Toward an objective characterization of an anhedonic phenotype: a signal-detection approach

Depression genetic risk score is associated with anhedonia-related markers across units of analysis

Investigations of pathophysiological mechanisms implicated in vulnerability to depression have been negatively impacted by the significant heterogeneity characteristic of psychiatric syndromes. Such challenges are also reflected in numerous null findings emerging from genome-wide association studies (GWAS) of depression. Bolstered by increasing sample sizes, recent GWAS studies have identified genetics variants linked to MDD. Among them, Okbay and colleagues (Nat. Genet. 2016 Jun;48(6):624-33) identified genetic variants associated with three well-validated depression-related phenotypes: subjective well-being, depressive symptoms, and neuroticism. Despite this progress, little is known about psychopathological and neurobiological mechanisms underlying such risk. To fill this gap, a genetic risk score (GRS) was computed from the Okbay's study for a sample of 88 psychiatrically healthy females. Across two sessions, participants underwent two well-validated psychosocial stressors, and performed two separate tasks probing reward learning both before and after stress. Analyses tested whether GRS scores predicted anhedonia-related phenotypes across three units of analyses: self-report (Snaith Hamilton Pleasure Scale), behavior (stress-induced changes in reward learning), and circuits (stress-induced changes in striatal reward prediction error; striatal volume). GRS scores were negatively associated with anhedonia-related phenotypes across all units of analyses but only circuit-level variables were significant. In addition, the amount of explained variance was systematically larger as variables were putatively closer to the effects of genes (self-report < behavior < neural circuitry). Collectively, findings implicate anhedonia-related phenotypes and neurobiological mechanisms in increased depression vulnerability, and highlight the value of focusing on fundamental dimensions of functioning across different units of analyses.

Effort-based decision-making is affected by overweight/obesity in major depressive disorder

BACKGROUND

Anhedonia and abnormalities in reward behavior are core features of major depressive disorder (MDD). Convergent evidence indicates that overweight/obesity (OW), a highly prevalent condition in MDD, is independently associated with reward disturbances. We therefore aimed to investigate the moderating effect of OW on the willingness to expend efforts for reward in individuals with MDD and healthy controls (HC).

METHODS

Forty-one adults (HC n = 20, MDD n = 21) completed the Effort Expenditure for Rewards Task (EEfRT), clinical and cognitive measures. Anthropometric parameters were assessed in all participants, and an additional evaluation of laboratorial parameters were conducted solely on those with MDD. Individuals with MDD were all on vortioxetine monotherapy (10-20 mg/day).

RESULTS

Interactions between reward magnitude, group and OW were observed (χ² = 9.192, p = 0.010); the OW-MDD group chose the hard task significantly less than normal weight (NW)-HC (p = 0.033) and OW-HC (p = 0.034), whereas there were no differences between NW-MDD and HCs. Within individuals with MDD, the proportion of hard task choices was more strongly correlated with body mass index (BMI) (r = -0.456, p = 0.043) and insulin resistance (HOMA2-IR) (r = -0.467, p = 0.038), than with depressive symptoms (r = 0.290, p = 0.214).

CONCLUSIONS

OW significantly moderated the association between MDD and willingness to make efforts for rewards. These findings offer novel evidence on the potential role of metabolic factors on the basis of anhedonia, and for the heuristic models proposing a pathophysiological connection between mood and metabolic disorders.

The role of avoidance motivation in the relationship between reward sensitivity and depression symptoms in adolescents: An ERP study

Blunted neural responses to reward in an EEG paradigm (RewP) are associated with vulnerability to depression, but the pathways linking this biomarker to depressive symptoms are unclear. We examined whether the relationship between reward response (RewP mean amplitude and latency) and depression was in part explained by approach-motivated behaviors in adolescents with varying levels of depression. EEG was collected during a game rigged to provide win/loss trials. Longer RewP latency was associated with depression symptoms only when scores on a measure of avoidance motivation were included. These results suggest that treatments targeting avoidance may decrease vulnerability to depressive episodes.

Difficulty in updating positive beliefs about negative cognition is associated with increased depressed mood

BACKGROUND AND OBJECTIVES

Depressed people hold positive beliefs about negative cognition (e.g., rumination is useful to find a solution), which may motivate those individuals to engage in sustained negative thinking. However, in reality, rumination often leads to unfavorable outcomes. Thus, such beliefs create a large discrepancy between one's expectations and the actual outcome. Therefore, we hypothesized that this prediction error would be associated with increased depressed mood.

METHODS

We observed how people update their positive beliefs about negative cognition within a volatile environment, in which negative cognition does not always result in a beneficial outcome. Forty-six participants were offered two response options (retrieving a negative or positive personal memory) and subsequently provided either an economic reward or punishment. Retrieving a negative (rather than positive) memory was initially reinforced, although this action-outcome contingency was reversed during the task. In the control condition, positive memory retrieval was initially reinforced, although a contingency reversal was employed to encourage negative memory retrieval.

RESULTS

Model-based computational modeling revealed that participants who showed a delay in switching from negative to positive (but not from positive to negative) responses experienced increased levels of depressed mood. This delay in switching was also found to be associated with depressive symptoms and trait rumination.

LIMITATIONS

The non-clinical nature of the sample may limit the clinical implications of the results.

CONCLUSIONS

Difficulty in updating positive beliefs (or outcome predictions) for negative cognition may play an important role in depressive symptomatology.

Cocaine-associated decision-making: Toward isolating preference

Ever-increasing evidence suggests that substance use disorder is mediated by decision-making processes, and as such, providing nondrug alternatives can shift maladaptive preferences away from drug reinforcers, such as cocaine. Of note, a recent hypothesis suggests that preference for cocaine is simply a byproduct of cocaine intake, such that the 'direct' effects of cocaine weaken the impact of non-drug alternatives while measuring choice. Conversely, existing quantitative theories of decision-making suggest preference is determined by various dimensions of concurrent reinforcers that in turn determine the relative value of available alternatives. Toward teasing apart the conflicting theories above, we developed a novel drug-choice procedure to control for reinforcer frequency and magnitude (two reinforcer dimensions well known to influence preference) that consequently controls for overall cocaine intake. As predicted by quantitative choice theory, results suggest that cocaine intake and preference are dissociable while measuring choice, with reinforcer frequency and magnitude having independent influence on the relative value of choice alternatives. Furthermore, we demonstrate that the choice procedure is sensitive to various manipulations known to alter cocaine reinforcement, all while keeping cocaine intake constant. Finally, the results point to the process of economic substitution as an important avenue of future neurobehavioral investigation toward the improvement of behavioral and pharmacological therapies for substance use disorders. Overall, the proposed choice procedure will allow for improved isolation of the neurobehavioral processes that mediate drug-associated decision-making in future studies.

Depressive symptoms are associated with blunted reward learning in social contexts

Depression is characterized by a marked decrease in social interactions and blunted sensitivity to rewards. Surprisingly, despite the importance of social deficits in depression, non-social aspects have been disproportionally investigated. As a consequence, the cognitive mechanisms underlying atypical decision-making in social contexts in depression are poorly understood. In the present study, we investigate whether deficits in reward processing interact with the social context and how this interaction is affected by self-reported depression and anxiety symptoms in the general population. Two cohorts of subjects (discovery and replication sample: N = 50 each) took part in an experiment involving reward learning in contexts with different levels of social information (absent, partial and complete). Behavioral analyses revealed a specific detrimental effect of depressive symptoms-but not anxiety-on behavioral performance in the presence of social information, i.e. when participants were informed about the choices of another player. Model-based analyses further characterized the computational nature of this deficit as a negative audience effect, rather than a deficit in the way others' choices and rewards are integrated in decision making. To conclude, our results shed light on the cognitive and computational mechanisms underlying the interaction between social cognition, reward learning and decision-making in depressive disorders.

