Aberrant Salience Is Related to Reduced Reinforcement Learning Signals and Elevated Dopamine Synthesis Capacity in Healthy Adults

Neurocomputational mechanisms underlying differential reinforcement learning from wins and losses in obesity with and without binge eating

BACKGROUND

Binge Eating Disorder (BED) is thought of as a disorder of cognitive control but evidence regarding its neurocognitive mechanisms is inconclusive. Key limitations in prior research are a lack of consistent separation between effects of BED and obesity, and a disregard for self-report evidence suggesting that neurocognitive alterations may emerge primarily in loss- or harm-avoidance contexts.

METHODS

Addressing these gaps, this longitudinal study investigated behavioral flexibility and its underlying neuro-computational processes in reward-seeking and loss-avoidance contexts. Obese participants with BED (BED), without BED (OB), and healthy normal-weight participants (NW) (Ntotal=96) performed a probabilistic reversal learning task during functional imaging, with different blocks focused on obtaining wins or avoiding losses. They were reinvited for a 6-months follow-up.

RESULTS

Analyses informed by computational models of reinforcement learning showed that unlike BED, OB performed worse in the win than the loss condition. Computationally, this was explained by differential learning sensitivities in the win vs loss conditions between groups. In the brain, this was echoed in differential neural learning signals in the ventromedial prefrontal cortex (vmPFC) per condition. The differences were subtle, but scaled with BED symptoms, such that more severe BED symptoms were associated with increasing bias towards improved learning from wins vs losses. Across conditions, OB switched more between choice options than NW. This was reflected in diminished representation of choice certainty in the vmPFC.

CONCLUSIONS

Our study highlights the importance of distinguishing between obesity with and without BED to identify unique neuro-computational alterations underlying different styles of maladaptive eating behavior.

Ghrelin decreases sensitivity to negative feedback and increases prediction-error related caudate activity in humans, a randomized controlled trial

The stomach-derived hormone ghrelin plays not only a role in feeding, starvation, and survival, but it has been suggested to also be involved in the stress response, in neuropsychiatric conditions, and in alcohol and drug use disorders. Mechanisms related to reward processing might mediate ghrelin's broader effects on complex behaviors, as indicated by animal studies and mostly correlative human studies. Here, using a within-subject double-blind placebo-controlled design with intravenous ghrelin infusion in healthy volunteers (n = 30), we tested whether ghrelin alters sensitivity to reward and punishment in a reward learning task. Parameters were derived from a computational model of participants' task behavior. The reversal learning task with monetary rewards was performed during functional brain imaging to investigate ghrelin effects on brain signals related to reward prediction errors. Compared to placebo, ghrelin decreased punishment sensitivity (t = -2.448, p = 0.021), while reward sensitivity was unaltered (t = 0.8, p = 0.43). We furthermore found increased prediction-error related activity in the dorsal striatum during ghrelin administration (region of interest analysis: t-values ≥ 4.21, p-values ≤ 0.044). Our results support a role for ghrelin in reward processing that extends beyond food-related rewards. Reduced sensitivity to negative outcomes and increased processing of prediction errors may be beneficial for food foraging when hungry but could also relate to increased risk taking and impulsivity in the broader context of addictive behaviors.

Impaired striatal glutamate/GABA regulation in violent offenders with antisocial personality disorder and psychopathy

Men with antisocial personality disorder (ASPD) with or without psychopathy (+/-P) are responsible for most violent crime in society. Development of effective treatments is hindered by poor understanding of the neurochemical underpinnings of the condition. Men with ASPD with and without psychopathy demonstrate impulsive decision-making, associated with striatal abnormalities in functional neuroimaging studies. However, to date, no study has directly examined the potential neurochemical underpinnings of such abnormalities. We therefore investigated striatal glutamate: GABA ratio using Magnetic Resonance Spectroscopy in 30 violent offenders (16 ASPD-P, 14 ASPD + P) and 21 healthy non-offenders. Men with ASPD +/- P had a significant reduction in striatal glutamate : GABA ratio compared to non-offenders. We report, for the first time, striatal Glutamate/GABA dysregulation in ASPD +/- P, and discuss how this may be related to core behavioral abnormalities in the disorders.

Diminished reinforcement sensitivity in adolescence is associated with enhanced response switching and reduced coding of choice probability in the medial frontal pole

Precisely charting the maturation of core neurocognitive functions such as reinforcement learning (RL) and flexible adaptation to changing action-outcome contingencies is key for developmental neuroscience and adjacent fields like developmental psychiatry. However, research in this area is both sparse and conflicted, especially regarding potentially asymmetric development of learning for different motives (obtain wins vs avoid losses) and learning from valenced feedback (positive vs negative). In the current study, we investigated the development of RL from adolescence to adulthood, using a probabilistic reversal learning task modified to experimentally separate motivational context and feedback valence, in a sample of 95 healthy participants between 12 and 45. We show that adolescence is characterized by enhanced novelty seeking and response shifting especially after negative feedback, which leads to poorer returns when reward contingencies are stable. Computationally, this is accounted for by reduced impact of positive feedback on behavior. We also show, using fMRI, that activity of the medial frontopolar cortex reflecting choice probability is attenuated in adolescence. We argue that this can be interpreted as reflecting diminished confidence in upcoming choices. Interestingly, we find no age-related differences between learning in win and loss contexts.

