Euthymic patients with bipolar disorder show decreased reward learning in a probabilistic reward task

Stereo-Electroencephalography-Guided Network Neuromodulation for Psychiatric Disorders: The Neurophysiology Monitoring Unit

BACKGROUND AND OBJECTIVES

Recent advances in stereotactic and functional neurosurgery have brought forth the stereo-electroencephalography approach which allows deeper interrogation and characterization of the contributions of deep structures to neural and affective functioning. We argue that this approach can and should be brought to bear on the notoriously intractable issue of defining the pathophysiology of refractory psychiatric disorders and developing patient-specific optimized stimulation therapies.

METHODS

We have developed a suite of methods for maximally leveraging the stereo-electroencephalography approach for an innovative application to understand affective disorders, with high translatability across the broader range of refractory neuropsychiatric conditions.

RESULTS

This article provides a roadmap for determining desired electrode coverage, tracking high-resolution research recordings across a large number of electrodes, synchronizing intracranial signals with ongoing research tasks and other data streams, applying intracranial stimulation during recording, and design choices for patient comfort and safety.

CONCLUSION

These methods can be implemented across other neuropsychiatric conditions needing intensive electrophysiological characterization to define biomarkers and more effectively guide therapeutic decision-making in cases of severe and treatment-refractory disease.

How to study psychological mechanisms of mania? A systematic review on the methodology of experimental studies on manic mood dysregulation of leading theories on bipolar disorder

INTRODUCTION

Although there are several psychological theories on bipolar disorders (BD), the empirical evidence on these theories through experimental studies is still limited. The current study systematically reviews experimental methods used in studies on the main theories of BD: Reward Hypersensitivity Theory (RST) or Behavioral Activation System (BAS), Integrative Cognitive Model (ICM), Positive Emotion Persistence (PEP), Manic Defense theory (MD), and Mental Imagery (MI). The primary aim is to provide an overview of the used methods and to identify limitations and suggest areas of improvement.

METHODS

A systematic search of six databases until October 2023 was conducted. Study selection involved two independent reviewers extracting data on experimental study design and methodology.

RESULTS

A total of 84 experimental studies were reviewed. BAS and RST were the most frequently studied theories. The majority of these experimental studies focus on mechanisms of reward sensitivity. Other important elements of the reviewed theories, such as goal setting and-attainment, situation selection (avoidance or approach), activation, affective/emotional reactivity, and regulatory strategies, are understudied. Self-report and neuropsychological tasks are most often used, while mood induction and physiological measures are rarely used.

CONCLUSION

There is a need for more consensus on the operationalization of psychological theories of mania. Standardization of test batteries could improve comparability among studies and foster a more systematic approach to experimental research. Research on affective (activated) states is still underrepresented in comparison with studies on trait vulnerabilities.

Peak Alpha Frequency in Schizophrenia, Bipolar Disorder, and Healthy Volunteers: Associations With Visual Information Processing and Cognition

BACKGROUND

Schizophrenia (SCZ) and bipolar disorder (BD) are associated with information processing abnormalities, including visual perceptual and cognitive impairments, that impact daily functioning. Recent work with healthy samples suggests that peak alpha frequency (PAF) is an electrophysiological index of visual information processing speed that is correlated with cognitive ability. There is evidence that PAF is slowed in SCZ, but it remains unclear whether PAF is reduced in BD or whether slower PAF is associated with impaired visual perception and cognition in these clinical disorders.

METHODS

We recorded resting-state brain activity (both eyes open and closed) with electroencephalography in 90 participants with SCZ, 62 participants with BD, and 69 healthy control participants. Most participants also performed a visual perception task (backward masking) and cognitive testing (MATRICS Concensus Cognitive Battery).

RESULTS

We replicated previous findings of reduced PAF in patients with SCZ compared with healthy control participants. In contrast, PAF in patients with BD did not differ significantly from that in healthy control participants. Furthermore, PAF was significantly correlated with performance on the perceptual and cognitive measures in SCZ but not BD. PAF was also correlated with visual perception in the healthy control group and showed a trend-level correlation with cognition.

CONCLUSIONS

Together, these results suggest that PAF deficits characterize SCZ, but not BD, and that individual differences in PAF are related to abnormalities in visual information processing and cognition in SCZ.

A Multimodal Preclinical Assessment of MDMA in Female and Male Rats: Prohedonic, Cognition Disruptive, and Prosocial Effects

Background

Frontline antidepressants such as selective serotonin reuptake inhibitors (SSRIs) leave many patients with unmet treatment needs. Moreover, even when SSRIs reduce depressive symptoms, anhedonia, the loss of pleasure to previously rewarding activities, often remains unabated. This state of affairs is disheartening and calls for the development of medications to more directly treat anhedonia. The atypical psychedelic 3,4-methylenedioxymethamphetamine (MDMA) might have promise as a prohedonic medication given its efficacious applications for treatment-resistant post-traumatic stress disorder and comorbid depression. However, in addition to its prosocial effects as an entactogen, MDMA is also associated with neurotoxic cognitive deficits. The present studies were designed to examine the relative potency of MDMA in female and male rats across three distinct behavioral domains to assist in defining a preclinical profile of MDMA as a candidate prohedonic therapeutic.

Methods

First, signal detection metrics of reward responsivity were examined using the touchscreen probabilistic reward task (PRT), a reverse-translated assay used to objectively quantify anhedonic phenotypes in humans. Second, to probe potential cognitive deficits, touchscreen-based assays of psychomotor vigilance and delayed matching-to-position were used to examine attentional processes and short-term spatial memory, respectively. Finally, MDMA's entactogenic effects were studied via pairwise assessments of social interaction facilitated by machine-learning analyses.

Results

Findings show (1) dose-dependent increases in reward responsivity as quantified by the PRT, (2) dose-dependent deficits in attention and short-term memory, and (3) dose-dependent increases in aspects of prosocial interaction in male but not female subjects. Neither the desirable (prohedonic) nor undesirable (cognition disruptive) effects of MDMA persisted beyond 24 h.

Conclusions

The present results characterize MDMA as a promising prohedonic treatment, notwithstanding some liability for short-lived cognitive impairment following acute administration.

Using Drift Diffusion and RL Models to Disentangle Effects of Depression On Decision-Making vs. Learning in the Probabilistic Reward Task

The Probabilistic Reward Task (PRT) is widely used to investigate the impact of Major Depressive Disorder (MDD) on reinforcement learning (RL), and recent studies have used it to provide insight into decision-making mechanisms affected by MDD. The current project used PRT data from unmedicated, treatment-seeking adults with MDD to extend these efforts by: (1) providing a more detailed analysis of standard PRT metrics-response bias and discriminability-to better understand how the task is performed; (2) analyzing the data with two computational models and providing psychometric analyses of both; and (3) determining whether response bias, discriminability, or model parameters predicted responses to treatment with placebo or the atypical antidepressant bupropion. Analysis of standard metrics replicated recent work by demonstrating a dependency between response bias and response time (RT), and by showing that reward totals in the PRT are governed by discriminability. Behavior was well-captured by the Hierarchical Drift Diffusion Model (HDDM), which models decision-making processes; the HDDM showed excellent internal consistency and acceptable retest reliability. A separate "belief" model reproduced the evolution of response bias over time better than the HDDM, but its psychometric properties were weaker. Finally, the predictive utility of the PRT was limited by small samples; nevertheless, depressed adults who responded to bupropion showed larger pre-treatment starting point biases in the HDDM than non-responders, indicating greater sensitivity to the PRT's asymmetric reinforcement contingencies. Together, these findings enhance our understanding of reward and decision-making mechanisms that are implicated in MDD and probed by the PRT.