Intact responses to non-drug rewards in long-term opioid maintenance treatment

Disruption of non-drug reward processing in addiction could stem from long-term drug use, addiction-related psychosocial stress, or a combination of these. It remains unclear whether long-term opioid maintenance treatment (OMT) disrupts reward processing. Here, we measured subjective and objective reward responsiveness in 26 previously heroin-addicted mothers in >7 years stable OMT with minimal psychosocial stress and illicit drug use. The comparison group was 30 healthy age-matched mothers (COMP). Objective reward responsiveness was assessed in a two-alternative forced-choice task with skewed rewards. Results were also compared to performance from an additional 968 healthy volunteers (meta-analytic approach). We further compared subprocesses of reward-based decisions across groups using computational modelling with a Bayesian drift diffusion model of decision making. Self-reported responsiveness to non-drug rewards was high for both groups (means: OMT = 6.59, COMP = 6.67, p = 0.84, BF₁₀ = 0.29), yielding moderate evidence against subjective anhedonia in this OMT group. Importantly, the mothers in OMT also displayed robust reward responsiveness in the behavioral task (t₁₉ = 2.72, p = 0.013, BF₁₀ = 3.98; d = 0.61). Monetary reward changed their task behavior to the same extent as the local comparison group (reward bias OMT = 0.12, COMP = 0.12, p = 0.96, BF₁₀ = 0.18) and in line with data from 968 healthy controls previously tested. Computational modelling revealed that long-term OMT did not even change decision subprocesses underpinning reward behavior. We conclude that reduced sensitivity to rewards and anhedonia are not necessary consequences of prolonged opioid use.

Engagement in Socially and Interpersonally Rewarding Activities as a Predictor of Outcome in "Engage" Behavioral Activation Therapy for Late-Life Depression

OBJECTIVE

Loneliness and social isolation are associated with depressive symptoms, cognitive and physical disabilities, and increased risk of mortality among older adults. Socially rewarding activities reduce loneliness, and neurobiological evidence suggests that these activities may activate neural reward systems in older adults to a greater extent than other rewarding experiences. The current study was designed to investigate whether engagement in social and interpersonal activities (i.e., exposure to social rewards) predicts subsequent increase in behavioral activation and reduction in depressive symptoms in reward exposure treatment for late-life depression.

METHODS

Forty-eight older adults without cognitive impairment and with major depression received nine sessions of "Engage" psychotherapy. Behavioral activation and depression severity were assessed by trained raters at baseline and weeks 6 and 9. Patients' weekly behavioral plans were categorized into three groups: 1) solitary activities; 2) social-group activities (attending a social gathering or a social setting such as church or a senior center); and 3) interpersonal-individual activities (engaging in an interpersonal interaction with a specific friend or family member).

RESULTS

Mixed-effects models showed reduction in depression severity and increase in behavioral activation over time. In linear regression models, a higher percentage of interpersonal-individual activities (but not solitary or social-group activities) predicted subsequent increase in behavioral activation and improvement of depression.

CONCLUSION

These findings highlight the importance of understanding the effects of engagement in specific types of rewarding activities in behavioral activation treatments for late-life depression. Exposure to socially rewarding interpersonal interactions could contribute to the efficacy of psychotherapy for late-life depression.

Incidental positive emotion modulates neural response to outcome valence in a monetarily rewarded gambling task

Choices are influenced by incidental emotions. To understand the neural mechanisms underlying the potential effects of incidental emotions on outcome processing, we conducted two experiments measuring feedback-related negativity (FRN) as a function of outcome (gain and loss) and emotional context. Experiment 1 used happy, neutral, and sad faces. Experiment 2 used pleasant, neutral, and unpleasant emotional scenes. We expected that incidental emotions would influence outcome processing at the behavioral level in line with the cognitive themes associated with each emotion. At a neural level, the effect of emotion based on outcome was expected in FRN. Participants chose one of two gambles presented on either side of an emotional face (Experiment 1) or on the scene (Experiment 2), and were later shown the outcome. Behaviorally, both the experiments showed emotion specific carryover effects on outcome experience in line with the cognitive appraisal tendencies associated with specific emotions. In both experiments, mean amplitude of FRN measured related to the outcome at Fz and FCz showed a significant effect of outcome with larger amplitude for loss compared to gain. The interaction between emotion and outcome was significant at FCz in Experiment 1 and at FPz in Experiment 2. The amplitude difference between loss and gain was larger for positive emotional context compared to neutral and negative emotional contexts, indicating a dopaminergic basis moderating the emotion-outcome processing interaction.

A neurophysiological measure of reward sensitivity and its association with anhedonia in psychiatrically healthy adolescents and young adults

Anhedonia (i.e., the attenuated ability to enjoy pleasurable stimuli) characterizes multiple mood disorders, but its neurophysiological underpinnings are not yet clear. Here, we measured event-related potentials in 116 adolescents and young adults engaged in an asymmetric reinforcement procedure designed to objectively characterize the anhedonic phenotype. In line with previous studies, the behavioral results showed that approximately 35% of the sample did not develop a response bias towards the more frequently rewarded stimuli (a sign of low hedonic capacity). The event-related potentials (ERPs) evoked by the reward feedback stimuli delivered during the task showed that individuals that did not develop a response bias had less cortical positivity at Fz from 224 ms to 316 ms post feedback onset compared to those that developed a response bias during the task. However, further analyses showed that this between groups difference was relatively weak, as it disappeared when we controlled for response-locked ERPs. Furthermore, the response bias observed in the asymmetric reinforcement procedure was not strongly associated with self-reported ratings of hedonic capacity. We conclude that even though the asymmetric reinforcement procedure may be used as a reward sensitivity measure in neurotypical adolescents and young adults, this task may only be able to detect clinically significant levels of anhedonia in this particular population.

Personalized prediction of antidepressant v. placebo response: evidence from the EMBARC study

BACKGROUND

Major depressive disorder (MDD) is a highly heterogeneous condition in terms of symptom presentation and, likely, underlying pathophysiology. Accordingly, it is possible that only certain individuals with MDD are well-suited to antidepressants. A potentially fruitful approach to parsing this heterogeneity is to focus on promising endophenotypes of depression, such as neuroticism, anhedonia, and cognitive control deficits.

METHODS

Within an 8-week multisite trial of sertraline v. placebo for depressed adults (n = 216), we examined whether the combination of machine learning with a Personalized Advantage Index (PAI) can generate individualized treatment recommendations on the basis of endophenotype profiles coupled with clinical and demographic characteristics.

RESULTS

Five pre-treatment variables moderated treatment response. Higher depression severity and neuroticism, older age, less impairment in cognitive control, and being employed were each associated with better outcomes to sertraline than placebo. Across 1000 iterations of a 10-fold cross-validation, the PAI model predicted that 31% of the sample would exhibit a clinically meaningful advantage [post-treatment Hamilton Rating Scale for Depression (HRSD) difference ⩾3] with sertraline relative to placebo. Although there were no overall outcome differences between treatment groups (d = 0.15), those identified as optimally suited to sertraline at pre-treatment had better week 8 HRSD scores if randomized to sertraline (10.7) than placebo (14.7) (d = 0.58).

CONCLUSIONS

A subset of MDD patients optimally suited to sertraline can be identified on the basis of pre-treatment characteristics. This model must be tested prospectively before it can be used to inform treatment selection. However, findings demonstrate the potential to improve individual outcomes through algorithm-guided treatment recommendations.

