Reward processing dysfunction in major depression, bipolar disorder and schizophrenia

Relationship altered between functional T1ρ and BOLD signals in bipolar disorder

INTRODUCTION

Functional neuroimaging typically relies on the blood-oxygen-level-dependent (BOLD) contrast, which is sensitive to the influx of oxygenated blood following neuronal activity. A new method, functional T1 relaxation in the rotating frame (fT1ρ) is thought to reflect changes in local brain metabolism, likely pH, and may more directly measure neuronal activity. These two methods were applied to study activation of the visual cortex in participants with bipolar disorder as compared to controls.

METHODS

Thirty-nine participants with bipolar disorder and 32 healthy controls underwent functional neuroimaging during a flashing checkerboard paradigm. Functional images were acquired in alternating blocks of BOLD and fT1ρ. Linear mixed-effect models were used to examine the relationship between these two functional imaging modalities and to test whether that relationship was altered in bipolar disorder.

RESULTS

BOLD and fT1ρ signal were strongly related in visual and cerebellar areas during the task in controls. The relationship between these two measures was reduced in bipolar disorder within the visual areas, cerebellum, striatum, and thalamus.

CONCLUSIONS

These results support a distinct mechanisms underlying BOLD and fT1ρ signals. The weakened relationship between these imaging modalities may provide a novel tool for measuring pathology in bipolar disorder and other psychiatric illnesses.

Reward learning deficits in Parkinson's disease depend on depression

BACKGROUND

Depression is one of the most common and debilitating non-motor symptoms of Parkinson's disease (PD). The neurocognitive mechanisms underlying depression in PD are unclear and treatment is often suboptimal.

METHODS

We investigated the role of striatal dopamine in reversal learning from reward and punishment by combining a controlled medication withdrawal procedure with functional magnetic resonance imaging in 22 non-depressed PD patients and 19 PD patients with past or present depression.

RESULTS

PD patients with a depression (history) exhibited impaired reward v. punishment reversal learning as well as reduced reward v. punishment-related BOLD signal in the striatum (putamen) compared with non-depressed PD patients. No effects of dopaminergic medication were observed.

CONCLUSIONS

The present findings demonstrate that impairments in reversal learning from reward v. punishment and associated striatal signalling depend on the presence of (a history of) depression in PD.

Striatal dopamine D2/3 receptor-mediated neurotransmission in major depression: Implications for anhedonia, anxiety and treatment response

Dopamine (DA) neurotransmission within the brain's reward circuit has been implicated in the pathophysiology of depression and in both, cognitive and pharmacological mechanisms of treatment response. Still, a direct relationship between measures of DA neurotransmission and reward-related deficits in patients with depression has not been demonstrated. To gain insight into the symptom-specific alterations in the DA system in patients with depression, we used positron emission tomography (PET) and the D_2/3 receptor-selective radiotracer [¹¹C]raclopride in twenty-three non-smoking un-medicated Major Depressive Disorder (MDD) patients and sixteen healthy controls (HC). We investigated the relationship between D_2/3 receptor availability and baseline measures of depression severity, anxiety, anhedonia, and cognitive and pharmacological mechanisms of treatment response. We found that, compared to controls, patients with depression showed greater D_2/3 receptor availability in several striatal regions, including the bilateral ventral pallidum/nucleus accumbens (vPAL/NAc), and the right ventral caudate and putamen. In the depressed sample, D_2/3 receptor availability in the caudal portion of the ventral striatum (NAc/vPAL) correlated with higher anxiety symptoms, whereas D_2/3 receptor availability in the rostral area of the ventral striatum correlated negatively with the severity of motivational anhedonia. Finally, MDD non-remitters showed greater baseline anxiety, greater D_2/3 availability in the NAc/vPAL, and greater placebo-induced DA release in the bilateral NAc. Our results demonstrate abnormally high D_2/3 receptor availability in the ventral striatum of patients with MDD, which seem to be associated with comorbid anxiety symptoms and lack of response to antidepressants.

Association between habenula dysfunction and motivational symptoms in unmedicated major depressive disorder

The lateral habenula plays a central role in reward and punishment processing and has been suggested to drive the cardinal symptom of anhedonia in depression. This hypothesis is largely based on observations of habenula hypermetabolism in animal models of depression, but the activity of habenula and its relationship with clinical symptoms in patients with depression remains unclear. High-resolution functional magnetic resonance imaging (fMRI) and computational modelling were used to investigate the activity of the habenula during a probabilistic reinforcement learning task with rewarding and punishing outcomes in 21 unmedicated patients with major depression and 17 healthy participants. High-resolution anatomical scans were also acquired to assess group differences in habenula volume. Healthy individuals displayed the expected activation in the left habenula during receipt of punishment and this pattern was confirmed in the computational analysis of prediction error processing. In depressed patients, there was a trend towards attenuated left habenula activation to punishment, while greater left habenula activation was associated with more severe depressive symptoms and anhedonia. We also identified greater habenula volume in patients with depression, which was associated with anhedonic symptoms. Habenula dysfunction may contribute to abnormal response to punishment in patients with depression, and symptoms such as anhedonia.

Schizophrenia: Reaction to Positive Life Events

Negative life events can exacerbate symptoms in schizophrenia, but there is no literature on the effect on psychotic symptoms of positive life events. The purpose of this review was to scan the literature that studies how the joy that accompanies positive life events can be dampened and dismissed or, alternatively, savored and maintained, and how this contrast applies to schizophrenia. A literature search elicited 53 articles relevant to schizophrenia. Schizophrenia was found to be linked with difficulties in the processing of reward, in feeling that one was deserving of a reward, in sharing news of positive events, in knowing with whom to share, in knowing how to elicit a positive response from listeners when communicating good news, and in ensuring that positive feelings endure. There was no evidence that positive life events reduce psychosis symptoms but teaching the various skills of how to capitalize on good fortune can nevertheless improve the quality of life of individuals with schizophrenia.

Association of Neural and Emotional Impacts of Reward Prediction Errors With Major Depression

IMPORTANCE

Major depressive disorder (MDD) is associated with deficits in representing reward prediction errors (RPEs), which are the difference between experienced and predicted reward. Reward prediction errors underlie learning of values in reinforcement learning models, are represented by phasic dopamine release, and are known to affect momentary mood.

OBJECTIVE

To combine functional neuroimaging, computational modeling, and smartphone-based large-scale data collection to test, in the absence of learning-related concerns, the hypothesis that depression attenuates the impact of RPEs.

DESIGN, SETTING, AND PARTICIPANTS

Functional magnetic resonance imaging (fMRI) data were collected on 32 individuals with moderate MDD and 20 control participants who performed a probabilistic reward task. A risky decision task with repeated happiness ratings as a measure of momentary mood was also tested in the laboratory in 74 participants and with a smartphone-based platform in 1833 participants. The study was conducted from November 20, 2012, to February 17, 2015.

MAIN OUTCOMES AND MEASURES

Blood oxygen level-dependent activity was measured in ventral striatum, a dopamine target area known to represent RPEs. Momentary mood was measured during risky decision making.

RESULTS

Of the 52 fMRI participants (mean [SD] age, 34.0 [9.1] years), 30 (58%) were women and 32 had MDD. Of the 74 participants in the laboratory risky decision task (mean age, 34.2 [10.3] years), 44 (59%) were women and 54 had MDD. Of the smartphone group, 543 (30%) had a depression history and 1290 (70%) had no depression history; 918 (50%) were women, and 593 (32%) were younger than 30 years. Contrary to previous results in reinforcement learning tasks, individuals with moderate depression showed intact RPE signals in ventral striatum (z = 3.16; P = .002) that did not differ significantly from controls (z = 0.91; P = .36). Symptom severity correlated with baseline mood parameters in laboratory (ρ = -0.54; P < 1 × 10-6) and smartphone (ρ = -0.30; P < 1 × 10-39) data. However, participants with depression showed an intact association between RPEs and happiness in a computational model of momentary mood dynamics (z = 4.55; P < .001) that was not attenuated compared with controls (z = -0.42; P = .67).