Validation of a touchscreen probabilistic reward task for mice: A reverse-translated assay with cross-species continuity

The Probabilistic Reward Task (PRT) is a laboratory-based technique used to objectively quantify responsivity to reward. The PRT was initially designed to identify reinforcement learning deficits in clinical populations and subsequently was reverse-translated for use in preclinical studies with rats and monkeys. In this task, subjects make visual discriminations and asymmetric probabilistic contingencies are arranged such that correct responses to one stimulus (rich) are reinforced more often than correct responses to the other (lean). Numerous studies have demonstrated that healthy subjects reliably develop a response bias toward the richly rewarded stimulus, whereas humans with anhedonia and laboratory animals with a history of chronic stress exhibit a blunted response bias. This is important because anhedonia, the loss of responsivity to previously rewarding stimuli, is a behavioral phenotype that is a cardinal feature of multiple neuropsychiatric conditions and is without approved pharmacotherapeutic options. To aid in addressing this critical treatment gap, this report describes validation of the first PRT designed for mice, which are a commonly utilized species in preclinical research toward neuropsychiatric medications development. Results reveal orderly psychophysical functions in response to asymmetric probabilistic contingencies in mice, with signal detection outcomes comparable to previous PRT findings in humans, rats, and monkeys. Taken together, such robust cross-species continuity in task performance confirms that the mouse is well-positioned to serve in bidirectional research efforts between human and animal laboratories. These efforts may accelerate the development of treatment options for anhedonia in the different neuropsychiatric conditions in which it is prominent.

Lifetime history of major depressive disorder is associated with decreased reward learning: Evidence from a novel online version of the probabilistic reward task

BACKGROUND

The Probabilistic Reward Task (PRT) is a signal detection task that assesses reward learning. In laboratory versions of the task, individuals with current or past major depressive disorder (MDD) were characterized by reduced response bias towards a more frequently rewarded stimuli, compared to controls. Our main goal was to develop and validate a novel online version of the PRT, and, in exploratory analyses, evaluate whether lifetime history of depression was associated with blunted reward learning.

METHODS

429 participants recruited via CloudResearch completed questionnaires assessing psychiatric history and an online PRT featuring visually appealing stimuli. 108 participants reported either current or past diagnosis of MDD (lifetime MDD group), and were compared to 321 without lifetime MDD.

RESULTS

Participants showed overall increase in response bias, validating the online PRT. Females with lifetime MDD (N = 43), compared to females without prior history of MDD (N = 173), exhibited blunted response bias towards the more frequently rewarded stimulus (i.e., reduced reward learning).

LIMITATIONS

Participants did not undergo a structured clinical interview, thus we cannot confirm whether they met full diagnostic criteria for depression.

CONCLUSIONS

The online PRT yielded similar psychometric properties as laboratory versions of the task. In exploratory analyses, females with lifetime MDD showed a lower propensity to modulate behavior as a function of rewards, which might contribute to heightened vulnerability for developing MDD in females. Future studies should consider social, cultural, and neurobiological factors contributing to sex differences in reward responsiveness and how factors may relate to disease prognosis and treatment outcomes.

Using the Beck Depression Inventory to Assess Anhedonia: A Scale Validation Study

Anhedonia is central to several psychological disorders and a frequent target of psychosocial and pharmacological treatments. We evaluated the psychometric properties of two widely used anhedonia measures derived from the Beck Depression Inventory: a 3-item (BDI-Anh3) and a 4-item version (BDI-Anh4). We evaluated these measures in a large undergraduate sample, a community sample, and a clinical sample. Both the BDI-Anh3 and the BDI-Anh4 showed adequate internal consistency, with BDI-Anh4 performing somewhat better, across the three samples. Both measures showed good convergent and discriminant validity, even after controlling for shared variance with other items on the BDI. These findings indicate that both measures have sufficient reliability and validity to support their use by researchers and clinicians.

Neurocognitive risk phenotyping to predict mood symptoms in adolescence

Predicting mood disorders in adolescence is a challenge that motivates research to identify neurocognitive predictors of symptom expression and clinical profiles. This study used machine learning to test whether neurocognitive variables predicted future manic or anhedonic symptoms in two adolescent samples risk-enriched for lifetime mood disorders (Sample 1, n = 73, ages = 13-25, M [SD] = 19.22 [2.49] years, 68% lifetime mood disorder) or familial mood disorders (Sample 2, n = 154, ages = 13-21, M [SD] = 16.46 [1.95] years, 62% first-degree family history of mood disorder). Participants completed cognitive testing and functional magnetic resonance imaging at baseline, for behavioral and neural measures of reward processing and executive functioning. Next, participants completed a daily diary procedure for 8-16 weeks. Penalized mixed-effects models identified neurocognitive predictors of future mood symptoms and stress-reactive changes in mood symptoms. Results included the following. In both samples, adolescents showing ventral corticostriatal reward hyposensitivity and lower reward performance reported more severe stress-reactive anhedonia. Poorer executive functioning behavior was associated with heightened anhedonia overall in Sample 1, but lower stress-reactive anhedonia in both samples. In Sample 1, adolescents showing ventral corticostriatal reward hypersensitivity and poorer executive functioning reported more severe stress-reactive manic symptoms. Clustering analyses identified, and replicated, five neurocognitive subgroups. Adolescents characterized by neural or behavioral reward hyposensitivities together with average-to-poor executive functioning reported unipolar symptom profiles. Adolescents showing neural reward hypersensitivity together with poor behavioral executive functioning reported a bipolar symptom profile (Sample 1 only). Together, neurocognitive phenotypes may hold value for predicting symptom expression and profiles of mood pathology. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Reinforcement learning and working memory in mood disorders: A computational analysis in a developmental transdiagnostic sample

BACKGROUND

Mood disorders commonly onset during adolescence and young adulthood and are conceptually and empirically related to reinforcement learning abnormalities. However, the nature of abnormalities associated with acute symptom severity versus lifetime diagnosis remains unclear, and prior research has often failed to disentangle working memory from reward processes.

METHODS

The present sample (N = 220) included adolescents and young adults with a lifetime history of unipolar disorders (n = 127), bipolar disorders (n = 28), or no history of psychopathology (n = 62), and varying severity of mood symptoms. Analyses fitted a reinforcement learning and working memory model to an instrumental learning task that varied working memory load, and tested associations between model parameters and diagnoses or current symptoms.

RESULTS

Current severity of manic or anhedonic symptoms negatively correlated with task performance. Participants reporting higher severity of current anhedonia, or with lifetime unipolar or bipolar disorders, showed lower reward learning rates. Participants reporting higher severity of current manic symptoms showed faster working memory decay and reduced use of working memory.

LIMITATIONS

Computational parameters should be interpreted in the task environment (a deterministic reward learning paradigm), and developmental population. Future work should test replication in other paradigms and populations.

CONCLUSIONS

Results indicate abnormalities in reinforcement learning processes that either scale with current symptom severity, or correspond with lifetime mood diagnoses. Findings may have implications for understanding reward processing anomalies related to state-like (current symptom) or trait-like (lifetime diagnosis) aspects of mood disorders.

