The formation of abnormal associations in schizophrenia: neural and behavioral evidence

An fMRI investigation of delay discounting in patients with schizophrenia

Schizophrenia (SZ) is associated with a reduced ability to set meaningful goals to reach desired outcomes. The delay-discounting (DD) task, in which one chooses between sooner smaller and later larger rewards, has proven useful in revealing executive function and reward deficits in various clinical groups. We used fMRI in patients with SZ and healthy controls (HC) to compare brain activation during performance of a DD task. Prior to the neuroimaging session, we obtained each participant's rate of DD, k, on a DD task and used it to select a version of the DD task for each participant's fMRI session. Because of the importance of comparing fMRI results from groups matched on performance, we used a criterion value of R (2) > 0.60 for response consistency on the DD task to analyze fMRI activation to DD task versus control trials from consistent SZ (n = 14) and consistent HC (n = 14). We also compared activation between the groups on contrasts related to trial difficulty. Finally, we contrasted the inconsistent SZ (n = 9) with the consistent HC and consistent SZ; these results should be interpreted with caution because of inconsistent SZ's aberrant performance on the task. Compared with consistent HC, consistent SZ showed reduced activation to DD task versus control trials in executive function and reward areas. In contrast, consistent SZ showed more activation in the precuneus and posterior cingulate, regions of the default mode network (DMN) that are typically deactivated during tasks, and in the insula, a region linked to emotional processing. Furthermore, consistent SZ had abnormal activation of lateral and medial frontal regions in relation to trial difficulty. These results point to disruption of several neural networks during decision making, including the executive, reward, default mode, and emotional networks, and suggest processes that are impaired during decision making in schizophrenia.

Ketamine effects on memory reconsolidation favor a learning model of delusions

Delusions are the persistent and often bizarre beliefs that characterise psychosis. Previous studies have suggested that their emergence may be explained by disturbances in prediction error-dependent learning. Here we set up complementary studies in order to examine whether such a disturbance also modulates memory reconsolidation and hence explains their remarkable persistence. First, we quantified individual brain responses to prediction error in a causal learning task in 18 human subjects (8 female). Next, a placebo-controlled within-subjects study of the impact of ketamine was set up on the same individuals. We determined the influence of this NMDA receptor antagonist (previously shown to induce aberrant prediction error signal and lead to transient alterations in perception and belief) on the evolution of a fear memory over a 72 hour period: they initially underwent Pavlovian fear conditioning; 24 hours later, during ketamine or placebo administration, the conditioned stimulus (CS) was presented once, without reinforcement; memory strength was then tested again 24 hours later. Re-presentation of the CS under ketamine led to a stronger subsequent memory than under placebo. Moreover, the degree of strengthening correlated with individual vulnerability to ketamine's psychotogenic effects and with prediction error brain signal. This finding was partially replicated in an independent sample with an appetitive learning procedure (in 8 human subjects, 4 female). These results suggest a link between altered prediction error, memory strength and psychosis. They point to a core disruption that may explain not only the emergence of delusional beliefs but also their persistence.

Nucleus accumbens GABAergic inhibition generates intense eating and fear that resists environmental retuning and needs no local dopamine

Intense fearful behavior and/or intense appetitive eating behavior can be generated by localized amino acid inhibitions along a rostrocaudal anatomical gradient within medial shell of nucleus accumbens of the rat. This can be produced by microinjections in medial shell of either the γ-aminobutyric acid (GABA)A agonist muscimol (mimicking intrinsic GABAergic inputs) or the AMPA (α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) antagonist DNQX (6,7-dinitroquinoxaline-2,3-dione), disrupting corticolimbic glutamate inputs). At rostral sites in medial shell, each drug robustly stimulates appetitive eating and food intake, whereas at more caudal sites the same drugs instead produce increasingly fearful behaviors such as escape, distress vocalizations and defensive treading (an antipredator behavior rodents emit to snakes and scorpions). Previously we showed that intense motivated behaviors generated by glutamate blockade require local endogenous dopamine and can be modulated in valence by environmental ambience. Here we investigated whether GABAergic generation of intense appetitive and fearful motivations similarly depends on local dopamine signals, and whether the valence of motivations generated by GABAergic inhibition can also be retuned by changes in environmental ambience. We report that the answer to both questions is 'no'. Eating and fear generated by GABAergic inhibition of accumbens shell does not need endogenous dopamine. Also, the appetitive/fearful valence generated by GABAergic muscimol microinjections resists environmental retuning and is determined almost purely by rostrocaudal anatomical placement. These results suggest that nucleus accumbens GABAergic release of fear and eating are relatively independent of modulatory dopamine signals, and more anatomically pre-determined in valence balance than release of the same intense behaviors by glutamate disruptions.

The scent of salience--is there olfactory-trigeminal conditioning in humans?

Pavlovian fear conditioning has been thoroughly studied in the visual, auditory and somatosensory domain, but evidence is scarce with regard to the chemosensory modality. Under the assumption that Pavlovian conditioning relies on the supra-modal mechanism of salience attribution, the present study was set out to attest the existence of chemosensory aversive conditioning in humans as a specific instance of salience attribution. fMRI was performed in 29 healthy subjects during a differential aversive conditioning paradigm. Two odors (rose, vanillin) served as conditioned stimuli (CS), one of which (CS+) was intermittently coupled with intranasally administered CO2. On the neural level, a robust differential response to the CS+ emerged in frontal, temporal, occipito-parietal and subcortical brain regions, including the amygdala. These changes were paralleled by the development of a CS+-specific connectivity profile of the anterior midcingulate cortex (aMCC), which is a key structure for processing salience information in order to guide adaptive response selection. Increased coupling could be found between key nodes of the salience network (anterior insula, neo-cerebellum) and sensorimotor areas, representing putative input and output structures of the aMCC for exerting adaptive motor control. In contrast, behavioral and skin conductance responses did not show significant effects of conditioning, which has been attributed to contingency unawareness. These findings imply substantial similarities of conditioning involving chemosensory and other sensory modalities, and suggest that salience attribution and adaptive control represent a general, modality-independent principle underlying Pavlovian conditioning.

