Methodological approaches and magnitude of the clinical unmet need associated with amotivation in mood disorders

Effect of venlafaxine on anhedonia and amotivation in patients with major depressive disorder

OBJECTIVE

Serotonin norepinephrine reuptake inhibitors (SNRIs) have been postulated to afford benefits in alleviating anhedonia and amotivation. This post hoc pooled analysis evaluated the effect of venlafaxine XR, an SNRI, on these symptoms in patients with major depressive disorder (MDD).

METHODS

Data was pooled from five short-term randomized, placebo-controlled studies of venlafaxine XR for the treatment of MDD, comprising 1087 (venlafaxine XR, n = 585; placebo, n = 502) adult subjects. The change from baseline score in the MADRS anhedonia factor (based on items 1 [apparent sadness], 2 [reported sadness], 6 [concentration difficulties], 7 [lassitude], and 8 [inability to feel]) for anhedonia, and in motivational deficits (based on 3 items of HAM-D17: involvement in work and activities, psychomotor retardation, and energy level [ie, general somatic symptoms]) for amotivation, were measured through 8 weeks. Mixed model repeated measures (MMRMs) were used to analyze changes over time and ANCOVA to analyze the change from baseline at week 8 with LOCF employed to handle missing data.

RESULTS

At the end of 8 weeks, the change from baseline was significantly greater in patients on venlafaxine XR in both anhedonia (mean, 95% CI: -2.73 [-3.63, -1.82], p < 0.0001) and amotivation scores (mean, 95% CI: -0.78 [-1.04, -0.52], p < 0.0001) than those on placebo. For both measures, the between-group separation from baseline was statistically significant starting from week 2 onwards, and it increased over time.

CONCLUSION

This analysis demonstrates that venlafaxine XR is effective in improving symptoms of anhedonia and motivational deficits in patients with MDD.

Estimating heterogeneity of treatment effect in psychiatric clinical trials

Currently, placebo-controlled clinical trials report mean change and effect sizes, which masks information about heterogeneity of treatment effects (HTE). Here, we present a method to estimate HTE and evaluate the null hypothesis (H0) that a drug has equal benefit for all participants (HTE=0). We developed measure termed 'estimated heterogeneity of treatment effect' or eHTE, which estimates variability in drug response by comparing distributions between study arms. This approach was tested across numerous large placebo-controlled clinical trials. In contrast with variance-based methods which have not identified heterogeneity in psychiatric trials, reproducible instances of treatment heterogeneity were found. For example, heterogeneous response was found in a trial of venlafaxine for depression (peHTE=0.034), and two trials of dasotraline for binge eating disorder (Phase 2, peHTE=0.002; Phase 3, 4mg peHTE=0.011; Phase 3, 6mg peHTE=0.003). Significant response heterogeneity was detected in other datasets as well, often despite no difference in variance between placebo and drug arms. The implications of eHTE as a clinical trial outcomes independent from central tendency of the group is considered and the important of the eHTE method and results for drug developers, providers, and patients is discussed.

Effects of a single dose of amisulpride on functional brain changes during reward- and motivation-related processing using task-based fMRI in healthy subjects and patients with major depressive disorder - study protocol for a randomized clinical trial

BACKGROUND

Anhedonia and other deficits in reward- and motivation-related processing in psychiatric patients, including patients with major depressive disorder (MDD), represent a high unmet medical need. Neurobiologically, these deficits in MDD patients are mainly associated with low dopamine function in a frontostriatal network. In this study, alterations in brain activation changes during reward processing and at rest in MDD patients compared with healthy subjects are explored and the effects of a single low dose of the dopamine D2 receptor antagonist amisulpride are investigated.

METHODS

This is a randomized, controlled, double-blind, single-dose, single-center parallel-group clinical trial to assess the effects of a single dose of amisulpride (100 mg) on blood-oxygenation-level-dependent (BOLD) responses during reward- and motivation-related processing in healthy subjects (n = 60) and MDD patients (n = 60). Using functional magnetic resonance imaging (fMRI), BOLD responses are assessed during the monetary incentive delay (MID) task (primary outcome). Exploratory outcomes include BOLD responses and behavioral measures during the MID task, instrumental learning task, effort-based decision-making task, social incentive delay task, and probabilistic reward task as well as changes in resting state functional connectivity and cerebral blood flow.

DISCUSSION

This study broadly covers all aspects of reward- and motivation-related processing as categorized by the National Institute of Mental Health Research Domain Criteria and is thereby an important step towards precision psychiatry. Results regarding the immediate effects of a dopaminergic drug on deficits in reward- and motivation-related processing not only have the potential to significantly broaden our understanding of underlying neurobiological processes but might eventually also pave the way for new treatment options.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05347199. April 12, 2022.

Elevated serum leptin is associated with attenuated reward anticipation in major depressive disorder independent of peripheral C-reactive protein levels

Major depressive disorder (MDD) is associated with immunologic and metabolic alterations linked to central processing dysfunctions, including attenuated reward processing. This study investigated the associations between inflammation, metabolic hormones (leptin, insulin, adiponectin), and reward-related brain processing in MDD patients with high (MDD-High) and low (MDD-Low) C-reactive protein (CRP) levels compared to healthy comparison subjects (HC). Participants completed a blood draw and a monetary incentive delay task during functional magnetic resonance imaging. Although groups did not differ in insulin or adiponectin concentrations, both MDD-High (Wilcoxon p = 0.004, d = 0.65) and MDD-Low (Wilcoxon p = 0.046, d = 0.53) showed higher leptin concentrations than HC but did not differ from each other. Across MDD participants, higher leptin levels were associated with lower brain activation during reward anticipation in the left insula (r = - 0.30, p = 0.004) and left dorsolateral putamen (r = -- 0.24, p = 0.025). In contrast, within HC, higher leptin concentrations were associated with higher activation during reward anticipation in the same regions (insula: r = 0.40, p = 0.007; putamen: r = 0.37, p = 0.014). Depression may be characterized by elevated pro-inflammatory signaling via leptin concentrations through alternate inflammatory pathways distinct to CRP.