Acute stress alters probabilistic reversal learning in healthy male adults

Behavioural adaptation is a fundamental cognitive ability, ensuring survival by allowing for flexible adjustment to changing environments. In laboratory settings, behavioural adaptation can be measured with reversal learning paradigms requiring agents to adjust reward learning to stimulus-action-outcome contingency changes. Stress is found to alter flexibility of reward learning, but effect directionality is mixed across studies. Here, we used model-based functional MRI (fMRI) in a within-subjects design to investigate the effect of acute psychosocial stress on flexible behavioural adaptation. Healthy male volunteers (n = 28) did a reversal learning task during fMRI in two sessions, once after the Trier Social Stress Test (TSST), a validated psychosocial stress induction method, and once after a control condition. Stress effects on choice behaviour were investigated using multilevel generalized linear models and computational models describing different learning processes that potentially generated the data. Computational models were fitted using a hierarchical Bayesian approach, and model-derived reward prediction errors (RPE) were used as fMRI regressors. We found that acute psychosocial stress slightly increased correct response rates. Model comparison revealed that double-update learning with altered choice temperature under stress best explained the observed behaviour. In the brain, model-derived RPEs were correlated with BOLD signals in striatum and ventromedial prefrontal cortex (vmPFC). Striatal RPE signals for win trials were stronger during stress compared with the control condition. Our study suggests that acute psychosocial stress could enhance reversal learning and RPE brain responses in healthy male participants and provides a starting point to explore these effects further in a more diverse population.

[Methods for assessing aberrant and adaptive salience]

The term «salience» is most often used to describe «aberrant salience», which means assigning false significance to insignificant facts and details, that is inherent to patients with schizophrenia. Most often it is used in combination with «aberrant salience», which is understood as the assignment of false significance to insignificant facts and details. The term «adaptive salience» is less commonly used and means the «correct» assignment of the significance to important biological information. It is believed that in schizophrenia there is a decrease of adaptive salience in combination with an increase of aberrant salience. The concepts of aberrant and adaptive salience are a kind of link between the dopamine imbalance underlying the pathogenesis of schizophrenia and the diverse clinic of the disease. This article provides a review of the literature on methods for assessing, including quantitatively assessment, salience in schizophrenia. The comparison of these methods and their possible clinical and scientific application are provided.

Sufficient reliability of the behavioral and computational readouts of a probabilistic reversal learning task

Task-based measures that capture neurocognitive processes can help bridge the gap between brain and behavior. To transfer tasks to clinical application, reliability is a crucial benchmark because it imposes an upper bound to potential correlations with other variables (e.g., symptom or brain data). However, the reliability of many task readouts is low. In this study, we scrutinized the retest reliability of a probabilistic reversal learning task (PRLT) that is frequently used to characterize cognitive flexibility in psychiatric populations. We analyzed data from N = 40 healthy subjects, who completed the PRLT twice. We focused on how individual metrics are derived, i.e., whether data were partially pooled across participants and whether priors were used to inform estimates. We compared the reliability of the resulting indices across sessions, as well as the internal consistency of a selection of indices. We found good to excellent reliability for behavioral indices as derived from mixed-effects models that included data from both sessions. The internal consistency was good to excellent. For indices derived from computational modeling, we found excellent reliability when using hierarchical estimation with empirical priors and including data from both sessions. Our results indicate that the PRLT is well equipped to measure individual differences in cognitive flexibility in reinforcement learning. However, this depends heavily on hierarchical modeling of the longitudinal data (whether sessions are modeled separately or jointly), on estimation methods, and on the combination of parameters included in computational models. We discuss implications for the applicability of PRLT indices in psychiatric research and as diagnostic tools.

An integrated cluster-wise significance measure for fMRI analysis

Cluster-wise inference is widely used in fMRI analysis. The cluster-level statistic is often obtained by counting the number of intra-cluster voxels which surpass a voxel-level statistical significance threshold. This measure can be sub-optimal regarding the power and false-positive error rate because the suprathreshold voxel count neglects the voxel-wise significance levels and ignores the dependence between voxels. This article aims to provide a new Integrated Cluster-wise significance Measure (ICM) for cluster-level significance determination in cluster-wise fMRI analysis by integrating cluster extent, voxel-level significance (e.g., p values), and activation dependence between within-cluster voxels. We develop a computationally efficient strategy for ICM based on probabilistic approximation theories. Consequently, the computational load for ICM-based cluster-wise inference (e.g., permutation tests) is affordable. We validate the proposed method via extensive simulations and then apply it to two fMRI data sets. The results demonstrate that ICM can improve the power with well-controlled family-wise error (FWE).

Neural Circuitry of Salience and Reward Processing in Psychosis

The processing of salient and rewarding stimuli is integral to engaging our attention, stimulating anticipation for future events, and driving goal-directed behaviors. Widespread impairments in these processes are observed in psychosis, which may be associated with worse functional outcomes or mechanistically linked to the development of symptoms. Here, we summarize the current knowledge of behavioral and functional neuroimaging in salience, prediction error, and reward. Although each is a specific process, they are situated in multiple feedback and feedforward systems integral to decision making and cognition more generally. We argue that the origin of salience and reward processing dysfunctions may be centered in the subcortex during the earliest stages of psychosis, with cortical abnormalities being initially more spared but becoming more prominent in established psychotic illness/schizophrenia. The neural circuits underpinning salience and reward processing may provide targets for delaying or preventing progressive behavioral and neurobiological decline.

Relative salience signaling within a thalamo-orbitofrontal circuit governs learning rate

Learning to predict rewards is essential for the sustained fitness of animals. Contemporary views suggest that such learning is driven by a reward prediction error (RPE)-the difference between received and predicted rewards. The magnitude of learning induced by an RPE is proportional to the product of the RPE and a learning rate. Here we demonstrate using two-photon calcium imaging and optogenetics in mice that certain functionally distinct subpopulations of ventral/medial orbitofrontal cortex (vmOFC) neurons signal learning rate control. Consistent with learning rate control, trial-by-trial fluctuations in vmOFC activity positively correlate with behavioral updating when the RPE is positive, and negatively correlates with behavioral updating when the RPE is negative. Learning rate is affected by many variables including the salience of a reward. We found that the average reward response of these neurons signals the relative salience of a reward, because it decreases after reward prediction learning or the introduction of another highly salient aversive stimulus. The relative salience signaling in vmOFC is sculpted by medial thalamic inputs. These results support emerging theoretical views that prefrontal cortex encodes and controls learning parameters.