Increased intrinsic brain activity in the striatum reflects symptom dimensions in schizophrenia

Striatal dysfunction is thought to be a fundamental element in schizophrenia. Striatal dopamine dysfunction impacts on reward processing and learning and is present even at rest. Here, we addressed the question whether and how spontaneous neuronal activity in the striatum is altered in schizophrenia. We therefore assessed intrinsic striatal activity and its relation with disorder states and symptom dimensions in patients with schizophrenia. We performed resting-state functional (rs-fMRI) and structural magnetic resonance imaging as well as psychometric assessment in 21 schizophrenic patients during psychosis. On average 9 months later, we acquired follow-up data during psychotic remission and with comparable levels of antipsychotic medication. Twenty-one age- and sex-matched healthy controls were included in the study. Independent component analysis of fMRI data yielded spatial maps and time-courses of coherent ongoing blood-oxygen-level-dependent signal fluctuations, which were used for group comparisons and correlation analyses with scores of the positive and negative syndrome scale. During psychosis, coherent intrinsic activity of the striatum was increased in the dorsal part and correlated with positive symptoms such as delusion and hallucination. In psychotic remission of the same patients, activity of the ventral striatum was increased and correlated with negative symptoms such as emotional withdrawal and blunted affect. Results were controlled for volumetric and medication effects. These data provide first evidence that in schizophrenia intrinsic activity is changed in the striatum and corresponds to disorder states and symptom dimensions.

Altered transfer of momentary mental states (ATOMS) as the basic unit of psychosis liability in interaction with environment and emotions

Psychotic disorders are thought to represent altered neural function. However, research has failed to map diagnostic categories to alterations in neural networks. It is proposed that the basic unit of psychotic psychopathology is the moment-to-moment expression of subtle anomalous experiences of subclinical psychosis, and particularly its tendency to persist from moment-to-moment in daily life, under the influence of familial, environmental, emotional and cognitive factors.

In a general population twin sample (n = 579) and in a study of patients with psychotic disorder (n = 57), their non-psychotic siblings (n = 59) and unrelated controls (n = 75), the experience sampling paradigm (ESM; repetitive, random sampling of momentary mental states and context) was applied. We analysed, in a within-person prospective design, (i) transfer of momentary anomalous experience at time point (t–1) to time point (t) in daily life, and (ii) moderating effects of negative affect, positive affect, daily stressors, IQ and childhood trauma. Additionally, (iii) familial associations between persistence of momentary anomalous experience and psychotic symptomatology were investigated. Higher level of schizotypy in the twins (but not higher level of psychotic symptoms in patients) predicted more persistence of momentary anomalous experience in daily life, both within subjects and across relatives. Persistence of momentary anomalous experience was highest in patients, intermediate in their siblings and lowest in controls. In both studies, persistence of momentary anomalous experience was moderated by higher levels of negative affect, daily stressors and childhood trauma (only in twins), and by lower levels of positive affect. The study of alterations in the moment-to-moment transfer of subtle anomalous experience of psychosis, resulting in their persistence, helps to explain why psychotic and emotional dysregulation tend to cluster in a single phenotype such as schizophrenia, and how familial and environmental risks increase the risk of expression of psychosis from, first, subtle momentary anomalous experience to, second, observable clinical symptoms.

Neurobiological correlates of delusion: beyond the salience attribution hypothesis

Dopamine dysfunction is a mainstay of theories aimed to explain the neurobiological correlates of schizophrenia symptoms, particularly positive symptoms such as delusions and passivity phenomena. Based on studies revealing dopamine dysfunction in addiction research, it has been suggested that phasic or chaotic firing of dopaminergic neurons projecting to the (ventral) striatum attribute salience to otherwise irrelevant stimuli and thus contribute to delusional mood and delusion formation. Indeed, several neuroimaging studies revealed that neuronal encoding of usually irrelevant versus relevant stimuli is blunted in unmedicated schizophrenia patients, suggesting that some stimuli that are irrelevant for healthy controls acquire increased salience for psychotic patients. However, salience attribution per se may not suffice to explain anxieties and feelings of threat that often accompany paranoid ideation. Here, we suggest that beyond ventral striatal dysfunction, dopaminergic dysregulation in limbic areas such as the amygdala in interaction with prefrontal and temporal cortex may contribute to the formation of delusions and negative symptoms. Neuroleptic medication, on the other hand, appears to interfere with anticipation of reward in the ventral striatum and can thus contribute to secondary negative symptoms such as apathy and avolition.

