Dissociation of hedonic reaction to reward and incentive motivation in an animal model of the negative symptoms of schizophrenia

Functional connectivity in a monetary and social incentive delay task in medicated patients with schizophrenia

Introduction

Numerous studies indicate impaired reward-related learning in individuals with schizophrenia, with various factors such as illness duration, medication, disease severity, and level of analysis (behavioral or neurophysiological data) potentially confounding the results. Patients with schizophrenia who are treated with second-generation antipsychotics have been found to have a less affected reward system. However, this finding does not explain the neural dysfunctions observed in previous studies. This study aimed to address the open question of whether the less impaired reward-related behavior is associated with unimpaired task-related functional connectivity or altered task-related functional connectivity.

Methods

The study included 23 participants diagnosed within the schizophrenia spectrum and 23 control participants matched in terms of age, sex, and education. Participants underwent an MRI while performing a monetary incentive delay task and a social incentive delay task. The collected data were analyzed in terms of behavior and functional connectivity.

Results

Both groups exhibited a main effect of reward type on behavioral performance, indicating faster reaction times in the social incentive delay task, but no main effect of reward level. Altered functional connectivity was observed in predictable brain regions within the patient group, depending on the chosen paradigm, but not when compared to healthy individuals.

Discussion

In addition to expected slower response times, patients with schizophrenia demonstrated similar response patterns to control participants at the behavioral level. The similarities in behavioral data may underlie different connectivity patterns. Our findings suggest that perturbations in reward processing do not necessarily imply disturbances in underlying connectivities. Consequently, we were able to demonstrate that patients with schizophrenia are indeed capable of exhibiting goal-directed, reward-responsive behavior, although there are differences depending on the type of reward.

Critical review of RDoC approaches to the study of motivation with animal models: effort valuation/willingness to work

The NIMH research domain criteria (RDoC) approach was instigated to refocus mental health research on the neural circuits that mediate psychological functions, with the idea that this would foster an understanding of the neural basis of specific psychiatric dysfunctions (i.e. 'symptoms and circuits') and ultimately facilitate treatment. As a general idea, this attempt to go beyond traditional diagnostic categories and focus on neural circuit dysfunctions related to specific symptoms spanning multiple disorders has many advantages. For example, motivational dysfunctions are present in multiple disorders, including depression, schizophrenia, Parkinson's disease, and other conditions. A critical aspect of motivation is effort valuation/willingness to work, and several clinical studies have identified alterations in effort-based decision making in various patient groups. In parallel, formal animal models focusing on the exertion of effort and effort-based decision making have been developed. This paper reviews the literature on models of effort-based motivational function in the context of a discussion of the RDoC approach, with an emphasis on the dissociable nature of distinct aspects of motivation. For example, conditions associated with depression and schizophrenia blunt the selection of high-effort activities as measured by several tasks in animal models (e.g. lever pressing, barrier climbing, wheel running). Nevertheless, these manipulations also leave fundamental aspects of hedonic reactivity, food motivation, and reinforcement intact. This pattern of effects demonstrates that the general emphasis of the RDoC on the specificity of the neural circuits mediating behavioral pathologies, and the dissociative nature of these dysfunctions, is a valid concept. Nevertheless, the specific placement of effort-related processes as simply a 'sub-construct' of 'reward processing' is empirically and conceptually problematic. Thus, while the RDoC is an excellent general framework for new ways to approach research and therapeutics, it still needs further refinement.

Characterizing Hedonic Responses to Flavors Paired with Internal Pain and Nausea through the Taste Reactivity Test in Rats

Feeding behavior is a complex experience that involves not only sensory (i.e., visual, odor, taste, or texture) but also affective or emotional aspects (i.e., pleasure, palatability, or hedonic value) of foods. As such, behavioral tests that assess the hedonic impact of foods are necessary to fully understand the factors involved in ingestive behavior. In this protocol, we use the taste reactivity (TR) test to characterize the hedonic responses of rats to flavors paired with either lithium chloride-induced nausea or internal pain produced by hypertonic NaCl, two treatments that reduce voluntary consumption. This application of the TR test demonstrates how emetic and non-emetic (somatic pain in particular) treatments produce dissociable patterns of hedonic reactions to fluids: only emetic treatments result in the production of aversive orofacial responses, reflecting conditioned nausea, whereas somatic pain produces immobility, reflecting conditioned fear. Other methods, such as the microstructural analysis of licking behavior, do not reliably distinguish conditioned nausea and fear, a key advantage of the more selective TR procedure. This protocol also contains guidance for adaptation to other species and designs.

Vigor, Effort-Related Aspects of Motivation and Anhedonia

In this chapter we provide an overview of the pharmacological and circuit mechanisms that determine the willingness to expend effort in pursuit of rewards. A particular focus will be on the role of the mesolimbic dopamine system, as well the contributing roles of limbic and cortical brains areas involved in the evaluation, selection, and invigoration of goal-directed actions. We begin with a review of preclinical studies, which have provided key insights into the brain systems that are necessary and sufficient for effort-based decision-making and have characterized novel compounds that enhance selection of high-effort activities. Next, we summarize translational studies identifying and expanding this circuitry in humans. Finally, we discuss the relevance of this work for understanding common motivational impairments as part of the broader anhedonia symptom domain associated with mental illness, and the identification of new treatment targets within this circuitry to improve motivation and effort-expenditure.

The instrumental role of operant paradigms in translational psychiatric research: Insights from a maternal immune activation model of schizophrenia risk

Rigorous behavioral analysis is essential to the translation of research conducted using animal models of neuropsychiatric disease. Here we discuss the use of operant paradigms within our lab as a powerful approach for exploring the biobehavioral bases of disease in the maternal immune activation rat model of schizophrenia. We have investigated a range of disease features in schizophrenia including abnormal perception of time, cognition, learning, motivation, and internal state (psychosis), providing complex insights into brain and behavior. Beyond simple phenotyping, implementing sophisticated operant procedures has been effective in delineating aspects of pathological behavior, identifying interacting pathologies, and isolating contributing mechanisms of disease. We provide comment on the strengths of operant techniques to support high-quality behavioral investigations in fundamental neuropsychiatric research.