Aberrant salience and reward processing: a comparison of measures in schizophrenia and anxiety

BACKGROUND

Aberrant salience may contribute to the development of schizophrenia symptoms via alterations in reward processing and motivation. However, tests of this hypothesis have yielded inconsistent results. These inconsistencies may reflect problems with the validity and specificity of measures of aberrant salience in schizophrenia. Therefore, we investigated relationships among measures of aberrant salience, reward, and motivation in schizophrenia and anxiety.

METHOD

Individuals with schizophrenia (n = 30), anxiety (n = 33) or unaffected by mental disorder (n = 30) completed measures of aberrant salience [Aberrant Salience Inventory (ASI), Salience Attribution Test (SAT)], motivation (Effort Expenditure for Reward Task), and reinforcer sensitivity (Stimulus Chase Task).

RESULTS

Schizophrenia participants scored higher than anxiety (d = 0.71) and unaffected (d = 1.54) groups on the ASI and exhibited greater aberrant salience (d = 0.60) and lower adaptive salience (d = 0.98) than anxious participants on the SAT. There was no evidence of a correlation between measures of aberrant salience. Schizophrenia was associated with related deficits in motivated behaviour and maladaptive reward processing. However, these differences in reward processing did not correlate with aberrant salience measures.

CONCLUSIONS

The results suggest that key measures of aberrant salience have limited specificity and validity. These problems may account for inconsistent findings reported in the literature.

Hippocampal Hyperactivity as a Druggable Circuit-Level Origin of Aberrant Salience in Schizophrenia

The development of current neuroleptics was largely aiming to decrease excessive dopaminergic signaling in the striatum. However, the notion that abnormal dopamine creates psychotic symptoms by causing an aberrant assignment of salience that drives maladaptive learning chronically during disease development suggests a therapeutic value of early interventions that correct salience-related neural processing. The mesolimbic dopaminergic output is modulated by several interconnected brain-wide circuits centrally involving the hippocampus and key relays like the ventral and associative striatum, ventral pallidum, amygdala, bed nucleus of the stria terminalis, nucleus reuniens, lateral and medial septum, prefrontal and cingulate cortex, among others. Unraveling the causal relationships between these circuits using modern neuroscience techniques holds promise for identifying novel cellular—and ultimately molecular—treatment targets for reducing transition to psychosis and symptoms of schizophrenia. Imaging studies in humans have implicated a hyperactivity of the hippocampus as a robust and early endophenotype in schizophrenia. Experiments in rodents, in turn, suggested that the activity of its output region—the ventral subiculum—may modulate dopamine release from ventral tegmental area (VTA) neurons in the ventral striatum. Even though these observations suggested a novel circuit-level target for anti-psychotic action, no therapy has yet been developed along this rationale. Recently evaluated treatment strategies—at least in part—target excess glutamatergic activity, e.g. N-acetyl-cysteine (NAC), levetiracetam, and mGluR2/3 modulators. We here review the evidence for the central implication of the hippocampus-VTA axis in schizophrenia-related pathology, discuss its symptom-related implications with a particular focus on aberrant assignment of salience, and evaluate some of its short-comings and prospects for drug discovery.

From apathy to addiction: Insights from neurology and psychiatry

The tendency to engage in addictive behaviors has long been tied to the actions of the dopamine system. Early theories were based on the fact that all addictive drugs and behaviors (such as gambling) increase dopamine levels in the striatum, and the evidence that dopamine signaled reward or reward prediction error. However, with a changing emphasis of addiction away from purely pharmacological models that emphasize tolerance and withdrawal, towards one of behavioral dyscontrol, is there still a place for abnormal dopamine signaling in addiction? Here we recast the dopamine theory of addiction based on the idea that tonic dopamine may index a continuous phenotype that goes from apathy to impulsivity and compulsivity. Higher tonic dopamine signaling would make individuals vulnerable to drug reinforcement and cue-induced craving. We relate this to computational models of dopamine signaling, and review clinical and neuroimaging evidence from Parkinson's Disease, schizophrenia and bipolar disorder in support of this model.

Striatal Dopamine and Reward Prediction Error Signaling in Unmedicated Schizophrenia Patients

Increased striatal dopamine synthesis capacity has consistently been reported in patients with schizophrenia. However, the mechanism translating this into behavior and symptoms remains unclear. It has been proposed that heightened striatal dopamine may blunt dopaminergic reward prediction error signaling during reinforcement learning. In this study, we investigated striatal dopamine synthesis capacity, reward prediction errors, and their association in unmedicated schizophrenia patients (n = 19) and healthy controls (n = 23). They took part in FDOPA-PET and underwent functional magnetic resonance imaging (fMRI) scanning, where they performed a reversal-learning paradigm. The groups were compared regarding dopamine synthesis capacity (Kicer), fMRI neural prediction error signals, and the correlation of both. Patients did not differ from controls with respect to striatal Kicer. Taking into account, comorbid alcohol abuse revealed that patients without such abuse showed elevated Kicer in the associative striatum, while those with abuse did not differ from controls. Comparing all patients to controls, patients performed worse during reversal learning and displayed reduced prediction error signaling in the ventral striatum. In controls, Kicer in the limbic striatum correlated with higher reward prediction error signaling, while there was no significant association in patients. Kicer in the associative striatum correlated with higher positive symptoms and blunted reward prediction error signaling was associated with negative symptoms. Our results suggest a dissociation between striatal subregions and symptom domains, with elevated dopamine synthesis capacity in the associative striatum contributing to positive symptoms while blunted prediction error signaling in the ventral striatum related to negative symptoms.