Ventral prefrontal network response to alcohol in young adults with bipolar disorder: a within-subject randomized placebo-controlled alcohol administration study

Bipolar disorder co-occurs with alcohol use disorder at a rate 3-5 times higher than the general population. We recently reported that individuals with bipolar disorder differ in the positive stimulating and anxiolytic effects of alcohol compared with healthy peers. This study used a randomized, placebo-controlled, cross-over, within-subject alcohol administration design to investigate neurobiological mechanisms within ventral prefrontal cortical (vPFC) systems that may underlie altered sensitivity to alcohol in bipolar disorder (NCT04063384). Forty-seven young adults (n = 23 with bipolar disorder, 64% women) completed clinical assessment and two beverage administration sessions (alcohol and placebo, counter-balanced). Participants were dosed to 0.08 g% breath alcohol concentration during the alcohol condition and completed measures of subjective response to alcohol and an emotional processing fMRI task during the ascending limb. Timing during the placebo condition mirrored the alcohol session. Acute alcohol was associated with reduced functional connectivity between the insula - subcallosal cingulate cortex, and increased connectivity between the left nucleus accumbens - ventromedial PFC in bipolar disorder, but with no change in functional connectivity between these regions in healthy peers. Alcohol-related increases in nucleus accumbens - ventromedial PFC functional connectivity was associated with greater positive stimulating effects of alcohol in bipolar disorder and heavier recent alcohol use. Results suggest vPFC brain systems respond differently to acute alcohol during emotional processing in young adults with bipolar disorder compared with healthy peers, and that vPFC system responses relate to the subjective experience of intoxication and recent alcohol use.

Reward and punishment learning deficits among bipolar disorder subtypes

BACKGROUND

Reward sensitivity is an essential dimension related to mood fluctuations in bipolar disorder (BD), but there is currently a debate around hypersensitivity or hyposensitivity hypotheses to reward in BD during remission, probably related to a heterogeneous population within the BD spectrum and a lack of reward bias evaluation. Here, we examine reward maximization vs. punishment avoidance learning within the BD spectrum during remission.

METHODS

Patients with BD-I (n = 45), BD-II (n = 34) and matched (n = 30) healthy controls (HC) were included. They performed an instrumental learning task designed to dissociate reward-based from punishment-based reinforcement learning. Computational modeling was used to identify the mechanisms underlying reinforcement learning performances.

RESULTS

Behavioral results showed a significant reward learning deficit across BD subtypes compared to HC, captured at the computational level by a lower sensitivity to rewards compared to punishments in both BD subtypes. Computational modeling also revealed a higher choice randomness in BD-II compared to BD-I that reflected a tendency of BD-I to perform better during punishment avoidance learning than BD-II.

LIMITATIONS

Our patients were not naive to antipsychotic treatment and were not euthymic (but in syndromic remission) according to the International Society for Bipolar Disorder definition.

CONCLUSIONS

Our results are consistent with the reward hyposensitivity theory in BD. Computational modeling suggests distinct underlying mechanisms that produce similar observable behaviors, making it a useful tool for distinguishing how symptoms interact in BD versus other disorders. In the long run, a better understanding of these processes could contribute to better prevention and management of BD.

Momentary gustative-olfactory sensitivity and tonic heart rate variability are independently associated with motivational behavior

Deficits in motivational functioning including impairments in reward learning or reward sensitivity are common in psychiatric disorders characterized by anhedonia. Recently, anhedonic symptoms have been exacerbated by the pandemic caused by the Coronavirus disease 2019 (COVID-19) in the general population. The present study examined the putative associations between loss of smell (anosmia) and taste (ageusia) sensitivity, irrespective of COVID-19 infection, and anhedonia, measured by a signal-detection task probing the ability to modify behavior as a function of rewards (Probabilistic Reward Task; PRT). Tonic heart rate variability (HRV) was included in the model, due to its association with both smell and taste sensitivity as well as motivational functioning. The sample included 114 healthy individuals (81 females; mean age 22.2 years), who underwent a laboratory session in which dispositional traits, resting HRV and PRT performance were assessed, followed by a 4-days ecological momentary assessment to obtain daily measures of anosmia and ageusia. Lower levels of tonic HRV and lower momentary levels of smell and taste sensitivity were associated with impaired reward responsiveness and ability to shape future behavioral choices based on prior reinforcement experiences. Overall, the current results provide initial correlational evidence that could be fruitfully used to inform future experimental investigations aimed at elucidating the disruptive worldwide mental health consequences triggered by the pandemic.

Development of cross-species translational paradigms for psychiatric research in the Research Domain Criteria era

The past 30 years of IBNS has included research attempting to treat the cognitive and behavioral deficits observed in people with psychiatric conditions. Early work utilized drugs identified from tests thought to be cognition-relevant, however the high failure rate crossing the translational-species barrier led to focus on developing valid cross-species translational tests. The face, predictive, and neurobiological validities used to assess animal models of psychiatry can be used to validate these tests. Clinical sensitivity is another important aspect however, for if the clinical population targeted for treatment does not exhibit task deficits, then why develop treatments? This review covers some work validating cross-species translational tests and suggests future directions. Also covered is the contribution IBNS made to fostering such research and my role in IBNS, making it more available to all including fostering mentor/mentee programs plus spearheading diversity and inclusivity initiatives. All science needs support and IBNS has supported research recreating the behavioral abnormalities that define psychiatric conditions with the aim to improve the lives of people with such conditions.

Electrophysiological signatures of reward learning in the rodent touchscreen-based Probabilistic Reward Task

Blunted reward learning and reward-related activation within the corticostriatal-midbrain circuitry have been implicated in the pathophysiology of anhedonia and depression. Unfortunately, the search for more efficacious interventions for anhedonic behaviors has been hampered by the use of vastly different preclinical and clinical assays. In a first step in addressing this gap, in the current study, we used event-related potentials and spectral analyses in conjunction with a touchscreen version of the rodent Probabilistic Reward Task (PRT) to identify the electrophysiological signatures of reward learning in rats. We trained 11 rats (5 females and 6 males) on the rodent touchscreen-based PRT and subsequently implanted them with deep electrodes in the anterior cingulate cortex (ACC) and nucleus accumbens (NAc) for local field potentials recordings during the PRT. Behaviorally, the expected responsivity-to-reward profile was observed. At the electrophysiological level, we identified a negative amplitude deflection 250-500 ms after feedback in the ACC and NAc electrodes, as well as power increase in feedback-locked delta (1-5 Hz) and alpha/beta (9-17 Hz) bands in both electrodes for rewarded trials. Using a reverse-translational approach, we identified electrophysiological signatures of reward learning in rats similar to those described in humans. These findings and approaches might provide a useful translational platform to efficiently evaluate novel therapeutics targeting anhedonia.

Mood Symptom Dimensions and Developmental Differences in Neurocognition in Adolescence

Adolescence is critical period of neurocognitive development as well as increased prevalence of mood pathology. This cross-sectional study replicated developmental patterns of neurocognition and tested whether mood symptoms moderated developmental effects. Participants were 419 adolescents (n=246 with current mood disorders) who completed reward learning and executive functioning tasks, and reported on age, puberty, and mood symptoms. Structural equation modeling revealed a quadratic relationship between puberty and reward learning performance that was moderated by symptom severity: in early puberty, adolescents reporting higher manic symptoms exhibited heightened reward learning performance (better maximizing of rewards on learning tasks), whereas adolescents reporting elevated anhedonia showed blunted reward learning performance. Models also showed a linear relationship between age and executive functioning that was moderated by manic symptoms: adolescents reporting higher mania showed poorer executive functioning at older ages. Findings suggest neurocognitive development is altered in adolescents with mood pathology and suggest directions for longitudinal studies.