CONCLUSIONS AND RELEVANCE

The neural and emotional impact of RPEs is intact in major depression. These results suggest that depression does not affect the expression of dopaminergic RPEs and that attenuated RPEs in previous reports may reflect downstream effects more closely related to aberrant behavior. The correlation between symptom severity and baseline mood parameters supports an association between depression and momentary mood fluctuations during cognitive tasks. These results demonstrate a potential for smartphones in large-scale computational phenotyping, which is a goal for computational psychiatry.

Secondary negative symptoms - A review of mechanisms, assessment and treatment

Negative symptoms in schizophrenia may be classified as primary or secondary. Primary negative symptoms are thought to be intrinsic to schizophrenia, while secondary negative symptoms are caused by positive symptoms, depression, medication side-effects, social deprivation or substance abuse. Most of the research on secondary negative symptoms has aimed at ruling them out in order to isolate primary negative symptoms. However, secondary negative symptoms are common and can have a major impact on patient-relevant outcomes. Therefore, the assessment and treatment of secondary negative symptoms are clinically relevant. Furthermore, understanding the mechanisms underlying secondary negative symptoms can contribute to an integrated model of negative symptoms. In this review we provide an overview of concepts, evidence, assessment and treatment for the major causes of secondary negative symptoms. We also summarize neuroimaging research relevant to secondary negative symptoms. We emphasize the relevance of recent developments in psychopathological assessment of negative symptoms, such as the distinction between amotivation and diminished expression, which have only rarely been applied in research on secondary negative symptoms.

Reward processing and mood-related symptoms: An RDoC and translational neuroscience perspective

BACKGROUND

Two objectives of the NIMH Research Domain Criteria (RDoC) initiative are to identify (a) mechanisms that are common to multiple psychiatric disorders, and (b) mechanisms that are unique to specific psychiatric symptoms, and that reflect markers of differential risk for these symptoms. With respect to these objectives, a brain-behavior dimension that has received considerable attention and that is directly relevant to the Positive Valence Systems domain of the RDoC initiative involves reward processing.

METHODS

The present review paper first examines the relationship between reward processing and mood-related symptoms from an RDoC perspective. We then place this work in a larger context by examining the relationship between reward processing abnormalities and psychiatric symptoms defined broadly, including mood-related symptoms, schizophrenia, and addiction.

RESULTS

Our review suggests that reward hyposensitivity relates to a subtype of anhedonia characterized by motivational deficits in unipolar depression, and reward hypersensitivity relates to a cluster of hypo/manic symptoms characterized by excessive approach motivation in the context of bipolar disorder. Integrating this perspective with research on reward processing abnormalities in schizophrenia and addiction, we further argue that the principles of equifinality and multifinality may be preferable to a transdiagnostic perspective for conceptualizing the relationship between reward processing and psychiatric symptoms defined broadly.

CONCLUSION

We propose that vulnerability to either motivational anhedonia or approach-related hypo/manic symptoms involve extreme and opposite profiles of reward processing. We further propose that an equifinality and multifinality perspective may serve as a useful framework for future research on reward processing abnormalities and psychiatric symptoms.

Common Dimensional Reward Deficits Across Mood and Psychotic Disorders: A Connectome-Wide Association Study

OBJECTIVE

Anhedonia is central to multiple psychiatric disorders and causes substantial disability. A dimensional conceptualization posits that anhedonia severity is related to a transdiagnostic continuum of reward deficits in specific neural networks. Previous functional connectivity studies related to anhedonia have focused on case-control comparisons in specific disorders, using region-specific seed-based analyses. Here, the authors explore the entire functional connectome in relation to reward responsivity across a population of adults with heterogeneous psychopathology.

METHOD

In a sample of 225 adults from five diagnostic groups (major depressive disorder, N=32; bipolar disorder, N=50; schizophrenia, N=51; psychosis risk, N=39; and healthy control subjects, N=53), the authors conducted a connectome-wide analysis examining the relationship between a dimensional measure of reward responsivity (the reward sensitivity subscale of the Behavioral Activation Scale) and resting-state functional connectivity using multivariate distance-based matrix regression.

RESULTS

The authors identified foci of dysconnectivity associated with reward responsivity in the nucleus accumbens, the default mode network, and the cingulo-opercular network. Follow-up analyses revealed dysconnectivity among specific large-scale functional networks and their connectivity with the nucleus accumbens. Reward deficits were associated with decreased connectivity between the nucleus accumbens and the default mode network and increased connectivity between the nucleus accumbens and the cingulo-opercular network. In addition, impaired reward responsivity was associated with default mode network hyperconnectivity and diminished connectivity between the default mode network and the cingulo-opercular network.

CONCLUSIONS

These results emphasize the centrality of the nucleus accumbens in the pathophysiology of reward deficits and suggest that dissociable patterns of connectivity among large-scale networks are critical to the neurobiology of reward dysfunction across clinical diagnostic categories.

A Transdiagnostic Review of Negative Symptom Phenomenology and Etiology

In the DSM5, negative symptoms are 1 of the 5 core dimensions of psychopathology evaluated for schizophrenia. However, negative symptoms are not pathognomonic-they are also part of the diagnostic criteria for other schizophrenia-spectrum disorders, disorders that sometimes have comorbid psychosis, diagnoses not in the schizophrenia-spectrum, and the general "nonclinical" population. Although etiological models of negative symptoms have been developed for chronic schizophrenia, there has been little attention given to whether these models have transdiagnostic applicability. In the current review, we examine areas of commonality and divergence in the clinical presentation and etiology of negative symptoms across diagnostic categories. It was concluded that negative symptoms are relatively frequent across diagnostic categories, but individual disorders may differ in whether their negative symptoms are persistent/transient or primary/secondary. Evidence for separate dimensions of volitional and expressive symptoms exists, and there may be multiple mechanistic pathways to the same symptom phenomenon among DSM-5 disorders within and outside the schizophrenia-spectrum (ie, equifinality). Evidence for a novel transdiagnostic etiological model is presented based on the Research Domain Criteria (RDoC) constructs, which proposes the existence of 2 such pathways-a hedonic pathway and a cognitive pathway-that can both lead to expressive or volitional symptoms. To facilitate treatment breakthroughs, future transdiagnostic studies on negative symptoms are warranted that explore mechanisms underlying volitional and expressive pathology.

A Brain on a Roller Coaster: Can the Dopamine Reward System Act as a Protagonist to Subdue the Ups and Downs of Bipolar Disorder?

One of the most interesting but tenebrous parts of the bipolar disorder (BD) story is the switch between (hypo)mania and depression, which can give bipolar patients a thrilling, but somewhat perilous, ‘ride’. Numerous studies have pointed out that there are some recognizable differences (either state-dependent or state-independent) in several brain regions of people with BD, including components of the brain’s reward system. Understanding the underpinning mechanisms of high and low mood statuses in BD has potential, not only for the development of highly specific and selective pharmaceutical agents, but also for better treatment approaches and psychological interventions to manage BD and, thus, give patients a safer ride. Herein, we review evidence that supports involvement of the reward system in the pathophysiology of mood swings, with the main focus on the mesocorticolimbic dopaminergic neural circuitry. Principally using findings from neuroimaging studies, we aim to signpost readers as to how mood alterations may affect different areas of the reward system and how antipsychotic drugs can influence the activity of these brain areas. Finally, we critically evaluate the hypothesis that the mesocorticolimbic dopamine reward system may act as a functional rheostat for different mood states.

Functional Neuroimaging Predictors of Self-Reported Psychotic Symptoms in Adolescents

OBJECTIVE

This study investigated the neural correlates of psychotic-like experiences in youths during tasks involving inhibitory control, reward anticipation, and emotion processing. A secondary aim was to test whether these neurofunctional correlates of risk were predictive of psychotic symptoms 2 years later.