Dopaminergic signaling of uncertainty and the aetiology of gambling addiction

Although there is increasing clinical recognition of behavioral addictions, of which gambling disorder is the prototype example, there is a limited understanding of the psychological properties of (non-substance-related) behaviors that enable them to become 'addictive' in a way that is comparable to drugs of abuse. According to an influential application of reinforcement learning to substance addictions, the direct effects of drugs to release dopamine can create a perpetual escalation of incentive salience. This article focusses on reward uncertainty, which is proposed to be the core feature of gambling that creates the capacity for addiction. We describe the neuro-dynamics of the dopamine response to uncertainty that may allow a similar escalation of incentive salience, and its relevance to behavioral addictions. We review translational evidence from both preclinical animal models and human clinical research, including studies in people with gambling disorder. Further, we describe the evidence for 1) the effects of the omission of expected reward as a stressor and to promote sensitization, 2) the effect of the resolution of reward uncertainty as a source of value, 3) structural characteristics of modern Electronic Gaming Machines (EGMs) in leveraging these mechanisms, 4) analogies to the aberrant salience hypothesis of psychosis for creating and maintaining gambling-related cognitive distortions. This neurobiologically-inspired model has implications for harm profiling of other putative behavioral addictions, as well as offering avenues for enhancing neurological, pharmacological and psychological treatments for gambling disorder, and harm reduction strategies for EGM design.

The interplay between childhood trauma, cognitive biases, and cannabis use on the risk of psychosis in nonclinical young adults in Poland

Background.

Childhood traumatic events are risk factors for psychotic-like experiences (PLEs). However, the mechanisms explaining how trauma may contribute to the development of PLEs are not fully understood. In our study, we investigated whether cannabis use and cognitive biases mediate the relationship between early trauma and PLEs.

Methods.

A total sample of 6,772 young adults (age 26.6 ± 4.7, 2,181 male and 3,433 female) was recruited from the general population to participate in an online survey. We excluded 1,158 individuals due to a self-reported lifetime diagnosis of any mental disorder. The online survey included selected items from the following questionnaires: Traumatic Experience Checklist (TEC, 3 items), Childhood Experience of Care and Abuse Questionnaire (CECA.Q, 3 items), Cannabis Problems Questionnaire (CPQ, 10 items), Davos Assessment of Cognitive Biases Scale (DACOBS-18, 9 items), and Prodromal Questionnaire-16 (PQ-16). Mediation analyses were performed with respect to different categories of traumatic experiences (emotional, physical and sexual abuse as well as emotional neglect).

Results.

Our results showed significant associations of any time of childhood trauma with higher scores of cannabis use (CPQ), cognitive biases (DACOBS), and PLEs (PQ-16) (p < 0.001). We found a direct effect of childhood trauma on PLEs as well as significant indirect effect mediated through cannabis use and cognitive biases. All models tested for the effects of specific childhood adversities revealed similar results. The percentage of variance in PQ-16 scores explained by serial mediation models varied between 32.8 and 34.2% depending on childhood trauma category.

Conclusion.

Cannabis use and cognitive biases play an important mediating role in the relationship between childhood traumatic events and the development of PLEs in a nonclinical young adult population.

Chronic psychosocial stressors are associated with alterations in salience processing and corticostriatal connectivity

Psychosocial stressors including childhood adversity, migration, and living in an urban environment, have been associated with several psychiatric disorders, including psychotic disorders. The neural and psychological mechanisms mediating this relationship remain unclear. In parallel, alterations in corticostriatal connectivity and abnormalities in the processing of salience, are seen in psychotic disorders. Aberrant functioning of these mechanisms secondary to chronic stress exposure, could help explain how common environmental exposures are associated with a diverse range of symptoms. In the current study, we recruited two groups of adults, one with a high degree of exposure to chronic psychosocial stressors (the exposed group, n = 20), and one with minimal exposure (the unexposed group, n = 22). All participants underwent a resting state MRI scan, completed the Aberrant Salience Inventory, and performed a behavioural task - the Salience Attribution Test (SAT). The exposed group showed reduced explicit adaptive salience scores (cohen's d = 0.69, p = 0.03) and increased aberrant salience inventory scores (d = 0.65, p = 0.04). The exposed group also showed increased corticostriatal connectivity between the ventral striatum and brain regions previously implicated in salience processing. Corticostriatal connectivity in these regions negatively correlated with SAT explicit adaptive salience (r = -0.48, p = 0.001), and positively correlated with aberrant salience inventory scores (r = 0.42, p = 0.006). Furthermore, in a mediation analysis there was tentative evidence that differences in striato-cortical connectivity mediated the group differences in salience scores.

Motivational deficits in schizophrenia relate to abnormalities in cortical learning rate signals

Individuals from across the psychosis spectrum display impairments in reinforcement learning. In some individuals, these deficits may result from aberrations in reward prediction error (RPE) signaling, conveyed by dopaminergic projections to the ventral striatum (VS). However, there is mounting evidence that VS RPE signals are relatively intact in medicated people with schizophrenia (PSZ). We hypothesized that, in PSZ, reinforcement learning deficits often are not related to RPE signaling per se but rather their impact on learning and behavior (i.e., learning rate modulation), due to dysfunction in anterior cingulate and dorsomedial prefrontal cortex (dmPFC). Twenty-six PSZ and 23 healthy volunteers completed a probabilistic reinforcement learning paradigm with occasional, sudden, shifts in contingencies. Using computational modeling, we found evidence of an impairment in trial-wise learning rate modulation (α) in PSZ before and after a reinforcement contingency shift, expressed most in PSZ with more severe motivational deficits. In a subsample of 22 PSZ and 22 healthy volunteers, we found little evidence for between-group differences in VS RPE and dmPFC learning rate signals, as measured with fMRI. However, a follow-up psychophysiological interaction analysis revealed decreased dmPFC-VS connectivity concurrent with learning rate modulation, most prominently in individuals with the most severe motivational deficits. These findings point to an impairment in learning rate modulation in PSZ, leading to a reduced ability to adjust task behavior in response to unexpected outcomes. At the level of the brain, learning rate modulation deficits may be associated with decreased involvement of the dmPFC within a greater RL network.