Pre-frontal stimulation does not reliably increase reward responsiveness

Depression is the leading cause of disability worldwide and its effects can be fatal, with over 800,000 people dying by suicide each year. Neuromodulatory treatments such as transcranial magnetic stimulation (TMS) are being used to treat depression. Despite its endorsement by two regulatory bodies: NICE (2016) and the FDA (2008), there are major questions about the treatment efficacy and biological mechanisms of TMS. Ahn et al.'s (2013) justified the use of TMS in a clinical context in an important study indicating that excitatory TMS increases reward responsiveness. A pseudo-replication of this study by Duprat et al., (2016) also found a similar effect of active TMS, but only with the addition of an exploratory covariate to the analyses-trait reward responsiveness. Here we replicate Ahn et al.'s (2013) key study, and to test the reliability of the effects, and their dependency on trait reward responsiveness as described by Duprat et al., (2016). Using excitatory and sham TMS, we tested volunteers using the probabilistic learning task to measure their reward responsiveness both before and after stimulation. We also examined affect (positive, negative) following stimulation. Irrespective of TMS, the task was shown to be sensitive to reward responsiveness. However, we did not show TMS to be effective in increasing reward responsiveness and we did not replicate Ahn et al., (2013) or Duprat et al., (2016)'s key findings for TMS efficacy, where we provide evidence favouring the null. Moreover, exploratory analyses suggested following active stimulation, positive affect was reduced. Given our findings, we question the basic effects, which support the use of TMS for depression, particularly considering potential deleterious effects of reduced positive affect in patients with depression.

Reorganization of the functional connectome from rest to a visual perception task in schizophrenia and bipolar disorder

Functional connectome organization is altered in schizophrenia (SZ) and bipolar disorder (BD). However, it remains unclear whether network reorganization during a task relative to rest is also altered in these disorders. This study examined connectome organization in patients with SZ (N = 43) and BD (N = 42) versus healthy controls (HC; N = 39) using fMRI data during a visual object-perception task and at rest. Graph analyses were conducted for the whole-brain network using indices selected a priori: three reflecting network segregation (clustering coefficient, local efficiency, modularity), two reflecting integration (characteristic path length, global efficiency). Group differences were limited to network segregation and were more evident in SZ (clustering coefficient, modularity) than in BD (clustering coefficient) compared to HC. State differences were found across groups for segregation (local efficiency) and integration (characteristic path length). There was no group-by-state interaction for any graph index. In summary, aberrant network organization compared to HC was confirmed, and was more evident in SZ than in BD. Yet, reorganization was largely intact in both disorders. These findings help to constrain models of dysconnection in SZ and BD, suggesting that the extent of functional dysconnectivity in these disorders tends to persist across changes in mental state.

Trajectory of aberrant reward processing in patients with bipolar disorder - A longitudinal fMRI study

BACKGROUND

Bipolar disorder (BD), and especially the mania phenotype, is characterized by heightened reward responsivity and aberrant reward processing. In this longitudinal fMRI study, we investigated neuronal response during reward anticipation as the computed expected value (EV) and outcome evaluation as reward prediction error (RPE) in recently diagnosed patients with BD.

METHODS

Eighty remitted patients with BD and 60 healthy controls (HC) underwent fMRI during which they performed a card guessing task. Of these, 41 patients and 36 HC were re-scanned after 16 months. We compared reward-related neural activity between groups at baseline and longitudinally and assessed the impact of mood relapse.

RESULTS

Patients showed lower RPE signal in areas of the ventrolateral prefrontal cortex (vlPFC) than HC. In these regions, the HC showed decrease in RPE signal over time, which was absent in patients. Patients further exhibited decreased EV signal in the occipital cortex across baseline and follow-up. Patients who remained in remission showed normalization of the EV signal at follow-up. Baseline activity in the identified regions was not associated with subsequent relapse.

LIMITATIONS

Follow-up scans were only available in a relatively small sample. Medication status, follow-up time and BD illness duration prior to diagnosis varied.

CONCLUSIONS

Lower RPE signal in the vlPFC in patients with BD at baseline and its lack of normative reduction over time may represent a trait marker of dysfunctional reward-based learning or habituation. The increase in EV signal in the occipital cortex over time in patients who remained in remission may indicate normalization of reward anticipation activity.

Effects of dopamine modulation on chronic stress-induced deficits in reward learning

Anhedonia is characteristically preceded by chronic stress, likely involving downstream effects of glucocorticoid alterations on dopamine (DA) function. To elucidate the neural underpinnings of this interaction, we examined whether acute pharmacological modulation of DA alters reward learning after chronic mild stress (CMS). Forty-eight male Wistar rats were exposed to a 21-day CMS regime (n = 48 no stress controls) before completing the probabilistic reward task (PRT), a well-validated cross-species test of reward learning. We first examined whether stress-induced reward dysfunction could be restored by systemic injections of low-dose amisulpride (AMI), which increases DA transmission via D2-like autoreceptor blockade. Then, we investigated region-specific effects through bilateral infusions of quinpirole (QUIN), a D2-like receptor agonist, into either the nucleus accumbens core (NAcc) or medial prefrontal cortex (mPFC). Blunted reward learning in CMS animals was reversed by acute AMI administration, but this treatment did not alter reward learning in the no stress group. Elevated adrenal gland weight, a proxy for stress reactivity, predicted lower reward learning in the untreated CMS group. This effect was extinguished following AMI treatment. These findings might be attributed to significantly higher D2 receptor density in the NAcc of high stress reactive animals. To this end, NAcc QUIN infusions potentiated reward learning relative to mPFC QUIN infusions in CMS rats, but there was no effect in no stress control rats. Collectively, these findings suggest that DA modulation reverses stress-induced reward dysfunction, even among the most stress-reactive animals. The effect might depend on D2-like receptor activation in the mesolimbic system.

Comparative effectiveness of repeated ketamine infusions in treating anhedonia in bipolar and unipolar depression

OBJECTIVES

Anhedonia is a common, persistent, and disabling phenomenon in patients with major depressive disorder (MDD) and bipolar depression (BD). This study was conducted to investigate the comparative effectiveness of repeated ketamine infusions in treating anhedonia in Chinese individuals suffering from MDD and BD.

METHODS

Ninety-seven individuals suffering from MDD (n = 77) or BD (n = 20) were treated with six intravenous infusions of ketamine (0.5 mg/kg) administered over 40 min. Anhedonia was measured through the Montgomery-Åsberg Depression Rating Scale (MADRS). The antianhedonic response and remission were defined as ≥ 50% and ≥ 75% reduction in MADRS anhedonia subscale score one day after the sixth infusion, respectively.

RESULTS

Anti-anhedonic response and remission rates after the sixth ketamine infusion were 48.5% (95% confidence interval =  38.3%-58.6%) and 30.9% (95% confidence interval = 21.6%-40.3%), respectively. When compared to baseline, a significant reduction in the MADRS anhedonia subscale score was observed at 4 h after the first infusion and was maintained with repeated infusions at any time point (all Ps < 0.05). The anti-anhedonic effect of ketamine did not differ between the MDD and BD groups.

CONCLUSION

This preliminary study found that repeated ketamine infusions appeared to be effective at rapidly ameliorating anhedonia, with similar efficacy in MDD and BD.

The effects of reward and frustration in patients with bipolar disorder: Evidence from a computerized task with non-contingent feedback

BACKGROUND

Bipolar disorder (BD) is characterized by mood changes that implies alterations in reward sensitivity and frustration tolerance. This study examined the effects of monetary reward and frustration on attentional performance and on affective experience across mood states in BD.

METHODS

An Affective Posner Task in which the nature of contingencies are divided in the three successive blocks (baseline condition, monetary reward and non-contingent feedback) was applied to BD individuals in their different episodes: mania (n = 30), depression (n = 30), and euthymia (n =  30) as well as to a group of healthy controls (n = 30).

RESULTS

Monetary reward improved performance (in terms of faster response times) in the euthymic group and the control group, whereas it impaired performance in the manic group and has not significant effect in the depressed group. In addition, an increased interference of frustration on response accuracy was exhibited in the three groups of BD patients (including euthymia) compared with healthy controls.

LIMITATIONS

Participants' affective experience was self-informed by a Likert scale, so the reliability of this measure can be undermined in symptomatic patients in terms of stability and objectivity. Although it was statistically controlled, at the time of testing, all BD patients were medicated.