Mechanisms linking childhood adversity with psychopathology: Learning as an intervention target

Exposure to childhood adversity is common and a powerful risk factor for many forms of psychopathology. In this opinion piece, we argue for greater translation of knowledge about the developmental processes that are influenced by childhood adversity into targeted interventions to prevent the onset of psychopathology. Existing evidence has consistently identified several neurodevelopmental pathways that serve as mechanisms linking adversity with psychopathology. We highlight three domains in which these mechanisms are well-established and point to clear targets for intervention: 1) threat-related social information processing biases; 2) heightened emotional reactivity and difficulties with emotion regulation; and 3) disruptions in reward processing. In contrast to these established pathways, knowledge of how childhood adversity influences emotional learning mechanisms, including fear and reward learning, is remarkably limited. We see the investigation of these mechanisms as a critical next step for the field that will not only advance understanding of developmental pathways linking childhood adversity with psychopathology, but also provide clear targets for behavioral interventions. Knowledge of the mechanisms linking childhood adversity with psychopathology has advanced rapidly, and the time has come to translate that knowledge into clinical interventions to prevent the onset of mental health problems in children who have experienced adversity.

Inflammation and dimensions of reward processing following exposure to the influenza vaccine

BACKGROUND

Alterations in reward processing are a central feature of depression and may be influenced by inflammation. Indeed, inflammation is associated with deficits in reward-related processes in animal models and with dysregulation in reward-related neural circuitry in humans. However, the downstream behavioral manifestations of such impairments are rarely examined in humans.

METHODS

The influenza vaccination was used to elicit a mild inflammatory response in 41 healthy young adults (age range: 18-22, 30 female). Participants provided blood samples and completed behavioral measures of three key aspects of reward-reward motivation, reward learning, and reward sensitivity-before and 1 day after receiving the influenza vaccine.

RESULTS

The influenza vaccine led to mild but significant increases in circulating levels of the pro-inflammatory cytokine interleukin-6 (IL-6) (p <  .001). Consistent with hypotheses, increases in IL-6 predicted lower reward motivation (p =  .029). However, contrary to hypotheses, increases in IL-6 predicted increased performance on a reward learning task (p =  .043) and were not associated with changes in reward sensitivity (p's > .288).

CONCLUSIONS

These findings contribute to an emerging literature on the nuanced associations between inflammation and reward and demonstrate that even mild alterations in inflammation are associated with multiple facets of reward processing.

Relation of depression symptoms to sustained reward and loss sensitivity

Depression is characterized by altered sensitivity to rewards, with recent evidence suggesting that the ability to sustain responses to rewards across long experimental tasks is diminished. Most work on sustained reward responsiveness has taken a categorical approach and focused on major depressive disorder. However, impairments in reward sensitivity are also found at lower levels of symptom severity and may be relevant for understanding basic mechanisms linking reward processing abnormalities to depression. The current study took a dimensional approach to examine the relation between depression symptoms and sustained reward responsiveness by examining how early neural responses to rewards and losses change over a short time course (i.e., during the experiment). In a sample of 45 unselected undergraduates, changes in the amplitude of the reward positivity (RewP) and feedback negativity (FN) were examined over the course of a simple gambling task using multilevel modeling. Amplitude of the RewP was sustained and amplitude of the FN increased during the task. Unlike prior work focused on clinical populations, depression symptoms in this unselected sample were associated with enhanced RewP and FN responding over the course of the task. Results echo prior work that underscores the importance of examining changes in response to reward across trials and further suggests that sustained responses to both rewards and losses vary in relation to symptom level.

Differences in Speed of Response of Depressive Symptom Dimensions in Older Persons During Electroconvulsive Therapy

INTRODUCTION

Electroconvulsive therapy (ECT) is an important and effective treatment for depression. However, research on course trajectories of depressive symptoms during ECT is limited. Insight into putative differences in speed of response of depressive symptom dimensions may enable clinicians to optimally inform patients and their relatives. Therefore, we aim to examine course trajectories of depressive symptom dimensions in depressed older persons during ECT.

METHODS

Data were derived from the Mood Disorders in Elderly treated with Electro Convulsive Therapy study, including 110 persons, aged 55 years or more, with a current diagnosis of major depressive disorder and referred for ECT. Exploratory factor analysis was used to identify symptom dimensions, using the 10 depression items of the Montgomery-Åsberg Depression Rating Scale (MADRS). Differences in course trajectories of symptom dimension during 2 weeks were examined by multilevel analyses.

RESULTS

Three symptom dimensions were identified: a "mood," "melancholic," and "suicidal" dimension. Mood showed a significantly greater severity decline as compared with melancholic and suicidal at the 1-week follow-up. At the 2-week follow-up, both mood and melancholic demonstrated a significantly greater decline as compared with suicidal. However, because scores on the suicidality item of the Montgomery-Asberg Depression Rating Scale were already lower at baseline compared with the other items, a floor effect cannot be ruled out.

DISCUSSION

All symptom dimensions of depression showed a rapid response to ECT. Our findings did not support the general assumption that suicidal symptoms may be the first to improve. However, a floor effect on the suicidality item cannot be ruled out.

Anxiety and anhedonia in depression: Associations with neuroticism and cognitive control

BACKGROUND

Despite the fact that higher levels of anxiety and anhedonia in Major Depressive Disorder (MDD) are linked to poorer treatment outcomes, mechanisms contributing to these clinical presentations remain unclear. Neuroticism, impaired cognitive control, and blunted reward learning may be critical processes involved in MDD and may help to explain symptoms of anxiety and anhedonia.

METHODS

Using baseline data from patients with early-onset MDD (N = 296) in the Establishing Moderators and Biosignatures of Antidepressant Response in Clinical Care (EMBARC) trial, we conducted a path analysis to model relationships between neuroticism, cognitive control, and reward learning to levels of anxiety and anhedonia.

RESULTS

Neuroticism was positively associated with both anhedonia (standardized coefficient = 0.26, p < .001) and anxiety (standardized coefficient = 0.40, p < .001). Cognitive control was negatively associated with anxiety (standardized coefficient = -0.18, p < .05). Reward learning was not significantly associated with either anxiety or anhedonia.

LIMITATIONS

Extraneous variables not included in the model may have even more influence in explaining symptoms of anxiety and anhedonia. Restricted range in these variables may have attenuated some of the hypothesized relationships. Most important, because this was a cross-sectional analysis in a currently depressed sample, we cannot draw any causal conclusions without experimental and longitudinal data.

CONCLUSIONS

These cross-sectional findings suggest that neuroticism may contribute to anxiety and anhedonia in patients with early onset and either chronic or recurrent MDD, while enhanced cognitive control may protect against anxiety.

Longitudinal increases in reward-related neural activity in early adolescence: Evidence from event-related potentials (ERPs)

Adolescence is frequently described as a developmental period characterized by increased sensitivity to rewards. However, previous research on age-related changes in the neural response to gains and losses have produced mixed results, with only some studies reporting potentiated neural responses during adolescence. The current study examined the ERP responses to gains and losses during a simple monetary reward (i.e., Doors) task in a large and longitudinal sample of 248 adolescent females assessed at two time points, separated by two years. At baseline, when the sample was 8- to 14-years-old, age related to larger (i.e., more positive) ERP responses to both gains and losses; moreover, age-related effects were stronger in relation to gains than losses. Overall, the amplitude of the ERP response to gains, but not losses, significantly increased from baseline to follow-up; however, this effect was moderated by age, such that reward-related ERPs only increased longitudinally among the younger participants. At the follow-up assessment, ERP responses to gains and losses were equally related to age. Collectively, these within- and between-subjects findings suggest a relatively specific developmental increase in reward-related neural activity during late childhood and early adolescence.

Using a data science approach to predict cocaine use frequency from depressive symptoms

BACKGROUND

Depressive symptoms may contribute to cocaine use. However, tests of the relationship between depression and severity of cocaine use have produced mixed results, possibly due to heterogeneity in individual symptoms of depression. Our goal was to establish which symptoms of depression are most strongly related to frequency of cocaine use (one aspect of severity) in a large sample of current cocaine users. We utilized generalized additive modeling to provide data-driven exploration of the relationships between depressive symptoms and cocaine use, including examination of non-linearity. We hypothesized that symptoms related to anhedonia would demonstrate the strongest relationship to cocaine use.