Reduced parietofrontal effective connectivity during a working-memory task in people with high delusional ideation

BACKGROUND

Working-memory impairment is a core cognitive dysfunction in people with schizophrenia and people at mental high risk. Recent imaging studies on working memory have suggested that abnormalities in prefrontal activation and in connectivity between the frontal and parietal regions could be neural underpinnings of the different stages of psychosis. However, it remains to be explored whether comparable alterations are present in people with subclinical levels of psychosis, as experienced by a small proportion of the general population who neither seek help nor show constraints in daily functioning.

METHODS

We compared 24 people with subclinical high delusional ideation and 24 people with low delusional ideation. Both groups performed an n-back working-memory task during functional magnetic resonance imaging. We characterized frontoparietal effective connectivity using dynamic causal modelling.

RESULTS

Compared to people who had low delusional ideation, people with high delusional ideation showed a significant increase in dorsolateral prefrontal activation during the working-memory task, as well as reduced working-memory-dependent parietofrontal effective connectivity in the left hemisphere. Group differences were not evident at the behavioural level.

LIMITATIONS

The current experimental design did not distinguish among the working-memory subprocesses; it remains unexplored whether differences in connectivity exist at that level.

CONCLUSION

These findings suggest that alterations in the working-memory network are also present in a nonclinical population with psychotic experiences who do not display cognitive deficits. They also suggest that alterations in working-memory-dependent connectivity show a putative continuity along the spectrum of psychotic symptoms.

The dark side of dopaminergic therapies in Parkinson's disease: shedding light on aberrant salience

Psychotic subjects and patients with Parkinson's disease (PD) "on" dopaminergic drugs, especially on dopamine agonists, present a hyperdopaminergic state that interferes with learning processing. These clinical populations present with distinct alterations of learning that share an increased potential motivational significance of stimuli: psychotic subjects may attribute salience to neutral stimuli, while medicated PD patients may overvalue rewards. Herein is discussed the speculative hypothesis that the hyperdopaminergic state induced by dopaminergic treatments, especially with dopamine agonists, may also facilitate the attribution of salience to neutral stimuli in PD patients, altering the physiological attribution of salience. Preliminary empirical evidence is in agreement with this speculative hypothesis, which needs further empirical investigation. The clinical implications of this hypothesis are discussed in relation to behavioral addictions, psychosis proneness, and enhanced creativity in medicated PD patients.

Multi-echo fMRI, resting-state connectivity, and high psychometric schizotypy

Disrupted striatal functional connectivity is proposed to play a critical role in the development of psychotic symptoms. Previous resting-state functional magnetic resonance imaging (rs-fMRI) studies typically reported disrupted striatal connectivity in patients with psychosis and in individuals at clinical and genetic high risk of the disorder relative to healthy controls. This has not been widely studied in healthy individuals with subclinical psychotic-like experiences (schizotypy). Here we applied the emerging technology of multi-echo rs-fMRI to examine corticostriatal connectivity in this group, which is thought to drastically maximize physiological noise removal and increase BOLD contrast-to-noise ratio. Multi-echo rs-fMRI data (echo times, 12, 28, 44, 60 ms) were acquired from healthy individuals with low (LS, n = 20) and high (HS, n = 19) positive schizotypy as determined with the Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE). After preprocessing to ensure optimal contrast and removal of non-BOLD signal components, whole-brain functional connectivity from six striatal seeds was compared between the HS and LS groups. Effects were considered significant at cluster-level p < .05 family-wise error correction. Compared to LS, HS subjects showed lower rs-fMRI connectivity between ventromedial prefrontal regions and ventral striatal regions. Lower connectivity was also observed between the dorsal putamen and the hippocampus, occipital regions, as well as the cerebellum. These results demonstrate that subclinical positive psychotic-like experiences in healthy individuals are associated with striatal hypoconnectivity as detected using multi-echo rs-fMRI. Further application of this approach may aid in characterizing functional connectivity abnormalities across the extended psychosis phenotype.

Modeling subjective relevance in schizophrenia and its relation to aberrant salience

In schizophrenia, increased aberrant salience to irrelevant events and reduced learning of relevant information may relate to an underlying deficit in relevance detection. So far, subjective estimates of relevance have not been probed in schizophrenia patients. The mechanisms underlying belief formation about relevance and their translation into decisions are unclear. Using novel computational methods, we investigated relevance detection during implicit learning in 42 schizophrenia patients and 42 healthy individuals. Participants underwent functional magnetic resonance imaging while detecting the outcomes in a learning task. These were preceded by cues differing in color and shape, which were either relevant or irrelevant for outcome prediction. We provided a novel definition of relevance based on Bayesian precision and modeled reaction times as a function of relevance weighted unsigned prediction errors (UPE). For aberrant salience, we assessed responses to subjectively irrelevant cue manifestations. Participants learned the contingencies and slowed down their responses following unexpected events. Model selection revealed that individuals inferred the relevance of cue features and used it for behavioral adaption to the relevant cue feature. Relevance weighted UPEs correlated with dorsal anterior cingulate cortex activation and hippocampus deactivation. In patients, the aberrant salience bias to subjectively task-irrelevant information was increased and correlated with decreased striatal UPE activation and increased negative symptoms. This study shows that relevance estimates based on Bayesian precision can be inferred from observed behavior. This underscores the importance of relevance detection as an underlying mechanism for behavioral adaptation in complex environments and enhances the understanding of aberrant salience in schizophrenia.