CONCLUSIONS

A dissociated effect of reward and frustration was found between symptomatic and euthymic states in BD: whereas the benefit from monetary reward is affected only during symptomatic episodes (i.e., a state), the notably increased interference of frustration is exhibited also during euthymia (i.e., a trait).

A cross-species assay demonstrates that reward responsiveness is enduringly impacted by adverse, unpredictable early-life experiences

Exposure to early-life adversity (ELA) is associated with several neuropsychiatric conditions, including major depressive disorder, yet causality is difficult to establish in humans. Recent work in rodents has implicated impaired reward circuit signaling in anhedonic-like behavior after ELA exposure. Anhedonia, the lack of reactivity to previously rewarding stimuli, is a transdiagnostic construct common to mental illnesses associated with ELA. Here, we employed an assay of reward responsiveness validated across species, the Probabilistic Reward Task (PRT). In the PRT, healthy participants reliably develop a response bias toward the more richly rewarded stimulus, whereas participants with anhedonia exhibit a blunted response bias that correlates with current and future anhedonia. In a well-established model of ELA that generates a stressful, chaotic, and unpredictable early-life environment, ELA led to blunted response biases in the PRT in two separate cohorts, recapitulating findings in humans with anhedonia. The same ELA rats had blunted sucrose preference, further supporting their anhedonic-like phenotypes. Probing the aspects of ELA that might provoke these deficits, we quantified the unpredictability of dam/pup interactions using entropy measures and found that the unpredictability of maternal care was significantly higher in the ELA groups in which PRT and sucrose preference reward deficits were present later in life. Taken together, these data position the PRT, established in clinical patient populations, as a potent instrument to assess the impact of ELA on the reward circuit across species. These findings also implicate the unpredictability of maternal signals during early life as an important driver of reward sensitivity deficits.

Anhedonia and Hyperhedonia in Autism and Related Neurodevelopmental Disorders

Although autism spectrum disorder (ASD) is defined by impaired social communication and restricted and repetitive behaviors and interests, ASD is also characterized by impaired motivational processes. The "social motivation theory of autism" describes how social motivation disruptions in ASD in early childhood may impede the drive to engage in reciprocal social behaviors and ultimately interfere with the development of neural networks critical for social communication (Chevallier et al., Trends Cogn Sci 16:231-239, 2012b). Importantly, clinical studies and preclinical research using model organisms for ASD indicate that motivational impairments in ASD are not constrained to social rewards but are evident in response to a range of nonsocial rewards as well. Additionally, translational studies on certain genetically defined neurodevelopmental disorders associated with ASD indicate that these syndromic forms of ASD are also characterized by motivational deficits and mesolimbic dopamine impairments. In this chapter we summarize clinical and preclinical research relevant to reward processing impairments in ASD and related neurodevelopmental disorders. We also propose a nosology to describe reward processing impairments in these disorders that uses a three-axes model. In this triaxial nosology, the first axis defines the direction of the reward response (i.e., anhedonic, hyperhedonic); the second axis defines the construct of the reward process (e.g., reward liking, reward wanting); and the third axis defines the context of the reward response (e.g., social, nonsocial). A more precise nosology for describing reward processing impairments in ASD and related neurodevelopmental disorders will aid in the translation of preclinical research to clinical investigations which will ultimately help to speed up the development of interventions that target motivational systems for ASD and related neurodevelopmental disorders.

Anhedonia in Depression and Bipolar Disorder

Anhedonia is a hallmark feature of depression and is highly prevalent among individuals with mood disorders. The history and neurobiology of anhedonia has been most extensively studied in the context of unipolar Major Depressive Disorder (MDD), with converging lines of evidence indicating that marked anhedonia heralds a more chronic and treatment-refractory illness course. Furthermore, findings from neuroimaging studies suggest that anhedonia in MDD is associated with aberrant reward-related activation in key brain reward regions, particularly blunted reward anticipation-related activation in the ventral striatum. However, the ongoing clinical challenge of treating anhedonia in the context of Bipolar Disorder (BD) also highlights important gaps in our understanding of anhedonia's prevalence, severity, and pathophysiology along the entire mood disorder spectrum. In addition, although current theoretical models posit a key role for reward hyposensitivity in BD depression, unlike studies in MDD, studies in BD do not clearly show evidence for reduced reward-related activation in striatal or other brain regions. Although further research is needed, the evidence to date hints at a divergent pathophysiology for anhedonia in unipolar and bipolar mood disorders, which, if better understood, could lead to significant improvements in the diagnosis and treatment of MDD and BD.

Probabilistic Reinforcement Learning and Anhedonia

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

Challenging the negative learning bias hypothesis of depression: reversal learning in a naturalistic psychiatric sample

BACKGROUND

Classic theories posit that depression is driven by a negative learning bias. Most studies supporting this proposition used small and selected samples, excluding patients with comorbidities. However, comorbidity between psychiatric disorders occurs in up to 70% of the population. Therefore, the generalizability of the negative bias hypothesis to a naturalistic psychiatric sample as well as the specificity of the bias to depression, remain unclear. In the present study, we tested the negative learning bias hypothesis in a large naturalistic sample of psychiatric patients, including depression, anxiety, addiction, attention-deficit/hyperactivity disorder, and/or autism. First, we assessed whether the negative bias hypothesis of depression generalized to a heterogeneous (and hence more naturalistic) depression sample compared with controls. Second, we assessed whether negative bias extends to other psychiatric disorders. Third, we adopted a dimensional approach, by using symptom severity as a way to assess associations across the sample.

METHODS

We administered a probabilistic reversal learning task to 217 patients and 81 healthy controls. According to the negative bias hypothesis, participants with depression should exhibit enhanced learning and flexibility based on punishment v. reward. We combined analyses of traditional measures with more sensitive computational modeling.

RESULTS

In contrast to previous findings, this sample of depressed patients with psychiatric comorbidities did not show a negative learning bias.

CONCLUSIONS

These results speak against the generalizability of the negative learning bias hypothesis to depressed patients with comorbidities. This study highlights the importance of investigating unselected samples of psychiatric patients, which represent the vast majority of the psychiatric population.

Neuromolecular Underpinnings of Negative Cognitive Bias in Depression

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

Extraversion but not depression predicts reward sensitivity: Revisiting the measurement of anhedonic phenotypes

Recently, increasing efforts have been made to define and measure dimensional phenotypes associated with psychiatric disorders. One example is a probabilistic reward task developed by Pizzagalli, Jahn, and O'Shea (2005) to assess anhedonia, by measuring response to a differential reinforcement schedule. This task has been used in many studies, which have connected blunted reward response in the task to depressive symptoms, across clinical groups and in the general population. The current study attempted to replicate these findings in a large community sample and also investigated possible associations with Extraversion, a personality trait linked to reward sensitivity. Participants (N = 299) completed the probabilistic reward task, as well as the Beck Depression Inventory, Personality Inventory for the DSM-5, Big Five Inventory, and Big Five Aspect Scales. Our direct replication attempts used bivariate correlations and analysis of variance models. Follow-up and extension analyses used structural equation models to assess relations among reward sensitivity, depression, Extraversion, and Neuroticism. No significant associations were found between reward sensitivity and depression, thus failing to replicate previous findings. Reward sensitivity (both modeled as response bias aggregated across blocks and as response bias controlling for baseline) showed positive associations with Extraversion, but not Neuroticism. Findings suggest reward sensitivity as measured by this task may be related primarily to Extraversion and its pathological manifestations, rather than to depression per se, consistent with existing models that conceptualize depressive symptoms as combining features of Neuroticism and low Extraversion. Findings are discussed in broader contexts of dimensional psychopathology frameworks, replicable science, and behavioral task reliability. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Neural reward circuit dysfunction as a risk factor for bipolar spectrum disorders and substance use disorders: A review and integration

Bipolar spectrum disorders (BSDs) and substance use disorders (SUDs) are associated with neural reward dysfunction. However, it is unclear what pattern of neural reward function underlies pre-existing vulnerability to BSDs and SUDs, or whether neural reward function explains their high co-occurrence. The current paper provides an overview of the separate literatures on neural reward sensitivity in BSDs and SUDs. We provide a systematic review of 35 studies relevant to identifying neural reward function vulnerability to BSDs and SUDs. These studies include those examining neural reward processing on a monetary reward task with prospective designs predicting initial onset of SUDs, familial risk studies that examine unaffected offspring or first-degree relatives of family members with BSDs or SUDs, and studies that examine individuals with BSDs or SUDs who are not currently in an episode of the disorder. Findings from the review highlight that aberrant responding and connectivity across neural regions associated with reward and cognitive control confers risk for the development of BSDs and SUDs. Discussion focuses on limitations of the extant literature. We conclude with an integration and theoretical model for understanding how aberrant neural reward responding may constitute a vulnerability to the development of both BSDs and SUDs.