Failure of neural responses to safety cues in schizophrenia

CONTEXT Abnormalities in associative memory processes, such as Pavlovian fear conditioning and extinction, have been observed in schizophrenia. The retrieval of fear extinction memories (safety signals) may be particularly affected; although schizophrenic patients can extinguish conditioned fear, they show a deficit in retrieving fear extinction memories after a delay. The neurobiological basis of this abnormality is unknown, but clues have emerged from studies in rodents and humans demonstrating that the ventromedial prefrontal cortex (vmPFC) is a key mediator of extinction memory retrieval. OBJECTIVE To measure autonomic and neural responses during the acquisition and extinction of conditioned fear and the delayed recall of fear and extinction memories in patients with schizophrenia and healthy control participants. DESIGN Cross-sectional case control, functional magnetic resonance imaging study. SETTING Academic medical center. PARTICIPANTS Twenty schizophrenic patients and 17 healthy control participants demographically matched to the patient group. MAIN OUTCOME MEASURES Skin conductance and blood oxygen level-dependent responses. RESULTS During fear conditioning, schizophrenic patients showed blunted autonomic responses and abnormal blood oxygen level-dependent responses, relative to control participants, within the posterior cingulate gyrus, hippocampus, and other regions. Several of these abnormalities were linked to negative symptoms. During extinction learning, patients with schizophrenia and control participants showed comparable autonomic and neural responses. Twenty-four hours after the learning phases, the control subjects exhibited decreased fear and increased vmPFC responses in the extinction (safe) context as expected, indicating successful retention of the extinction memory. In contrast, the schizophrenic patients showed inappropriately elevated fear and poor vmPFC responses in the safe context. CONCLUSION Failure of extinction memory retrieval in schizophrenia is associated with vmPFC dysfunction. In future studies, abnormalities in fear learning and extinction recall may serve as quantitative phenotypes that can be linked to genetic, symptom, or outcome profiles in schizophrenia and those at risk for the disorder.

Cognition-emotion dysinteraction in schizophrenia

Evolving theories of schizophrenia emphasize a "disconnection" in distributed fronto-striatal-limbic neural systems, which may give rise to breakdowns in cognition and emotional function. We discuss these diverse domains of function from the perspective of disrupted neural circuits involved in "cold" cognitive vs. "hot" affective operations and the interplay between these processes. We focus on three research areas that highlight cognition-emotion dysinteractions in schizophrenia: First, we discuss the role of cognitive deficits in the "maintenance" of emotional information. We review recent evidence suggesting that motivational abnormalities in schizophrenia may in part arise due to a disrupted ability to "maintain" affective information over time. Here, dysfunction in a prototypical "cold" cognitive operation may result in "affective" deficits in schizophrenia. Second, we discuss abnormalities in the detection and ascription of salience, manifest as excessive processing of non-emotional stimuli and inappropriate distractibility. We review emerging evidence suggesting deficits in some, but not other, specific emotional processes in schizophrenia - namely an intact ability to perceive emotion "in-the-moment" but poor prospective valuation of stimuli and heightened reactivity to stimuli that ought to be filtered. Third, we discuss abnormalities in learning mechanisms that may give rise to delusions, the fixed, false, and often emotionally charged beliefs that accompany psychosis. We highlight the role of affect in aberrant belief formation, mostly ignored by current theoretical models. Together, we attempt to provide a consilient overview for how breakdowns in neural systems underlying affect and cognition in psychosis interact across symptom domains. We conclude with a brief treatment of the neurobiology of schizophrenia and the need to close our explanatory gap between cellular-level hypotheses and complex behavioral symptoms observed in this illness.

Cognition-emotion dysinteraction in schizophrenia

Evolving theories of schizophrenia emphasize a "disconnection" in distributed fronto-striatal-limbic neural systems, which may give rise to breakdowns in cognition and emotional function. We discuss these diverse domains of function from the perspective of disrupted neural circuits involved in "cold" cognitive vs. "hot" affective operations and the interplay between these processes. We focus on three research areas that highlight cognition-emotion dysinteractions in schizophrenia: First, we discuss the role of cognitive deficits in the "maintenance" of emotional information. We review recent evidence suggesting that motivational abnormalities in schizophrenia may in part arise due to a disrupted ability to "maintain" affective information over time. Here, dysfunction in a prototypical "cold" cognitive operation may result in "affective" deficits in schizophrenia. Second, we discuss abnormalities in the detection and ascription of salience, manifest as excessive processing of non-emotional stimuli and inappropriate distractibility. We review emerging evidence suggesting deficits in some, but not other, specific emotional processes in schizophrenia - namely an intact ability to perceive emotion "in-the-moment" but poor prospective valuation of stimuli and heightened reactivity to stimuli that ought to be filtered. Third, we discuss abnormalities in learning mechanisms that may give rise to delusions, the fixed, false, and often emotionally charged beliefs that accompany psychosis. We highlight the role of affect in aberrant belief formation, mostly ignored by current theoretical models. Together, we attempt to provide a consilient overview for how breakdowns in neural systems underlying affect and cognition in psychosis interact across symptom domains. We conclude with a brief treatment of the neurobiology of schizophrenia and the need to close our explanatory gap between cellular-level hypotheses and complex behavioral symptoms observed in this illness.

Ventral striatal activation during attribution of stimulus saliency and reward anticipation is correlated in unmedicated first episode schizophrenia patients

Patients with schizophrenia show deficits in motivation, reward anticipation and salience attribution. Several functional magnetic resonance imaging (fMRI) investigations revealed neurobiological correlates of these deficits, raising the hypothesis of a common basis in midbrain dopaminergic signaling. However, investigations of drug-naïve first-episode patients with comprehensive fMRI tasks are still missing. We recruited unmedicated schizophrenia spectrum patients (N=27) and healthy control subjects (N=27) matched for sex, age and educational levels. An established monetary reward anticipation task in combination with a novel task aiming at implicit salience attribution without the confound of monetary incentive was applied. Patients showed reduced right ventral striatal activation during reward anticipation. Furthermore, patients with a more pronounced hypoactivation attributed more salience to neutral stimuli, had more positive symptoms and better executive functioning. In the patient group, a more differentially active striatum during reward anticipation was correlated positively to differential ventral striatal activation in the implicit salience attribution task. In conclusion, a deficit in ventral striatal activation during reward anticipation can already be seen in drug-naïve, first episode schizophrenia patients. The data suggest that rather a deficit in differential ventral striatal activation than a generally reduced activation underlies motivational deficits in schizophrenia and that this deficit is related to the aberrant salience attribution.