Schizophrenia patients display deficits in the appropriate attribution of meaningfulness to stimuli; such as aberrantly increased processing of irrelevant and insufficient processing of relevant information. We aimed to investigate the subjective nature of relevance detection and its deficit in schizophrenia and developed an implicit learning paradigm that allowed for parallel learning from relevant and irrelevant information. Based on the idea that subjective relevance might be captured by Bayesian precision we set up different computational models of how subjective relevance guides learning and behavioral adaptation. We found that subjects use Bayesian precision to estimate stimulus relevance in order to integrate multidimensional information and adapt more to the subjectively relevant stimuli. This relevance weighted adaptation correlated with brain activation within the salience network. Further, schizophrenia patients displayed an increased aberrant tendency to irrelevant events which related to decreased striatal coding of the relevant learning signal. To conclude, our findings demonstrate how individual beliefs about relevance can be inferred from computational models. Furthermore, we suggest that aberrant salience observed in patients with schizophrenia reflects an idiosyncratic bias in states of high subjective uncertainty.

Intact striatal dopaminergic modulation of reward learning and daily-life reward-oriented behavior in first-degree relatives of individuals with psychotic disorder

BACKGROUND

Abnormalities in reward learning in psychotic disorders have been proposed to be linked to dysregulated subcortical dopaminergic (DA) neurotransmission, which in turn is a suspected mechanism for predisposition to psychosis. We therefore explored the striatal dopaminergic modulation of reward processing and its behavioral correlates in individuals at familial risk for psychosis.

METHODS

We performed a DA D2/3 receptor [18F]fallypride positron emission tomography scan during a probabilistic reinforcement learning task in 16 healthy first-degree relatives of patients with psychosis and 16 healthy volunteers, followed by a 6-day ecological momentary assessment study capturing reward-oriented behavior in the everyday life.

RESULTS

We detected significant reward-induced DA release in bilateral caudate, putamen and ventral striatum of both groups, with no group differences in its magnitude nor spatial extent. In both groups alike, greater extent of reward-induced DA release in all regions of interest was associated with better performance in the task, as well as in greater tendency to be engaged in reward-oriented behavior in the daily life.

CONCLUSIONS

These findings suggest intact striatal dopaminergic modulation of reinforcement learning and reward-oriented behavior in individuals with familial predisposition to psychosis. Furthermore, this study points towards a key link between striatal reward-related DA release and pursuit of ecologically relevant rewards.

The link between schizophrenia and substance use disorder: A unifying hypothesis

Substance use disorders occur commonly in patients with schizophrenia and dramatically worsen their overall clinical course. While the exact mechanisms contributing to substance use in schizophrenia are not known, a number of theories have been put forward to explain the basis of the co-occurrence of these disorders. We propose here a unifying hypothesis that combines recent evidence from epidemiological and genetic association studies with brain imaging and pre-clinical studies to provide an updated formulation regarding the basis of substance use in patients with schizophrenia. We suggest that the genetic determinants of risk for schizophrenia (especially within neural systems that contribute to the risk for both psychosis and addiction) make patients vulnerable to substance use. Since this vulnerability may arise prior to the appearance of psychotic symptoms, an increased use of substances in adolescence may both enhance the risk for developing a later substance use disorder, and also serve as an additional risk factor for the appearance of psychotic symptoms. Future studies that assess brain circuitry in a prospective longitudinal manner during adolescence prior to the appearance of psychotic symptoms could shed further light on the mechanistic underpinnings of these co-occurring disorders while identifying potential points of intervention for these difficult-to-treat co-occurring disorders.

The effects of cannabis use on salience attribution: a systematic review

OBJECTIVE

The relationship between cannabis use and the onset of psychosis is well established. Aberrant salience processing is widely thought to underpin many of these symptoms. Literature explicitly investigating the relationship between aberrant salience processing and cannabis use is scarce; with those few studies finding that acute tetrahydrocannabinol (THC) administration (the main psychoactive component of cannabis) can result in abnormal salience processing in healthy cohorts, mirroring that observed in psychosis. Nevertheless, the extent of and mechanisms through which cannabis has a modulatory effect on aberrant salience, following both acute and chronic use, remain unclear.

METHODS

Here, we systematically review recent findings on the effects of cannabis use - either through acute THC administration or in chronic users - on brain regions associated with salience processing (through functional MRI data); and performance in cognitive tasks that could be used as either direct or indirect measures of salience processing. We identified 13 studies either directly or indirectly exploring salience processing. Three types of salience were identified and discussed - incentive/motivational, emotional/affective, and attentional salience.

RESULTS

The results demonstrated an impairment of immediate salience processing, following acute THC administration. Amongst the long-term cannabis users, normal salience performance appeared to be underpinned by abnormal neural processes.

CONCLUSIONS

Overall, the lack of research specifically exploring the effects of cannabis use on salience processing, weaken any conclusions drawn. Additional research explicitly focussed on salience processing and cannabis use is required to advance our understanding of the neurocognitive mechanisms underlying the association between cannabis use and development of psychosis.