Dopamine D1 receptor and effort-based decision making in rats: The moderating effect of sex

Dopamine is a modulating factor in effort-based decision-making, and emerging evidence from pharmacological research suggests that the dopamine D1 receptor is the primary regulator. Given the limited selectivity of pharmacological tools, we further explored this hypothesis using dopamine D1 mutant (DAD1^-/-) rats which have a specific genetic reduction in functional D1 receptors. Moreover, given the strong focus on males in neuroscience research in general and in the role of D1 receptors in effort-based learning, we compared both sexes in the present study. Adult male and female DAD1^-/- mutant rats and wild type controls were trained to press a lever for a reinforcer. Once trained, subjects completed multiple fixed ratio, progressive ratio, and operant effort-choice (concurrent progressive ratio/chow feeding task [PROG/chow]) experiments. We predicted that DAD1^-/- mutant rats would press the lever significantly less than controls across all experiments, have lower breakpoints, and consume more freely available food. As predicted, DAD1^-/- mutant rats (regardless of sex) pressed the lever significantly less than controls and had lower breakpoints. Interestingly, there was a sex * genotype interaction for acquisition rates of lever pressing and change in breakpoints with free food available. Only 31% of DAD1^-/- mutant males acquired lever pressing while 73% of DAD1^-/- mutant females acquired lever pressing. Additionally, DAD1^-/- mutant males had significantly larger decreases in breakpoints when free food was available. These findings extend the pharmacological research suggesting that the dopamine D1 receptor modulates decisions based on effort, which has implications for the development of treatment targeting amotivation in neuropsychiatric disorders. The sex * genotype interaction highlights the importance of including both sexes in future research, especially when there are sex differences in incidences and severity of neuropsychiatric disorders.

Low doses of lysergic acid diethylamide (LSD) increase reward-related brain activity

Renewed interest in classic psychedelics as treatments for psychiatric disorders warrants a deeper understanding of their neural mechanisms. Single, high doses of psychedelic drugs have shown promise in treating depressive disorders, perhaps by reversing deficits in reward processing in the brain. In addition, there are anecdotal reports that repeated ingestion of low doses of LSD, or "microdosing", improve mood, cognition, and feelings of wellbeing. However, the effects of low doses of classic psychedelics on reward processing have not been studied. The current study examined the effects of two single, low doses of LSD compared to placebo on measures of reward processing. Eighteen healthy adults completed three sessions in which they received placebo (LSD-0), 13 μg LSD (LSD-13) and 26 μg LSD (LSD-26) in a within-subject, double-blind design. Neural activity was recorded while participants completed the electrophysiological monetary incentive delay task. Event-related potentials were measured during feedback processing (Reward-Positivity: RewP, Feedback-P3: FB-P3, and Late-Positive Potential: LPP). Compared to placebo, LSD-13 increased RewP and LPP amplitudes for reward (vs. neutral) feedback, and LSD-13 and LSD-26 increased FB-P3 amplitudes for positive (vs. negative) feedback. These effects were unassociated with most subjective measures of drug effects. Thus, single, low doses of LSD (vs. placebo) increased three reward-related ERP components reflecting increased hedonic (RewP), motivational (FB-P3), and affective processing of feedback (LPP). These results constitute the first evidence that low doses of LSD increase reward-related brain activity in humans. These findings may have important implications for the treatment of depressive disorders.

Elevated Effort Cost Identified by Computational Modeling as a Distinctive Feature Explaining Multiple Behaviors in Patients With Depression

BACKGROUND

Motivational deficit is a core clinical manifestation of depression and a strong predictor of treatment failure. However, the underlying mechanisms, which cannot be accessed through conventional questionnaire-based scoring, remain largely unknown. According to decision theory, apathy could result either from biased subjective estimates (of action costs or outcomes) or from dysfunctional processes (in making decisions or allocating resources).

METHODS

Here, we combined a series of behavioral tasks with computational modeling to elucidate the motivational deficits of 35 patients with unipolar or bipolar depression under various treatments compared with 35 matched healthy control subjects.

RESULTS

The most striking feature, which was observed independent of medication across preference tasks (likeability ratings and binary decisions), performance tasks (physical and mental effort exertion), and instrumental learning tasks (updating choices to maximize outcomes), was an elevated sensitivity to effort cost. By contrast, sensitivity to action outcomes (reward and punishment) and task-specific processes were relatively spared.

CONCLUSIONS

These results highlight effort cost as a critical dimension that might explain multiple behavioral changes in patients with depression. More generally, they validate a test battery for computational phenotyping of motivational states, which could orientate toward specific medication or rehabilitation therapy, and thereby help pave the way for more personalized medicine in psychiatry.

Decreased reward circuit connectivity during reward anticipation in major depression

An important symptom of major depressive disorder (MDD) is the inability to experience pleasure, possibly due to a dysfunction of the reward system. Despite promising insights regarding impaired reward-related processing in MDD, circuit-level abnormalities remain largely unexplored. Furthermore, whereas studies contrasting experimental conditions from incentive tasks have revealed important information about reward processing, temporal difference modeling of reward-related prediction error (PE) signals might give a more accurate representation of the reward system. We used a monetary incentive delay task during functional MRI scanning to explore PE-related striatal and ventral tegmental area (VTA) activation in response to anticipation and delivery of monetary rewards in 24 individuals with MDD versus 24 healthy controls (HCs). Furthermore, we investigated group differences in temporal difference related connectivity with a generalized psychophysiological interaction (gPPI) analysis with the VTA, ventral striatum (VS) and dorsal striatum (DS) as seeds during reward versus neutral, both in anticipation and delivery. Relative to HCs, MDD patients displayed a trend-level (p = 0.052) decrease in temporal difference-related activation in the VS during reward anticipation and delivery combined. Moreover, gPPI analyses revealed that during reward anticipation, MDD patients exhibited decreased functional connectivity between the VS and anterior cingulate cortex / medial prefrontal cortex, anterior cingulate gyrus, angular/middle orbital gyrus, left insula, superior/middle frontal gyrus (SFG/MFG) and precuneus/superior occipital gyrus/cerebellum compared to HC. Moreover, MDD patients showed decreased functional connectivity between the VTA and left insula compared to HC during reward anticipation. Exploratory analysis separating medication free patients from patients using antidepressant revealed that these decreased functional connectivity patterns were mainly apparent in the MDD group that used antidepressants. These results suggest that MDD is characterized by alterations in reward circuit connectivity rather than isolated activation impairments. These findings represent an important extension of the existing literature since improved understanding of neural pathways underlying depression-related reward dysfunctions, may help currently unmet diagnostic and therapeutic efforts.