Subcortical Brain Morphometry Differences between Adults with Autism Spectrum Disorder and Schizophrenia

Autism spectrum disorder (ASD) and schizophrenia (SZ) are neuropsychiatric disorders that overlap in symptoms associated with social-cognitive impairment. Subcortical structures play a significant role in cognitive and social-emotional behaviors and their abnormalities are associated with neuropsychiatric conditions. This exploratory study utilized ABIDE II/COBRE MRI and corresponding phenotypic datasets to compare subcortical volumes of adults with ASD (n = 29), SZ (n = 51) and age and gender matched neurotypicals (NT). We examined the association between subcortical volumes and select behavioral measures to determine whether core symptomatology of disorders could be explained by subcortical association patterns. We observed volume differences in ASD (viz., left pallidum, left thalamus, left accumbens, right amygdala) but not in SZ compared to their respective NT controls, reflecting morphometric changes specific to one of the disorder groups. However, left hippocampus and amygdala volumes were implicated in both disorders. A disorder-specific negative correlation (r = −0.39, p = 0.038) was found between left-amygdala and scores on the Social Responsiveness Scale (SRS) Social-Cognition in ASD, and a positive association (r = 0.29, p = 0.039) between full scale IQ (FIQ) and right caudate in SZ. Significant correlations between behavior measures and subcortical volumes were observed in NT groups (ASD-NT range; r = −0.53 to −0.52, p = 0.002 to 0.004, SZ-NT range; r = −0.41 to −0.32, p = 0.007 to 0.021) that were non-significant in the disorder groups. The overlap of subcortical volumes implicated in ASD and SZ may reflect common neurological mechanisms. Furthermore, the difference in correlation patterns between disorder and NT groups may suggest dysfunctional connectivity with cascading effects unique to each disorder and a potential role for IQ in mediating behavior and brain circuits.

How changes in dopamine D2 receptor levels alter striatal circuit function and motivation

It was first posited, more than five decades ago, that the etiology of schizophrenia involves overstimulation of dopamine receptors. Since then, advanced clinical research methods, including brain imaging, have refined our understanding of the relationship between striatal dopamine and clinical phenotypes as well as disease trajectory. These studies point to striatal dopamine D2 receptors, the main target for all current antipsychotic medications, as being involved in both positive and negative symptoms. Simultaneously, animal models have been central to investigating causal relationships between striatal dopamine D2 receptors and behavioral phenotypes relevant to schizophrenia. We begin this article by reviewing the circuit, cell-type and subcellular locations of dopamine D2 receptors and their downstream signaling pathways. We then summarize results from several mouse models in which D2 receptor levels were altered in various brain regions, cell-types and developmental periods. Behavioral, electrophysiological and anatomical consequences of these D2 receptor perturbations are reviewed with a selective focus on striatal circuit function and alterations in motivated behavior, a core negative symptom of schizophrenia. These studies show that D2 receptors serve distinct physiological roles in different cell types and at different developmental time points, regulating motivated behaviors in sometimes opposing ways. We conclude by considering the clinical implications of this complex regulation of striatal circuit function by D2 receptors.

Dopamine D2R upregulation in ventral striatopallidal neurons does not affect Pavlovian or go/no-go learning

Ventral striatal dopamine is thought to be important for associative learning. Dopamine exerts its role via activation of dopamine D1 and D2 receptors in the ventral striatum. Upregulation of dopamine D2R in ventral striatopallidal neurons impairs incentive motivation via inhibiting synaptic transmission to the ventral pallidum. Here, we determined whether upregulation of D2Rs and the resulting impairment in ventral striatopallidal pathway function modulates associative learning in an auditory Pavlovian reward learning task as well as Go/No-Go learning in an operant based reward driven Go/No-Go task. We found that upregulation of D2Rs did not affect Pavlovian learning or the extinction of Pavlovian responses, and neither did it alter No-Go learning. We however observed a delay in the Go component of the task which may indicate a deficit in learning though it could also be attributed to the established locomotor hyperactivity of the mice. In combination with previously published findings, our data suggest that D2Rs in ventral striatopallidal neurons play a specific role in regulating motivation by balancing cost/benefit computations but do not necessarily affect associative learning. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

A role for reward valuation in the serotonergic modulation of impulsivity

RATIONALE

Impulsive behavior is a deleterious component of a number of mental health disorders but has few targeted pharmacotherapies. One contributing factor to the difficulty in understanding the neural substrates of disordered impulsivity is the diverse presentations of impulsive behavior. Defining the behavioral and cognitive processes which contribute to different subtypes of impulsivity is important for understanding the neural underpinnings of dysregulated impulsive behavior.

METHODS

Using a mouse model for disordered impulsivity, our goal was to identify behavioral and cognitive processes that are associated with increased impulsivity. Specifically, we were interested in the facets of impulsivity modulated by serotonin signaling. We used mice lacking the serotonin 1B receptor (5-HT_1BR) and measured different types of impulsivity as well as goal-directed responding, extinction, habitual-like behavior, cue reactivity, and reward reactivity.

RESULTS

Mice lacking expression of 5-HT_1BR had increased levels of impulsive action, goal-directed responding, and motivation, with no differences seen in rate of extinction, development of habitual behavior, delay discounting, or effort-based discounting. Interestingly, mice lacking 5-HT_1BR expression also showed an overall increase in the choice of higher value rewards, increased hedonic responses to sweet rewards, and responded more for cues that predict reward. We developed a novel paradigm to demonstrate that increasing anticipated reward value could directly increase impulsive action. Furthermore, we found that 5-HT_1BR KO-induced impulsivity could be ameliorated by decreasing the reward value relative to controls, suggesting that the increased 5-HT_1BR-associated impulsive action may be a result of increased reward valuation.

CONCLUSIONS

Taken together, these data show that the effects of serotonin on impulsive action are mediated through the modulation of hedonic value, which may alter the reward representations that motivate action. Overall, this data supports a role for reward value as an important substrate in impulsive action which may drive clinically relevant increases in impulsivity.

Dissociating the effects of dopamine D2 receptors on effort-based versus value-based decision making using a novel behavioral approach

Cost-benefit decision making is essential for organisms to adapt to their ever-changing environment. Most studies of cost-benefit decision making involve choice conditions in which effort and value are varied simultaneously. This prevents identification of the aspects of cost-benefit decision making that are affected by experimental manipulations. We developed operant assays to isolate the individual impacts of effort and value manipulations on cost-benefit decision making. In the concurrent effort choice (CEC) task, mice choose between exerting two distinct types of effort: the number of responses and the duration of a response, to earn the same reward. By parametrically varying response cost, psychometric functions are obtained that reflect how the two types of effort scale against one another. Direct manipulations of effort shift the functions. Because reward value is held constant in this task, differences in scaling of the two response types must be related to the effort manipulations. In the concurrent value choice (CVC) task, mice make the same type of response to earn rewards of different value (e.g., pellets vs. sucrose solutions). Here the effort required to earn one reward type is parametrically varied to obtain the psychometric function that scales the value of the two rewards into the number of responses subjects will pay to earn one reward over the other. Direct value manipulations shift these functions. We tested the effect of the dopamine D2 receptor antagonist, haloperidol, on performance in the CEC and CVC assays and found that D2R signaling is important for effort-based, but not value-based decision making. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Network Analysis Indicates That Avolition Is the Most Central Domain for the Successful Treatment of Negative Symptoms: Evidence From the Roluperidone Randomized Clinical Trial