METHOD

772 individuals screened for cocaine use disorder treatment studies. To measure depressive symptoms, we used the items of the Beck Depression Inventory, 2nd Edition. Cocaine use frequency was measured as proportion of self-reported days of cocaine use over the last 30 days using the Addiction Severity Index.

RESULTS

Models identified 18 significant predictors of past-30-day cocaine use. The strongest predictors were Crying, Pessimism, Changes in Appetite, Indecisiveness, and Loss of Interest. Noteworthy effect sizes were found for specific response options on Suicidal Thoughts, Worthlessness, Agitation, Concentration Difficulty, Tiredness, and Self Dislike items.

CONCLUSIONS

The strongest predictors did not conform to previously hypothesized "subtypes" of depression. Non-linear relationships between items and use were typical, suggesting BDI-II items may not be monotonically increasing ordinal measures with respect to predicting cocaine use. Qualitative analysis of strongly predictive response options suggested emotional volatility and disregard for the future as important predictors of use.

Reduced reward responsiveness moderates the effect of maternal depression on depressive symptoms in offspring: evidence across levels of analysis

BACKGROUND

Reduced reward responsiveness (RR) may contribute to depression vulnerability. At the neurophysiological level, RR is reliably and validly assessed using the reward positivity (RewP) event-related potential component. We previously identified a blunted RewP in 9-year-old children at high risk for depression due to maternal depression, but the role of RR in pathways from parental history to the development of depressive symptoms has not been examined.

METHODS

At age 9, never-depressed children (N = 369) completed a task in which RewP was measured in response to monetary reward and loss feedback. Parental history of depression was assessed using semistructured interviews, and children reported on their depressive symptoms. At age 12, youth depressive symptoms were reassessed, along with a self-report measure of RR. We tested RR as a moderator of the effects of parental depression on depressive symptoms at age 12, using both neurophysiological and self-report measures and controlling for age 9 symptoms.

RESULTS

Main effects of RR and interactions with maternal depression were significant. Maternal depression predicted greater depressive symptoms in youth with blunted and average RewP but was not a significant predictor in youth with an enhanced RewP. A similar pattern was observed for self-reported RR. The two measures of RR were not correlated with each other and accounted for unique variance in symptoms. Interactions between RR and paternal depression were not significant.

CONCLUSIONS

Reduced RR, as measured by neurophysiology and self-report, moderates the effects of maternal depression on depressive symptoms in offspring. Assessment of RR along with risk factors such as parental depression may aid in identifying children at greatest risk and enhancing RR could be a potential target for prevention. Results highlight the utility of multimethod approaches for advancing understanding of depression risk.

Striatal Functional Connectivity Alterations After Two-Week Antidepressant Treatment Associated to Enduring Clinical Improvement in Major Depressive Disorder

Background: Only less than 40% of patients with Major depressive disorder (MDD) can achieve remission after several weeks of initial antidepressant treatment. Predicting whether the prescribed treatment is effective in the following course may help clinicians modify the treatment regimen in time, and reduce the staggering burden for patients and society. However, there are not yet reliable markers based on neurobiological change after a treatment regimen steadily applied, for predicting clinical treatment outcome. The striatal circuits often exhibit abnormality for MDD patients, and are implicated in antidepressant treatments. Methods: Nineteen first-episode drug-naive MDD patients (nine females, mean age was 30 years old) were recruited to undergo clinical symptom assessment and resting state fMRI scanning at baseline, after 2 and 8 weeks of treatment with duloxetine. A seed-based analysis was used to obtain functional connectivity (FC) maps of six sub-regions of the stratum, then we explored the relationship of 2-week changes of striatal FC with clinical symptom improvement after 8-week duloxetine treatment. Results: The results revealed that 2-week FC changes of the striatal cognitive and affective subdivisions with the frontoparietal regions positively correlated with 8-week symptom improvement. We also found that early FC changes between the striatal motor subdivision and the motor-related cortical regions negatively correlated with later symptom improvement. Conclusions: These findings suggest that change of the FC of the cortical-striatal circuits at the early stage of treatment is critical for later remission of MDD. Furthermore, the association between the FC change and symptom improvement may have significant implication for clinical practice to regard neural changes as reference for evaluating how antidepressant treatment works.

"It's so Cute I Could Crush It!": Understanding Neural Mechanisms of Cute Aggression

The urge people get to squeeze or bite cute things, albeit without desire to cause harm, is known as “cute aggression.” Using electrophysiology (ERP), we measured components related to emotional salience and reward processing. Participants aged 18–40 years (n = 54) saw four sets of images: cute babies, less cute babies, cute (baby) animals, and less cute (adult) animals. On measures of cute aggression, feeling overwhelmed by positive emotions, approachability, appraisal of cuteness, and feelings of caretaking, participants rated more cute animals significantly higher than less cute animals. There were significant correlations between participants’ self-report of behaviors related to cute aggression and ratings of cute aggression in the current study.

N200: A significant effect of “cuteness” was observed for animals such that a larger N200 was elicited after more versus less cute animals. A significant correlation between N200 amplitude and the tendency to express positive emotions in a dimorphous manner (e.g., crying when happy) was observed.

RewP: For animals and babies separately, we subtracted the less cute condition from the more cute condition. A significant correlation was observed between RewP amplitude to cute animals and ratings of cute aggression toward cute animals. RewP amplitude was used in mediation models.

Mediation Models: Using PROCESS (Hayes, 2018), mediation models were run. For both animals and babies, the relationship between appraisal and cute aggression was significantly mediated by feeling overwhelmed. For cute animals, the relationship between N200 amplitude and cute aggression was significantly mediated by feeling overwhelmed. For cute animals, there was significant serial mediation for RewP amplitude through caretaking, to feeling overwhelmed, to cute aggression, and RewP amplitude through appraisal, to feeling overwhelmed, to cute aggression. Our results indicate that feelings of cute aggression relate to feeling overwhelmed and feelings of caretaking. In terms of neural mechanisms, cute aggression is related to both reward processing and emotional salience.

Anhedonia and suicidal thoughts and behaviors in psychiatric outpatients: The role of acuity

BACKGROUND

Anhedonia-impairment related to the experience of pleasure-has been identified as a potential risk factor for suicide, with some mixed findings. The current study sought to clarify the role of acuity of anhedonia in the relationship between anhedonia and suicidal thoughts and behaviors by comparing acutely and chronically anhedonic subjects on severity of suicidal ideation (SI) and suicide attempt (SA) history.

METHODS

Psychiatric outpatients (N = 395) were administered the Columbia Suicide Severity Rating Scale, the Beck Scale for Suicidal Ideation and a modified version of the Snaith-Hamilton Pleasure Scale (SHPS); SI measures were readministered at a 1-month follow-up (N = 289, 73%). Participants were classified as acutely anhedonic, chronically anhedonic and nonanhedonic based on their responses to the SHPS at initial assessment.

RESULTS

Controlling for symptoms of anxiety and depression, acute anhedonia was cross-sectionally and prospectively associated with greater severity of SI compared to the nonanhedonic group; no differences in severity of SI were found between the chronically anhedonic and nonanhedonic group at either time point. Anhedonia grouping was not associated with SA history.

CONCLUSION

Changes in capacity to experience pleasure may be more informative of near-term SI than typically low pleasure levels. Future investigation should focus on the relationship between acute anhedonia and imminent suicidal behavior.

Neural response to reward and psychosocial risk factors independently predict antenatal depressive symptoms

While psychosocial risk factors for peripartum depression are well-researched, studies on neural risk factors are scarce. Previous studies suggest a blunted neural response to reward may be a biomarker of depression and risk. In a sample of 86 pregnant women, the present study examined whether a reduced Reward Positivity (RewP), an event-related potential (ERP) elicited to feedback indicating monetary reward, relates to greater antenatal depressive symptoms. We also examined whether the RewP explains unique variance in antenatal depressive symptoms relative to other indices of risk, including annual income, history of a major depressive episodes, and score on a validated psychosocial risk measure, the Pregnancy Risk Questionnaire (PRQ). Zero-order correlations revealed that lower annual income, greater PRQ scores, and a blunted RewP were associated with greater antenatal depressive symptoms. The RewP and PRQ scores were identified as the best predictors of antenatal depressive symptoms in a stepwise regression, and together predicted 48 percent of the variance in antenatal depressive symptoms. PRQ scores accounted for 44% of the variance in antenatal depressive symptoms while the RewP accounted for 4% of additional incremental variance. This is the first study to combine self-report and neural activity to examine depressive symptoms in pregnant women. Future directions for research on perinatal depression are discussed.