Probabilistic Reinforcement Learning and Anhedonia

Despite the prominence of anhedonic symptoms associated with diverse neuropsychiatric conditions, there are currently no approved therapeutics designed to attenuate the loss of responsivity to previously rewarding stimuli. However, the search for improved treatment options for anhedonia has been reinvigorated by a recent reconceptualization of the very construct of anhedonia, including within the Research Domain Criteria (RDoC) initiative. This chapter will focus on the RDoC Positive Valence Systems construct of reward learning generally and sub-construct of probabilistic reinforcement learning specifically. The general framework emphasizes objective measurement of a subject's responsivity to reward via reinforcement learning under asymmetrical probabilistic contingencies as a means to quantify reward learning. Indeed, blunted reward responsiveness and reward learning are central features of anhedonia and have been repeatedly described in major depression. Moreover, these probabilistic reinforcement techniques can also reveal neurobiological mechanisms to aid development of innovative treatment approaches. In this chapter, we describe how investigating reward learning can improve our understanding of anhedonia via the four RDoC-recommended tasks that have been used to probe sensitivity to probabilistic reinforcement contingencies and how such task performance is disrupted in various neuropsychiatric conditions. We also illustrate how reverse translational approaches of probabilistic reinforcement assays in laboratory animals can inform understanding of pharmacological and physiological mechanisms. Next, we briefly summarize the neurobiology of probabilistic reinforcement learning, with a focus on the prefrontal cortex, anterior cingulate cortex, striatum, and amygdala. Finally, we discuss treatment implications and future directions in this burgeoning area.

Chronic social defeat stress impairs goal-directed behavior through dysregulation of ventral hippocampal activity in male mice

Chronic stress is a risk factor for a variety of psychiatric disorders, including depression. Although impairments to motivated behavior are a major symptom of clinical depression, little is known about the circuit mechanisms through which stress impairs motivation. Furthermore, research in animal models for depression has focused on impairments to hedonic aspects of motivation, whereas patient studies suggest that impairments to appetitive, goal-directed motivation contribute significantly to motivational impairments in depression. Here, we characterized goal-directed motivation in repeated social defeat stress (R-SDS), a well-established mouse model for depression in male mice. R-SDS impaired the ability to sustain and complete goal-directed behavior in a food-seeking operant lever-press task. Furthermore, stress-exposed mice segregated into susceptible and resilient subpopulations. Interestingly, susceptibility to stress-induced motivational impairments was unrelated to stress-induced social withdrawal, another prominent effect of R-SDS in mouse models. Based on evidence that ventral hippocampus (vHP) modulates sustainment of goal-directed behavior, we monitored vHP activity during the task using fiber photometry. Successful task completion was associated with suppression of ventral hippocampal neural activity. This suppression was diminished after R-SDS in stress-susceptible but not stress-resilient mice. The serotonin selective reuptake inhibitor (SSRI) escitalopram and ketamine both normalized vHP activity during the task and restored motivated behavior. Furthermore, optogenetic vHP inhibition was sufficient to restore motivated behavior after stress. These results identify vHP hyperactivity as a circuit mechanism of stress-induced impairments to goal-directed behavior and a putative biomarker that is sensitive to antidepressant treatments and that differentiates susceptible and resilient individuals.

The Effects of Anhedonia in Social Context

Purpose of Review

Anhedonia is a transdiagnostic symptom comprising reduced subjective reward or pleasure. Anhedonia influences subjective anticipation and in-the-moment experiences. This review draws together affective learning and engagement evidence for anhedonia affecting subjective experiences of social environments.

Recent Findings

While social engagement is diminished consistently, subjective appraisals of social contexts vary across different mental health disorders. Low positive affect during social experiences or stimuli is reported in PTSD, mood, schizophrenia, and anxiety disorders. Diminished neural reward networks underpin the anticipation of social experiences in ADHD, schizophrenia spectrum, and autistic spectrum disorders. Multiple theories exist to explain how anhedonia might interfere with social environments.

Summary

Anhedonia is a barrier to engagement, motivation, and enjoyment of social contexts. While many studies characterize experiences during social contexts, learning theories provide the most promise for developing targeted interventions.

Elevated peripheral inflammation is associated with attenuated striatal reward anticipation in major depressive disorder

BACKGROUND

Major depressive disorder (MDD) is the leading cause of years lived with disability worldwide, and up to 40% of individuals with MDD do not respond to current treatments. Studies suggest that peripheral inflammation plays an important role in the striatal mesolimbic dopamine pathway and corticostriatal reward circuitry in MDD. Although MDD patients show blunted striatal responses to reward, the link between degree of inflammation and attenuation of reward processing is unclear. We investigated whether MDD patients with elevated peripheral inflammation exhibit attenuated reward responses to enhance our understanding of MDD pathophysiology and develop more effective treatments for current non-responders.

METHODS

MDD subjects varying on serum C-reactive protein (CRP) concentrations (MDD-High CRP, >3 mg/L, n = 44; MDD-Low CRP, <3 mg/L, n = 44) and healthy comparisons (HC, n = 44) completed a monetary incentive delay (MID) task and provided blood samples to measure inflammation-related markers. MDD-High and MDD-Low were propensity score-matched on age, sex, body mass index (BMI), smoking status, exercise and MID task head motion. Percent change in blood oxygen level-dependent (BOLD) signal during anticipation of wins and losses was extracted from bilateral nucleus accumbens, dorsal caudate and dorsolateral putamen regions of interest (ROIs). A linear mixed-effects model was used to test group (MDD-High, MDD-Low and HC), condition (large-win, small-win and no win), and their interaction for these ROIs as well as whole-brain voxelwise data. Analyses also tested group differences in inflammatory mediators. Correlations were used to explore the relationship between inflammatory mediators and brain regions showing differences between MDD-High and MDD-Low.

RESULTS

MDD-High exhibited: (a) lower BOLD signal change in dorsal caudate, thalamus, left insula and left precuneus during anticipation of small wins than MDD-Low; and (b) higher serum soluble intercellular adhesion molecule 1 (sICAM-1) and interleukin 6 (IL-6) concentrations than MDD-Low and HC. MDD as a whole, regardless of CRP-based inflammation, exhibited: (a) lower precuneus BOLD signal change to large wins than HC; and (b) higher Interleukin 1 receptor antagonist (IL-1ra), macrophage-derived chemokine (MDC) and macrophage inflammatory protein-1 alpha (MIP-1α) concentrations than HC. Higher serum sICAM-1 concentrations were associated with lower caudate BOLD signal change to small wins only within the MDD-High group.

CONCLUSION

Within MDD patients, high inflammation (CRP, sICAM-1) was linked to reduced striatal activation recruited to discriminate intermediate reward magnitudes. These findings support an association between levels of peripheral inflammation and the degree of reward-related activation in individuals with MDD.

REGISTRATION OF CLINICAL TRIALS

The ClinicalTrials.gov identifier for the clinical protocol associated with data published in this current paper is NCT02450240, "Latent Structure of Multi-level Assessments and Predictors of Outcomes in Psychiatric Disorders."