A recent conceptual development in schizophrenia is to view its manifestations as interactive networks rather than individual symptoms. Negative symptoms, which are associated with poor functional outcome and reduced rates of recovery, represent a critical need in schizophrenia therapeutics. MIN101 (roluperidone), a compound in development, demonstrated efficacy in the treatment of negative symptoms in schizophrenia. However, it is unclear how the drug achieved its effect from a network perspective. The current study evaluated the efficacy of roluperidone from a network perspective. In this randomized clinical trial, participants with schizophrenia and moderate to severe negative symptoms were randomly assigned to roluperidone 32 mg (n = 78), 64 mg (n = 83), or placebo (N = 83). Macroscopic network properties were evaluated to determine whether roluperidone altered the overall density of the interconnections among symptoms. Microscopic properties were evaluated to examine which individual symptoms were most influential (ie, interconnected) on other symptoms in the network and are responsible for successful treatment effects. Participants receiving roluperidone did not differ from those randomized to placebo on macroscopic properties. However, microscopic properties (degree and closeness centrality) indicated that avolition was highly central in patients receiving placebo and that roluperidone reduced this level of centrality. These findings suggest that decoupling the influence of motivational processes from other negative symptom domains is essential for producing global improvements. The search for pathophysiological mechanisms and targeted treatment development should be focused on avolition, with the expectation of improvement in the entire constellation of negative symptoms if avolition is effectively treated.

Pharmacological studies of effort-related decision making using mouse touchscreen procedures: effects of dopamine antagonism do not resemble reinforcer devaluation by removal of food restriction

RATIONALE

Effort-based decision-making tasks offer animals choices between preferred reinforcers that require high effort to obtain vs. low effort/low reward options. The neural mechanisms of effort-based choice are widely studied in rats, and evidence indicates that mesolimbic dopamine (DA) and related neural systems play a key role. Fewer studies of effort-based choice have been performed in mice.

OBJECTIVES

The present studies used touchscreen operant procedures (Bussey-Saksida boxes) to assess effort-based choice in mice.

METHODS

CD1 mice were assessed on a concurrent fixed ratio 1 panel pressing/choice procedure. Mice were allowed to choose between rearing to press an elevated panel on the touchscreen for a preferred food (strawberry milkshake) vs. consuming a concurrently available less preferred alternative (high carbohydrate pellets).

RESULTS

The DA D₂ antagonist haloperidol (0.05-0.15 mg/kg IP) produced a dose-related decrease in panel pressing. Intake of food pellets was not reduced by haloperidol, and in fact, there was a significant quadratic trend, indicating a tendency for pellet intake to increase at low/moderate doses. In contrast, reinforcer devaluation by removing food restriction substantially decreased both panel pressing and pellet intake. In free-feeding choice tests, mice strongly preferred milkshake vs. pellets. Haloperidol did not affect food intake or preference.

CONCLUSION

Haloperidol reduced the tendency to work for food, but this reduction was not due to decreases in primary food motivation or preference. Mouse touchscreen procedures demonstrate effects of haloperidol that are similar but not identical to those shown in rats. These rodent studies may be relevant for understanding motivational dysfunctions in humans.

Affective valence in the brain: modules or modes?

How do brain systems evaluate the affective valence of a stimulus - that is, its quality of being good or bad? One possibility is that a neural subsystem, or 'module' (such as a subregion of the brain, a projection pathway, a neuronal population or an individual neuron), is permanently dedicated to mediate only one affective function, or at least only one specific valence - an idea that is termed here the 'affective modules' hypothesis. An alternative possibility is that a given neural module can exist in multiple neurobiological states that give it different affective functions - an idea termed here the 'affective modes' hypothesis. This suggests that the affective function or valence mediated by a neural module need not remain permanently stable but rather can change dynamically across different situations. An evaluation of evidence for the 'affective modules' versus 'affective modes' hypotheses may be useful for advancing understanding of the affective organization of limbic circuitry.

Emerging roles of striatal dopamine D2 receptors in motivated behaviour: Implications for psychiatric disorders

Impaired motivation has been a long recognized negative symptom of schizophrenia, as well as a common feature of non-psychotic psychiatric disorders, responsible for a significant share of functional burden, and with limited treatment options. The striatum and dopamine signalling system play a central role in extracting motivationally relevant information from the environment, selecting which behavioural direction the animal should follow, and the vigour with which to engage it. Much of this function relies on striatal projection neurons, known as medium spiny neurons (MSNs) expressing dopamine D2 receptors (D2Rs), or D2-MSNs. However, determining the precise nature of D2-MSNs in regulating motivated behaviour in both healthy individuals and experimental manipulations of D2-MSN function has at times yielded a somewhat confusing picture since their activity has been linked to either enhancement or dampening of motivation in animal models. In this MiniReview, we describe the latest data from rodent studies that investigated how D2Rs exert their modulatory effect on motivated behaviour by regulating striatal indirect pathway neuronal activity. We will include a discussion about how functional selectivity of D2Rs towards G protein-dependent or β-arrestin-dependent signalling differentially affects motivated behaviour. Lastly, we will describe a recent preclinical attempt to improve motivation by exploiting serotonin receptor-mediated modulation of dopamine transmission in the striatum.

Decrease in Operant Responding Under Obesogenic Diet Exposure is not Related to Deficits in Incentive or Hedonic Processes

OBJECTIVE

A growing body of evidence suggests that obesity could result from alterations in reward processing. In rodent models, chronic exposure to an obesogenic diet leads to blunted dopamine signaling and related incentive responding. This study aimed to determine which reward-related behavioral dimensions are actually impacted by obesogenic diet exposure.

METHODS

Mice were chronically exposed to an obesogenic diet. Incentive and hedonic processes were tested through operant conditioning and licking microstructures, respectively. In parallel, mesolimbic dopamine transmission was assessed using microdialysis.

RESULTS

Prolonged high-fat (HF) diet exposure led to blunted mesolimbic dopamine release, paralleled by a decrease in operant responding in all schedules tested. HF-fed and control animals similarly decreased their operant responding in an effort-based choice task, and HF-fed animals displayed an overall lower calorie intake in this task. Analysis of the licking microstructures during consumption of a freely accessible reward suggested a decrease in basal hunger and a potentiation of gastrointestinal inhibition in HF-fed animals, without changes in hedonic reactivity.

CONCLUSIONS

These results suggest that the decrease in operant responding under prolonged HF diet exposure is mainly driven by decrease in hunger as well as stronger postingestive negative feedback mechanisms, rather than by a decrease in incentive or hedonic responses.