The impact of overweight/obesity on monetary reward processing: A systematic review

OBJECTIVE

Converging evidence suggests abnormalities in monetary reward processing may underlie the shared pathophysiology between major depressive disorder and obesity. As such, there is a need to parse deficits in specific subcomponents of monetary reward functioning (i.e., valuation, learning and anticipation).

METHODS

PsycINFO, Google Scholar and PubMed databases were searched for English-language articles published between database inception to June 6th, 2020. Studies were identified using the following medical search heading (MeSH) terms and search strings: (reward (valuation OR motivation OR anticipation OR learning OR functioning OR decision-making OR reinforcement)) AND ((obesity OR overweight OR obese).

RESULTS

Findings were reviewed from 11 studies evaluating the association between obesity and monetary reward processing. Four studies found significant differences in reward learning in individuals with obesity compared to normal-weight participants. Five studies found body mass index (BMI) to be predictive of willingness to expend effort (i.e., valuation) for a monetary reward. Three studies found changes in neural activations in the ventral striatum during anticipatory phases preceding receipt of a monetary reward in participants with obesity.

CONCLUSIONS

Participants with obesity demonstrated significantly poorer performance in task-based measures of reward learning, valuation, and anticipation, resulting in lower monetary reward outcomes across all studies compared to healthy controls. Notably, participants with obesity and comorbid depression performed worse than participants with no comorbid depression.

LIMITATIONS

There persists heterogeneity between studies with regards to inclusion of mood disorder populations and exclusion of psychiatric comorbidities in groups with obesity.

Interpretation bias training for bipolar disorder: A randomized controlled trial

BACKGROUND

Bipolar disorder (BD) is associated with emotion interpretation biases that can exacerbate depressed mood. Interpretation bias training (IBT) may help; according to the "virtuous cycle" hypothesis, interpreting others' emotions as positive can lead to interactions that improve mood. Our goals were to determine whether IBT can shift emotion interpretation biases and demonstrate clinical benefits (lower depressed mood, improved social function) in people with BD.

METHOD

Young adults with BD were recruited for three sessions of computer-based IBT. Active IBT targets negative emotion bias by training judgments of ambiguous face emotions towards happy judgments. Participants were randomized to active or sham IBT. Participants reported on mood and functioning at baseline, intervention end (week two), and week 10.

RESULTS

Fifty participants (average age 22, 72% female) enrolled, 38 completed the week 10 follow-up. IBT shifted emotion interpretations (Hedges g = 1.63). There was a group-by-time effect (B = -13.88, p < .0001) on self-reported depression; the IBT group had a larger decrease in depressed mood. The IBT group also had a larger increase in perceived familial support (B = 3.88, p < .0001). Baseline learning rate (i.e., how quickly emotion judgments were updated) was associated with reduced clinician- (B = -54.70, p < 0.001) and self-reported depression (B = -58.20, p = 0.009).

CONCLUSION

Our results converge with prior work demonstrating that IBT may reduce depressed mood. Additionally, our results provide support for role of operant conditioning in the treatment of depression. People with BD spend more time depressed than manic; IBT, an easily disseminated intervention, could augment traditional forms of treatment without significant expense or side effects.

Associations between insomnia and reward learning in clinical depression

BACKGROUND

Depression and insomnia commonly co-occur. Yet, little is known about the mechanisms through which insomnia influences depression. Recent research and theory highlight reward system dysfunction as a potential mediator of the relationship between insomnia and depression. This study is the first to examine the impact of insomnia on reward learning, a key component of reward system functioning, in clinical depression.

METHODS

The sample consisted of 72 veterans with unipolar depression who endorsed sleep disturbance symptoms. Participants completed the Structured Clinical Interview for DSM-IV, self-report measures of insomnia, depression, and reward processing, and a previously validated signal detection task (Pizzagalli et al., 2005, Biological Psychiatry, 57(4), 319-327). Trial-by-trial response bias (RB) estimates calculated for each of the 200 task trials were examined using linear mixed-model analyses to investigate change in reward learning.

RESULTS

Findings demonstrated diminished rate and magnitude of reward learning in the Insomnia group relative to the Hypersomnia/Mixed Symptom group across the task. Within the Insomnia group, participants with more severe insomnia evidenced the lowest rates of reward learning, with increased RB across the task with decreasing insomnia severity.

CONCLUSIONS

Among individuals with depression, insomnia is associated with decreased ability to learn associations between neutral stimuli and rewarding outcomes and/or modify behavior in response to differential receipt of reward. This attenuated reward learning may contribute to clinically meaningful decreases in motivation and increased withdrawal in this comorbid group. Results extend existing theory by highlighting impairments in reward learning specifically as a potential mediator of the association between insomnia and depression.

Mapping Disease Course Across the Mood Disorder Spectrum Through a Research Domain Criteria Framework

BACKGROUND

The National Institute of Mental Health Research Domain Criteria (RDoC) initiative aims to establish a neurobiologically valid framework for classifying mental illness. Here, we examined whether the RDoC construct of reward learning and three aspects of its underlying neurocircuitry predicted symptom trajectories in individuals with mood pathology.

METHODS

Aligning with the RDoC approach, we recruited individuals (n = 80 with mood disorders [58 unipolar and 22 bipolar] and n = 32 control subjects; 63.4% female) based on their performance on a laboratory-based reward learning task rather than clinical diagnosis. We then assessed 1) anterior cingulate cortex prediction errors using electroencephalography, 2) striatal reward prediction errors using functional magnetic resonance imaging, and 3) medial prefrontal cortex glutamatergic function (mPFC Gln/Glu) using ¹H magnetic resonance spectroscopy. Severity of anhedonia, (hypo)mania, and impulsivity were measured at baseline, 3 months, and 6 months.

RESULTS

Greater homogeneity in aspects of brain function (mPFC Gln/Glu) was observed when individuals were classified according to reward learning ability rather than diagnosis. Furthermore, mPFC Gln/Glu levels predicted more severe (hypo)manic symptoms cross-sectionally, predicted worsening (hypo)manic symptoms longitudinally, and explained greater variance in future (hypo)manic symptoms than diagnostic information. However, rather than being transdiagnostic, this effect was specific to individuals with bipolar disorder. Prediction error indices were unrelated to symptom severity.

CONCLUSIONS

Although findings are preliminary and require replication, they suggest that heightened mPFC Gln/Glu warrants further consideration as a predictor of future (hypo)mania. Importantly, this work highlights the value of an RDoC approach that works in tandem with, rather than independent of, traditional diagnostic frameworks.