Translational Assessments of Reward Responsiveness in the Marmoset

BACKGROUND

Anhedonia, the loss of pleasure in previously rewarding activities, is a prominent feature of major depressive disorder and often resistant to first-line antidepressant treatment. A paucity of translatable cross-species tasks to assess subdomains of anhedonia, including reward learning, presents a major obstacle to the development of effective therapeutics. One assay of reward learning characterized by orderly behavioral and pharmacological findings in both humans and rats is the probabilistic reward task. In this computerized task, subjects make discriminations across numerous trials in which correct responses to one alternative are rewarded more often (rich) than correct responses to the other (lean). Healthy control subjects reliably develop a response bias to the rich alternative. However, participants with major depressive disorder as well as rats exposed to chronic stress typically exhibit a blunted response bias.

METHODS

The present studies validated a touchscreen-based probabilistic reward task for the marmoset, a small nonhuman primate with considerable translational value. First, probabilistic reinforcement contingencies were parametrically examined. Next, the effects of ketamine (1.0-10.0 mg/kg), a US Food and Drug Administration-approved rapid-acting antidepressant, and phencyclidine (0.01-0.1 mg/kg), a pharmacologically similar N-methyl-D-aspartate receptor antagonist with no known antidepressant efficacy, were evaluated.

RESULTS

Increases in the asymmetry of rich:lean probabilistic contingencies produced orderly increases in response bias. Consistent with their respective clinical profiles, ketamine but not phencyclidine produced dose-related increases in response bias at doses that did not reduce task discriminability.

CONCLUSIONS

Collectively, these findings confirm task and pharmacological sensitivity in the marmoset, which may be useful in developing medications to counter anhedonia across neuropsychiatric disorders.

Empirical validation of a touchscreen probabilistic reward task in rats

Anhedonia, the loss of pleasure from previously rewarding activities, is implicated in several neuropsychiatric conditions, including major depressive disorder (MDD). In order to accelerate drug development for mood disorders, quantitative approaches are needed to objectively measure responsiveness to reward as a means to identify deficits. One such approach, the probabilistic reward task (PRT), uses visual discrimination methodology to quantify reward learning. In this computerized task, humans make visual discriminations, and probabilistic contingencies are arranged such that correct responses to one alternative are rewarded more often (rich) than correct responses to the other (lean). Healthy participants consistently develop a response bias in favor of the rich alternative. However, participants with MDD typically exhibit lower response biases, and this blunting correlates with current and future anhedonia. The present studies validated a touchscreen-based PRT in rodents with formal and functional similarity to the human task. First, rats were trained to discriminate between two lines that differed in length. Next, parametric manipulations of probabilistic contingencies, line-length stimuli, and drug treatment (amphetamine, 0.32-3.2 mg/kg; scopolamine, 0.1-1.0 mg/kg; oxycodone, 0.1-1.0 mg/kg) on response bias were evaluated. Results demonstrated orderly shifts in bias and discriminability that varied as a function of, respectively, the asymmetry of rich/lean probabilities and disparity in line lengths. Drugs that enhance reward responsiveness (amphetamine and scopolamine, but not oxycodone) increased bias, verifying pharmacological task sensitivity. Finally, performance outcomes under optimized conditions were replicated in female rats. Collectively, the touchscreen-based rodent PRT appears to have high preclinical value as a quantitative assay of reward learning.

Changing the future: An initial test of Future Specificity Training (FeST)

A range of psychiatric disorders are characterised by impairments in episodic future thinking (EFT), and particularly simulating specific, spatiotemporally-located future events. No study has examined whether training can lead to sustained improvement in specific EFT. In this study, participants (N = 60; M age = 31, SD = 13.2) were randomized to a two-session, group-based future thinking program (Future Specificity Training; FeST) or wait-list. At follow-up the training group, relative to wait-list, showed large, statistically-significant improvements in the ability to mentally simulate specific EFT (d = .82), increases in detail (d = 1.32), use of mental imagery (d = 1.32), anticipated (d = 1.78) and anticipatory pleasure (d = 1.07), perceived control (d = 1.20), and likelihood of occurrence (d = 1.09). Some effects were also observed on positive, generalised future self-states. In the context of inherent limitations of subjective reporting in trials, this study provides evidence that EFT specificity can be enhanced, and the effects of FeST indicate a possible avenue to disrupt psychopathological processes.

Anhedonia in Depressive Disorder: A Narrative Review

Since the introduction of DSM-III anhedonia has become a core depressive criterion and is defined as the loss of interest or pleasure. Although the origin of the word goes back to the end of the 19th century and numerous anhedonic symptoms are described in classic texts on depression, this centrality in the diagnosis of depression is only recent. Anhedonia is best described as a symptom complex with unclear boundaries cutting across the tripartite model of the mind (affect, volition, and cognition). Popular concepts of anhedonia pertain to the pleasure cycle and positive affectivity. These concepts partially overlap and are often mixed up, but clearly stem from different theoretical backgrounds: the affective science of reward processing versus more general, dimensional modelling of affect. The former concept seems more suitable to understand anhedonic emotions, the latter more suitable to understand anhedonic mood or trait. This narrative review covers the history of "anhedonia," the different anhedonic phenomena, and psychopathological concepts. An attempt is made to go beyond a merely descriptive psychopathology. Neurobiological and psychological insights shed a light on how symptoms are made and interconnected; these insights possibly call for a new psychopathological language.

Impairments in episodic future thinking for positive events and anticipatory pleasure in major depression

BACKGROUND

Characteristic of the cardinal symptom of anhedonia, people with clinical depression report lower levels of anticipatory pleasure. However, the psychological mechanisms underlying these deficits are poorly understood. This is the first study to assess whether, and to what extent, phenomenological characteristics of episodic future thinking for positive future events are associated with anticipatory pleasure among depressed individuals.

METHODS

Individuals with a Major Depressive Episode (MDE; N = 117) and without (N = 47) completed ratings scales for depressive symptoms and trait anticipatory and consummatory pleasure. They then provided descriptions of personally-relevant positive future events and rated them for phenomenological characteristics and state anticipatory pleasure.

RESULTS

Between-groups analysis showed that those with MDE reported lower trait anticipatory and consummatory pleasure. They also simulated future events with less specificity, less detail/vividness, less use of mental imagery, less use of first-person perspective, less plausibility/perceived likelihood of occurring, and reported less associated state anticipatory pleasure. In regression analyses in the depressed group, lower scores for detail/vividness, mental imagery, and personal significance all uniquely predicted lower state anticipatory pleasure.