Pavlovian reward prediction and receipt in schizophrenia: relationship to anhedonia

Reward processing abnormalities have been implicated in the pathophysiology of negative symptoms such as anhedonia and avolition in schizophrenia. However, studies examining neural responses to reward anticipation and receipt have largely relied on instrumental tasks, which may confound reward processing abnormalities with deficits in response selection and execution. 25 chronic, medicated outpatients with schizophrenia and 20 healthy controls underwent functional magnetic resonance imaging using a pavlovian reward prediction paradigm with no response requirements. Subjects passively viewed cues that predicted subsequent receipt of monetary reward or non-reward, and blood-oxygen-level-dependent signal was measured at the time of cue presentation and receipt. At the group level, neural responses to both reward anticipation and receipt were largely similar between groups. At the time of cue presentation, striatal anticipatory responses did not differ between patients and controls. Right anterior insula demonstrated greater activation for nonreward than reward cues in controls, and for reward than nonreward cues in patients. At the time of receipt, robust responses to receipt of reward vs. nonreward were seen in striatum, midbrain, and frontal cortex in both groups. Furthermore, both groups demonstrated responses to unexpected versus expected outcomes in cortical areas including bilateral dorsolateral prefrontal cortex. Individual difference analyses in patients revealed an association between physical anhedonia and activity in ventral striatum and ventromedial prefrontal cortex during anticipation of reward, in which greater anhedonia severity was associated with reduced activation to money versus no-money cues. In ventromedial prefrontal cortex, this relationship held among both controls and patients, suggesting a relationship between anticipatory activity and anhedonia irrespective of diagnosis. These findings suggest that in the absence of response requirements, brain responses to reward receipt are largely intact in medicated individuals with chronic schizophrenia, while reward anticipation responses in left ventral striatum are reduced in those patients with greater anhedonia severity.

Disambiguating ventral striatum fMRI-related BOLD signal during reward prediction in schizophrenia

Reward detection, surprise detection and prediction-error signaling have all been proposed as roles for the ventral striatum (vStr). Previous neuroimaging studies of striatal function in schizophrenia have found attenuated neural responses to reward-related prediction errors; however, as prediction errors represent a discrepancy in mesolimbic neural activity between expected and actual events, it is critical to examine responses to both expected and unexpected rewards (URs) in conjunction with expected and UR omissions in order to clarify the nature of ventral striatal dysfunction in schizophrenia. In the present study, healthy adults and people with schizophrenia were tested with a reward-related prediction-error task during functional magnetic resonance imaging to determine whether schizophrenia is associated with altered neural responses in the vStr to rewards, surprise prediction errors or all three factors. In healthy adults, we found neural responses in the vStr were correlated more specifically with prediction errors than to surprising events or reward stimuli alone. People with schizophrenia did not display the normal differential activation between expected and URs, which was partially due to exaggerated ventral striatal responses to expected rewards (right vStr) but also included blunted responses to unexpected outcomes (left vStr). This finding shows that neural responses, which typically are elicited by surprise, can also occur to well-predicted events in schizophrenia and identifies aberrant activity in the vStr as a key node of dysfunction in the neural circuitry used to differentiate expected and unexpected feedback in schizophrenia.

Subjective emotional over-arousal to neutral social scenes in paranoid schizophrenia

From the clinical practice and some experimental studies, it is apparent that paranoid schizophrenia patients tend to assign emotional salience to neutral social stimuli. This aberrant cognitive bias has been conceptualized to result from increased emotional arousal, but direct empirical data are scarce. The aim of the present study was to quantify the subjective emotional arousal (SEA) evoked by emotionally non-salient (neutral) compared to emotionally salient (negative) social stimuli in schizophrenia patients and healthy controls. Thirty male inpatients with paranoid schizophrenia psychosis and 30 demographically matched healthy controls rated their level of SEA in response to neutral and negative social scenes from the International Affective Picture System and the Munich Affective Picture System. Schizophrenia patients compared to healthy controls had an increased overall SEA level. This relatively higher SEA was evoked only by the neutral but not by the negative social scenes. To our knowledge, the present study is the first designed to directly demonstrate subjective emotional over-arousal to neutral social scenes in paranoid schizophrenia. This finding might explain previous clinical and experimental data and could be viewed as the missing link between the primary neurobiological and secondary psychological mechanisms of paranoid psychotic-symptom formation. Furthermore, despite being very short and easy to perform, the task we used appeared to be sensitive enough to reveal emotional dysregulation, in terms of emotional disinhibition/hyperactivation in paranoid schizophrenia patients. Thus, it could have further research and clinical applications, including as a neurobehavioral probe for imaging studies.

Striatal function in relation to negative symptoms in schizophrenia

BACKGROUND

Previous studies have suggested that motivational aspects of executive functioning, which may be disrupted in schizophrenia patients with negative symptoms, are mediated in part by the striatum. Negative symptoms have been linked to impaired recruitment of both the striatum and the dorsolateral prefrontal cortex (DLPFC). Here we tested the hypothesis that negative symptoms are associated primarily with striatal dysfunction, using functional magnetic resonance imaging (fMRI).