Translational Assessments of Reward Responsiveness in the Marmoset

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The dual-system theory of bipolar spectrum disorders: A meta-analysis

Bipolar spectrum disorders are characterized by alternating intervals of extreme positive and negative affect. We performed a meta-analysis to test the hypothesis that such disorders would be related to dysregulated reinforcement sensitivity. First, we reviewed 23 studies that reported the correlation between self-report measures of (hypo)manic personality and measures of reinforcement sensitivity. A large relationship was found between (hypo)manic personality and BAS sensitivity (g = .74), but not with BIS sensitivity (g = -.08). This stands in contrast to self-reported depression which has a small, negative relationship with BAS sensitivity and a large positive one with BIS sensitivity (Katz et al., 2020). Next, we reviewed 33 studies that compared reinforcement sensitivity between euthymic, bipolar participants and healthy controls. There, bipolar disorder had a small, positive relationship with BAS sensitivity (g = .20) and a medium, positive relationship with BIS sensitivity (g = .64). These findings support a dualsystem theory of bipolar disorders, wherein BAS sensitivity is more closely related to mania and BIS sensitivity more closely to bipolar depression. Bipolar disorders show diatheses for both states with euthymic participants being BAS- and BIS- hypersensitive. Implications for further theory and research practice are expounded upon in the discussion.

Dissociable mechanisms underpinning effort-cost decision-making across the psychosis spectrum

Recent theoretical models propose that abnormal effort-cost decision-making (ECDM) likely has divergent underpinnings across mood and psychotic disorders. However, whether this same model applies to individuals across the psychosis spectrum, including individuals with affective psychosis, remains unclear. This study aimed to empirically test whether two component processes - working memory and reward learning - contribute to ECDM impairment across the psychosis spectrum. ECDM was assessed using the Effort Expenditure for Rewards Task in individuals with psychotic disorders (n = 190) and healthy controls (n = 52). Working memory was assessed using a Digit Sequencing Task and reward learning was assessed using a Probabilistic Reward Task. Relative to the control group, the psychosis group showed reduced willingness to expend effort for higher probability, higher value rewards. This effect was most pronounced in individuals with schizophrenia and schizoaffective disorder relative to individuals with psychotic bipolar disorder. Across the whole sample, better working memory but not reward learning predicted greater willingness to expend effort for higher probability rewards. However, the link between working memory and ECDM differed as a function of patient symptom profile. Specifically, working memory was only predictive of ECDM for individuals with less severe negative symptoms and minimal depressive symptoms. For individuals with more severe negative symptoms, poorer ECDM was instead predicted by deficits in reward learning. Although these findings reiterate the important link between working memory and ECDM in individuals with psychotic disorders, they also show that this link varies in accordance with the presence of prominent negative and depressive symptoms.

Empirical validation of a touchscreen probabilistic reward task in rats

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

What is bipolar disorder? A disease model of dysregulated energy expenditure

Advances in the understanding and management of bipolar disorder (BD) have been slow to emerge. Despite notable recent developments in neurosciences, our conceptualization of the nature of this mental disorder has not meaningfully progressed. One of the key reasons for this scenario is the continuing lack of a comprehensive disease model. Within the increasing complexity of modern research methods, there is a clear need for an overarching theoretical framework, in which findings are assimilated and predictions are generated. In this review and hypothesis article, we propose such a framework, one in which dysregulated energy expenditure is a primary, sufficient cause for BD. Our proposed model is centered on the disruption of the molecular and cellular network regulating energy production and expenditure, as well its potential secondary adaptations and compensatory mechanisms. We also focus on the putative longitudinal progression of this pathological process, considering its most likely periods for onset, such as critical periods that challenges energy homeostasis (e.g. neurodevelopment, social isolation), and the resulting short and long-term phenotypical manifestations.

Shared and dissociable features of apathy and reward system dysfunction in bipolar I disorder and schizophrenia

BACKGROUND

Bipolar disorder I (BD-I) is defined by episodes of mania, depression and euthymic states. These episodes are among other symptoms characterized by altered reward processing and negative symptoms (NS), in particular apathy. However, the neural correlates of these deficits are not well understood.

METHODS

We first assessed the severity of NS in 25 euthymic BD-I patients compared with 25 healthy controls (HC) and 27 patients with schizophrenia (SZ). Then, we investigated ventral (VS) and dorsal striatal (DS) activation during reward anticipation in a Monetary Incentive Delayed Task and its association with NS.

RESULTS

In BD-I patients NS were clearly present and the severity of apathy was comparable to SZ patients. Apathy scores in the BD-I group but not in the SZ group correlated with sub-syndromal depression scores. At the neural level, we found significant VS and DS activation in BD-I patients and no group differences with HC or SZ patients. In contrast to patients with SZ, apathy did not correlate with striatal activation during reward anticipation. Explorative whole-brain analyses revealed reduced extra-striatal activation in BD-I patients compared with HC and an association between reduced activation of the inferior frontal gyrus and apathy.

CONCLUSION

This study found that in BD-I patients apathy is present to an extent comparable to SZ, but is more strongly related to sub-syndromal depressive symptoms. The findings support the view of different pathophysiological mechanisms underlying apathy in the two disorders and suggest that extra-striatal dysfunction may contribute to impaired reward processing and apathy in BD-I.

How obsessive-compulsive and bipolar disorders meet each other? An integrative gene-based enrichment approach

BACKGROUND

The novel approaches to psychiatric classification assume that disorders, contrary to what was previously thought, are not completely separate phenomena. In this regard, in addition to symptom-based criteria, disturbances are also considered on the basis of lower level components. With this viewpoint, identifying common biochemical markers would be beneficial in adopting a comprehensive strategy for prevention, diagnosis and treatment.

MAIN BODY

One of the problematic areas in clinical settings is the coexistence of both obsessive-compulsive disorder (OCD) and bipolar disorder (BD) that is challenging and difficult to manage. In this study, using a system biologic approach we aimed to assess the interconnectedness of OCD and BD at different levels. Gene Set Enrichment Analysis (GSEA) method was used to identify the shared biological network between the two disorders. The results of the analysis revealed 34 common genes between the two disorders, the most important of which were CACNA1C, GRIA1, DRD2, NOS1, SLC18A1, HTR2A and DRD1. Dopaminergic synapse and cAMP signaling pathway as the pathways, dopamine binding and dopamine neurotransmitter receptor activity as the molecular functions, dendrite and axon part as the cellular component and cortex and striatum as the brain regions were the most significant commonalities.

SHORT CONCLUSION

The results of this study highlight the role of multiple systems, especially the dopaminergic system in linking OCD and BD. The results can be used to estimate the disease course, prognosis, and treatment choice, particularly in the cases of comorbidity. Such perspectives, going beyond symptomatic level, help to identify common endophenotypes between the disorders and provide diagnostic and therapeutic approaches based on biological in addition to the symptomatic level.

Abnormal Anhedonia as a Potential Endophenotype in Obsessive-Compulsive Disorder

BACKGROUND

Obsessive-compulsive disorder (OCD) is often accompanied by cognitive, particularly executive function, impairments. Recently, anhedonia has emerged as an apparently important symptom of OCD reflecting altered emotion regulation. These two aspects are often comorbid in OCD. However, little is known about whether anhedonia may be a trait marker for OCD.

METHODS

To verify the role of executive function and evaluate the role of anhedonia in OCD and its relationship with OCD symptoms, we recruited 60 OCD patients, 30 unaffected first-degree relatives (FDRs), and 60 healthy controls (HCs). Participants completed psychometric testing to assess depression, anxiety, and anhedonia symptoms, as well as two cognitive tests to assess executive function, namely the Wisconsin Card Sorting Test (WCST) and the Stroop Color-Word Test (SCWT).