LIMITATIONS

Cognitive functioning was not assessed, which may help clarify deficits that underpin these findings. History of previous depressive episodes in the comparison group were not assessed, which may mean the observed between-group effects are underestimated.

CONCLUSIONS

This study provides further evidence of deficits in episodic future thinking and anticipatory pleasure in depressed individuals. It also establishes links between particular characteristics of episodic future thinking and state anticipatory pleasure, and indicates cognitive targets that may be amenable to intervention in order to reduce anhedonia.

Machine Learning Identifies Large-Scale Reward-Related Activity Modulated by Dopaminergic Enhancement in Major Depression

BACKGROUND

Theoretical models have emphasized systems-level abnormalities in major depressive disorder (MDD). For unbiased yet rigorous evaluations of pathophysiological mechanisms underlying MDD, it is critically important to develop data-driven approaches that harness whole-brain data to classify MDD and evaluate possible normalizing effects of targeted interventions. Here, using an experimental therapeutics approach coupled with machine learning, we investigated the effect of a pharmacological challenge aiming to enhance dopaminergic signaling on whole-brain response to reward-related stimuli in MDD.

METHODS

Using a double-blind, placebo-controlled design, we analyzed functional magnetic resonance imaging data from 31 unmedicated MDD participants receiving a single dose of 50 mg amisulpride (MDD_Amisulpride), 26 MDD participants receiving placebo (MDD_Placebo), and 28 healthy control subjects receiving placebo (HC_Placebo) recruited through two independent studies. An importance-guided machine learning technique for model selection was used on whole-brain functional magnetic resonance imaging data probing reward anticipation and consumption to identify features linked to MDD (MDD_Placebo vs. HC_Placebo) and dopaminergic enhancement (MDD_Amisulpride vs. MDD_Placebo).

RESULTS

Highly predictive classification models emerged that distinguished MDD_Placebo from HC_Placebo (area under the curve = 0.87) and MDD_Placebo from MDD_Amisulpride (area under the curve = 0.89). Although reward-related striatal activation and connectivity were among the most predictive features, the best truncated models based on whole-brain features were significantly better relative to models trained using striatal features only.

CONCLUSIONS

Results indicate that in MDD, enhanced dopaminergic signaling restores abnormal activation and connectivity in a widespread network of regions. These findings provide new insights into the pathophysiology of MDD and pharmacological mechanism of antidepressants at the system level in addressing reward processing deficits among depressed individuals.

Affective biases and their interaction with other reward-related deficits in rodent models of psychiatric disorders

Major depressive disorder (MDD) is one of the leading global causes of disability. Symptoms of MDD can vary person to person, and current treatments often fail to alleviate the poor quality of life that patients experience. One of the two core diagnostic criteria for MDD is the loss of interest in previously pleasurable activities, which suggests a link between the disease aetiology and reward processing. Cognitive impairments are also common in patients with MDD, and more recently, emotional processing deficits known as affective biases have been recognised as a key feature of the disorder. Studies in animals have found similar affective biases related to reward. In this review we consider these affective biases in the context of other reward-related deficits and examine how affective biases associated with learning and memory may interact with the wider behavioural symptoms seen in MDD. We discuss recent developments in how analogues of affective biases and other aspects of reward processing can be assessed in rodents, as well as how these behaviours are influenced in models of MDD. We subsequently discuss evidence for the neurobiological mechanisms contributing to one or more reward-related deficits in preclinical models of MDD, identified using these behavioural assays. We consider how the relationships between these selective behavioural assays and the neurobiological mechanisms for affective bias and reward processing could be used to identify potential treatment strategies.

Updating Apathy: Using Research Domain Criteria to Inform Clinical Assessment and Diagnosis of Disorders of Motivation

Clinical observations regarding apathy and motivation derived from many psychiatric and neurological conditions have generated divergent descriptions of apathy-related syndromes. Stimulated by complex cases presenting with prominent apathy, uses of the term "apathy" and "related phenomena" in the Diagnostic and Statistical Manual of Mental Disorders, diagnostic proposals for apathy as a syndrome and disorder of motivation, Research Domain Criteria (RDoC) systems governing motivational processes, and their clinical intersections are reviewed. Clinical apathy and associated dysfunctions can be addressed using constructs suggested by the RDoC domain of Positive Valence Systems, including approach motivation and component processes of reward valuation, effort valuation/willingness to work, expectancy/reward prediction error, and responses to reward and reward learning. Although apathy syndromes have been validated, defining potentially distinct disorders of motivation (not simply subordinated to mood, psychotic, cognitive, or substance use disorders) will require additional research to better delineate etiology and pathogenesis, predictive validators, reliable diagnostic methods, treatments, and demonstrations of use for these diagnostic proposals.

Aberrant reward dynamics in trait anticipatory anhedonia

As a cardinal feature of several psychiatric disorders, anhedonia includes a consummatory component (deficits in hedonic response to rewards) and an anticipatory component (a reduced motivation to pursue them). Although being conceptualized as impairments of reward system, the neural characterization of reward processing in anhedonia is hampered by the enormous heterogeneity in the reward phase (‘wanting’ vs ‘liking’) and comorbidity (inherent to disease states). The current event-related potential (ERP) study examined the reward dynamics of anticipatory anhedonia in a non-clinical sample. Anticipatory and consummatory ERP components were assessed with a monetary incentive delay task in a high anticipatory anhedonia (HAA) group and a low anticipatory anhedonia (LAA) group. HAA vs LAA group showed a diminished reward-related speeding during behavioral performance and reported overall reduced positive affect during anticipation and receipt of outcomes. Importantly, neural dynamics underlying reward processing were negatively associated with anticipatory anhedonia across the anticipatory phase indexed by the contingent negative variation and the consummatory phase indexed by the feedback P3. Our results suggest that anticipatory anhedonia in non-clinical individuals is linked to a poor modulation during both anticipatory and consummatory phases of reward processing.