Ventral Striatal Dysfunction and Symptom Expression in Individuals With Schizotypal Personality Traits and Early Psychosis

Striatal abnormalities play a crucial role in the pathophysiology of schizophrenia. Growing evidence suggests an association between aberrant striatal activity during reward anticipation and symptom dimensions in schizophrenia. However, it is not clear whether this holds across the psychosis continuum. The aim of the present study was to investigate alterations of ventral striatal activation during reward anticipation and its relationship to symptom expression in persons with schizotypal personality traits (SPT) and first-episode psychosis. Twenty-six individuals with high SPT, 26 patients with non-affective first-episode psychosis (including 13 with brief psychotic disorder (FEP-BPD) and 13 with first-episode schizophrenia [FEP-SZ]) and 25 healthy controls underwent event-related functional magnetic resonance imaging while performing a variant of the Monetary Incentive Delay task. Ventral striatal activation was positively correlated with total symptom severity, in particular with levels of positive symptoms. This association was observed across the psychosis continuum and within each subgroup. Patients with FEP-SZ showed the strongest elevation of striatal activation during reward anticipation, although symptom levels did not differ between groups in the psychosis continuum. While our results provide evidence that variance in striatal activation is mainly explained by dimensional symptom expression, patients with schizophrenia show an additional dysregulation of striatal activation. Trans-diagnostic approaches are promising in order to disentangle dimensional and categorical neural mechanisms in the psychosis continuum.

Dopamine D2/D3 imbalance during migraine attack and allodynia in vivo

OBJECTIVE

To evaluate in vivo the dynamics of endogenous dopamine (DA) neurotransmission during migraine ictus with allodynia.

METHODS

We examined 8 episodic migraineurs and 8 healthy controls (HC) using PET with [¹¹C]raclopride. The uptake measure of [¹¹C]raclopride, nondisplaceable binding potential (BP_ND), would increase when there was a reduction in endogenous DA release. The opposite is true for a decrease in [¹¹C]raclopride BP_ND. Patients were scanned twice: one PET session was during a spontaneous migraine ictus at rest, followed by a sustained thermal pain threshold (STPT) challenge on the trigeminal region, eliciting an allodynia experience; another was during interictal phase.

RESULTS

Striatal BP_ND of [¹¹C]raclopride in migraineurs did not differ from HC. We found a significant increase in [¹¹C]raclopride BP_ND in the striatum region of migraineurs during both headache attack and allodynia relative to interictal phase. However, when compared to the migraine attack at rest, migraineurs during the STPT challenge had a significant sudden reduction in [¹¹C]raclopride BP_ND in the insula. Such directional change was also observed in the caudate of HC relative to the interictal phase during challenge. Furthermore, ictal changes in [¹¹C]raclopride BP_ND in migraineurs at rest were positively correlated with the chronicity of migraine attacks, and negatively correlated with the frequency during challenge.

CONCLUSIONS

Our findings demonstrate that there is an imbalanced uptake of [¹¹C]raclopride during the headache attack and ictal allodynia, which indicates reduction and fluctuation in ictal endogenous DA release in migraineurs. Moreover, the longer the history and recurrence of migraine attacks, the lower the ictal endogenous DA release.

Striatal dopamine, reward, and decision making in schizophrenia

Elevated striatal dopamine function is one of the best-established findings in schizophrenia. In this review, we discuss causes and consequences of this striata! dopamine alteration. We first summarize earlier findings regarding striatal reward processing and anticipation using functional neuroimaging. Secondly, we present a series of recent studies that are exemplary for a particular research approach: a combination of theory-driven reinforcement learning and decision-making tasks in combination with computational modeling and functional neuroimaging. We discuss why this approach represents a promising tool to understand underlying mechanisms of symptom dimensions by dissecting the contribution of multiple behavioral control systems working in parallel. We also discuss how it can advance our understanding of the neurobiological implementation of such functions. Thirdly, we review evidence regarding the topography of dopamine dysfunction within the striatum. Finally, we present conclusions and outline important aspects to be considered in future studies.

An Integrative Perspective on the Role of Dopamine in Schizophrenia

We propose that schizophrenia involves a combination of decreased phasic dopamine responses for relevant stimuli and increased spontaneous phasic dopamine release. Using insights from computational reinforcement-learning models and basic-science studies of the dopamine system, we show that each of these two disturbances contributes to a specific symptom domain and explains a large set of experimental findings associated with that domain. Reduced phasic responses for relevant stimuli help to explain negative symptoms and provide a unified explanation for the following experimental findings in schizophrenia, most of which have been shown to correlate with negative symptoms: reduced learning from rewards; blunted activation of the ventral striatum, midbrain, and other limbic regions for rewards and positive prediction errors; blunted activation of the ventral striatum during reward anticipation; blunted autonomic responding for relevant stimuli; blunted neural activation for aversive outcomes and aversive prediction errors; reduced willingness to expend effort for rewards; and psychomotor slowing. Increased spontaneous phasic dopamine release helps to explain positive symptoms and provides a unified explanation for the following experimental findings in schizophrenia, most of which have been shown to correlate with positive symptoms: aberrant learning for neutral cues (assessed with behavioral and autonomic responses), and aberrant, increased activation of the ventral striatum, midbrain, and other limbic regions for neutral cues, neutral outcomes, and neutral prediction errors. Taken together, then, these two disturbances explain many findings in schizophrenia. We review evidence supporting their co-occurrence and consider their differential implications for the treatment of positive and negative symptoms.

Longitudinal alterations in motivational salience processing in ultra-high-risk subjects for psychosis

BACKGROUND

Impairments in the attribution of salience are thought to be fundamental to the development of psychotic symptoms and the onset of psychotic disorders. The aim of the present study was to explore longitudinal alterations in salience processing in ultra-high-risk subjects for psychosis.

METHOD

A total of 23 ultra-high-risk subjects and 13 healthy controls underwent functional magnetic resonance imaging at two time points (mean interval of 17 months) while performing the Salience Attribution Test to assess neural responses to task-relevant (adaptive salience) and task-irrelevant (aberrant salience) stimulus features.

