two stimuli. The animals are tested after they have attained stable discrimination performance. The ambiguous-cue test consists of a discrimination task, as described above, but includes the presentation of additional tones with frequencies that are intermediate between the trained positive and negative tones. The lever-press response pattern to these ambiguous cues is considered an indicator of the rat's expectation of a positive or negative event; in other words, it is a measure of 'optimism' or 'pessimism', respectively. © 2017 by John Wiley & Sons, Inc.

Making Decisions under Ambiguity: Judgment Bias Tasks for Assessing Emotional State in Animals

Judgment bias tasks (JBTs) are considered as a family of promising tools in the assessment of emotional states of animals. JBTs provide a cognitive measure of optimism and/or pessimism by recording behavioral responses to ambiguous stimuli. For instance, a negative emotional state is expected to produce a negative or pessimistic judgment of an ambiguous stimulus, whereas a positive emotional state produces a positive or optimistic judgment of the same ambiguous stimulus. Measuring an animal's emotional state or mood is relevant in both animal welfare research and biomedical research. This is reflected in the increasing use of JBTs in both research areas. We discuss the different implementations of JBTs with animals, with a focus on their potential as an accurate measure of emotional state. JBTs have been successfully applied to a very broad range of species, using many different types of testing equipment and experimental protocols. However, further validation of this test is deemed necessary. For example, the often extensive training period required for successful judgment bias testing remains a possible factor confounding results. Also, the issue of ambiguous stimuli losing their ambiguity with repeated testing requires additional attention. Possible improvements are suggested to further develop the JBTs in both animal welfare and biomedical research.

Diffusion Modelling Reveals the Decision Making Processes Underlying Negative Judgement Bias in Rats

Human decision making is modified by emotional state. Rodents exhibit similar biases during interpretation of ambiguous cues that can be altered by affective state manipulations. In this study, the impact of negative affective state on judgement bias in rats was measured using an ambiguous-cue interpretation task. Acute treatment with an anxiogenic drug (FG7142), and chronic restraint stress and social isolation both induced a bias towards more negative interpretation of the ambiguous cue. The diffusion model was fit to behavioural data to allow further analysis of the underlying decision making processes. To uncover the way in which parameters vary together in relation to affective state manipulations, independent component analysis was conducted on rate of information accumulation and distances to decision threshold parameters for control data. Results from this analysis were applied to parameters from negative affective state manipulations. These projected components were compared to control components to reveal the changes in decision making processes that are due to affective state manipulations. Negative affective bias in rodents induced by either FG7142 or chronic stress is due to a combination of more negative interpretation of the ambiguous cue, reduced anticipation of the high reward and increased anticipation of the low reward.

Dopamine induces an optimism bias in rats-Pharmacological proof for the translational validity of the ambiguous-cue interpretation test

Recent findings have revealed that pharmacological enhancement of dopaminergic (DA) function by the administration of a dopaminergic precursor (dihydroxy-l-phenylalanine; l-DOPA) increases an optimism bias in humans. This effect is due to l-DOPA's impairment of the ability to update beliefs in response to undesirable information about the future. To test whether an 'optimistic' bias is also mediated by dopamine in animals, first, two groups of rats received either a dopaminergic precursor, l-DOPA, or a D2 receptor antagonist, haloperidol, and were subsequently tested using the ambiguous-cue interpretation (ACI) paradigm. To test whether similar effects might be observed when manipulating another neurotransmitter implicated in learning about reward and punishment, we administered the serotonin (5-HT) reuptake inhibitor escitalopram to a third group of animals and the selective and irreversible tryptophan hydroxylase inhibitor para-chlorophenylalanine (PCPA) to a fourth group. The results of our study demonstrated that prolonged (2 weeks), but not acute, l-DOPA administration induced optimistic bias in rats. Neither acute nor chronic treatment with the other tested compounds had significant effects on the cognitive judgment bias of rats. The convergence of these results with human studies suggests the translational validity of the ambiguous-cue interpretation paradigm in testing the effects of pharmacological manipulations on cognitive judgment bias (optimism/pessimism) in rats.

Happy hamsters? Enrichment induces positive judgement bias for mildly (but not truly) ambiguous cues to reward and punishment in Mesocricetus auratus

Recent developments in the study of animal cognition and emotion have resulted in the 'judgement bias' model of animal welfare. Judgement biases describe the way in which changes in affective state are characterized by changes in information processing. In humans, anxiety and depression are characterized by increased expectation of negative events and negative interpretation of ambiguous information. Positive wellbeing is associated with enhanced expectation of positive outcomes and more positive interpretation of ambiguous information. Mood-congruent judgement biases for ambiguous information have been demonstrated in a range of animal species, with large variation in the way tests are administered and in the robustness of analyses. We highlight and address some issues using a laboratory species not previously tested: the Syrian hamster (Mesocricetus auratus). Hamsters were tested using a spatial judgement go/no-go task in enriched and unenriched housing. We included a number of controls and additional behavioural tests and applied a robust analytical approach using linear mixed effects models. Hamsters approached the ambiguous cues significantly more often when enriched than unenriched. There was no effect of enrichment on responses to the middle cue. We discuss these findings in light of mechanisms underlying processing cues to reward, punishment and true ambiguity, and the implications for the welfare of laboratory hamsters.

Effects of optimism on motivation in rats

In humans, optimism is a cognitive construct related to motivation; optimists exert effort, whereas pessimists disengage from effort. In this study, using a recently developed ambiguous-cue interpretation (ACI) paradigm we took the unique opportunity to investigate whether "optimism" as a trait is correlated with motivation in rodents. In a series of ACI tests (cognitive bias screening, CBS), we identified rats displaying "pessimistic" and "optimistic" traits. Subsequently, we investigated the trait differences in the motivation of these rats to gain reward and to avoid punishment using a progressive ratio (PR) schedule of reinforcement paradigm. Although "optimistic" and "pessimistic" animals did not differ in their motivation to avoid punishment, the "optimistic" rats were significantly more motivated to gain reward than their "pessimistic" conspecifics. For the first time, we showed an association between cognitive judgment bias and motivation in an animal model. Because both investigated processes are closely related to mental health and wellbeing, our results may be valuable for preclinical modeling of many psychiatric disorders.