METHOD

Functional imaging responses to three paradigms-the stop-signal, monetary incentive delay, and faces tasks-were collected in youths at age 14, as part of the IMAGEN study. At baseline, youths from London and Dublin sites were assessed on psychotic-like experiences, and those reporting significant experiences were compared with matched control subjects. Significant brain activity differences between the groups were used to predict, with cross-validation, the presence of psychotic symptoms in the context of mood fluctuation at age 16, assessed in the full sample. These prediction analyses were conducted with the London-Dublin subsample (N=246) and the full sample (N=1,196).

RESULTS

Relative to control subjects, youths reporting psychotic-like experiences showed increased hippocampus/amygdala activity during processing of neutral faces and reduced dorsolateral prefrontal activity during failed inhibition. The most prominent regional difference for classifying 16-year-olds with mood fluctuation and psychotic symptoms relative to the control groups (those with mood fluctuations but no psychotic symptoms and those with no mood symptoms) was hyperactivation of the hippocampus/amygdala, when controlling for baseline psychotic-like experiences and cannabis use.

CONCLUSIONS

The results stress the importance of the limbic network's increased response to neutral facial stimuli as a marker of the extended psychosis phenotype. These findings might help to guide early intervention strategies for at-risk youths.

Reduced levels of Cacna1c attenuate mesolimbic dopamine system function

Genetic variation in CACNA1C, which codes for the L-type calcium channel (LTCC) Cav 1.2, is associated with clinical diagnoses of bipolar disorder, depression and schizophrenia. Dysregulation of the mesolimbic-dopamine (ML-DA) system is linked to these syndromes and LTCCs are required for normal DAergic neurotransmission between the ventral tegmental area (VTA) and nucleus accumbens (NAc). It is unclear, however, how variations in CACNA1C genotype, and potential subsequent changes in expression levels in these regions, modify risk. Using constitutive and conditional knockout mice, and treatment with the LTCC antagonist nimodipine, we examined the role of Cacna1c in DA-mediated behaviors elicited by psychomotor stimulants. Using fast-scan cyclic voltammetry, DA release and reuptake in the NAc were measured. We find that subsecond DA release in Cacna1c haploinsufficient mice lacks normal sensitivity to inhibition of the DA transporter (DAT). Constitutive haploinsufficiency of Cacna1c led to attenuation of hyperlocomotion following acute administration of stimulants specific to DAT, and locomotor sensitization of these mice to the DAT antagonist GBR12909 did not reach the same level as wild-type mice. The maintenance of sensitization to GBR12909 was attenuated by administration of nimodipine. Sensitization to GBR12909 was attenuated in mice with reduced Cacna1c selectively in the VTA but not in the NAc. Our findings show that Cacna1c is crucial for normal behavioral responses to DA stimulants and that its activity in the VTA is required for behavioral sensitization. Cacna1c likely exerts these effects through modifications to presynaptic ML-DA system function.

Circuits Regulating Pleasure and Happiness in Bipolar Disorder

According to our model, the motivation for appetitive-searching vs. distress-avoiding behaviors is regulated by two parallel cortico-striato-thalamo-cortical (CSTC) re-entry circuits that include the core and the shell parts of the nucleus accumbens, respectively. An entire series of basal ganglia, running from the caudate nucleus on one side to the centromedial amygdala on the other side, control the intensity of these reward-seeking and misery-fleeing behaviors by stimulating the activity of the (pre)frontal and limbic cortices. Hyperactive motivation to display behavior that potentially results in reward induces feelings of hankering (relief leads to pleasure); while, hyperactive motivation to exhibit behavior related to avoidance of aversive states results in dysphoria (relief leads to happiness). These two systems collaborate in a reciprocal fashion. We hypothesized that the mechanism inducing the switch from bipolar depression to mania is the most essential characteristic of bipolar disorder. This switch is attributed to a dysfunction of the lateral habenula, which regulates the activity of midbrain centers, including the dopaminergic ventral tegmental area (VTA). From an evolutionary perspective, the activity of the lateral habenula should be regulated by the human homolog of the habenula-projecting globus pallidus, which in turn might be directed by the amygdaloid complex and the phylogenetically old part of the limbic cortex. In bipolar disorder, it is possible that the system regulating the activity of this reward-driven behavior is damaged or the interaction between the medial and lateral habenula may be dysfunctional. This may lead to an adverse coupling between the activities of the misery-fleeing and reward-seeking circuits, which results in independently varying activities.

Myelination of the brain in Major Depressive Disorder: An in vivo quantitative magnetic resonance imaging study

Evidence from post-mortem, genetic, neuroimaging, and non-human animal research suggests that Major Depressive Disorder (MDD) is associated with abnormalities in brain myelin content. Brain regions implicated in this research, and in MDD more generally, include the nucleus accumbens (NAcc), lateral prefrontal cortex (LPFC), insula, subgenual anterior cingulate cortex (sgACC), and medial prefrontal cortex (mPFC). We examined whether MDD is characterized by reduced myelin at the whole-brain level and in NAcc, LPFC, insula, sgACC, and mPFC. Quantitative magnetic resonance imaging (qMRI) permits the assessment of myelin content, in vivo, in the human brain through the measure of R1. In this study we used qMRI to measure R1 in 40 MDD and 40 healthy control (CTL) participants. We found that the MDD participants had lower levels of myelin than did the CTL participants at the whole-brain level and in the NAcc, and that myelin in the LPFC was reduced in MDD participants who had experienced a greater number of depressive episodes. Although further research is needed to elucidate the role of myelin in affecting emotional, cognitive, behavioral, and clinical aspects of MDD, the current study provides important new evidence that a fundamental property of brain composition, myelin, is altered in this disorder.

Accelerated aging of the putamen in patients with major depressive disorder

BACKGROUND

Growing evidence indicates that major depressive disorder (MDD) is characterized by accelerated biological aging, including greater age-related changes in physiological functioning. The disorder is also associated with abnormal neural reward circuitry, particularly in the basal ganglia (BG). Here we assessed age-related changes in BG volume in both patients with MDD and healthy control participants.

METHODS

We obtained whole-brain T₁-weighted images from patients with MDD and healthy controls. We estimated grey matter volumes of the BG, including the nucleus accumbens, caudate, pallidum and putamen. Volumes were assessed using multivariate analysis of covariance (MANCOVA) with age as a covariate, followed by appropriate post hoc tests.

RESULTS

We included 232 individuals (116 patients with MDD) in our analysis. The MANCOVA yielded a significant group × age interaction (p = 0.043). Analyses for each region yielded a significant group × age interaction in the putamen (univariate test, p = 0.005; permutation test, p = 0.004); this effect was not significant in the other regions. The negative association between age and putamen volume was twice as large in the MDD than in the control group (-35.2 v. -16.7 mm³/yr), indicating greater age-related volumetric decreases in the putamen in individuals with MDD than in controls.

LIMITATIONS

These findings are cross-sectional; future studies should assess the longitudinal impact of accelerated aging on anhedonia and neural indices of reward processing.

CONCLUSION

Our results indicate that putamen aging is accelerated in patients with MDD. Thus, the putamen may uniquely contribute to the adverse long-term effects of depressive psychopathology and may be a useful target for the treatment of MDD across the lifespan.

Social defeat disrupts reward learning and potentiates striatal nociceptin/orphanin FQ mRNA in rats

RATIONALE

Mood disorders can be triggered by stress and are characterized by deficits in reward processing, including disrupted reward learning (the ability to modulate behavior according to past rewards). Reward learning is regulated by the anterior cingulate cortex (ACC) and striatal circuits, both of which are implicated in the pathophysiology of mood disorders.

OBJECTIVES

Here, we assessed in rats the effects of a potent stressor (social defeat) on reward learning and gene expression in the ACC, ventral tegmental area (VTA), and striatum.

METHODS

Adult male Wistar rats were trained on an operant probabilistic reward task (PRT) and then exposed to 3 days of social defeat before assessment of reward learning. After testing, the ACC, VTA, and striatum were dissected, and expression of genes previously implicated in stress was assessed.