Investigating dopamine and glucocorticoid systems as underlying mechanisms of anhedonia

RATIONALE

Anhedonia, a deficit in reward processing, is an endophenotype of several neuropsychiatric conditions. Despite its prevalence and debilitating effects, treatments for anhedonia are lacking, primarily because its underlying mechanisms are poorly understood. Dopamine (DA) has been implicated in anhedonia through its role in reward-related learning; glucocorticoid systems may also be involved in that anhedonia is often preceded by chronic stress.

OBJECTIVE

This study investigated DA and glucocorticoid systems in anhedonia using a rat version of the probabilistic reward task (PRT).

METHODS

Adult male Wistar rats were trained on the PRT and then tested following: (1) activation or inhibition of DA activity induced by amphetamine (AMPH) or pramipexole (PRAMI) injections, (2) chronic mild stress (CMS), or (3) glucocorticoid system activation (dexamethasone (DEX)) or inhibition (mifepristone (MIFE)).

RESULTS

AMPH increased and PRAMI decreased response bias, pointing to enhanced and diminished reward responsiveness with DA agonism and antagonism, respectively. CMS reduced response bias but only in a subpopulation of rats. DEX also decreased response bias, suggesting that glucocorticoid processes contribute to anhedonia, although glucocorticoid inhibition (MIFE) had no effect. None of the manipulations altered the ability to detect and respond to reward-paired stimuli.

CONCLUSIONS

These results confirm a role of DA in anhedonia and elucidate the contribution of the glucocorticoid system to this effect. In addition, chronic stress may interfere with normal DA functioning, leading to impaired reward-related learning in some animals. These findings may direct future treatment of anhedonia by targeting DA and glucocorticoid systems, as well as a possible interaction between the two.

Dopamine Release in Antidepressant-Naive Major Depressive Disorder: A Multimodal [11C]-(+)-PHNO Positron Emission Tomography and Functional Magnetic Resonance Imaging Study

BACKGROUND

Mesolimbic dopamine system dysfunction is believed to contribute to major depressive disorder (MDD), but molecular neuroimaging of striatal dopamine neurotransmission has yielded mixed results, possibly owing to limited sensitivity of antagonist radioligands used with positron emission tomography to assess dopamine release capacity. This study used an agonist radioligand with agonist challenge to assess dopamine release capacity and D₂/D₃ receptor availability in MDD.

METHODS

Twenty-six treatment-naive adults with MDD and 26 healthy comparison participants underwent functional magnetic resonance imaging during a probabilistic reinforcement task, and positron emission tomography with the D₃-preferring ligand [¹¹C]-(+)-PHNO, before and after oral dextroamphetamine. MDD participants then received pramipexole treatment for 6 weeks.

RESULTS

MDD participants had trend-level greater dopamine release capacity in the ventral striatum, as measured by percent change in baseline binding potential relative to nondisplaceable compartment (ΔBP_ND) (-34% vs. -30%; p = .072, d = 0.58) but no difference in D₂/D₃ receptor availability (BP_ND). Striatal and extrastriatal BP_ND and percent change in baseline BP_ND were not significantly associated with blood oxygen level-dependent response to reward prediction error in the ventral striatum, severity of depression and anhedonia, or antidepressant response to pramipexole (response rate = 72.7%).

CONCLUSIONS

[¹¹C]-(+)-PHNO demonstrated high sensitivity to displacement by amphetamine-induced dopamine release, but dopamine release capacity and D₂/D₃ availability were not associated with ventral striatal activation to reward prediction error or clinical features, in this study powered to detect large effects. While a preponderance of indirect evidence implicates dopaminergic dysfunction in MDD, these findings suggest that presynaptic dopamine dysregulation may not be a feature of MDD or a prerequisite for treatment response to dopamine agonists.

Reward Network Modulation as a Mechanism of Change in Behavioral Activation

Behavioral Activation (BA) is a contemporary third-wave psychosocial treatment approach that emphasizes helping individuals become more active in ways that are meaningful to them as a means of improving mood and quality of life. BA has been designated as a well-established, validated treatment for depression by the American Psychological Association following several decades of accumulated empirical support demonstrating that BA techniques successfully reduce depression symptoms and produce other desirable outcomes across a variety of populations and contexts. The purported mechanism of change underlying BA treatment lies in increasing activation, which in turn increases contact with positive reinforcement thereby reversing the cycle of depression. Current studies are further investigating how increasing activation and subsequent contact with mood reinforcers can influence mood and behavior. Specifically, there is growing evidence that BA modifies function of reward-related networks in the brain, and that these changes are associated with clinical improvement. Herein, we provide a brief history of BA, describe the primary components of BA treatment, and describe BA's purported mechanisms of change at behavioral, neural, and subjective activation levels. We present limitations as well as gaps in the current state of knowledge regarding mechanisms of action of BA.

Animal models in addiction research: A dimensional approach

Drug addiction affects approximately 10% of the population and these numbers are rising. Treatment and prevention of addiction are impeded by current diagnostic systems, such as DSM-5, which are based on outcomes rather than processes. Here, we review the importance of adopting a dimensional framework, specifically the Research Domain Criteria (RDoC), to identify protective and vulnerability mechanisms in addiction. We discuss how preclinical researchers should work within this framework to develop animal models based on domains of function. We highlight RDoC paradigms related to addiction and discuss how these can be used to investigate the biological underpinnings of an addiction cycle (i.e., binge/intoxication, negative affect, and craving). Using this information, we then outline the critical role of animal research in ongoing revisions to the RDoC matrix (specifically the functional significance of domains, constructs and subconstructs) and its contribution to the development and refinement of addiction theories. We conclude with an overview of the contribution that animal research has made to the development of pharmacological and behavioural treatments for addiction.

Accelerated iTBS treatment in depressed patients differentially modulates reward system activity based on anhedonia

OBJECTIVES

Accelerated intermittent theta-burst stimulation (aiTBS) anti-depressive working mechanisms are still unclear. Because aiTBS may work through modulating the reward system and the level of anhedonia may influence this modulation, we investigated the effect of aiTBS on reward responsiveness in high and low anhedonic MDD patients.

METHODS

In this registered RCT (NCT01832805), 50 MDD patients were randomised to a sham-controlled cross-over aiTBS treatment protocol over the left dorsolateral prefrontal cortex (DLPFC). Patients performed a probabilistic learning task in fMRI before and after each week of stimulation.

RESULTS

Task performance analyses did not show any significant effects of aiTBS on reward responsiveness, nor differences between both groups of MDD patients. However, at baseline, low anhedonic patients displayed higher neural activity in the caudate and putamen. After the first week of aiTBS treatment, in low anhedonic patients we found a decreased neural activity within the reward system, in contrast to an increased activity observed in high anhedonic patients. No changes were observed in reward related neural regions after the first week of sham stimulation.

CONCLUSIONS

Although both MDD groups showed no differences in task performance, our brain imaging findings suggest that left DLPFC aiTBS treatment modulates the reward system differently according to anhedonia severity.