METHOD

Working-memory load-dependent activation and gray matter volumes of the striatum and DLPFC were measured using a region-of-interest (ROI) approach, in 147 schizophrenia patients and 160 healthy controls. In addition to testing for a linear relationships between striatal function and negative symptoms, we chose a second, categorical analytic strategy in which we compared three demographically and behaviorally matched subgroups: patients with a high burden of negative symptoms, patients with minimal negative symptoms, and healthy subjects.

RESULTS

There were no differences in striatal response magnitudes between schizophrenia patients and healthy controls, but right DLPFC activity was higher in patients than in controls. Negative symptoms were inversely associated with striatal, but not DLPFC, activity. In addition, patients with a high burden of negative symptoms exhibited significantly lower bilateral striatal, but not DLPFC, activation than schizophrenia patients with minimal negative symptoms. Working memory performance, antipsychotic exposure and changes in gray matter volumes did not account for these differences.

CONCLUSIONS

These data provide further evidence for a robust association between negative symptoms and diminished striatal activity. Future work will determine whether low striatal activity in schizophrenia patients could serve as a reliable biomarker for negative symptoms.

Does the salience network play a cardinal role in psychosis? An emerging hypothesis of insular dysfunction

The insular cortex is one of the brain regions that show consistent abnormalities in both structural and functional neuroimaging studies of schizophrenia. In healthy individuals, the insula has been implicated in a myriad of physiologic functions. The anterior cingulate cortex (ACC) and insula together constitute the salience network, an intrinsic large-scale network showing strong functional connectivity. Considering the insula as a functional unit along with the ACC provides an integrated understanding of the role of the insula in information processing. In this review, we bring together evidence from imaging studies to understand the role of the salience network in schizophrenia and propose a model of insular dysfunction in psychosis.

Role of dopamine D(2) receptors for antipsychotic activity

This review summarizes the current state of knowledge regarding the proposed mechanisms by which antipsychotic agents reduce the symptoms of schizophrenia while giving rise to adverse side effects. The first part summarizes the contribution of neuroimaging studies to our understanding of the neurochemical substrates of schizophrenia, putting emphasis on direct evidence suggestive of a presynaptic rather than a postsynaptic dysregulation of dopaminergic neurotransmission in this disorder. The second part addresses the role of D(2) and non-D(2) receptor blockade in the treatment of schizophrenia and highlights a preponderant role of D(2) receptors in the mechanism of antipsychotic action. Neuroimaging studies have defined a narrow, but optimal, therapeutic window of 65-78 % D(2) receptor blockade within which most antipsychotics achieve optimal clinical efficacy with minimal side effects. Some antipsychotics though do not conform to that therapeutic window, notably clozapine. The reasons for its unexcelled clinical efficacy despite subthreshold levels of D(2) blockade are unclear and current theories on clozapine's mechanisms of action are discussed, including transiency of its D(2) receptor blocking effects or preferential blockade of limbic D(2) receptors. Evidence is also highlighted to consider the use of extended antipsychotic dosing to achieve transiency of D(2) blockade as a way to optimize functional outcomes in patients. We also present some critical clinical considerations regarding the mechanisms linking dopamine disturbance to the expression of psychosis and its blockade to the progressive resolution of psychosis, keeping in perspective the speed and onset of antipsychotic action. Finally, we discuss potential novel therapeutic strategies for schizophrenia.

The dopamine dysfunction in schizophrenia revisited: new insights into topography and course

Schizophrenia has long been associated with an imbalance in dopamine (DA) neurotransmission, and brain imaging has played an important role in advancing our knowledge and providing evidence for the dopaminergic abnormalities. This chapter reviews the evidence for DA dysfunction in different brain regions in schizophrenia, in particular striatal, extrastriatal, and prefrontal regions, with emphasis on recently published findings. As opposed to the traditional view that most striatal dopaminergic excess, associated with the positive symptoms of schizophrenia, involves the dopaminergic mesolimbic pathway, recent evidence points to the nigrostriatal pathway as the area of highest dysregulation. Furthermore, evidence from translational research suggests that dopaminergic excess may be present in the prodromal phase, and may by itself, as suggested by the phenotype observed in transgenic mice with developmental overexpression of dorso-striatal D(2) receptors, be an early pathogenic condition, leading to irreversible cortical dysfunction.

Exploring the neural correlates of delusions of reference

BACKGROUND

Referential delusions are the most common symptom of schizophrenia and offer an opportunity to examine the neural correlates of delusions because they occur in discrete episodes that can be studied in the scanner. The cortical midline structures (CMS) and subcortical regions, including the amygdala and striatum, are linked with self-reference in healthy adults. Less is known about the neural substrates of altered self-reference in schizophrenia.

METHODS

In this study, patients with schizophrenia experiencing prominent referential delusions (n = 18) and healthy control subjects (n = 17) were presented with ambiguous sentences while in the magnetic resonance imaging scanner and asked to rate whether they felt the sentences had been written specifically about them. The sentences were either generic (nonpersonalized) or individually tailored personalized sentences, designed to induce referential ideation. We hypothesized that both groups would show activity in the CMS, limbic, and striatal regions and that induced referential ideation would be associated with greater activity in striatal areas in patients with schizophrenia.

RESULTS

A robust main effect of endorsement (endorsed vs. nonendorsed) was observed in the CMS, as well as subcortical regions, including the nucleus accumbens/ventral striatum, amygdala, insula, and midbrain dopamine regions. A group-by-endorsement interaction was seen in the medial prefrontal cortex, insula and nucleus accumbens/ventral striatum. Activity in insula and ventral striatum also correlated with the strength of the delusions of reference.