RESULT

Social defeat blunted reward learning (manifested as reduced response bias toward a more frequently rewarded stimulus) and was associated with increased nociceptin/orphanin FQ (N/OFQ) peptide mRNA levels in the striatum and decreased Fos mRNA levels in the VTA. Moreover, N/OFQ peptide and nociceptin receptor mRNA levels in the ACC, VTA and striatum were inversely related to reward learning.

CONCLUSIONS

The behavioral findings parallel previous data in humans, suggesting that stress similarly disrupts reward learning in both species. Increased striatal N/OFQ mRNA in stressed rats characterized by impaired reward learning is consistent with accumulating evidence that antagonism of nociceptin receptors, which bind N/OFQ, has antidepressant-like effects. These results raise the possibility that nociceptin systems represent a molecular substrate through which stress produces reward learning deficits in mood disorders.

The roles of valuation and reward processing in cognitive function and psychiatric disorders

In neuroeconomics, valuation refers to the process of assigning values to states and actions on the basis of the animal's current representation of the environment, while reward processing corresponds to processing the feedback received from the environment to update the values of states and actions. In this article, we review the brain circuits associated with valuation and reward processing and argue that these are fundamental processes critical to many cognitive functions. Specifically, we focus on the role of valuation and reward processing in attention, memory, decision making, and learning. Next, the extant neuroimaging literature on a number of psychiatric disorders is reviewed (i.e., addiction, pathological gambling, schizophrenia, and mood disorders), and an argument is made that associated deficits in cognitive functions can be explained in terms of abnormal valuation and reward processing. The review concludes with the impact of this framework in clinical settings and prescriptions for future research, in particular with regard to the conversions of qualitatively different valuation systems into a system of common currency.

New insights into early-life stress and behavioral outcomes

Adverse early-life experiences, including various forms of early-life stress, have consistently been linked with vulnerability to cognitive and emotional disorders later in life. Understanding the mechanisms underlying the enduring consequences of early-life stress is an active area of research, because this knowledge is critical for developing potential interventions. Animal models of early-life stress typically rely on manipulating maternal/parental presence and care, because these are the major source of early-life experiences in humans. Diverse models have been created, and have resulted in a wealth of behavioral outcomes. Here we focus on recent findings highlighting early-life stress-induced behavioral disturbances, ranging from hippocampus-dependent memory deficits to problems with experiencing pleasure (anhedonia). The use of naturalistic animal models of chronic early-life stress provides insight into the spectrum of cognitive and emotional outcomes and enables probing the underlying mechanisms using molecular-, cellular-, and network-level approaches.

Depressive Symptoms and the Anticipation and Experience of Uplifting Events in Everyday Life

OBJECTIVE

Despite proliferation of laboratory-based studies examining reward functioning in depression, few studies have examined these processes in everyday life. We addressed this shortcoming by exploring experience and anticipation of uplifting experiences under ecologically valid conditions METHOD: One hundred fifty-seven young adults, oversampled for depressive symptoms, completed a 14-day diary tracking mood in relation to recent and anticipated positive events RESULTS: Consistent with studies supporting "mood-brightening" effects in depression, participants with greater baseline dysphoria showed stronger associations between elevated daily uplifts and lower daily depressive symptoms, particularly when events were interpersonal in nature. Baseline dysphoria was associated with lower daily anticipation of positive next-day experiences; however, when dysphoric individuals did anticipate positive experiences, they experienced greater reductions in depressed mood CONCLUSION: Results suggest that despite reward processing deficits found in laboratory studies, dysphoric individuals show improvements in mood in conjunction with anticipation and consumption of uplifting events in daily life.

Struggling toward reward: Recent experience of anhedonia interacts with motivation to predict reward pursuit in the face of a stressful manipulation

Anhedonia, or the loss of interest and/or pleasure, is a core symptom of depression. Individuals experiencing anhedonia have difficulty motivating themselves to pursue rewarding stimuli, which can result in dysfunction. Action orientation is a motivational factor that might interact with anhedonia to potentially buffer against this dysfunction, as action-oriented individuals upregulate positive affect to quickly motivate themselves to complete goals in the face of stress. The Effort-Expenditure for Rewards Task (EEfRT) is a promising new method for examining differences in motivation in individuals experiencing anhedonia. In the EEfRT, participants choose either easier tasks associated with smaller monetary rewards or harder tasks associated with larger monetary rewards. We examined the relationship between action orientation and EEfRT performance following a negative mood induction in a sample with varying levels of anhedonia. There were two competing hypotheses: (1) action orientation would act as a buffer against anhedonia such that action-oriented individuals, regardless of anhedonic symptoms, would be motivated to pursue greater rewards despite stress, or (2) anhedonia would act as a debilitating factor such that individuals with elevated anhedonic symptoms, regardless of action orientation, would not pursue greater rewards. We examined these hypotheses via Generalized Estimating Equations and found an interaction between anhedonia and action orientation. At low levels of anhedonia, action orientation was associated with effort for reward, but this relationship was not present at high levels of anhedonia. Thus, at low levels of anhedonia, action orientation acted as a buffer against stress, but at high levels, anhedonia debilitated action orientation so that it was no longer a promotive factor.

Resting state functional connectivity in women with bipolar disorder during clinical remission

OBJECTIVES

Periods of euthymia in bipolar disorder (BD) serve as a valuable time to study trait-based pathophysiology. The use of resting state functional connectivity (Rs-FC) can aid in the understanding of BD pathophysiology free of task or mood state biases. The present study investigated two unexplored areas of Rs-FC research in bipolar remission: (i) Rs-FC in women, controlling for the potential influence of premenstrual symptoms, and (ii) the use of both independent component analysis (ICA) and seed-based analysis (SBA) to investigate Rs-FC.

METHODS

We investigated Rs-FC of the default mode network, meso-paralimbic network and fronto-parietal network in a sample of 32 euthymic women with BD and 36 age-matched controls during the mid-follicular phase of their menstrual cycle. Rs-FC was assessed with ICA and SBA using the posterior cingulate cortex (PCC), amygdala and dorsolateral prefrontal cortex (dlPFC) as seed points for their respective resting state networks.

RESULTS

In BD, compared to controls, SBAs revealed increased coupling between the PCC and the angular gyrus (P=.002, false discovery rate [FDR]-corrected) and between the right dlPFC and the brainstem (P=.03, FDR-corrected). In BD only, PCC-angular gyrus coupling was correlated with anxiety symptoms. Group differences in Rs-FC using ICA did not survive multiple comparisons.

CONCLUSIONS

Negative findings from whole-brain ICA Rs-FC may reflect a state of clinical remission in BD. Heightened activation between the PCC and the angular gyrus and between the dlPFC and the brainstem may reflect (i) an abnormal trait integration of affective information during clinical remission and/or (ii) an adaptive compensatory mechanism required for clinical stabilization.

The effects of medication and current mood upon facial emotion recognition: findings from a large bipolar disorder cohort study

OBJECTIVES

Emotional processing abnormalities have been implicated in bipolar disorder (BD) but studies are typically small and uncontrolled. Here, facial expression recognition was explored in a large and naturalistically recruited cohort of BD patients.

METHODS

271 patients with BD completed the facial expression recognition task. The effects of current medication together with the influence of current mood state and diagnostic subtype were assessed whilst controlling for the effects of demographic variables.

RESULTS

Patients who were currently receiving treatment with lithium demonstrated significantly poorer accuracy in recognising angry faces, an effect that held in a monotherapy sub-analysis comparing those participants on lithium only and those who were medication-free. Accuracy in recognising angry faces was also lower amongst participants currently taking dopamine antagonists (antipsychotics). Higher levels of current depressive symptoms were linked to poorer accuracy at identifying happy faces.

CONCLUSION

Use of lithium and possibly dopamine antagonists may be associated with reduced processing of anger cues in BD. Findings support the existence of mood-congruent negative biases associated with depressive symptoms in BD. Observational cohort studies provide opportunities to explore the substantial effects of demographic, psychometric and clinical variables on cognitive performance and emotional processing.