Overexpression of striatal D2 receptors reduces motivation thereby decreasing food anticipatory activity

Dopamine has been implicated in circadian timing underlying the food entrainable oscillator (FEO) circuitry and overexpression of the dopamine D2 receptor (D2R) in the striatum has been reported to reduce motivation to obtain food rewards in operant tasks. In the present study, we explored both of these mechanisms by examining food anticipatory activity (FAA) in dopamine D2 receptor-overexpressing (D2R-OE) mice under various durations of food availability. First, we noted that at baseline, there were no differences between D2R-OE mice and their littermates in activity level, food intake, and body weight or in circadian activity. Under conditions of very restricted food availability (4 or 6 hr), both genotypes displayed FAA. In contrast, under 8-hr food availability, control mice showed FAA, but D2R-OE mice did not. Normalization of D2R by administration of doxycycline, a tetracycline analogue, rescued FAA under 8-hr restricted food. We next tested for circadian regulation of FAA. When given ad libitum access to food, neither D2R-OE nor controls were active during the daytime. However, after an interval of food restriction, all mice showed elevated locomotor activity at the time of previous food availability in the day, indicating circadian timing of anticipatory activity. In summary, motivation is reduced in D2R-OE mice but circadian timing behavior is not affected. We conclude that an increase in striatal D2R reduces FAA by modulating motivation and not by acting on a clock mechanism.

Maternal Exposure to Dietary Selenium Causes Dopaminergic Hyperfunction and Cognitive Impairment in Zebrafish Offspring

Maternal exposure to environmental contaminants is a predisposing factor for neurodevelopmental disorders with associated cognitive and social deficits in offspring. In this study, we investigated the effects of maternal exposure to selenium (Se), a contaminant of potential environmental concern in aquatic ecosystems, on cognitive performance and the underlying mechanisms in F1-generation adult zebrafish. Adult female zebrafish were exposed to different concentrations of dietary Se (3.5, 11.1, or 27.4 μg Se/g dry weight) for a period of 60 days. Fish were subsequently bred, and their offspring were collected and raised for 6 months on a normal diet. Maternal exposure to all concentrations of dietary Se induced learning impairment in F1-zebrafish tested in a latent learning task. The results also showed a hyperfunctioning dopaminergic system in fish exhibiting the learning deficit. The hyperfunction of the dopaminergic system was associated with enhanced oxidative stress and alterations in the mRNA abundance of several immediate early and late response genes in the zebrafish brain. Taken together, these results suggest that maternal exposure to dietary Se via alterations in the dopaminergic system leads to persistent neurobehavioral deficits in F1-generation adult zebrafish.

Striatal dopamine D2 receptors regulate effort but not value-based decision making and alter the dopaminergic encoding of cost

Deficits in goal-directed motivation represent a debilitating symptom for many patients with schizophrenia. Impairments in motivation can arise from deficits in processing information about effort and or value, disrupting effective cost-benefit decision making. We have previously shown that upregulated dopamine D2 receptor expression within the striatum (D2R-OE mice) decreases goal-directed motivation. Here, we determine the behavioral and neurochemical mechanisms behind this deficit. Female D2R-OE mice were tested in several behavioral paradigms including recently developed tasks that independently assess the impact of Value or Effort manipulations on cost-benefit decision making. In vivo microdialysis was used to measure extracellular dopamine in the striatum during behavior. In a value-based choice task, D2R-OE mice show normal sensitivity to changes in reward value and used reward value to guide their actions. In an effort-based choice task, D2R-OE mice evaluate the cost of increasing the number of responses greater relative to the effort cost of longer duration responses compared to controls. This shift away from choosing to repeatedly execute a response is accompanied by a dampening of extracellular dopamine in the striatum during goal-directed behavior. In the ventral striatum, extracellular dopamine level negatively correlates with response cost in controls, but this relationship is lost in D2R-OE mice. These results show that D2R signaling in the striatum, as observed in some patients with schizophrenia, alters the relationship between effort expenditure and extracellular dopamine. This dysregulation produces motivation deficits that are specific to effort but not value-based decision making, paralleling the effort-based motivational deficits observed in schizophrenia.

Disrupted salience processing involved in motivational deficits for real-life activities in patients with schizophrenia

Motivational deficits in patients with schizophrenia adversely affect various domains of daily living. This symptom in everyday life situations manifests in a complex behavioral pattern whose root cannot be simplified to an impaired reward-motivation scheme. This study aimed to identify impairment of the salience network that underlies motivational deficits seen in patients with schizophrenia in real-life situations. During the functional magnetic resonance imaging scan, 20 patients with schizophrenia and 20 normal controls performed a task mimicking real-life situations, in which an avatar proposed participation in a daily activity with either an intrinsic or extrinsic reward. Group and type-of-reward effects were evaluated with respect to brain activity. Further, psychophysiological interactions were analyzed for the dorsal anterior cingulate cortex (dACC) and insula, which are the key nodes of the salience network. The acceptance of the proposal was significantly higher for intrinsic than for extrinsic rewards in controls, whereas patients showed no difference. The imaging results showed a group effect in the dACC, right insula, thalamus, and lingual gyrus. The dACC showed negative contrast interaction with regions of the left dorsolateral prefrontal cortex, and the right insula showed positive contrast interaction with the occipital gyrus and precentral gyrus. These results suggest that patients exhibit no different participation behavior between activities with intrinsic and extrinsic rewards, which can be explained by the floor effect. Disrupted salience processing in schizophrenia including aberrant salience network and a disconnection of the salience and reward networks may account for the lack of motivation for daily activities.

The pathophysiological mechanisms of motivational deficits in Parkinson's disease

Parkinson's disease (PD) is a progressive degenerative disorder that leads to disabling motor symptoms and a wide variety of neuropsychiatric symptoms. Apathy is the most common psychiatric disorder in the early stages of untreated PD and can be defined as a hypodopaminergic syndrome, which also includes anxiety and depression. Apathy is also considered the core feature of the parkinsonian triad (apathy, anxiety and depression) of behavioural non-motor signs, including a motivational deficit. Moreover, apathy is recognised as a distinct chronic neuropsychiatric behavioural disorder based on specific diagnostic criteria. Given the prevalence of apathy in approximately 40% of the general Parkinson's disease population, this appears to be a contributing factor to dementia in PD; also, apathy symptoms are factors that potentially contribute to morbidity, leading to a major impairment of health-related quality of life, thus stressing the importance of understanding the pathophysiology of this disease. Several studies have clearly established a prominent role for DA-mediated signals in PD apathy. However, synergistic interaction between dopaminergic impairment resulting from the neurodegenerative process and deep brain stimulation of the subthalamic nucleus may cause or exacerbate apathy. Furthermore, serotoninergic mechanism signalling is also likely to be of importance in this pathophysiology.