CONCLUSIONS

Referential ideation in persons with delusions is associated with heightened CMS, limbic and striatal activity and reduced differentiation between self- and non-self-relevant information.

Nucleus accumbens dopamine/glutamate interaction switches modes to generate desire versus dread: D(1) alone for appetitive eating but D(1) and D(2) together for fear

The medial shell of nucleus accumbens (NAc) and its mesolimbic dopamine inputs mediate forms of fearful as well as of incentive motivation. For example, either appetitive and/or actively fearful behaviors are generated in a keyboard pattern by localized glutamate disruptions in NAc (via microinjection of the AMPA receptor antagonist DNQX) at different anatomical locations along a rostrocaudal gradient within the medial shell of rats. Rostral glutamate disruptions produce intense increases in eating, but more caudally placed disruptions produce increasingly fearful behaviors: distress vocalizations and escape attempts to human touch, and a spontaneous and directed antipredator response called defensive treading/burying. Local endogenous dopamine is required for either intense motivation to be generated by AMPA disruptions. Here we report that only endogenous local signaling at D(1) dopamine receptors is needed for rostral generation of excessive eating, potentially implicating a direct output pathway contribution. In contrast, fear generation at caudal sites requires both D(1) and D(2) signaling simultaneously, potentially implicating an indirect output pathway contribution. Finally, when motivation valence generated by AMPA disruptions at intermediate sites was flipped by manipulating environmental ambience, from mostly appetitive in a comfortable home environment to mostly fearful in a stressful environment, the roles of local D(1) and D(2) signaling in dopamine/glutamate interaction at microinjection sites also switched dynamically to match the motivation valence generated at the moment. Thus, NAc D(1) and D(2) receptors, and their associated neuronal circuits, play different and dynamic roles in enabling desire and dread to be generated by localized NAc glutamate disruptions in medial shell.

Identifying a network of brain regions involved in aversion-related processing: a cross-species translational investigation

The ability to detect and respond appropriately to aversive stimuli is essential for all organisms, from fruit flies to humans. This suggests the existence of a core neural network which mediates aversion-related processing. Human imaging studies on aversion have highlighted the involvement of various cortical regions, such as the prefrontal cortex, while animal studies have focused largely on subcortical regions like the periaqueductal gray and hypothalamus. However, whether and how these regions form a core neural network of aversion remains unclear. To help determine this, a translational cross-species investigation in humans (i.e., meta-analysis) and other animals (i.e., systematic review of functional neuroanatomy) was performed. Our results highlighted the recruitment of the anterior cingulate cortex, the anterior insula, and the amygdala as well as other subcortical (e.g., thalamus, midbrain) and cortical (e.g., orbitofrontal) regions in both animals and humans. Importantly, involvement of these regions remained independent of sensory modality. This study provides evidence for a core neural network mediating aversion in both animals and humans. This not only contributes to our understanding of the trans-species neural correlates of aversion but may also carry important implications for psychiatric disorders where abnormal aversive behavior can often be observed.

A stable sparse fear memory trace in human amygdala

Pavlovian fear conditioning is highly conserved across species, providing a powerful model of aversive learning. In rodents, fear memory is stored and reactivated under the influence of the amygdala. There is no evidence for an equivalent mechanism in primates, and an opposite mechanism is proposed whereby primate amygdala contributes only to an initial phase of aversive learning, subsequently ceding fear memory to extra-amygdalar regions. Here, we reexamine this question by exploiting human high-resolution functional magnetic resonance imaging in conjunction with multivariate methods. By assuming a sparse neural coding, we show it is possible, at an individual subject level, to discriminate responses to conditioned (CS+ and CS-) stimuli in both basolateral and centro-cortical amygdala nuclei. The strength of this discrimination increased over time and was tightly coupled to the behavioral expression of fear, consistent with an expression of a stable fear memory trace. These data highlight that the human basolateral and centro-cortical amygdala support initial learning as well more enduring fear memory storage. A sparse neuronal representation for fear, here revealed by multivariate pattern classification, resolves why an enduring memory trace has proven elusive in previous human studies.

Normalization of cortical gray matter deficits in nonpsychotic siblings of patients with childhood-onset schizophrenia

OBJECTIVE

Cortical gray matter (GM) abnormalities in patients with childhood-onset schizophrenia (COS) progress during adolescence ultimately localizing to prefrontal and temporal cortices by early adult age. A previous study of 52 nonpsychotic siblings of COS probands had significant prefrontal and temporal GM deficits that appeared to "normalize" by age 17 years. Here we present a replication with nonoverlapping groups of healthy full siblings and healthy controls.

METHOD

Using an automated measure and prospectively acquired anatomical brain magnetic resonance images, we mapped cortical GM thickness in nonpsychotic full siblings (n = 43, 68 scans; ages 5 through 26 years) of patients with COS, contrasting them with age-, gender-, and scan interval-matched healthy controls (n = 86, 136 scans). The false-discovery rate procedure was used to control for type I errors due to multiple comparisons.

RESULTS

As in our previous study, young nonpsychotic siblings (<17 years) showed significant GM deficits in bilateral prefrontal and left temporal cortices and, in addition, smaller deficits in the parietal and right inferior temporal cortices. These deficits in nonpsychotic siblings normalized with age with minimal abnormalities remaining by age 17.