Defining biotypes for depression and anxiety based on large-scale circuit dysfunction: a theoretical review of the evidence and future directions for clinical translation

Complex emotional, cognitive and self-reflective functions rely on the activation and connectivity of large-scale neural circuits. These circuits offer a relevant scale of focus for conceptualizing a taxonomy for depression and anxiety based on specific profiles (or biotypes) of neural circuit dysfunction. Here, the theoretical review first outlines the current consensus as to what constitutes the organization of large-scale circuits in the human brain identified using parcellation and meta-analysis. The focus is on neural circuits implicated in resting reflection (default mode), detection of "salience," affective processing ("threat" and "reward"), "attention," and "cognitive control." Next, the current evidence regarding which type of dysfunctions in these circuits characterize depression and anxiety disorders is reviewed, with an emphasis on published meta-analyses and reviews of circuit dysfunctions that have been identified in at least two well-powered case:control studies. Grounded in the review of these topics, a conceptual framework is proposed for considering neural circuit-defined "biotypes." In this framework, biotypes are defined by profiles of extent of dysfunction on each large-scale circuit. The clinical implications of a biotype approach for guiding classification and treatment of depression and anxiety is considered. Future research directions will develop the validity and clinical utility of a neural circuit biotype model that spans diagnostic categories and helps to translate neuroscience into clinical practice in the real world.

Vulnerability or Sensitivity to the Environment? Methodological Issues, Trends, and Recommendations in Gene-Environment Interactions Research in Human Behavior

Research on the potential role of gene-environment interactions (GxE) in explaining vulnerability to psychopathology in humans has witnessed a shift from a diathesis-stress perspective to differential susceptibility approaches. This paper critically reviews methodological issues and trends in this body of research. Databases were screened for studies of GxE in the prediction of personality traits, behavior, and mental health disorders in humans published between January 2002 and January 2015. In total, 315 papers were included. Results showed that 34 candidate genes have been included in GxE studies. Independent of the type of environment studied (early or recent life events, positive or negative environments), about 67-83% of studies have reported significant GxE interactions, which is consistent with a social susceptibility model. The percentage of positive results does not seem to differ depending on the gene studied, although publication bias might be involved. However, the number of positive findings differs depending on the population studied (i.e., young adults vs. older adults). Methodological considerations limit the ability to draw strong conclusions, particularly as almost 90% (n = 283/315) of published papers are based on samples from North America and Europe, and about 70% of published studies (219/315) are based on samples that were also used in other reports. At the same time, there are clear indications of methodological improvements over time, as is shown by a significant increase in longitudinal and experimental studies as well as in improved minimum genotyping. Recommendations for future research, such as minimum quality assessment of genes and environmental factors, specifying theoretical models guiding the study, and taking into account of cultural, ethnic, and lifetime perspectives, are formulated.

Inflammation, Glutamate, and Glia: A Trio of Trouble in Mood Disorders

Increasing data indicate that inflammation and alterations in glutamate neurotransmission are two novel pathways to pathophysiology in mood disorders. The primary goal of this review is to illustrate how these two pathways may converge at the level of the glia to contribute to neuropsychiatric disease. We propose that a combination of failed clearance and exaggerated release of glutamate by glial cells during immune activation leads to glutamate increases and promotes aberrant extrasynaptic signaling through ionotropic and metabotropic glutamate receptors, ultimately resulting in synaptic dysfunction and loss. Furthermore, glutamate diffusion outside the synapse can lead to the loss of synaptic fidelity and specificity of neurotransmission, contributing to circuit dysfunction and behavioral pathology. This review examines the fundamental role of glia in the regulation of glutamate, followed by a description of the impact of inflammation on glial glutamate regulation at the cellular, molecular, and metabolic level. In addition, the role of these effects of inflammation on glia and glutamate in mood disorders will be discussed along with their translational implications.

EEG marker of inhibitory brain activity correlates with resting-state cerebral blood flow in the reward system in major depression

Frontal alpha band asymmetry (FAA) is a marker of altered reward processing in major depressive disorder (MDD), associated with reduced approach behavior and withdrawal. However, its association with brain metabolism remains unclear. The aim of this study was to investigate FAA and its correlation with resting-state cerebral blood flow (rCBF). We hypothesized an association of FAA with regional rCBF in brain regions relevant to reward processing and motivated behavior, such as the striatum. We enrolled 20 patients and 19 healthy subjects. FAA scores and rCBF were quantified with the use of EEG and arterial spin labeling. Correlations of the two were evaluated, as well as the association with FAA and psychometric assessments of motivated behavior and anhedonia. Patients showed a left-lateralized pattern of frontal alpha activity and a correlation of FAA lateralization with subscores of Hamilton Depression Rating Scale linked to motivated behavior. An association of rCBF and FAA scores was found in clusters in the dorsolateral prefrontal cortex bilaterally (patients), in the left medial frontal gyrus, in the right caudate head and in the right inferior parietal lobule (whole group). No correlations were found in healthy controls. Higher inhibitory right-lateralized alpha power was associated with lower rCBF values in prefrontal and striatal regions, predominantly in the right hemisphere, which are involved in the processing of motivated behavior and reward. Inhibitory brain activity in the reward system may contribute to some of the motivational problems observed in MDD.

Reward Sensitivity Enhances Ventrolateral Prefrontal Cortex Activation during Free Choice

Expressing one's preference via choice can be rewarding, particularly when decisions are voluntarily made as opposed to being forced. An open question is whether engaging in choices involving rewards recruits distinct neural systems as a function of sensitivity to reward. Reward sensitivity is a trait partly influenced by the mesolimbic dopamine system, which can impact an individual's neural and behavioral response to reward cues. Here, we investigated how reward sensitivity contributes to neural activity associated with free and forced choices. Participants underwent a simple decision-making task, which presented free- or forced-choice trials in the scanner. Each trial presented two cues (i.e., points or information) that led to monetary reward at the end of the task. In free-choice trials, participants were offered the opportunity to choose between different reward cues (e.g., points vs. information), whereas forced-choice trials forced individuals to choose within a given reward cue (e.g., information vs. information, or points vs. points). We found enhanced ventrolateral prefrontal cortex (VLPFC) activation during free choice compared to forced choice in individuals with high reward sensitivity scores. Next, using the VLPFC as a seed, we conducted a PPI analysis to identify brain regions that enhance connectivity with the VLPFC during free choice. Our PPI analyses on free vs. forced choice revealed increased VLPFC connectivity with the posterior cingulate and precentral gyrus in reward sensitive individuals. These findings suggest reward sensitivity may recruit attentional control processes during free choice potentially supporting goal-directed behavior and action selection.

Loss of NMDA receptors in dopamine neurons leads to the development of affective disorder-like symptoms in mice

The role of changes in dopamine neuronal activity during the development of symptoms in affective disorders remains controversial. Here, we show that inactivation of NMDA receptors on dopaminergic neurons in adult mice led to the development of affective disorder-like symptoms. The loss of NMDA receptors altered activity and caused complete NMDA-insensitivity in dopamine-like neurons. Mutant mice exhibited increased immobility in the forced swim test and a decrease in social interactions. Mutation also led to reduced saccharin intake, however the preference of sweet taste was not significantly decreased. Additionally, we found that while mutant mice were slower to learn instrumental tasks, they were able to reach the same performance levels, had normal sensitivity to feedback and showed similar motivation to exert effort as control animals. Taken together these results show that inducing the loss of NMDA receptor-dependent activity in dopamine neurons is associated with development of affective disorder-like symptoms.