RESULTS

At presentation, high-risk subjects were less likely than controls to attribute salience to relevant features, and more likely to attribute salience to irrelevant stimulus features. These behavioural differences were no longer evident at follow-up. When attributing salience to relevant cue features, ultra-high-risk subjects showed less activation than controls in the ventral striatum at both baseline and follow-up. Within the high-risk sample, amelioration of abnormal beliefs over the follow-up period was correlated with an increase in right ventral striatum activation during the attribution of salience to relevant cue features.

CONCLUSIONS

These findings confirm that salience processing is perturbed in ultra-high-risk subjects for psychosis, that this is linked to alterations in ventral striatum function, and that clinical outcomes are related to longitudinal changes in ventral striatum function during salience processing.

Salience attribution and its relationship to cannabis-induced psychotic symptoms

BACKGROUND

Cannabis is a widely used drug associated with increased risk for psychosis. The dopamine hypothesis of psychosis postulates that altered salience processing leads to psychosis. We therefore tested the hypothesis that cannabis users exhibit aberrant salience and explored the relationship between aberrant salience and dopamine synthesis capacity.

METHOD

We tested 17 cannabis users and 17 age- and sex-matched non-user controls using the Salience Attribution Test, a probabilistic reward-learning task. Within users, cannabis-induced psychotic symptoms were measured with the Psychotomimetic States Inventory. Dopamine synthesis capacity, indexed as the influx rate constant K i cer , was measured in 10 users and six controls with 3,4-dihydroxy-6-[18F]fluoro-l-phenylalanine positron emission tomography.

RESULTS

There was no significant difference in aberrant salience between the groups [F 1,32 = 1.12, p = 0.30 (implicit); F 1,32 = 1.09, p = 0.30 (explicit)]. Within users there was a significant positive relationship between cannabis-induced psychotic symptom severity and explicit aberrant salience scores (r = 0.61, p = 0.04) and there was a significant association between cannabis dependency/abuse status and high implicit aberrant salience scores (F 1,15 = 5.8, p = 0.03). Within controls, implicit aberrant salience was inversely correlated with whole striatal dopamine synthesis capacity (r = -0.91, p = 0.01), whereas this relationship was non-significant within users (difference between correlations: Z = -2.05, p = 0.04).

CONCLUSIONS

Aberrant salience is positively associated with cannabis-induced psychotic symptom severity, but is not seen in cannabis users overall. This is consistent with the hypothesis that the link between cannabis use and psychosis involves alterations in salience processing. Longitudinal studies are needed to determine whether these cognitive abnormalities are pre-existing or caused by long-term cannabis use.

Validating the construct of aberrant salience in schizophrenia - Behavioral evidence for an automatic process

Suspecting significance behind ordinary events is a common feature in psychosis and it is assumed to occur due to aberrant salience attribution. The Salience Attribution Test (SAT; Roiser et al., 2009) measures aberrant salience as a bias towards one out of two equally reinforced cue features as opposed to adaptive salience towards features indicating high reinforcement. This is the first study to validate the latent constructs involved in salience attribution in patients. Forty-nine schizophrenia patients and forty-four healthy individuals completed the SAT, a novel implicit salience paradigm (ISP), a reversal learning task and a neuropsychological test battery. First, groups were compared on raw measures. Second and within patients, these were correlated and then used for a principal component analysis (PCA). Third, sum scores matching the correlation and component pattern were correlated with psychopathology. Compared to healthy individuals, patients exhibited more implicit aberrant salience in the SAT and ISP and less implicit and explicit adaptive salience attribution in the SAT. Implicit aberrant salience from the SAT and ISP positively correlated with each other and negatively with reversal learning. Whereas explicit aberrant salience was associated with cognition, implicit and explicit adaptive salience were positively correlated. A similar pattern emerged in the PCA and implicit aberrant salience was associated with negative symptoms. Taken together, implicit aberrant salience from the SAT and ISP seems to reflect an automatic process that is independent from deficient salience ascription to relevant events. Its positive correlation with negative symptoms might reflect motivational deficits present in chronic schizophrenia patients.

Phasic dopamine release in the rat nucleus accumbens predicts approach and avoidance performance

Dopamine (DA) is critical for reward processing, but significantly less is known about its role in punishment avoidance. Using a combined approach-avoidance task, we measured phasic DA release in the nucleus accumbens (NAc) of rats during presentation of cues that predicted reward, punishment or neutral outcomes and investigated individual differences based on avoidance performance. Here we show that DA release within a single microenvironment is higher for reward and avoidance cues compared with neutral cues and positively correlated with poor avoidance behaviour. We found that DA release delineates trial-type during sessions with good avoidance but is non-selective during poor avoidance, with high release correlating with poor performance. These data demonstrate that phasic DA is released during cued approach and avoidance within the same microenvironment and abnormal processing of value signals is correlated with poor performance.

Models of neuromodulation for computational psychiatry

Psychiatry faces fundamental challenges: based on a syndrome-based nosology, it presently lacks clinical tests to infer on disease processes that cause symptoms of individual patients and must resort to trial-and-error treatment strategies. These challenges have fueled the recent emergence of a novel field-computational psychiatry-that strives for mathematical models of disease processes at physiological and computational (information processing) levels. This review is motivated by one particular goal of computational psychiatry: the development of 'computational assays' that can be applied to behavioral or neuroimaging data from individual patients and support differential diagnosis and guiding patient-specific treatment. Because the majority of available pharmacotherapeutic approaches in psychiatry target neuromodulatory transmitters, models that infer (patho)physiological and (patho)computational actions of different neuromodulatory transmitters are of central interest for computational psychiatry. This article reviews the (many) outstanding questions on the computational roles of neuromodulators (dopamine, acetylcholine, serotonin, and noradrenaline), outlines available evidence, and discusses promises and pitfalls in translating these findings to clinical applications. WIREs Cogn Sci 2017, 8:e1420. doi: 10.1002/wcs.1420 For further resources related to this article, please visit the WIREs website.