CONCLUSIONS

Our results support previous findings showing nonpsychotic siblings of COS probands to have early GM deficits that ameliorate with time. At early ages, prefrontal and/or temporal loss may serve as a familial/trait marker for COS. Late adolescence appears to be a critical period for greatest localization of deficits in probands or normalization in nonpsychotic siblings.

Is our self nothing but reward?

Neuroscience has increasingly explored the neural mechanisms underlying our sense of self. Recent studies have demonstrated the recruitment of regions like the ventral tegmental area, ventromedial prefrontal cortex, and the ventral striatum to self-specific stimuli-regions typically associated with reward-related processing. This raises the question of whether there is a relationship between self and reward and, if so, how these different fields can be linked. Three relationship models that aim to explore the relationship between self and reward are discussed here: integration, segregation, and parallel processing. Their pros and cons are reviewed in light of the most recent findings. The conclusion is that both the fields of self and reward may benefit from increased interaction. This interaction may help to fill in some of the missing pieces regarding reward-related processing, as well as illuminate how brain function can bring forward the philosophical concept and psychological reality of self.

Optimizing vs. matching: response strategy in a probabilistic learning task is associated with negative symptoms of schizophrenia

Previous research indicates that behavioral performance in simple probability learning tasks can be organized into response strategy classifications that are thought to predict important personal characteristics and individual differences. Typically, relatively small proportion of subjects can be identified as optimizers for effectively exploiting the environment and choosing the more rewarding stimulus nearly all of the time. In contrast, the vast majority of subjects behaves sub-optimally and adopts the matching or super-matching strategy, apportioning their responses in a way that matches or slightly exceeds the probabilities of reinforcement. In the present study, we administered a two-choice probability learning paradigm to 51 individuals with schizophrenia (SZ) and 29 healthy controls (NC) to examine whether there are differences in the proportion of subjects falling into these response strategy classifications, and to determine whether task performance is differentially associated with symptom severity and neuropsychological functioning. Although the sample of SZ patients did not differ from NC in overall rate of learning or end performance, significant clinical differences emerged when patients were divided into optimizing, super-matching and matching subgroups based upon task performance. Patients classified as optimizers, who adopted the most advantageous learning strategy, exhibited higher levels of positive and negative symptoms than their matching and super-matching counterparts. Importantly, when both positive and negative symptoms were considered together, only negative symptom severity was a significant predictor of whether a subject would behave optimally, with each one standard deviation increase in negative symptoms increasing the odds of a patient being an optimizer by as much as 80%. These data provide a rare example of a greater clinical impairment being associated with better behavioral performance.

Decreased self-reported arousal in schizophrenia during aversive picture viewing compared to bipolar disorder and healthy controls

Both schizophrenia (SCZ) and bipolar disorder (BD) are associated with disturbances in emotion processing. Previous studies suggest that patients with SCZ assess unpleasant pictures as less arousing than healthy controls (HC), while patients with BD assess neutral pictures as more arousing than HC. No previous studies have investigated whether there is a difference in emotional response across all three groups. Our aim was to explore whether there was a difference in the evaluation of valence and in arousal between SCZ, BD and HC for aversive and neutral pictures. We showed 72 pictures (neutral, non-socially aversive and socially aversive) from the International Affective Picture System (IAPS) to 347 subjects. There was a clear interaction effect between the diagnostic group and increasing picture aversiveness for both valence and arousal. There were no significant differences in valence ratings between the different groups or in arousal ratings on any type of stimuli between BD patients and HC. However, SCZ patients reported significantly lower arousal for aversive stimuli, particularly with a social content, when compared to BD patients and HC. This was more pronounced in females. The presence of lifetime psychotic symptoms did not influence emotional responses.

Metabotropic glutamate receptor blockade in nucleus accumbens shell shifts affective valence towards fear and disgust

Glutamatergic inputs to the nucleus accumbens (NAc) modulate both appetitive and fearful motivation. It has been suggested that pathological disturbances of glutamate signaling in NAc contribute to motivation disorders, ranging from excessive desire in drug addiction to paranoia in schizophrenia. Metabotropic glutamate receptors are of special interest, as metabotropic Group II receptor (mglu2/3) agonists have been proposed as potential treatments for both addiction and schizophrenia. Here we tested whether local mglu2/3 receptor blockade in the medial shell of the rat NAc can generate intense distortions of motivation or affect, which might model clinical dysfunction. We found that microinjection of the mglu2/3 antagonist LY341495 at sites throughout medial shell suppressed appetitive motivation to eat and drink. Simultaneously, LY341495 microinjections generated fearful motivation in the form of defensive treading or burying. To assess whether the valence shift extended into a parallel hedonic shift from affective 'liking' to 'disliking' we employed the taste reactivity test, which measures affective orofacial reactions to the sensory pleasure or displeasure of tastes. We found that LY341495 microinjections reduced positive 'liking' reactions to sucrose and enhanced 'disliking' reactions. Overall, mglu2/3 antagonism at most shell sites produced a similar valence shift from positive to negative. This pattern comprised (i) generation of fearful behaviors, and (ii) induction of aversive affective reactions, together with (iii) loss of appetitive ingestion and (iv) loss of 'liking' for rewards. These results are discussed in terms of implications for clinical disorders and the influence of corticolimbic glutamate inputs to NAc in the generation of motivation and affect.