How emotion context modulates unconscious goal activation during motor force exertion

Priming participants with emotional or action-related concepts influences goal formation and motor force output during effort exertion tasks, even without awareness of priming information. However, little is known about neural processes underpinning how emotional cues interact with action (or inaction) goals to motivate (or demotivate) motor behaviour. In a novel functional neuroimaging paradigm, visible emotional images followed by subliminal action or inaction word primes were presented before participants performed a maximal force exertion. In neutral emotional contexts, maximum force was lower following inaction than action primes. However, arousing emotional images had interactive motivational effects on the motor system: Unpleasant images prior to inaction primes increased force output (enhanced effort exertion) relative to control primes, and engaged a motivation-related network involving ventral striatum, extended amygdala, as well as right inferior frontal cortex. Conversely, pleasant images presented before action (versus control) primes decreased force and activated regions of the default-mode network, including inferior parietal lobule and medial prefrontal cortex. These findings show that emotional context can determine how unconscious goal representations influence motivational processes and are transformed into actual motor output, without direct rewarding contingencies. Furthermore, they provide insight into altered motor behaviour in psychopathological disorders with dysfunctional motivational processes.

Frequency-specific alterations in functional connectivity in treatment-resistant and -sensitive major depressive disorder

Major depressive disorder (MDD) may involve alterations in brain functional connectivity in multiple neural circuits and present large-scale network dysfunction. Patients with treatment-resistant depression (TRD) and treatment-sensitive depression (TSD) show different responses to antidepressants and aberrant brain functions. This study aims to investigate functional connectivity patterns of TRD and TSD at the whole brain resting state. Seventeen patients with TRD, 17 patients with TSD, and 17 healthy controls matched with age, gender, and years of education were recruited in this study. The brain was divided using an automated anatomical labeling atlas into 90 regions of interest, which were used to construct the entire brain functional networks. An analysis method called network-based statistic was used to explore the dysconnected subnetworks of TRD and TSD at different frequency bands. At resting state, TSD and TRD present characteristic patterns of network dysfunction at special frequency bands. The dysconnected subnetwork of TSD mainly lies in the fronto-parietal top-down control network. Moreover, the abnormal neural circuits of TRD are extensive and complex. These circuits not only depend on the abnormal affective network but also involve other networks, including salience network, auditory network, visual network, and language processing cortex. Our findings reflect that the pathological mechanism of TSD may refer to impairment in cognitive control, whereas TRD mainly triggers the dysfunction of emotion processing and affective cognition. This study reveals that differences in brain functional connectivity at resting state reflect distinct pathophysiological mechanisms in TSD and TRD. These findings may be helpful in differentiating two types of MDD and predicting treatment responses.

Brain functional effects of psychopharmacological treatments in bipolar disorder

Functional magnetic resonance imaging (fMRI) studies have contributed to the understanding of bipolar disorder. However the effect of medication on brain activation remains poorly understood. We conducted an extensive literature review on PubMed and ScienceDirect to investigate the influence of medication in fMRI studies, including both longitudinal and cross-sectional studies, which aimed at assessing this influence. Although we reported all reviewed studies, we gave greater emphasis to studies with the most robust methodology. One hundred and forty studies matched our inclusion criteria and forty-seven studies demonstrated an effect of pharmacological treatment on fMRI blood oxygen level dependent (BOLD) signal in adults and children with bipolar disorder. Out of these studies, nineteen were longitudinal. Most of cross-sectional studies suffered from methodological bias, due to post-hoc analyses performed on a limited number of patients and did not find any effect of medication. However, both longitudinal and cross-sectional studies showing an impact of treatment tend to suggest that medication prescribed to patients with bipolar disorder mostly influenced brain activation in prefrontal regions, when measured by tasks involving emotional regulation and processing as well as non-emotional cognitive tasks. FMRI promises to elucidate potential new biomarkers in bipolar disorder and could be used to evaluate the effect of new therapeutic compounds. Further research is needed to disentangle the effect of medication and the influence of the changes in mood state on brain activation in patients with bipolar disorder.

Stress and reward processing in bipolar disorder: a functional magnetic resonance imaging study

OBJECTIVES

A link between negative life stress and the onset of mood episodes in bipolar disorder (BD) has been established, but processes underlying such a link remain unclear. Growing evidence suggests that stress can negatively affect reward processing and related neurobiological substrates, indicating that a dysregulated reward system may provide a partial explanation. The aim of this study was to test the impact of stress on reward-related neural functioning in BD.

METHODS

Thirteen euthymic or mildly depressed individuals with BD and 15 controls performed a Monetary Incentive Delay (MID) task while undergoing functional magnetic resonance imaging during no-stress and stress (negative psychosocial stressor involving poor performance feedback and threat of monetary deductions) conditions.

RESULTS

In hypothesis-driven region-of-interest analyses, a significant group-by-condition interaction emerged in the amygdala during reward anticipation. Relative to controls, while anticipating a potential reward, subjects with BD were characterized by amygdalar hyperactivation in the no-stress condition but hypoactivation during stress. Moreover, relative to controls, subjects with BD had significantly larger amygdala volumes. After controlling for structural differences, the effects of stress on amygdalar function remained, whereas groups no longer differed during the no-stress condition. During reward consumption, a group-by-condition interaction emerged in the putamen due to increased putamen activation in response to rewards in participants with BD during stress, but an opposite pattern in controls.

CONCLUSIONS

Overall, findings highlight possible impairments in using reward-predicting cues to adaptively engage in goal-directed actions in BD, combined with stress-induced hypersensitivity to reward consumption. Potential clinical implications are discussed.

Exercising control over bipolar disorder

Following extensive research exercise has emerged as an effective treatment for major depressive disorder, and it is now a recognised therapy alongside other interventions. In contrast, there is a paucity of research examining the therapeutic effects of exercise for those with bipolar disorder. Given that dysfunctional reward processing is central to bipolar disorder, research suggests that exercise can perhaps be framed as a reward-related event that may have the potential to precipitate a manic episode. The behavioural activation system (BAS) is a neurobehavioural system that is associated with responding to reward and provides an appropriate framework to theoretically examine and better understand the effects of exercise treatment on bipolar disorder. This article discusses recent research findings and provides an overview of the extant literature related to the neurobiological underpinnings of BAS and exercise as they relate to bipolar disorder. This is important clinically because depending on mood state in bipolar disorder, we postulate that exercise could be either beneficial or deleterious with positive or negative effects on the illness. Clearly, this complicates the evaluation of exercise as a potential treatment in terms of identifying its optimal characteristics in this population.

L-type Ca2+ channels in mood, cognition and addiction: integrating human and rodent studies with a focus on behavioural endophenotypes

Brain Cav 1.2 and Cav 1.3 L-type Ca2+ channels play key physiological roles in various neuronal processes that contribute to brain function. Genetic studies have recently identified CACNA1C as a candidate risk gene for bipolar disorder (BD), schizophrenia (SCZ), major depressive disorder (MDD) and autism spectrum disorder (ASD), and CACNA1D for BD and ASD, suggesting a contribution of Cav 1.2 and Cav 1.3 Ca2+ signalling to the pathophysiology of neuropsychiatric disorders. Once considered sole clinical entities, it is now clear that BD, SCZ, MDD and ASD share common phenotypic features, most likely due to overlapping neurocircuitry and common molecular mechanisms. A major future challenge lies in translating the human genetic findings to pathological mechanisms that are translatable back to the patient. One approach for tackling such a daunting scientific endeavour for complex behaviour-based neuropsychiatric disorders is to examine intermediate biological phenotypes in the context of endophenotypes within distinct behavioural domains. This will better allow us to integrate findings from genes to behaviour across species, and improve the chances of translating preclinical findings to clinical practice.