RESULTS

Compared to HCs, OCD patients and FDRs had significantly lower anticipatory and consummatory pleasure scores. The severity of anticipatory anhedonia correlated positively with obsessive-compulsive symptoms (r = 0.253, p = 0.009), even after controlling for depression and anxiety symptoms. Compared to HCs, OCD patients and FDRs made more errors and achieved fewer categories in the WCST. For all three SWCT components, OCD patients and FDRs took more time to name colors than HCs, but the three groups had similar numbers of errors.

CONCLUSION

This family-based study showed dampened pleasure together with cognitive dysfunction in OCD patients. The similar consummatory pleasure findings between OCD and FDR groups suggest anhedonia may be considered as a candidate OCD endophenotype.

Reduced Reward Responsiveness in Women With Moderate - to - Severe Premenstrual Syndrome: Evidence From a Probabilistic Reward Task

Nearly 50% of women of reproductive age worldwide experience premenstrual syndrome (PMS). Women with PMS exhibit low positive affect and low frontal electroencephalography asymmetry scores, both of which are associated with reward processing. These findings suggest that women with PMS may exhibit deficiencies in reward processing. A probabilistic reward task based on signal detection approach was used to assess reward responsiveness in 30 women with moderate-to-severe PMS and 31 controls without PMS. The results revealed that in the late luteal phase, the women with moderate-to-severe PMS exhibited lower response bias and lower hit rate toward more frequently rewarded stimuli (rich stimuli) than the controls. By contrast, the response bias and hit rate did not differ between the two groups in the follicular phase. The group differences still remained after controlling for anhedonic symptoms. Furthermore, trial-by-trial probability analyses revealed that women with moderate-to-severe PMS exhibited a trend of having a higher miss rate for rich stimuli than the controls. In particular, when a rich stimulus was preceded by an infrequently rewarded stimulus (a rewarded lean stimulus), participants in the PMS group exhibited a trend for higher miss rate than those in the control group in the late luteal and follicular phases. However, group differences in the probability analyses were nonsignificant after controlling for anhedonic symptoms. These results provide preliminary evidence that women with moderate-to-severe PMS exhibit dysfunctional reward responsiveness and impaired ability to modulate their behavior as a function of prior reinforcement.

Affective cognition in bipolar disorder: A systematic review by the ISBD targeting cognition task force

BACKGROUND

Impairments in affective cognition are part of the neurocognitive profile and possible treatment targets in bipolar disorder (BD), but the findings are heterogeneous. The International Society of Bipolar Disorder (ISBD) Targeting Cognition Task Force conducted a systematic review to (i) identify the most consistent findings in affective cognition in BD, and (ii) provide suggestions for affective cognitive domains for future study and meta-analyses.

METHODS

The review included original studies reporting behavioral measures of affective cognition in BD patients vs controls following the procedures of the Preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA) statement. Searches were conducted on PubMed/MEDLINE, EMBASE, and PsychInfo from inception until November 2018.

RESULTS

A total of 106 articles were included (of which nine included data for several affective domains); 41 studies assessed emotional face processing; 23 studies investigated reactivity to emotional words and images; 3 investigated explicit emotion regulation; 17 assessed implicit emotion regulation; 31 assessed reward processing and affective decision making. In general, findings were inconsistent. The most consistent findings were trait-related difficulties in facial emotion recognition and implicit emotion regulation, and impairments in reward processing and affective decision making during mood episodes. Studies using eye-tracking and facial emotion analysis revealed subtle trait-related abnormalities in emotional reactivity.

CONCLUSION

The ISBD Task Force recommends facial expression recognition, implicit emotion regulation, and reward processing as domains for future research and meta-analyses. An important step to aid comparability between studies in the field would be to reach consensus on an affective cognition test battery for BD.

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

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

Reward and punishment learning in schizophrenia and bipolar disorder

Prior studies on reward learning deficits in psychiatric disorders have used probabilistic learning tasks, making it unclear whether impairment is due to the probabilistic nature of the task rather than reward processing. In this study, we tested probabilistic vs. deterministic reward and punishment learning in healthy controls and three patient groups: schizophrenia (SZ), psychotic bipolar disorder (BD), and nonpsychotic BD. Experimental results show that reward learning was impaired in patients with SZ and patients with psychotic BD in the probabilistic learning task compared to patients with nonpsychotic BD and healthy controls. In contrast, punishment learning in the probabilistic task was impaired in patients with nonpsychotic BD compared to the other patient groups and healthy controls. There were no significant differences among all groups in the deterministic learning task scores. We also found that Hamilton Depression Scale scores negatively correlated with probabilistic learning performance. Our data may suggest that reward learning impairment may be due to the nature of the task as well as subtype of BD.

Linking resting-state networks and social cognition in schizophrenia and bipolar disorder

Individuals with schizophrenia and bipolar disorder show alterations in functional neural connectivity during rest. However, resting-state network (RSN) disruptions have not been systematically compared between the two disorders. Further, the impact of RSN disruptions on social cognition, a key determinant of functional outcome, has not been studied. Forty-eight individuals with schizophrenia, 46 with bipolar disorder, and 48 healthy controls completed resting-state functional magnetic resonance imaging. An atlas-based approach was used to examine functional connectivity within nine RSNs across the cortex. RSN connectivity was assessed via nonparametric permutation testing, and associations with performance on emotion perception, mentalizing, and emotion management tasks were examined. Group differences were observed in the medial and lateral visual networks and the sensorimotor network. Individuals with schizophrenia demonstrated reduced connectivity relative to healthy controls in all three networks. Individuals with bipolar disorder demonstrated reduced connectivity relative to controls in the medial visual network and connectivity within this network was significantly positively correlated with emotion management. In healthy controls, connectivity within the medial and lateral visual networks positively correlated with mentalizing. No significant correlations were found for either visual network in schizophrenia. Results highlight the role of altered early visual processing in social cognitive deficits in both schizophrenia and bipolar disorder. However, individuals with bipolar disorder appear to compensate for disrupted visual network connectivity on social cognitive tasks, whereas those with schizophrenia do not. The current study adds clarity on the neurophysiology underlying social cognitive deficits that result in impaired functioning in serious mental illness.

The Titrated Monetary Incentive Delay Task: Sensitivity, convergent and divergent validity, and neural correlates in an RDoC sample

INTRODUCTION

Neuropsychological tests are designed to assay brain function via performance measurements. Many tests corresponding to visual and motor cortex function have been validated. Tests probing reward circuitry, including the ventral striatum (VS), could benefit assessment of numerous neurological and psychiatric disorders in which reward or VS function is disturbed. The present study sought to examine convergent and divergent validity of our modified, titrated version of the Monetary Incentive Delay Task, such that it may in the future stand as a validated neuropsychological test for reward function.

METHOD

Participants were 132 individuals with a history of mood disturbance (HMD) and 43 healthy comparisons, ages 18-30 years. In addition to a standard neuropsychological battery and symptom measures, participants completed a modified version of the Monetary Incentive Delay Task (T-MIDT) during functional magnetic resonance imaging (fMRI), which involved a multistage titration procedure to incrementally increase or decrease the response window time per each participant's psychomotor speed and optimize individual performance.

RESULTS

Across groups after titration, performance on the T-MIDT diverged from measures of processing speed, attention, and spatial working memory, but not inhibitory control. Performance in the HMD group was differentially correlated with executive function measures before and after titration. The reward circuit (e.g., subcortical, insular, medial prefrontal) was activated during reward anticipation.

CONCLUSION

The present findings provide preliminary evidence that the T-MIDT measures a construct distinct from many executive functions and that individualized titration of the task parameters is critical in parsing reward from executive function. The T-MIDT correlated with residual mood symptoms in individuals with remitted depression or bipolar disorder, implying that behavioral or brain activation group differences are only to be observed in the active state of illness.