LPS-induced cortical kynurenic acid and neurogranin-NFAT signaling is associated with deficits in stimulus processing during Pavlovian conditioning

The N-Methyl-d-Aspartate receptor (NMDAR) antagonist kynurenic acid (KYNA) and the post-synaptic calmodulin binding protein neurogranin (Nrgn) have been implicated in neurological and neuropsychiatric conditions including Alzheimer's disease and schizophrenia. This study indicates that systemic dual-lipopolysaccharide (LPS) injections increases KYNA in the medial prefrontal cortex (mPFC), which is accompanied with increased phosphorylation of nuclear factor kappa chain of activated B cells (NFκB) and activation of the nuclear factor of activated T- cells (NFAT). Our results also indicate that dual-LPS increases Nrgn phosphorylation and concomitantly reduces phosphorylation of calmodulin kinase-II (CaMKII). We confirmed that systemic blockade of kynurenine-3 monooxygenase in conjunction with kynurenine administration results in significant increases in Nrgn phosphorylation and a significant reduction of CaMKII phosphorylation in the mPFC. Consequently, dual-LPS administration induced significant impairments in stimulus processing during Pavlovian conditioning. Taken together, our study indicates that elevations in KYNA in the mPFC can directly regulate NMDA-Nrgn-CaMKII signaling, suggesting that neuroinflammatory conditions affecting this pathway may be associated with cognitive dysfunction.

Genetic Basis of Positive and Negative Symptom Domains in Schizophrenia

Schizophrenia is a highly heritable disorder, the genetic etiology of which has been well established. Yet despite significant advances in genetics research, the pathophysiological mechanisms of this disorder largely remain unknown. This gap has been attributed to the complexity of the polygenic disorder, which has a heterogeneous clinical profile. Examining the genetic basis of schizophrenia subphenotypes, such as those based on particular symptoms, is thus a useful strategy for decoding the underlying mechanisms. This review of literature examines the recent advances (from 2011) in genetic exploration of positive and negative symptoms in schizophrenia. We searched electronic databases PubMed, Web of Science, and Cumulative Index to Nursing and Allied Health Literature using key words schizophrenia, symptoms, positive symptoms, negative symptoms, cognition, genetics, genes, genetic predisposition, and genotype in various combinations. We identified 115 articles, which are included in the review. Evidence from these studies, most of which are genetic association studies, identifies shared and unique gene associations for the symptom domains. Genes associated with neurotransmitter systems and neuronal development/maintenance primarily constitute the shared associations. Needed are studies that examine the genetic basis of specific symptoms within the broader domains in addition to functional mechanisms. Such investigations are critical to developing precision treatment and care for individuals afflicted with schizophrenia.

Maternal immune activation alters sensitivity to action-outcome contingency in adult rat offspring

Epidemiological studies have provided convincing evidence for a role of maternal immune activation in the pathogenesis of neurodevelopmental disorders such as autism and schizophrenia. In recent years, several research groups have capitalised on this discovery and developed animal models such as the maternal immune activation (MIA) model that emulates many phenotypes characteristic of disorders such as schizophrenia. In the present series of experiments we used the MIA model to examine motivation, a core component of the negative symptomatology in schizophrenia. Contrary to what we expected, in the progressive ratio task, which assesses an animals' willingness to work for a reward under increasing effort requirements, we found that MIA rats appeared more motivated than controls. Subsequent tests showed that this seemingly enhanced motivation was not due to an overall increase in responding, nor due to enhanced attribution of incentive salience to reward associated responses. Instead, we found that the increased willingness to work exhibited by MIA animals was due to an inability to detect changes in the contingency between their behaviour and the resulting rewarding outcome. With regard to motivation, the experiments reported here are the first to subject the MIA model to a rigorous experimental analysis of behaviour by parsing underlying processes that give rise to the overt symptoms in psychiatric disease.

Gambling disorder: an integrative review of animal and human studies

Gambling disorder (GD), previously called pathological gambling and classified as an impulse control disorder in DSM-III and DSM-IV, has recently been reclassified as an addictive disorder in the DSM-5. It is widely recognized as an important public health problem associated with substantial personal and social costs, high rates of psychiatric comorbidity, poor physical health, and elevated suicide rates. A number of risk factors have been identified, including some genetic polymorphisms. Animal models have been developed in order to study the underlying neural basis of GD. Here, we discuss recent advances in our understanding of the risk factors, disease course, and pathophysiology. A focus on a phenotype-based dissection of the disorder is included in which known neural correlates from animal and human studies are reviewed. Finally, current treatment approaches are discussed, as well as future directions for GD research.

Insights About Striatal Circuit Function and Schizophrenia From a Mouse Model of Dopamine D2 Receptor Upregulation

The dopamine hypothesis of schizophrenia is supported by a large number of imaging studies that have identified an increase in dopamine binding at the D₂ receptor selectively in the striatum. We review a decade of work using a regionally restricted and temporally regulated transgenic mouse model to investigate the behavioral, molecular, electrophysiological, and anatomical consequences of selective D₂ receptor upregulation in the striatum. These studies have identified new and potentially important biomarkers at the circuit and molecular level that can now be explored in patients with schizophrenia. They provide an example of how animal models and their detailed level of neurobiological analysis allow a deepening of our understanding of the relationship between neuronal circuit function and symptoms of schizophrenia, and as a consequence generate new hypotheses that are testable in patients.

Neural substrates underlying effort, time, and risk-based decision making in motivated behavior

All mobile organisms rely on adaptive motivated behavior to overcome the challenges of living in an environment in which essential resources may be limited. A variety of influences ranging from an organism's environment, experiential history, and physiological state all influence a cost-benefit analysis which allows motivation to energize behavior and direct it toward specific goals. Here we review the substantial amount of research aimed at discovering the interconnected neural circuits which allow organisms to carry-out the cost-benefit computations which allow them to behave in adaptive ways. We specifically focus on how the brain deals with different types of costs, including effort requirements, delays to reward and payoff riskiness. An examination of this broad literature highlights the importance of the extended neural circuits which enable organisms to make decisions about these different types of costs. This involves Cortical Structures, including the Anterior Cingulate Cortex (ACC), the Orbital Frontal Cortex (OFC), the Infralimbic Cortex (IL), and prelimbic Cortex (PL), as well as the Baso-Lateral Amygdala (BLA), the Nucleus Accumbens (NAcc), the Ventral Pallidal (VP), the Sub Thalamic Nucleus (STN) among others. Some regions are involved in multiple aspects of cost-benefit computations while the involvement of other regions is restricted to information relating to specific types of costs.