Medial reward and lateral non-reward orbitofrontal cortex circuits change in opposite directions in depression

The first brain-wide voxel-level resting state functional connectivity neuroimaging analysis of depression is reported, with 421 patients with major depressive disorder and 488 control subjects. Resting state functional connectivity between different voxels reflects correlations of activity between those voxels and is a fundamental tool in helping to understand the brain regions with altered connectivity and function in depression. One major circuit with altered functional connectivity involved the medial orbitofrontal cortex Brodmann area 13, which is implicated in reward, and which had reduced functional connectivity in depression with memory systems in the parahippocampal gyrus and medial temporal lobe, especially involving the perirhinal cortex Brodmann area 36 and entorhinal cortex Brodmann area 28. The Hamilton Depression Rating Scale scores were correlated with weakened functional connectivity of the medial orbitofrontal cortex Brodmann area 13. Thus in depression there is decreased reward-related and memory system functional connectivity, and this is related to the depressed symptoms. The lateral orbitofrontal cortex Brodmann area 47/12, involved in non-reward and punishing events, did not have this reduced functional connectivity with memory systems. Second, the lateral orbitofrontal cortex Brodmann area 47/12 had increased functional connectivity with the precuneus, the angular gyrus, and the temporal visual cortex Brodmann area 21. This enhanced functional connectivity of the non-reward/punishment system (Brodmann area 47/12) with the precuneus (involved in the sense of self and agency), and the angular gyrus (involved in language) is thus related to the explicit affectively negative sense of the self, and of self-esteem, in depression. A comparison of the functional connectivity in 185 depressed patients not receiving medication and 182 patients receiving medication showed that the functional connectivity of the lateral orbitofrontal cortex Brodmann area 47/12 with these three brain areas was lower in the medicated than the unmedicated patients. This is consistent with the hypothesis that the increased functional connectivity of the lateral orbitofrontal cortex Brodmann area 47/12 is related to depression. Relating the changes in cortical connectivity to our understanding of the functions of different parts of the orbitofrontal cortex in emotion helps to provide new insight into the brain changes related to depression.

Investigating the Impact of a Genome-Wide Supported Bipolar Risk Variant of MAD1L1 on the Human Reward System

Recent genome-wide association studies have identified MAD1L1 (mitotic arrest deficient-like 1) as a susceptibility gene for bipolar disorder and schizophrenia. The minor allele of the single-nucleotide polymorphism (SNP) rs11764590 in MAD1L1 was associated with bipolar disorder. Both diseases, bipolar disorder and schizophrenia, are linked to functional alterations in the reward system. We aimed at investigating possible effects of the MAD1L1 rs11764590 risk allele on reward systems functioning in healthy adults. A large homogenous sample of 224 young (aged 18-31 years) participants was genotyped and underwent functional magnetic resonance imaging (fMRI). All participants performed the 'Desire-Reason Dilemma' paradigm investigating the neural correlates that underlie reward processing and active reward dismissal in favor of a long-term goal. We found significant hypoactivations of the ventral tegmental area (VTA), the bilateral striatum and bilateral frontal and parietal cortices in response to conditioned reward stimuli in the risk allele carriers compared with major allele carriers. In the dilemma situation, functional connectivity between prefrontal brain regions and the ventral striatum was significantly diminished in the risk allele carriers. Healthy risk allele carriers showed a significant deficit of their bottom-up response to conditioned reward stimuli in the bilateral VTA and striatum. Furthermore, functional connectivity between the ventral striatum and prefrontal areas exerting top-down control on the mesolimbic reward system was reduced in this group. Similar alterations in reward processing and disturbances of prefrontal control mechanisms on mesolimbic brain circuits have also been reported in bipolar disorder and schizophrenia. Together, these findings suggest the existence of an intermediate phenotype associated with MAD1L1.

Dopamine Receptor Genes Modulate Associative Memory in Old Age

Previous research shows that associative memory declines more than item memory in aging. Although the underlying mechanisms of this selective impairment remain poorly understood, animal and human data suggest that dopaminergic modulation may be particularly relevant for associative binding. We investigated the influence of dopamine (DA) receptor genes on item and associative memory in a population-based sample of older adults (n = 525, aged 60 years), assessed with a face-scene item associative memory task. The effects of single-nucleotide polymorphisms of DA D1 (DRD1; rs4532), D2 (DRD2/ANKK1/Taq1A; rs1800497), and D3 (DRD3/Ser9Gly; rs6280) receptor genes were examined and combined into a single genetic score. Individuals carrying more beneficial alleles, presumably associated with higher DA receptor efficacy (DRD1 C allele; DRD2 A2 allele; DRD3 T allele), performed better on associative memory than persons with less beneficial genotypes. There were no effects of these genes on item memory or other cognitive measures, such as working memory, executive functioning, fluency, and perceptual speed, indicating a selective association between DA genes and associative memory. By contrast, genetic risk for Alzheimer disease (AD) was associated with worse item and associative memory, indicating adverse effects of APOE ε4 and a genetic risk score for AD (PICALM, BIN1, CLU) on episodic memory in general. Taken together, our results suggest that DA may be particularly important for associative memory, whereas AD-related genetic variations may influence overall episodic memory in older adults without dementia.

Planning to make economic decisions in the future, but choosing impulsively now: are preference reversals related to symptoms of ADHD and depression?

A preference for smaller immediate rewards over larger delayed rewards (delay discounting, DD) is common in attention deficit hyperactivity disorder (ADHD), but rarely investigated in depression. Whether this preference is due to sensitivity to reward immediacy or delay aversion remains unclear. To investigate this, we examined whether ADHD and depressive symptoms are associated with preference reversals: a switch from smaller immediate rewards to larger delayed rewards when smaller rewards are also delayed. We also examined whether these symptoms differentially affect DD of losses. In Study 1 undergraduates completed a questionnaire about ADHD symptoms, and performed a hypothetical DD task. In the NOW condition, participants were presented with choices between a small reward available today and a large reward available after one year. In the FUTURE condition both rewards were delayed with +1 year. In Study 2 undergraduates completed questionnaires about ADHD and depressive symptoms and performed a DD task with gains and losses. Participants showed preference reversals in both studies and tasks. Losses were less steeply discounted than gains. ADHD and depressive symptoms did not influence these effects. Depressive symptoms, but not ADHD symptoms, were associated with less economic choices in general. These findings suggest that impulsive choice in depression is not explained by sensitivity to reward immediacy. Copyright © 2016 John Wiley & Sons, Ltd.

Future Research Directions in the Positive Valence Systems: Measurement, Development, and Implications for Youth Unipolar Depression

The Positive Valence Systems (PVS) have been introduced by the National Institute of Mental Health as a domain to help organize multiple constructs focusing on reward-seeking behaviors. However, the initial working model for this domain is strongly influenced by adult constructs and measures. Thus, the present review focuses on extending the PVS into a developmental context. Specifically, the review provides some hypotheses about the structure of the PVS, how PVS components may change throughout development, how family history of depression may influence PVS development, and potential means of intervening on PVS function to reduce onsets of depression. Future research needs in each of these areas are highlighted.

Divergent relationship of depression severity to social reward responses among patients with bipolar versus unipolar depression

Neuroimaging studies of mood disorders demonstrate abnormalities in brain regions implicated in reward processing. However, there is a paucity of research investigating how social rewards affect reward circuit activity in these disorders. Here, we evaluated the relationship of both diagnostic category and dimensional depression severity to reward system function in bipolar and unipolar depression. In total, 86 adults were included, including 24 patients with bipolar depression, 24 patients with unipolar depression, and 38 healthy comparison subjects. Participants completed a social reward task during 3T BOLD fMRI. On average, diagnostic groups did not differ in activation to social reward. However, greater depression severity significantly correlated with reduced bilateral ventral striatum activation to social reward in the bipolar depressed group, but not the unipolar depressed group. In addition, decreased left orbitofrontal cortical activation correlated with more severe symptoms in bipolar depression, but not unipolar depression. These differential dimensional effects resulted in a significant voxelwise group by depression severity interaction. Taken together, these results provide initial evidence that deficits in social reward processing are differentially related to depression severity in the two disorders.

Molecular Mechanism for Stress-Induced Depression Assessed by Sequencing miRNA and mRNA in Medial Prefrontal Cortex

Background

Major depression is a prevalent mood disorder. Chronic stress is presumably main etiology that leads to the neuron and synapse atrophies in the limbic system. However, the intermediate molecules from stresses to neuronal atrophy remain elusive, which we have studied in the medial prefrontal cortices from depression mice.