Why not try harder? Computational approach to motivation deficits in neuro-psychiatric diseases

Motivation deficits, such as apathy, are pervasive in both neurological and psychiatric diseases. Even when they are not the core symptom, they reduce quality of life, compromise functional outcome and increase the burden for caregivers. They are currently assessed with clinical scales that do not give any mechanistic insight susceptible to guide therapeutic intervention. Here, we present another approach that consists of phenotyping the behaviour of patients in motivation tests, using computational models. These formal models impose a precise and operational definition of motivation that is embedded in decision theory. Motivation can be defined as the function that orients and activates the behaviour according to two attributes: a content (the goal) and a quantity (the goal value). Decision theory offers a way to quantify motivation, as the cost that patients would accept to endure in order to get the benefit of achieving their goal. We then review basic and clinical studies that have investigated the trade-off between the expected cost entailed by potential actions and the expected benefit associated with potential rewards. These studies have shown that the trade-off between effort and reward involves specific cortical, subcortical and neuromodulatory systems, such that it may be shifted in particular clinical conditions, and reinstated by appropriate treatments. Finally, we emphasize the promises of computational phenotyping for clinical purposes. Ideally, there would be a one-to-one mapping between specific neural components and distinct computational variables and processes of the decision model. Thus, fitting computational models to patients' behaviour would allow inferring of the dysfunctional mechanism in both cognitive terms (e.g. hyposensitivity to reward) and neural terms (e.g. lack of dopamine). This computational approach may therefore not only give insight into the motivation deficit but also help personalize treatment.

Targeting opioid dysregulation in depression for the development of novel therapeutics

Since the serendipitous discovery of the first class of modern antidepressants in the 1950's, all pharmacotherapies approved by the Food and Drug Administration for major depressive disorder (MDD) have shared a common mechanism of action, increased monoaminergic neurotransmission. Despite the widespread availability of antidepressants, as many as 50% of depressed patients are resistant to these conventional therapies. The significant length of time required to produce meaningful symptom relief with these medications, 4-6 weeks, indicates that other mechanisms are likely involved in the pathophysiology of depression which may yield more viable targets for drug development. For decades, no viable candidate target with a different mechanism of action to that of conventional therapies proved successful in clinical studies. Now several exciting avenues for drug development are under intense investigation. One of these emerging targets is modulation of endogenous opioid tone. This review will evaluate preclinical and clinical evidence pertaining to opioid dysregulation in depression, focusing on the role of the endogenous ligands endorphin, enkephalin, dynorphin, and nociceptin/orphanin FQ (N/OFQ) and their respective receptors, mu (MOR), delta (DOR), kappa (KOR), and the N/OFQ receptor (NOP) in mediating behaviors relevant to depression and anxiety. Finally, putative opioid based antidepressants that are under investigation in clinical trials, ALKS5461, JNJ-67953964 (formerly LY2456302 and CERC-501) and BTRX-246040 (formerly LY-2940094) will be discussed. This review will illustrate the potential therapeutic value of targeting opioid dysregulation in developing novel therapies for MDD.

Reward systems and cognitions in Major Depressive Disorder

A lack of motivation and anhedonia represent frequent and pervasive symptoms in depression, although with poor specificity. Historically described as a response bias, reward-related impairments in depression may account for the important aspects of the cognitive impairments associated with diagnosis of major depressive disorder. Reward processing is a broad psychological construct that can be parsed into 3 distinct components known as "reinforcement learning" (learning), "reward responsiveness" (liking), and "motivation to obtain a reward" (wanting). Depressed patients respond hyposensitively to reward and maladaptively to punishment: this pattern is related to a dysfunction in the frontostriatal systems modulated by the monoamine systems; seems to be observed in medicated and unmedicated patients with depression and in healthy individuals with high levels of anhedonia; and could be observed in patients with a history of depression, even when in full remission. Considered to be cognitive impairments, reward-related-impairments may also constitute part of an underlying neurobiological vulnerability to major depressive disorder (MDD). For example, the reward-related impairment is state dependent and, more or less, correlated with symptom severity in some studies but has also been proposed as being trait like, with endophenotype characteristics, possibly contributing to the persistence of the disease or treatment resistance. The 3 core aspects of reward processing have specific neurobiological correlates that involve the ventral and dorsal striatum, lateral habenula, ventral tegmental area, orbitofrontal cortex, anterior cingulate cortex, and ventromedial and dorsolateral prefrontal cortex. These structures underline the important role of the dopaminergic mesolimbic pathway, but glutamate and serotonin could also have an important role, at least in some aspects of reward-related impairments.

Translational Assessments of Reward and Anhedonia: A Tribute to Athina Markou

Loss of pleasure (clinically referred to as anhedonia), impairments in other reward-related processes such as reward learning, motivation, and reward valuation, and blunted affect characterize several mood and other psychiatric disorders. Despite the availability of many therapeutic options for these disorders, reward-related impairments remain challenging to treat and often persist despite alleviation of other symptoms. Lack of animal models of reward-related impairments and affect that have high construct and predictive validity is a key obstacle to developing novel treatments. This review highlights 1) guidelines to consider when developing translatable animal models; and 2) recent efforts to develop new reward-related assessments in humans and nonhuman animals that have been translated or back-translated from one species to another. The procedures described in this review are used to assess aspects of reward learning, motivated behavior, reward valuation, and affect. In several cases, researchers have attempted to implement task parameters that are as identical as possible to the parallel parameters used in existing cross-species tasks, with the goal of improving the translation of preclinical drug discovery findings to the clinic. In this regard, Dr. Athina Markou, who worked tirelessly throughout her career to understand and treat reward-related impairments across several psychiatric disorders, had great influence on conceptualizing the development and use of translational animal models of reward-related processes.

La motivation dans tous ses K

La motivation peut être définie comme la fonction qui oriente et active le comportement. Nous résumons dans cette revue les acquis récents des neurosciences concernant les bases cérébrales des fonctions motivationnelles. En clinique neuropsychiatrique, les troubles de la motivation sont fréquents et actuellement évalués par des échelles qui ne renseignent pas sur les mécanismes sous-jacents. Nous présentons ici une nouvelle approche, dite computationnelle. Elle consiste à phénotyper le comportement des patients dans des tests de motivation, au moyen de modèles computationnels. Ces phénotypes computationnels caractérisent l’état du patient et pourraient aider au suivi et à la personnalisation du traitement.

Depression severity and quality of life of qualified and unqualified patients with a mood disorder for a research study targeting anhedonia in a clinical sample

OBJECTIVE

To investigate the depression severity and quality of life of qualified and unqualified patients with a mood disorder for a research study based on anhedonia severity.

METHODS

Diagnosis of major depressive disorder (MDD) or bipolar disorder (BPD) was ascertained with the MINI International Neuropsychiatric Interview. The severity of depression was measured with the 16-item Quick Inventory of Depressive Symptomatology-Self-Report (QIDS-16-SR), and Item 5, "feeling sad (sadness)," QIDS-16-SR Item 13, "change in general interest," was used to measure the severity of anhedonia. The quality of life was measured with the Quality of Life, Enjoyment and Satisfaction Questionnaire (Q-LES-Q).