Using human brain imaging studies as a guide toward animal models of schizophrenia

Schizophrenia is a heterogeneous and poorly understood mental disorder that is presently defined solely by its behavioral symptoms. Advances in genetic, epidemiological and brain imaging techniques in the past half century, however, have significantly advanced our understanding of the underlying biology of the disorder. In spite of these advances clinical research remains limited in its power to establish the causal relationships that link etiology with pathophysiology and symptoms. In this context, animal models provide an important tool for causally testing hypotheses about biological processes postulated to be disrupted in the disorder. While animal models can exploit a variety of entry points toward the study of schizophrenia, here we describe an approach that seeks to closely approximate functional alterations observed with brain imaging techniques in patients. By modeling these intermediate pathophysiological alterations in animals, this approach offers an opportunity to (1) tightly link a single functional brain abnormality with its behavioral consequences, and (2) to determine whether a single pathophysiology can causally produce alterations in other brain areas that have been described in patients. In this review we first summarize a selection of well-replicated biological abnormalities described in the schizophrenia literature. We then provide examples of animal models that were studied in the context of patient imaging findings describing enhanced striatal dopamine D2 receptor function, alterations in thalamo-prefrontal circuit function, and metabolic hyperfunction of the hippocampus. Lastly, we discuss the implications of findings from these animal models for our present understanding of schizophrenia, and consider key unanswered questions for future research in animal models and human patients.

Negative symptoms are associated with an increased subjective cost of cognitive effort

Motivational deficits in schizophrenia are proposed to be attributable in part to abnormal effort-cost computations. Inflated subjective cognitive effort costs may explain diminished functioning in schizophrenia to the extent that they drive avoidance of complex decision-making and planning. Although previous data support inflated subjective physical effort costs for individuals with schizophrenia, evidence on cognitive effort is mixed. We exploited the methodological advantages of a recently developed cognitive effort-discounting paradigm (Westbrook, Kester, & Braver, 2013) to examine effort-cost computations in schizophrenia. The paradigm quantifies subjective costs in terms of explicit, continuous discounting of monetary rewards based on parametrically varied demands (levels N of the N-back working memory task), holding objective features of task duration and reward likelihood constant. Both healthy participants (N = 25) and schizophrenia patients (N = 25) showed systematic influences of reward and task demands on choice patterns. Critically, however, participants with schizophrenia discounted rewards more steeply as a function of effort, indicating that effort was more costly for this group. Moreover, discounting varied robustly with symptomatology, such that schizophrenia patients with greater clinically rated negative symptom severity discounted rewards more steeply. These findings extend the current literature on abnormal-effort cost computations in schizophrenia by establishing a clear relationship between the costliness of cognitive effort and negative symptoms. (PsycINFO Database Record

Activational and effort-related aspects of motivation: neural mechanisms and implications for psychopathology

Motivation has been defined as the process that allows organisms to regulate their internal and external environment, and control the probability, proximity and availability of stimuli. As such, motivation is a complex process that is critical for survival, which involves multiple behavioural functions mediated by a number of interacting neural circuits. Classical theories of motivation suggest that there are both directional and activational aspects of motivation, and activational aspects (i.e. speed and vigour of both the instigation and persistence of behaviour) are critical for enabling organisms to overcome work-related obstacles or constraints that separate them from significant stimuli. The present review discusses the role of brain dopamine and related circuits in behavioural activation, exertion of effort in instrumental behaviour, and effort-related decision-making, based upon both animal and human studies. Impairments in behavioural activation and effort-related aspects of motivation are associated with psychiatric symptoms such as anergia, fatigue, lassitude and psychomotor retardation, which cross multiple pathologies, including depression, schizophrenia, and Parkinson's disease. Therefore, this review also attempts to provide an interdisciplinary approach that integrates findings from basic behavioural neuroscience, behavioural economics, clinical neuropsychology, psychiatry, and neurology, to provide a coherent framework for future research and theory in this critical field. Although dopamine systems are a critical part of the brain circuitry regulating behavioural activation, exertion of effort, and effort-related decision-making, mesolimbic dopamine is only one part of a distributed circuitry that includes multiple neurotransmitters and brain areas. Overall, there is a striking similarity between the brain areas involved in behavioural activation and effort-related processes in rodents and in humans. Animal models of effort-related decision-making are highly translatable to humans, and an emerging body of evidence indicates that alterations in effort-based decision-making are evident in several psychiatric and neurological disorders. People with major depression, schizophrenia, and Parkinson's disease show evidence of decision-making biases towards a lower exertion of effort. Translational studies linking research with animal models, human volunteers, and clinical populations are greatly expanding our knowledge about the neural basis of effort-related motivational dysfunction, and it is hoped that this research will ultimately lead to improved treatment for motivational and psychomotor symptoms in psychiatry and neurology.

Dopamine D₂-Like Receptors and Behavioral Economics of Food Reinforcement

Previous studies suggest dopamine (DA) D2-like receptor involvement in the reinforcing effects of food. To determine contributions of the three D2-like receptor subtypes, knockout (KO) mice completely lacking DA D2, D3, or D4 receptors (D2R, D3R, or D4R KO mice) and their wild-type (WT) littermates were exposed to a series of fixed-ratio (FR) food-reinforcement schedules in two contexts: an open economy with additional food provided outside the experimental setting and a closed economy with all food earned within the experimental setting. A behavioral economic model was used to quantify reinforcer effectiveness with food pellets obtained as a function of price (FR schedule value) plotted to assess elasticity of demand. Under both economies, as price increased, food pellets obtained decreased more rapidly (ie, food demand was more elastic) in DA D2R KO mice compared with WT littermates. Extinction of responding was studied in two contexts: by eliminating food deliveries and by delivering food independently of responding. A hyperbolic model quantified rates of extinction. Extinction in DA D2R KO mice occurred less rapidly compared with WT mice in both contexts. Elasticity of food demand was higher in DA D4R KO than WT mice in the open, but not closed, economy. Extinction of responding in DA D4R KO mice was not different from that in WT littermates in either context. No differences in elasticity of food demand or extinction rate were obtained in D3R KO mice and WT littermates. These results indicate that the D2R is the primary DA D2-like receptor subtype mediating the reinforcing effectiveness of food.

The pharmacology of effort-related choice behavior: Dopamine, depression, and individual differences

This review paper is focused upon the involvement of mesolimbic dopamine (DA) and related brain systems in effort-based processes. Interference with DA transmission affects instrumental behavior in a manner that interacts with the response requirements of the task, such that rats with impaired DA transmission show a heightened sensitivity to ratio requirements. Impaired DA transmission also affects effort-related choice behavior, which is assessed by tasks that offer a choice between a preferred reinforcer that has a high work requirement vs. less preferred reinforcer that can be obtained with minimal effort. Rats and mice with impaired DA transmission reallocate instrumental behavior away from food-reinforced tasks with high response costs, and show increased selection of low reinforcement/low cost options. Tests of effort-related choice have been developed into models of pathological symptoms of motivation that are seen in disorders such as depression and schizophrenia. These models are being employed to explore the effects of conditions associated with various psychopathologies, and to assess drugs for their potential utility as treatments for effort-related symptoms. Studies of the pharmacology of effort-based choice may contribute to the development of treatments for symptoms such as psychomotor slowing, fatigue or anergia, which are seen in depression and other disorders.