Making Sense of Rodent Models of Anhedonia

A markedly reduced interest or pleasure in activities previously considered pleasurable is a main symptom in mood disorder and psychosis and is often present in other psychiatric disorders and neurodegenerative diseases. This condition can be labeled as "anhedonia," although in its most rigorous connotation the term refers to the lost capacity to feel pleasure that is one aspect of the complex phenomenon of processing and responding to reward. The responses to rewarding stimuli are relatively easy to study in rodents, and the experimental conditions that consistently and persistently impair these responses are used to model anhedonia. To this end, long-term exposure to environmental aversive conditions is primarily used, and the resulting deficits in reward responses are often accompanied by other deficits that are mainly reminiscent of clinical depressive symptoms. The different components of impaired reward responses induced by environmental aversive events can be assessed by different tests or protocols that require different degrees of time allocation, technical resources, and equipment. Rodent models of anhedonia are valuable tools in the study of the neurobiological mechanisms underpinning impaired behavioral responses and in the screening and characterization of drugs that may reverse these behavioral deficits. In particular, the antianhedonic or promotivational effects are relevant features in the spectrum of activities of drugs used in mood disorders or psychosis. Thus, more than the model, it is the choice of tests that is crucial since it influences which facets of anhedonia will be detected and should be tuned to the purpose of the study.

Is the encoding of Reward Prediction Error reliable during development?

Reward Prediction Errors (RPEs), defined as the difference between the expected and received outcomes, are integral to reinforcement learning models and play an important role in development and psychopathology. In humans, RPE encoding can be estimated using fMRI recordings, however, a basic measurement property of RPE signals, their test-retest reliability across different time scales, remains an open question. In this paper, we examine the 3-month and 3-year reliability of RPE encoding in youth (mean age at baseline = 10.6 ± 0.3 years), a period of developmental transitions in reward processing. We show that RPE encoding is differentially distributed between the positive values being encoded predominantly in the striatum and negative RPEs primarily encoded in the insula. The encoding of negative RPE values is highly reliable in the right insula, across both the long and the short time intervals. Insula reliability for RPE encoding is the most robust finding, while other regions, such as the striatum, are less consistent. Striatal reliability appeared significant as well once covarying for factors, which were possibly confounding the signal to noise ratio. By contrast, task activation during feedback in the striatum is highly reliable across both time intervals. These results demonstrate the valence-dependent differential encoding of RPE signals between the insula and striatum, and the consistency of RPE signals or lack thereof, during childhood and into adolescence. Characterizing the regions where the RPE signal in BOLD fMRI is a reliable marker is key for estimating reward-processing alterations in longitudinal designs, such as developmental or treatment studies.

Reward Responsivity in Parenting: Development of a Novel Measure in Mothers of Young Children

The purpose of the current study was to develop and evaluate a measure of maternal reward responsivity in parenting. Deficits in reward responsivity, a common feature of depression, may contribute to maladaptive parenting behaviors. Reward responsivity is an individual difference in reactivity to pleasurable stimuli and represents a key motivational component that could contribute to the frequency and quality of mothers' interactions with their infants. However, there is currently no measure of reward responsivity in parenting, which would be necessary to evaluate the link between mother reward responsivity, behaviors towards their infant, and infant behavior. Therefore, the current study reports on the development and initial evaluation of a self-report measure of reward responsivity in parenting, the Mother Inventory of Reward Experience (MIRE). We evaluated the MIRE among 200 mothers (M =28.45, SD = 5.50) recruited from a pediatric primary care center. After item analysis, 22 items were retained and displayed high internal consistency reliability and test re-test reliability. Convergent validity was established via a significant correlation with global reward responsivity. Concurrent validity was established via significant correlations with depressive symptoms, parenting stress, and child behavior problems. Incremental validity of the MIRE over a measure of global reward responsivity was supported. These results support the reliability and validity of the MIRE as a measure of reward responsivity in parenting.

Maternal behavior predicts neural underpinnings of inhibitory control in preschoolers

Separate lines of research have revealed that the rapid development of inhibitory control in the preschool period is closely tied to normative brain development and influenced by early mother-child interactions. One potential theory is that maternal behavior in the context of early interactions influences the neural underpinnings of inhibitory control in development, with implications for child behavior. The purpose of this paper was to examine whether maternal emotional support, measured during a mother-child problem-solving game, predicted child neural responses (frontal-central N2 event-related potential) and behavioral performance (discrimination index, d') in a go/no-go task of inhibitory control in a large, diverse sample of mother-child dyads (N = 276) observed in children's last year of preschool (mean age = 56 months). Results of a structural equation model revealed significant direct effects from maternal emotional support to child right hemisphere frontal-central N2 responses to no-go (inhibitory control) trials; greater observed emotional support predicted larger N2 responses. Larger right hemisphere N2 responses to no-go trials were also associated with better overall observed task performance (d'). A test of indirect effects from maternal emotional support to child observed performance via right hemisphere N2 responses was significant, suggesting that underlying neurophysiology is one mechanism through which maternal emotional support is associated with a child's rapidly developing inhibitory control behavior in the preschool period. This work joins a growing literature demonstrating that caregiver behavior within a "normative" range is an important environmental factor contributing to the development of neural processes supporting child functioning.

Impaired reward responsiveness in schizophrenia

BACKGROUND

Anhedonia is a core negative symptom of schizophrenia. Schizophrenia patients report largely intact pleasure in consuming rewards, but have impairments in generating motivated behavior to pursue rewards, and show reduced fMRI activation of the reward pathway during presentation of rewarded stimuli. A computer based task measuring the development of a response bias in favor of rewarded stimuli permits assessment of reward-induced motivation. We hypothesized that subjects with schizophrenia would be impaired on this task.

METHODS

58 schizophrenia subjects (SCZ) and 52 healthy controls (CON) were studied with a signal detection task to assess reward responsiveness. In multiple trials over three blocks subjects were asked to correctly identify two stimuli that were paired with unequal chance of monetary reward. The critical outcome variable was response bias, the development of a greater percent correct identification of the stimulus that was rewarded more often.

RESULTS

An ANOVA on response bias with Block as a repeated-measures factor and Diagnosis as a between-group factor indicated that SCZ subjects achieved a lower bias to rewarded stimuli than CON subjects (F(1,105)=8.82, p=0.004, η²=0.078). Post hoc tests indicated that SCZ subjects had significantly impaired bias in Block 1 (p=0.002) and Block 2 (p=0.05), indicating that SCZ were slower to achieve normal levels of bias during the session.

CONCLUSIONS

SCZ subjects were slower to develop response bias to rewarded stimuli than CON subjects. This finding is consonant with the hypothesis that people with schizophrenia have a blunted capacity to modify behavior in response to reward.

Chronic Social Stress Leads to Reduced Gustatory Reward Salience and Effort Valuation in Mice

Pathology of reward processing is a major clinical feature of stress-related neuropsychiatric disorders including depression. Several dimensions of reward processing can be impacted, including reward valuation/salience, learning, expectancy and effort valuation. To establish the causal relationships between stress, brain changes, and reward processing pathologies, valid animal models are essential. Here, we present mouse experiments investigating behavioral effects of chronic social stress (CSS) in association learning tests of gustatory reward salience and effort valuation. The reward salience test (RST) comprised Pavlovian pairing of a tone with gustatory reward. The effort valuation test (EVT) comprised operant responding for gustatory reinforcement on a progressive ratio schedule (PRS). All testing was conducted with mice at 100% baseline body weight (BBW). In one experiment, mice underwent 15-day CSS or control handling (CON) and testing was conducted using sucrose pellets. In the RST on days 16–17, CSS mice made fewer feeder responses and had a longer tone response latency, than CON mice. In a shallow EVT on days 19–20, CSS mice attained a lower final ratio than CON mice. In a second CSS experiment, mice underwent CSS or CON and testing was conducted with chocolate pellets and in the presence of standard diet (low effort/low reward). In the RST on days 16–18, CSS mice made fewer feeder responses and had a longer tone response latency, than CON mice. In a steep EVT on days 19–20, CSS and CON mice attained less pellets than in the RST, and CSS mice attained a lower final ratio than CON mice. At day 21, blood levels of glucose and the satiety adipokine leptin were similar in CSS and CON mice. Therefore, CSS leads to consistent reductions in reward salience and effort valuation in tests based on association learning. These reward pathology models are being applied to identify the underlying neurobiology and putative molecular targets for therapeutic pharmacology.