RESULTS

Of 96 patients with MDD and 147 with bipolar I or II disorder, the severity rating on sadness and anhedonia was similar. The severities of anhedonia and sadness were highly correlated with R² of ≥0.91. Without considering depressive severity, 55% of patients would be eligible for a study if≥mild anhedonia was used as a severity criterion, but only 26% of patients eligible for a study if≥moderate anhedonia was used without considering substance use and medical comorbidities. If patients with ≥ moderate overall depressive symptoms were considered, 88.1% of patients would be eligible if≥mild anhedonia was required for a study, and 45.2% of patients would be eligible for a study if≥moderate anhedonia was required. For those who were unqualified for the study based on≥moderate anhedonia, about 1/3 had≥moderate overall depressive symptoms and less than 40% of maximum possible scores of Q-LES-Q. If only patients in remission based on overall depressive symptom severity were considered for a study of anhedonia, no patient would be eligible for the study.

CONCLUSION

Depressive mood and anhedonia are highly correlated. Screening patients with a mood disorder and an overall moderate depressive severity is a cost-effective approach for a study targeting anhedonia, especially for a study requiring≥moderate severity of anhedonia. However, 1/3 of the unqualified patients will have≥moderate overall depressive symptoms and poor quality of life.

Effects of levomilnacipran ER on noradrenergic symptoms, anxiety symptoms, and functional impairment in adults with major depressive disorder: Post hoc analysis of 5 clinical trials

OBJECTIVE

To evaluate the effects of levomilnacipran extended-release (LVM-ER; 40-120mg/day) on noradrenergic (NA) and anxiety-related symptoms in adults with major depressive disorder (MDD) and explore the relationship between these symptoms and functional impairment.

METHODS

Data were pooled from 5 randomized, double-blind, placebo-controlled trials (N=2598). Anxiety and NA Cluster scores were developed by adding selected item scores from the Montgomery-Åsberg Depression Rating Scale (MADRS) and 17-item Hamilton Depression Rating Scale (HAMD₁₇). A path analysis was conducted to estimate the direct effects of LVM-ER on functional impairment (Sheehan Disability Scale [SDS] total score) and the indirect effects through changes in NA and Anxiety Cluster scores.

RESULTS

Mean improvements from baseline in NA and Anxiety Cluster scores were significantly greater with LVM-ER versus placebo (both P<0.001), as were the response rates (≥50% score improvement): NA Cluster (44% vs 34%; odds ratio=1.56; P<0.0001); Anxiety Cluster (39% vs 36%; odds ratio=1.19; P=0.041). Mean improvement in SDS total score was also significantly greater with LVM-ER versus placebo (-7.3 vs -5.6; P<0.0001). LVM-ER had an indirect effect on change in SDS total score that was mediated more strongly through NA Cluster score change (86%) than Anxiety Cluster score change (18%); the direct effect was negligible.

LIMITATIONS

NA and Anxiety Cluster scores, developed based on the face validity of individual MADRS and HAMD₁₇ items, were not predefined as efficacy outcomes in any of the studies.

CONCLUSION

In adults with MDD, LVM-ER indirectly improved functional impairment mainly through improvements in NA symptoms and less so via anxiety symptoms.

The International College of Neuropsychopharmacology (CINP) Treatment Guidelines for Bipolar Disorder in Adults (CINP-BD-2017), Part 4: Unmet Needs in the Treatment of Bipolar Disorder and Recommendations for Future Research

BACKGROUND

The current fourth paper on the International College of Neuropsychopharmacology guidelines for the treatment of bipolar disorder reports on the unmet needs that became apparent after an extensive review of the literature and also serves as a conclusion to the project of the International College of Neuropsychopharmacology workgroup.

MATERIALS AND METHODS

The systematic review of the literature that was performed to develop the International College of Neuropsychopharmacology guidelines for bipolar disorder identified and classified a number of potential shortcomings.

RESULTS

Problems identified concerned the reliability and validity of the diagnosis of bipolar disorder and especially of bipolar depression. This, in turn, has profound consequences for early detection and correct treatment of the disorder. Another area that needs improvement is the unsatisfactory efficacy and effectiveness of therapeutic options, especially in special populations such as those with mixed features and rapid cycling course. Gender issues and adherence problems constitute an additional challenge. The literature suggests that while treatment providers are concerned more with treatment-related issues, patients and their caregivers worry more about issues pertaining to the availability of services and care, quality of life, and various types of burden. The workgroup identified additional unmet needs related to the current standard of research in bipolar disorder. These include the fragmentation of bipolar disorder into phases that are handled as being almost absolutely independent from each other, and thus the development of an overall therapeutic strategy on the basis of the existing evidence is very difficult. Trials are not always designed in a way that outcomes cover the most important aspects of bipolar disorder, and often the reporting of the results is biased and unsatisfactory. The data on combination treatments and high dosages are sparse, whereas they are common in real world practice.

CONCLUSIONS

The workgroup endorses the full release of raw study data to the scientific community, and the development of uniform clinical trial standards (also including more realistic outcomes) and the reporting of results. The 2 large appendices summarize the results of this systematic review with regard to the areas of lack of knowledge where further focused research is necessary.

Effects of levomilnacipran extended-release on motivation/energy and functioning in adults with major depressive disorder

The objective of this post-hoc analysis was to investigate the relationship between motivation/energy and functional impairment in patients with major depressive disorder (MDD). Data were taken from a phase 3 trial of levomilnacipran extended-release (ER) in adults with MDD (NCT01034462; N=429) that used the 18-item Motivation and Energy Inventory (MEI) to assess motivation/energy. Two subgroups with lower and higher motivation/energy were defined using baseline MEI total scores (≤28 and >28, respectively). Change from baseline in the Sheehan Disability Scale (SDS) total score was analyzed in the intent-to-treat (ITT) population and both subgroups. Path analyses were carried out in the ITT population and a lower MEI subgroup to assess the direct and indirect effects of levomilnacipran ER on SDS total score change. In the ITT population and the lower MEI subgroup, significant differences were found between levomilnacipran ER and placebo for changes in the SDS total score (-2.6 and -3.9, both P<0.01), but not in the higher MEI subgroup. The indirect effect of levomilnacipran ER on SDS total score improvement, as mediated by MEI total score change, was 79.9% in the lower MEI subgroup and 67.2% in the ITT population. Levomilnacipran ER was previously shown to improve motivation/energy in adults with MDD. The current analysis indicates that improvements in functional impairment were considerably mediated by improvements in motivation/energy, particularly in patients with lower motivation/energy at baseline.