Measuring anhedonia: impaired ability to pursue, experience, and learn about reward

Ribot’s (1896) long standing definition of anhedonia as “the inability to experience pleasure” has been challenged recently following progress in affective neuroscience. In particular, accumulating evidence suggests that reward consists of multiple subcomponents of wanting, liking and learning, as initially outlined by Berridge and Robinson (2003), and these processes have been proposed to relate to appetitive, consummatory and satiety phases of a pleasure cycle. Building on this work, we recently proposed to reconceptualize anhedonia as “impairments in the ability to pursue, experience, and/or learn about pleasure, which is often, but not always accessible to conscious awareness.” (Rømer Thomsen et al., 2015). This framework is in line with Treadway and Zald’s (2011) proposal to differentiate between motivational and consummatory types of anhedonia, and stresses the need to combine traditional self-report measures with behavioral measures or procedures. In time, this approach may lead to improved clinical assessment and treatment. In line with our reconceptualization, increasing evidence suggests that reward processing deficits are not restricted to impaired hedonic impact in major psychiatric disorders. Successful translations of animal models have led to strong evidence of impairments in the ability to pursue and learn about reward in psychiatric disorders such as major depressive disorder, schizophrenia, and addiction. It is of high importance that we continue to systematically target impairments in all phases of reward processing across disorders using behavioral testing in combination with neuroimaging techniques. This in turn has implications for diagnosis and treatment, and is essential for the purposes of identifying the underlying neurobiological mechanisms. Here I review recent progress in the development and application of behavioral procedures that measure subcomponents of anhedonia across relevant patient groups, and discuss methodological caveats as well as implications for assessment and treatment.

Effort-Based Decision-Making Paradigms for Clinical Trials in Schizophrenia: Part 2—External Validity and Correlates

Effort-based decision making has strong conceptual links to the motivational disturbances that define a key subdomain of negative symptoms. However, the extent to which effort-based decision-making performance relates to negative symptoms, and other clinical and functionally important variables has yet to be systematically investigated. In 94 clinically stable outpatients with schizophrenia, we examined the external validity of 5 effort-based paradigms, including the Effort Expenditure for Rewards, Balloon Effort, Grip Strength Effort, Deck Choice Effort, and Perceptual Effort tasks. These tasks covered 3 types of effort: physical, cognitive, and perceptual. Correlations between effort related performance and 6 classes of variables were examined, including: (1) negative symptoms, (2) clinically rated motivation and community role functioning, (3) self-reported motivational traits, (4) neurocognition, (5) other psychiatric symptoms and clinical/demographic characteristics, and (6) subjective valuation of monetary rewards. Effort paradigms showed small to medium relationships to clinical ratings of negative symptoms, motivation, and functioning, with the pattern more consistent for some measures than others. They also showed small to medium relations with neurocognitive functioning, but were generally unrelated to other psychiatric symptoms, self-reported traits, antipsychotic medications, side effects, and subjective valuation of money. There were relatively strong interrelationships among the effort measures. In conjunction with findings from a companion psychometric article, all the paradigms warrant further consideration and development, and 2 show the strongest potential for clinical trial use at this juncture.

Social behavior in a genetic model of dopamine dysfunction at different neurodevelopmental time points

Impairments in social behavior characterize many neurodevelopmental psychiatric disorders. In fact, the temporal emergence and trajectory of these deficits can define the disorder, specify their treatment and signal their prognosis. The sophistication of mouse models with neurobiological endophenotypes of many aspects of psychiatric diseases has increased in recent years, with the necessity to evaluate social behavior in these models. We adapted an assay for the multimodal characterization of social behavior at different development time points (juvenile, adolescent and adult) in control mice in different social contexts (specifically, different sex pairings). Although social context did not affect social behavior in juvenile mice, it did have an effect on the quantity and type of social interaction as well as ultrasonic vocalizations in both adolescence and adulthood. We compared social development in control mice to a transgenic mouse model of the increase in postsynaptic striatal D2R activity observed in patients with schizophrenia (D2R-OE mice). Genotypic differences in social interactions emerged in adolescence and appeared to become more pronounced in adulthood. That vocalizations emitted from dyads with a D2R-OE subject were negatively correlated with active social behavior while vocalizations from control dyads were positively correlated with both active and passive social behavior also suggest social deficits. These data show that striatal dopamine dysfunction plays an important role in the development of social behavior and mouse models such as the one studied here provide an opportunity for screening potential therapeutics at different developmental time points.

Improving temporal cognition by enhancing motivation

Increasing motivation can positively impact cognitive performance. Here we employed a cognitive timing task that allows us to detect changes in cognitive performance that are not influenced by general activity or arousal factors such as the speed or persistence of responding. This approach allowed us to manipulate motivation using three different methods; molecular/genetic, behavioral and pharmacological. Increased striatal D2Rs resulted in deficits in temporal discrimination. Switching off the transgene improved motivation in earlier studies, and here partially rescued the temporal discrimination deficit. To manipulate motivation behaviorally, we altered reward magnitude and found that increasing reward magnitude improved timing in control mice and partially rescued timing in the transgenic mice. Lastly, we manipulated motivation pharmacologically using a functionally selective 5-HT2C receptor ligand, SB242084, which we previously found to increase incentive motivation. SB242084 improved temporal discrimination in both control and transgenic mice. Thus, while there is a general intuitive belief that motivation can affect cognition, we here provide a direct demonstration that enhancing motivation, in a variety of ways, can be an effective strategy for enhancing temporal cognition. Understanding the interaction of motivation and cognition is of clinical significance since many psychiatric disorders are characterized by deficits in both domains.

Selection of sucrose concentration depends on the effort required to obtain it: studies using tetrabenazine, D1, D2, and D3 receptor antagonists

RATIONALE

Low doses of dopamine (DA) antagonists and accumbens DA depletions reduce food-reinforced instrumental behavior but do not impair primary food motivation, causing animals to reallocate behavior away from food-reinforced tasks with high response requirements and select less effortful alternatives. However, it is uncertain if this same pattern of effects would occur if sucrose was used as the reinforcer.

OBJECTIVES

These experiments studied the impact of DA depletion and antagonism on performance of an effort-related choice task using sucrose as the reinforcer, as well as sucrose consumption, preference, and taste reactivity tests.

METHODS

The effects of DA manipulations were assessed using a task in which rats chose between lever pressing on a fixed ratio 7 schedule for 5.0 % sucrose versus freely consuming a less concentrated solution (0.3 %).