Introjective Individuals Tend Toward Anhedonia: Self-Report and Experimental Evidence

A broad line of research has conceptualized personality based on the interaction of two aspects: interpersonal relatedness and self-definition. This theoretical corpus understands these functions as two poles according to the patterns of interaction and relevance in personality. Additionally, the exacerbation of one of these poles generates a psychopathological model that identifies three types of depressive experience: anaclitic, introjective, or mixed pattern. Understanding the lack of interest as a key symptom of depression, this experiment evaluates a relation for anhedonia and the polarities model configuration using an empirical and experimental protocol. We tested 177 individuals using the Beck Depression Inventory (BDI) subscale for anhedonia and a visual discrimination task with a specific reward system, which was implemented to study reinforcement sensitivity. Participants were classified into four groups by the polarities of experience model. The subscale's results showed that individuals with an introjective character exhibited an enhanced anhedonic symptomatology but no co-occurrence of this evidence on the experimental protocol. These results empirically support the two polarities of the depressive personality model and raise new questions regarding how to experimentally test this relation.

Effects of transcranial direct current stimulation for treating depression: A modeling study

BACKGROUND

Transcranial direct current stimulation (tDCS) above the left dorsolateral prefrontal cortex (lDLPFC) has been widely used to improve symptoms of major depressive disorder (MDD). However, the effects of different stimulation protocols in the entire frontal lobe have not been investigated in a large sample including patient data.

METHODS

We used 38 head models created from structural magnetic resonance imaging data of 19 healthy adults and 19 MDD patients and applied computational modeling to simulate the spatial distribution of tDCS-induced electric fields (EFs) in 20 frontal regions. We evaluated effects of seven bipolar and two multi-electrode 4 × 1 tDCS protocols.

RESULTS

For bipolar montages, EFs were of comparable strength in the lDLPFC and in the medial prefrontal cortex (MPFC). Depending on stimulation parameters, EF cortical maps varied to a considerable degree, but were found to be similar in controls and patients. 4 × 1 montages produced more localized, albeit weaker effects.

LIMITATIONS

White matter anisotropy was not modeled. The relationship between EF strength and clinical response to tDCS could not be evaluated.

CONCLUSIONS

In addition to lDLPFC stimulation, excitability changes in the MPFC should also be considered as a potential mechanism underlying clinical efficacy of bipolar montages. MDD-associated anatomical variations are not likely to substantially influence current flow. Individual modeling of tDCS protocols can substantially improve cortical targeting. We make recommendations for future research to explicitly test the contribution of lDLPFC vs. MPFC stimulation to therapeutic outcomes of tDCS in this disorder.

Nicotine Increases Activation to Anticipatory Valence Cues in Anterior Insula and Striatum

Introduction

Smoking is associated with significant morbidity and mortality. Understanding the neurobiology of the rewarding effects of nicotine promises to aid treatment development for nicotine dependence. Through its actions on mesolimbic dopaminergic systems, nicotine engenders enhanced responses to drug-related cues signaling rewards, a mechanism hypothesized to underlie the development and maintenance of nicotine addiction.

Methods

We evaluated the effects of acute nicotine on neural responses to anticipatory cues signaling (nondrug) monetary reward or loss among 11 nonsmokers who had no prior history of tobacco smoking. In a double-blind, crossover design, participants completed study procedures while wearing nicotine or placebo patches at least 1 week apart. In each drug condition, participants underwent functional magnetic resonance imaging while performing the monetary incentive delay task and performed a probabilistic monetary reward task, probing reward responsiveness as measured by response bias toward a more frequently rewarded stimulus.

Results

Nicotine administration was associated with enhanced activation, compared with placebo, of right fronto-anterior insular cortex and striatal regions in response to cues predicting possible rewards or losses and to dorsal anterior cingulate for rewards. Response bias toward rewarded stimuli correlated positively with insular activation to anticipatory cues.

Conclusion

Nicotinic enhancement of monetary reward-related brain activation in the insula and striatum in nonsmokers dissociated acute effects of nicotine from effects on reward processing due to chronic smoking. Reward responsiveness predicted a greater nicotinic effect on insular activation to salient stimuli.

Implications

Previous research demonstrates that nicotine enhances anticipatory responses to rewards in regions targeted by midbrain dopaminergic systems. The current study provides evidence that nicotine also enhances responses to rewards and losses in the anterior insula. A previous study found enhanced insular activation to rewards and losses in smokers and ex-smokers, a finding that could be due to nicotine sensitization or factors related to current or past smoking. Our finding of enhanced anterior insula response after acute administration of nicotine in nonsmokers provides support for nicotine-induced sensitization of insular response to rewards and losses.

People who need people: Trait loneliness influences positive affect as a function of interpersonal context

Trait loneliness is associated with negative health consequences; understanding involved processes may elucidate its contributory role. Evolutionary and reaffiliative models associate loneliness with negative affect and dysregulated cortisol responding, while the social monitoring system model associates loneliness with heightened salience of social cues. We hypothesized that loneliness would be associated with greater negative affect and cortisol reactivity, comparing a negative-evaluative audience Trier Social Stress Test ("audience condition;" n = 55) versus a no-audience control condition (n = 69) in non-depressed young adults. Opposing hypotheses, multilevel growth curve models indicated that loneliness was not associated with negative affect or cortisol reactivity in the audience versus no-audience condition. Loneliness was, however, associated with greater positive affect reactivity in the audience versus no-audience condition. In particular, the positive affect subfacet "Interest" was heightened in the audience condition but blunted in the no-audience condition as a function of loneliness, echoing a social monitoring system model of loneliness.

Parsing affective dynamics to identify risk for mood and anxiety disorders

Emotional dysregulation is thought to underlie risk for both anxiety and depressive disorders. However, despite high rates of comorbidity, anxiety and depression are phenotypically different. Apart from nosological differences (e.g., worry for anxiety, low mood for depression), it remains unclear how the emotional dysregulation inherent in individual differences in trait anxiety and depression severity present on a day-to-day basis. One approach that may facilitate addressing these questions is to utilize Ecological Momentary Assessment (EMA) using mobile phones to parse the temporal dynamics of affective experiences into specific parameters. An emerging literature in affective science suggests that risk for anxiety and depressive disorders may be associated with variation in the mean and instability/variability of emotion. Here we examine the extent to which distinct temporal dynamic parameters uniquely predict risk for anxiety versus depression. Over 10 days, 105 individuals rated their current positive and negative affective state several times each day. Using two distinct approaches to statistically assess mean and instability of positive and negative affect, we found that individual differences in trait anxiety was generally associated with increased instability of positive and negative affect whereas mean levels of positive and negative affect were generally associated with individual differences in depression. These data provide evidence that the emotional dysregulation underlying risk for mood versus anxiety disorders unfolds in distinct ways and highlights the utility in examining affective dynamics to understand psychopathology. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

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.

The impact bias in self and others: Affective and empathic forecasting in individuals with social anxiety

People tend to overestimate the intensity and duration of affect (i.e., impact bias) when making predictions about their own and others' responding, termed affective and empathic forecasting, respectively. Research links impact biases to clinical symptoms of affective disorders, but little work has been done to examine how social anxiety is related to affective and empathic forecasting biases. The current investigation included two studies examining these associations in independent samples of young adults with dimensionally distributed social anxiety symptoms. Study 1 (N = 100) examined the associations between social anxiety and affective and empathic forecasts in response to a series of novel hypothetical vignettes in which a second-person narrator (i.e., the self) elicited anger, disgust, or happiness from another person (i.e., the other). Study 2 utilized an innovative experimental paradigm involving N = 68 participant dyads. Overall, results supported the existence of affective and empathic forecasting biases. Further, symptoms of social anxiety were associated with the tendency to overestimate one's own and others' negative affect and underestimate others' positive affect. Such forecasting biases may help to explain the avoidance that is characteristic of individuals with social anxiety and could represent a fruitful target of cognitive behavioral intervention.