Selective amotivation deficits following chronic psychosocial stress in mice

Amotivation is a major symptom of several psychiatric disorders. However, which specific motivations are most affected in various illnesses is not well understood. In major depressive disorder (MDD), anecdotal evidence suggests the motivation to explore may be especially affected, but direct evidence from either patients or animal models is lacking. To investigate the potential for, and nature of, exploratory drive deficits in MDD, we subjected mice to a chronic social defeat (CSD) manipulation that gives rise to a MDD-like behavioural ensemble, and performed a behavioural battery to examine bodyweight homeostasis, ambulation, anxiety, exploratory behaviour motivated by either novelty or fear, and short-term memory. Consistent with previous reports, we found a disruption of bodyweight homeostasis and reduced ambulation following CSD treatment, but we found no evidence for anxiogenic effects or impairments in short-term memory. Surprisingly, we also observed profoundly delayed and diminished exploration of novel, safe space following CSD, while exploration motivated by fear remained intact. These results extend our knowledge of the behavioural phenotypes in mice resulting from CSD by homing in on specific motivational drives. In MDD patients, reduced exploration could compound disease symptomatology by preventing engagement in what could be rewarding exploration experiences, and targeting deficits in the motivation to explore may represent a novel avenue for treatment.

Reward Processing and Risk for Depression Across Development

Striatal response to reward has been of great interest in the typical development and psychopathology literatures. These parallel lines of inquiry demonstrate that although typically developing adolescents show robust striatal response to reward, adolescents with major depressive disorder (MDD) and those at high risk for MDD show a blunted response to reward. Understanding how these findings intersect is crucial for the development and application of early preventative interventions in at-risk children, ideally before the sharp increase in the rate of MDD onset that occurs in adolescence. Robust findings relating blunted striatal response to reward and MDD risk are reviewed and situated within a normative developmental context. We highlight the need for future studies investigating longitudinal development, specificity to MDD, and roles of potential moderators and mediators.

Diminished effort on a progressive ratio task in both unipolar and bipolar depression

BACKGROUND

Amotivation, or decisional anhedonia, is a prominent and disabling feature of depression. However, this aspect of depression remains understudied, and no prior work has applied objective laboratory tests of motivation in both unipolar and bipolar depression.

METHODS

We assessed motivation deficits using a Progressive Ratio Task (PRT) that indexes willingness to exert effort for monetary reward. The PRT was administered to 96 adults ages 18-60 including 25 participants with a current episode of unipolar depression, 28 with bipolar disorder (current episode depressed), and 43 controls without any Axis I psychiatric disorders.

RESULTS

Depressed participants exhibited significantly lower motivation than control participants as objectively defined by progressive ratio breakpoints. Both the unipolar and bipolar groups were lower than controls but did not differ from each other.

LIMITATIONS

Medication use differed across groups, and we did not have a separate control task to measure psychomotor activity; however neither medication effects or psychomotor slowing are likely to explain our findings.

CONCLUSIONS

Our study fills an important gap in the literature by providing evidence that diminished effort on the PRT is present across depressed patients who experience either unipolar or bipolar depression. This adds to growing evidence for shared mechanisms of reward and motivation dysfunction, and highlights the importance of improving the assessment and treatment of motivation deficits across the mood disorders spectrum.

Motivational deficits in major depressive disorder: Cross-sectional and longitudinal relationships with functional impairment and subjective well-being

BACKGROUND

Many individuals with major depressive disorder present with prominent motivational deficits; however, the effect of these symptoms on functional outcomes in the illness remains unclear.

METHOD

Individuals with major depression who participated in the Sequenced Treatment Alternatives to Relieve Depression study were included in the present investigation (N=1563). Motivational deficits were evaluated using a derived measure from the Hamilton Depression Rating Scale, while functioning was assessed using the Work and Social Adjustment Scale. Subjective outcomes were also evaluated using the Quality of Life Enjoyment and Satisfaction Questionnaire.

RESULTS

After treatment with citalopram, over 70% of participants continued to experience some degree of motivational deficits. These deficits were significantly associated with greater functional impairments both globally and in each domain of functioning evaluated. These symptoms were also linked to worse subjective outcomes such as overall life satisfaction and quality of life. Change in the severity of motivational deficits over time was significantly linked with changes in outcome. Motivational deficits continued to demonstrate a significant association with outcomes, even after controlling for potentially confounding variables such as duration of depressive episode and severity of other depressive symptoms.

CONCLUSIONS

Motivational deficits are significantly linked to the functional impairment present in many people with major depression, just as they are in other psychiatric illnesses such as schizophrenia. A greater understanding of the underlying mechanisms of these motivational deficits in particular, beyond other depressive symptoms, is critical to the development of strategies aimed at enhancing functional recovery and improved subjective well-being.

Dysfunctional Reward Processing in Depression

Anhedonia - diminished pleasure and/or decreased reactivity to pleasurable stimuli - is a core feature of depression that frequently persists after treatment. As a result, extensive effort has been directed towards characterizing the psychological and biological processes that mediate dysfunctional reward processing in depression. Reward processing can be parsed into sub-components that include motivation, reinforcement learning, and hedonic capacity, which, according to preclinical and neuroimaging evidence, involve partially dissociable brain systems. In line with this, recent findings indicate that behavioral impairments and neural abnormalities in depression vary across distinct reward-related constructs. Ultimately, improved understanding of precise reward-related dysfunctions in depression promises to improve diagnostic and therapeutic efforts in depression.

Reward processing dysfunction in major depression, bipolar disorder and schizophrenia

PURPOSE OF REVIEW

This article reviews the recent literature on reward processing dysfunction in major depression (MDD), bipolar disorder and schizophrenia, with a focus on approach motivation, reward learning and reward-based decision-making.

RECENT FINDINGS

Emerging evidence indicates the presence of reward processing abnormalities across all three disorders, supporting a transdiagnostic approach. In particular, findings are consistent with a role of abnormal phasic striatal dopamine signaling, which is critical for reinforcement learning, efficient mobilization of effort to obtain reward and allocation of attention to reward-predictive cues. Specifically, reward-related striatal signaling appears blunted in MDD and the negative symptoms of schizophrenia, elevated in bipolar (hypo)mania, and contextually misallocated in the positive symptoms of psychosis. However, whether shared or distinct pathophysiological mechanisms contribute to abnormal striatal signaling across the three disorders remains unknown.

SUMMARY

New evidence of reward processing abnormalities in MDD, bipolar disorder and schizophrenia has led to a greater understanding of the neural processes associated with symptomatology common across these conditions (e.g., anhedonia). Dissecting various subcomponents of reward processing that map onto partially different neurobiological pathways and investigating their dysregulation in different psychiatric disorders holds promise for developing more targeted, and hopefully efficacious treatment and intervention strategies.