RESULTS

The DA depleting agent tetrabenazine shifted effort-related choice, decreasing lever pressing for 5.0 % sucrose but increasing intake of the concurrently available 0.3 % sucrose. Tetrabenazine did not affect sucrose appetitive taste reactivity, or sucrose consumption or preference, in free consumption tests. The D1 antagonist ecopipam and the D2 antagonist haloperidol also shifted choice behavior at doses that did not alter sucrose consumption or preference. In contrast, sucrose pre-exposure reduced consumption across all conditions. D3 antagonism had no effects.

CONCLUSIONS

D1 and D2 receptor blockade and DA depletion reduce the tendency to work for sucrose under conditions that leave fundamental aspects of sucrose motivation (intake, preference, hedonic reactivity) intact. These findings have implications for studies employing sucrose intake or preference in animal models of depression.

Effort discounting and its association with negative symptoms in schizophrenia

INTRODUCTION

Deficits in the initiation and persistence of goal-directed behaviour are key aspects of schizophrenia. In this study, the association between these motivational deficits and discounting of reward value in function of increasing physical effort costs was investigated.

METHODS

Effort-based decision-making was investigated in 40 patients with a DSM-IV diagnosis of schizophrenia and 30 age- and sex-matched healthy control subjects by means of an effort discounting task. To assess negative symptom severity, we made use of the Scale for the Assessment of Negative Symptoms as well as objective measurements of hedonic response to stimuli and motor activity levels.

RESULTS

Patients as well as control subjects discounted the subjective value of rewards significantly with increasing physical effort costs. However, we failed to find a difference in the discounting curves between patients and controls. Furthermore, effort discounting was not associated with any of the negative symptoms measures.

CONCLUSIONS

Physical effort discounting was not found to be associated with motivational symptoms in schizophrenia if other decision costs are constant. However, recent findings show that more cognitive effort and/or an interaction between effort and other decision costs (e.g. temporal delay or uncertainty) are associated with negative symptoms in schizophrenia. This should be investigated further in future research.

Orbitofrontal cortex mediates the differential impact of signaled-reward probability on discrimination accuracy

Orbitofrontal cortex (OFC) function is critical to decision making and behavior based on the value of expected outcomes. While some of the roles the OFC plays in value computations and behavior have been identified, the role of the OFC in modulating cognitive resources based on reward expectancy has not been explored. Here we assessed the involvement of OFC in the interaction between motivation and attention. We tested mice in a sustained-attention task in which explicitly signaling the probability of reward differentially modulates discrimination accuracy. Using pharmacogenetic methods, we generated mice in which neuronal activity in the OFC could be transiently and reversibly inhibited during performance of our signaled-probability task. We found that inhibiting OFC neuronal activity abolished the ability of reward-associated cues to differentially impact accuracy of sustained-attention performance. This failure to modulate attention occurred despite evidence that mice still processed the differential value of the reward-associated cues. These data indicate that OFC function is critical for the ability of a reward-related signal to impact other cognitive and decision-making processes and begin to delineate the neural circuitry involved in the interaction between motivation and attention.

The impact of motivation on cognitive performance in an animal model of the negative and cognitive symptoms of schizophrenia

Interactions between motivation and cognition are implicated in producing functional impairments and poor quality of life in psychiatric patients. This interaction, however, is not well understood at either the behavioral or neural level. We developed a procedure for mice in which a cognitive measure, sustained attention, is modulated by a motivationally relevant signal that predicts reward probability on a trial-by-trial basis. Using this paradigm, we tested the interaction between motivation and cognition in mice that model the increased striatal D2 receptor activity observed in schizophrenia patients (D2R-OE mice). In control mice, attention was modulated by signaled-reward probability. In D2R-OE mice, however, attention was not modulated by reward-related cues. This impairment was not due to any global deficits in attention or maintenance of the trial-specific information in working memory. Turning off the transgene in D2R-OE mice rescued the motivational modulation of attention. These results indicate that deficits in motivation impair the ability to use reward-related cues to recruit attention and that improving motivation improves functional cognitive performance. These results further suggest that addressing motivational impairments in patients is critical to achieving substantive cognitive and functional gains.

When chocolate seeking becomes compulsion: gene-environment interplay

BACKGROUND

Eating disorders appear to be caused by a complex interaction between environmental and genetic factors, and compulsive eating in response to adverse circumstances characterizes many eating disorders.

MATERIALS AND METHODS

We compared compulsion-like eating in the form of conditioned suppression of palatable food-seeking in adverse situations in stressed C57BL/6J and DBA/2J mice, two well-characterized inbred strains, to determine the influence of gene-environment interplay on this behavioral phenotype. Moreover, we tested the hypothesis that low accumbal D2 receptor (R) availability is a genetic risk factor of food compulsion-like behavior and that environmental conditions that induce compulsive eating alter D2R expression in the striatum. To this end, we measured D1R and D2R expression in the striatum and D1R, D2R and α1R levels in the medial prefrontal cortex, respectively, by western blot.

RESULTS

Exposure to environmental conditions induces compulsion-like eating behavior, depending on genetic background. This behavioral pattern is linked to decreased availability of accumbal D2R. Moreover, exposure to certain environmental conditions upregulates D2R and downregulates α1R in the striatum and medial prefrontal cortex, respectively, of compulsive animals. These findings confirm the function of gene-environment interplay in the manifestation of compulsive eating and support the hypothesis that low accumbal D2R availability is a "constitutive" genetic risk factor for compulsion-like eating behavior. Finally, D2R upregulation and α1R downregulation in the striatum and medial prefrontal cortex, respectively, are potential neuroadaptive responses that parallel the shift from motivated to compulsive eating.

Reconceptualizing anhedonia: novel perspectives on balancing the pleasure networks in the human brain

Anhedonia, the lack of pleasure, has been shown to be a critical feature of a range of psychiatric disorders. Yet, it is currently measured primarily through subjective self-reports and as such has been difficult to submit to rigorous scientific analysis. New insights from affective neuroscience hold considerable promise in improving our understanding of anhedonia and for providing useful objective behavioral measures to complement traditional self-report measures, potentially leading to better diagnoses and novel treatments. Here, we review the state-of-the-art of hedonia research and specifically the established mechanisms of wanting, liking, and learning. Based on this framework we propose to conceptualize anhedonia as impairments in some or all of these processes, thereby departing from the longstanding view of anhedonia as solely reduced subjective experience of pleasure. We discuss how deficits in each of the reward components can lead to different expressions, or subtypes, of anhedonia affording novel ways of measurement. Specifically, we review evidence suggesting that patients suffering from depression and schizophrenia show impairments in wanting and learning, while some aspects of conscious liking seem surprisingly intact. Furthermore, the evidence suggests that anhedonia is heterogeneous across psychiatric disorders, depending on which parts of the pleasure networks are most affected. This in turn has implications for diagnosis and treatment of anhedonia.