Evidence of a diurnal rhythm in implicit reward learning

Many aspects of hedonic behavior, including self-administration of natural and drug rewards, as well as human positive affect, follow a diurnal cycle that peaks during the species-specific active period. This variation has been linked to circadian modulation of the mesolimbic dopamine system, and is hypothesized to serve an adaptive function by driving an organism to engage with the environment during times where the opportunity for obtaining rewards is high. However, relatively little is known about whether more complex facets of hedonic behavior - in particular, reward learning - follow the same diurnal cycle. The current study aimed to address this gap by examining evidence for diurnal variation in reward learning on a well-validated probabilistic reward learning task (PRT). PRT data from a large normative sample (N = 516) of non-clinical individuals, recruited across eight studies, were examined for the current study. The PRT uses an asymmetrical reinforcement ratio to induce a behavioral response bias, and reward learning was operationalized as the strength of this response bias across blocks of the task. Results revealed significant diurnal variation in reward learning, however in contrast to patterns previously observed in other aspects of hedonic behavior, reward learning was lowest in the middle of the day. Although a diurnal pattern was also observed on a measure of more general task performance (discriminability), this did not account for the variation observed in reward learning. Taken together, these findings point to a distinct diurnal pattern in reward learning that differs from that observed in other aspects of hedonic behavior. The results of this study have important implications for our understanding of clinical disorders characterized by both circadian and reward learning disturbances, and future research is needed to confirm whether this diurnal variation has a truly circadian origin.

Using Multilevel Modeling to Examine Blunted Neural Responses to Reward in Major Depression

BACKGROUND

Major depressive disorder (MDD) is a pernicious disorder characterized by deficits in reward processing. A better understanding of these deficits may help to elucidate the underlying pathophysiology and guide treatment development.

METHODS

This study assessed reward positivity and feedback negativity event-related potentials and their difference scores elicited in response to monetary gains and losses among 100 young adults (52 with MDD). Multilevel modeling was used to assess individual- and trial-level change in neural responses over time.

RESULTS

Trial-level analyses indicated that a diagnosis of MDD and depressive symptom severity significantly moderated the trajectory of reward positivity, with individuals with higher symptoms of depression demonstrating less sensitivity to rewards over time.

CONCLUSIONS

These results provide further support for reward dysfunction in MDD and highlight important individual differences in the trajectory of neural responses to reward. Future studies are warranted to investigate reward sensitivity over time to elucidate important individual- and trial-level differences in reward processing.

Effort-cost decision-making in psychosis and depression: could a similar behavioral deficit arise from disparate psychological and neural mechanisms?

Motivational impairment is a common feature of both depression and psychosis; however, the psychological and neural mechanisms that give rise to motivational impairment in these disorders are poorly understood. Recent research has suggested that aberrant effort-cost decision-making (ECDM) may be a potential contributor to motivational impairment in both psychosis and depression. ECDM refers to choices that individuals make regarding the amount of 'work' they are willing to expend to obtain a certain outcome or reward. Recent experimental work has suggested that those with psychosis and depression may be less willing to expend effort to obtain rewards compared with controls, and that this effort deficit is related to motivational impairment in both disorders. In the current review, we aim to summarize the current literature on ECDM in psychosis and depression, providing evidence for transdiagnostic impairment. Next, we discuss evidence for the hypothesis that a seemingly similar behavioral ECDM deficit might arise from disparate psychological and neural mechanisms. Specifically, we argue that effort deficits in psychosis might be largely driven by deficits in cognitive control and the neural correlates of cognitive control processes, while effort deficits in depression might be largely driven by reduced reward responsivity and the associated neural correlates of reward responsivity. Finally, we will provide some discussion regarding future directions, as well as interpretative challenges to consider when examining ECDM transdiagnostically.

Chronic social stress induces peripheral and central immune activation, blunted mesolimbic dopamine function, and reduced reward-directed behaviour in mice

Psychosocial stress is a major risk factor for depression, stress leads to peripheral and central immune activation, immune activation is associated with blunted dopamine (DA) neural function, DA function underlies reward interest, and reduced reward interest is a core symptom of depression. These states might be inter-independent in a complex causal pathway. Whilst animal-model evidence exists for some specific steps in the pathway, there is currently no animal model in which it has been demonstrated that social stress leads to each of these immune, neural and behavioural states. Such a model would provide important existential evidence for the complex pathway and would enable the study of causality and mediating mechanisms at specific steps in the pathway. Therefore, in the present mouse study we investigated for effects of 15-day resident-intruder chronic social stress (CSS) on each of these states. Relative to controls, CSS mice exhibited higher spleen levels of granulocytes, inflammatory monocytes and T helper 17 cells; plasma levels of inducible nitric oxide synthase; and liver expression of genes encoding kynurenine pathway enzymes. CSS led in the ventral tegmental area to higher levels of kynurenine and the microglia markers Iba1 and Cd11b and higher binding activity of DA D1 receptor; and in the nucleus accumbens (NAcc) to higher kynurenine, lower DA turnover and lower c-fos expression. Pharmacological challenge with DA reuptake inhibitor identified attenuation of DA stimulatory effects on locomotor activity and NAcc c-fos expression in CSS mice. In behavioural tests of operant responding for sucrose reward validated as sensitive assays for NAcc DA function, CSS mice exhibited less reward-directed behaviour. Therefore, this mouse study demonstrates that a chronic social stressor leads to changes in each of the immune, neural and behavioural states proposed to mediate between stress and disruption of DA-dependent reward processing. The model can now be applied to investigate causality and, if demonstrated, underlying mechanisms in specific steps of this immune-neural-behavioural pathway, and thereby to identify potential therapeutic targets.

•

Mouse chronic social stress (CSS) leads to spleen and liver immune activation.

•

Mouse CSS leads to mesolimbic immune activation and blunted dopamine function.

•

Mouse CSS leads to reduced reward-directed behaviour in operant tests.

•

This constitutes an important model for the study of pathophysiological mechanisms.

Anhedonia and emotional numbing in treatment-seeking veterans: behavioural and electrophysiological responses to reward

Background: Anhedonia is a common symptom following exposure to traumatic stress and a feature of the PTSD diagnosis. In depression research, anhedonia has been linked to deficits in reward functioning, reflected in behavioural and neural responses. Such deficits following exposure to trauma, however, are not well understood. Objective: The current study aims to estimate the associations between anhedonia, PTSD symptom-clusters and behavioural and electrophysiological responses to reward. Methods: Participants (N = 61) were recruited among Danish treatment-seeking veterans at the Department of Military Psychology in the Danish Defence. Before entering treatment, participants were screened with symptom measurement instruments and participated in a joint behavioural-electrophysiological experiment. The experimental paradigm consisted of a signal-detection task aimed at assessing reward-driven learning. Simultaneous electrophysiological-recordings were analysed to evaluate neural responses upon receiving reward, as indicated by the Feedback-Related Negativity (FRN) component. Result: Anhedonia as conceptualized in depression correlated with behavioural learning (r = -0.28, p = .032). Neither anhedonia nor behavioural learning correlated with FRN. However, the anhedonia symptom cluster of PTSD did correlate with FRN (r = 0.29, p = .023). Extending upon this in an exploratory analysis, the specific PTSD-symptom emotional numbing was found to correlate moderately with FRN (r = 0.38, p = .003). Conclusion: The present data suggest that anhedonia in trauma-exposed individuals is related to the anticipatory aspect of reward, whereas the neural consummatory reward response seems unlinked. Interestingly, emotional numbing in the same population is related to the consummatory phase of reward, correlating with the FRN response. This suggests that anhedonia and emotional numbing in response to trauma might pertain to different phases of reward processing.

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

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