Methods and Results

The mice were treated by the chronic unpredictable mild stress (CUMS) until they expressed depression-like behaviors confirmed by the tests of sucrose preference, forced swimming and Y-maze. High-throughput sequencings of microRNA and mRNA in the medial prefrontal cortices were performed in CUMS-induced depression mice versus control mice to demonstrate the molecular profiles of major depression. In the medial prefrontal cortices of depression-like mice, the levels of mRNAs that translated the proteins for the GABAergic synapses, dopaminergic synapses, myelination, synaptic vesicle cycle and neuronal growth were downregulated. miRNAs of regulating these mRNAs are upregulated.

Conclusion

The deteriorations of GABAergic and dopaminergic synapses as well as axonal growth are associated with CUMS-induced depression.

Multifaceted Contributions by Different Regions of the Orbitofrontal and Medial Prefrontal Cortex to Probabilistic Reversal Learning

Different subregions of the prefrontal cortex (PFC) contribute to the ability to respond flexibly to changes in reward contingencies, with the medial versus orbitofrontal cortex (OFC) subregions contributing differentially to processes such as set-shifting and reversal learning. To date, the manner in which these regions may facilitate reversal learning in situations involving reward uncertainty remains relatively unexplored. We investigated the involvement of five distinct regions of the rat OFC (lateral and medial) and medial PFC (prelimbic, infralimbic, and anterior cingulate) on probabilistic reversal learning wherein "correct" versus "incorrect" responses were rewarded on 80% and 20% of trials, respectively. Contingencies were reversed repeatedly within a session. In well trained rats, inactivation of the medial or lateral OFC induced dissociable impairments in performance (indexed by fewer reversals completed) when outcomes were probabilistic, but not when they were assured. Medial OFC inactivation impaired probabilistic learning during the first discrimination, increased perseverative responding and reduced sensitivity to positive and negative feedback, suggestive of a deficit in incorporating information about previous action outcomes to guide subsequent behavior. Lateral OFC inactivation preferentially impaired performance during reversal phases. In contrast, prelimbic inactivation caused an apparent improvement in performance by increasing the number of reversals completed. This was associated with enhanced sensitivity to recently rewarded actions and reduced sensitivity to negative feedback. Infralimbic inactivation had no effect, whereas the anterior cingulate appeared to play a permissive role in this form of reversal learning. These results clarify the dissociable contributions of different regions of the frontal lobes to probabilistic learning.

SIGNIFICANCE STATEMENT

The ability to adjust behavior in response to changes involving uncertain or probabilistic reward contingencies is an essential survival skill that is impaired in a variety of psychiatric disorders. It is well established that different forms of cognitive flexibility are mediated by anatomically distinct regions of the frontal lobes when reinforcement contingencies are assured, however, less is known about the contribution of these regions to probabilistic reinforcement learning. Here we show that different regions of the orbitofrontal and medial prefrontal cortex make distinct contributions to probabilistic reversal learning. These findings provide novel information about the complex interplay between frontal lobe regions in mediating these processes and accordingly provide insight into possible pathophysiology that underlies impairments in cognitive flexibility observed in mental illnesses.

Positive Affectivity is Dampened in Youths with Histories of Major Depression and Their Never-Depressed Adolescent Siblings

While hedonic capacity is diminished during clinical depression, it is unclear whether that deficit constitutes a risk factor and/or persists after depression episodes remit. To examine these issues, adolescents with current/past major depression (probands; n=218), never depressed biological siblings of probands (n=207), and emotionally-well controls (n=183) were exposed to several positively valenced probes. Across baseline and hedonic probe conditions, controls consistently reported higher levels of positive affect than high-risk siblings, and siblings reported higher levels of positive affect than probands (remitted and depressed probands' reports were similar). Extent of positive affect across the protocol predicted adolescents' self-reports of social support network and parental reports of offspring's use of various adaptive mood repair responses in daily life. Attenuated hedonic responding among youths remitted from depression offers partial support for anhedonia as a trait, while its presence among never depressed high-risk siblings argues for anhedonia as a potential diathesis for clinical depression.

Anticipation-related brain connectivity in bipolar and unipolar depression: a graph theory approach

Bipolar disorder is often misdiagnosed as major depressive disorder, which leads to inadequate treatment. Depressed individuals versus healthy control subjects, show increased expectation of negative outcomes. Due to increased impulsivity and risk for mania, however, depressed individuals with bipolar disorder may differ from those with major depressive disorder in neural mechanisms underlying anticipation processes. Graph theory methods for neuroimaging data analysis allow the identification of connectivity between multiple brain regions without prior model specification, and may help to identify neurobiological markers differentiating these disorders, thereby facilitating development of better therapeutic interventions. This study aimed to compare brain connectivity among regions involved in win/loss anticipation in depressed individuals with bipolar disorder (BDD) versus depressed individuals with major depressive disorder (MDD) versus healthy control subjects using graph theory methods. The study was conducted at the University of Pittsburgh Medical Center and included 31 BDD, 39 MDD, and 36 healthy control subjects. Participants were scanned while performing a number guessing reward task that included the periods of win and loss anticipation. We first identified the anticipatory network across all 106 participants by contrasting brain activation during all anticipation periods (win anticipation + loss anticipation) versus baseline, and win anticipation versus loss anticipation. Brain connectivity within the identified network was determined using the Independent Multiple sample Greedy Equivalence Search (IMaGES) and Linear non-Gaussian Orientation, Fixed Structure (LOFS) algorithms. Density of connections (the number of connections in the network), path length, and the global connectivity direction ('top-down' versus 'bottom-up') were compared across groups (BDD/MDD/healthy control subjects) and conditions (win/loss anticipation). These analyses showed that loss anticipation was characterized by denser top-down fronto-striatal and fronto-parietal connectivity in healthy control subjects, by bottom-up striatal-frontal connectivity in MDD, and by sparse connectivity lacking fronto-striatal connections in BDD. Win anticipation was characterized by dense connectivity of medial frontal with striatal and lateral frontal cortical regions in BDD, by sparser bottom-up striatum-medial frontal cortex connectivity in MDD, and by sparse connectivity in healthy control subjects. In summary, this is the first study to demonstrate that BDD and MDD with comparable levels of current depression differed from each other and healthy control subjects in density of connections, connectivity path length, and connectivity direction as a function of win or loss anticipation. These findings suggest that different neurobiological mechanisms may underlie aberrant anticipation processes in BDD and MDD, and that distinct therapeutic strategies may be required for these individuals to improve coping strategies during expectation of positive and negative outcomes.

Transdiagnostic Psychiatric Symptoms and Event-Related Potentials following Rewarding and Aversive Outcomes

There is a need for a better understanding of transdiagnostic psychiatric symptoms that relate to neurophysiological abnormalities following rewarding and aversive feedback in order to inform development of novel targeted treatments. To address this need, we examined a transdiagnostic sample of 44 adults (mean age: 35.52; 57% female), which consisted of individuals with broadly-defined schizophrenia-spectrum disorders (n = 16), bipolar disorders (n = 10), other mood and anxiety disorders (n = 5), and no history of a psychiatric disorder (n = 13). Participants completed a Pavlovian monetary reward prediction task during 32-channel electroencephalogram recording. We assessed the event-related potentials (ERPs) of feedback-related negativity (FRN), feedback-related positivity (FRP), and the late positive potential (LPP), following better and worse than expected outcomes. Examination of symptom relationships using stepwise regressions across the entire sample revealed that an increase in the clinician-rated Negative Symptoms factor score from the Positive and Negative Syndrome Scale, was related to a decreased LPP amplitude during better than expected (i.e., rewarding) outcomes. We also found that increased self-reported scores on the Schizotypal Personality Questionnaire (Brief-Revised) Disorganized factor related to an increased FRN amplitude during worse than expected (i.e., aversive) outcomes. Across the entire sample, the FRP component amplitudes did not show significant relationships to any of the symptoms examined. Analyses of the three diagnostic groups of schizophrenia-spectrum disorders, bipolar disorders, and nonpsychiatric controls did not reveal any statistically significant differences across the ERP amplitudes and conditions. These findings suggest relationships between specific neurophysiological abnormalities following rewarding and aversive outcomes and particular transdiagnostic psychiatric symptoms.