Aberrant Effective Connectivity in Schizophrenia Patients during Appetitive Conditioning

It has recently been suggested that schizophrenia involves dysfunction in brain connectivity at a neural level, and a dysfunction in reward processing at a behavioral level. The purpose of the present study was to link these two levels of analyses by examining effective connectivity patterns between brain regions mediating reward learning in patients with schizophrenia and healthy, age-matched controls. To this aim, we used functional magnetic resonance imaging and galvanic skin recordings (GSR) while patients and controls performed an appetitive conditioning experiment with visual cues as the conditioned (CS) stimuli, and monetary reward as the appetitive unconditioned stimulus (US). Based on explicit stimulus contingency ratings, conditioning occurred in both groups; however, based on implicit, physiological GSR measures, patients failed to show differences between CS+ and CS− conditions. Healthy controls exhibited increased blood-oxygen-level dependent (BOLD) activity across striatal, hippocampal, and prefrontal regions and increased effective connectivity from the ventral striatum to the orbitofrontal cortex (OFC BA 11) in the CS+ compared to the CS− condition. Compared to controls, patients showed increased BOLD activity across a similar network of brain regions, and increased effective connectivity from the striatum to hippocampus and prefrontal regions in the CS− compared to the CS+ condition. The findings of increased BOLD activity and effective connectivity in response to the CS− in patients with schizophrenia offer insight into the aberrant assignment of motivational salience to non-reinforced stimuli during conditioning that is thought to accompany schizophrenia.

Dysfunction of a cortical midline network during emotional appraisals in schizophrenia

A cardinal feature of schizophrenia is the poor comprehension, or misinterpretation, of the emotional meaning of social interactions and events, which can sometimes take the form of a persecutory delusion. It has been shown that the comprehension of the emotional meaning of the social world involves a midline paralimbic cortical network. However, the function of this network during emotional appraisals in patients with schizophrenia is not well understood. In this study, hemodynamic responses were measured in 14 patients with schizophrenia and 18 healthy subjects during the evaluation of descriptions of social situations with negative, positive, and neutral affective valence. The healthy and schizophrenia groups displayed opposite patterns of responses to emotional and neutral social situations within the medial prefrontal and posterior cingulate cortices--healthy participants showed greater activity to the emotional compared to the neutral situations, while patients exhibited greater responses to the neutral compared to the emotional situations. Moreover, the magnitude of the response within bilateral cingulate gyri to the neutral social stimuli predicted delusion severity in the patients with schizophrenia. These findings suggest that impaired functioning of cortical midline structures in schizophrenia may underlie faulty interpretations of social events, contributing to delusion formation.

The emerging biology of delusions

This article examines a model of how delusions may arise, not just in schizophrenia but also in a number of neurological and psychiatric conditions, through a combination of dysregulated dopamine release from ascending midbrain pathways and reasoning bias. Negative symptoms may also be related to dopamine dysregulation, with the precise mixture of positive and negative symptoms depending on the relative degree of dopamine dysregulation in particular mesocorticolimbic circuits. Evidence for this model is examined, and predictions arising from this model are described.

Are psychiatric diagnoses of psychosis scientific and useful? The case of schizophrenia

BACKGROUND

Insurance systems, scientific journals, professional groups, educational initiatives, regulatory bodies and organisation of services appear to be fixed in 19th century diagnostic metaphors for psychosis, providing natural protection against change. Furthermore, the existence of two separate diagnostic systems in psychiatry, DSM and ICD, produces a bias that is conservative rather than anti-conservative, reducing the probability of non-cosmetic change.

METHODS

A qualitative review of the validity, usefulness and acceptability of the diagnosis of 'schizophrenia', in order to assess possible discrepancies between actual diagnostic practice in mental health services and alternatives dictated by scientific evidence and societal developments.

RESULTS

A 21st century concept of psychotic disorder should refer to an experience that can be understood as a variation of normal human mentation that can be expressed quantitatively. For the purpose of diagnosis, use can be made of scientific evidence of specificity yielding high diagnostic likelihood ratios rather than evidence of weak mean differences yielding low diagnostic likelihood ratios. In the case of psychosis, the evidence appears to favour a syndromal system of classification combining categorical and dimensional representations. The concept of 'salience' has the potential to make the public recognise psychosis as relating to an aspect of human mentation and experience that is universal.

CONCLUSIONS

The debate about alternatives to diagnose expressions of psychosis is often misunderstood as a misguided attempt to change societal stigma. In reality, however, it is about reduction of iatrogenic stigma occasioned by the use of unscientific and mystifying terminology. Scientific and societal developments have largely caught up with diagnostic traditions applied to psychosis phenotypes and although the traditional diagnostic system is deeply ingrained in all aspects of clinical and academic activities, change is possible if professional bodies actively promote a modern system of evidence-based diagnostic practice.

Intact associative learning in patients with schizophrenia: evidence from a Go/NoGo paradigm

OBJECTIVE

Schizophrenia is associated with deficits in executive control and associative learning. In the present study, we investigated the effect of associative learning during a Go/NoGo task in healthy controls subjects and patients with schizophrenia.

METHODS

Thirty patients with schizophrenia and 30 age-and-gender matched healthy control subjects performed 15 blocks of training and 3 blocks of test trials. The trials consisted of responding to words denoting either living or non-living objects. In the training condition, subjects were instructed to respond by pressing the space bar (Go-task) to one of the word types (living or non-living objects), but not the other. In the test phase, the Go/NoGo mapping was reversed. Subjects were instructed to respond as quickly and as accurately as possible. Reaction times (RT) and accuracy were recorded for each trial and all subjects were debriefed upon completion of the test trials.

RESULTS

Patients with schizophrenia had significantly longer Go RTs when compared to the control group, during both training and test trials. However, the two groups did not differ on any measure of associative learning.

CONCLUSIONS

Our findings suggest that associative learning is intact in schizophrenia patients during the performance of a relational Go/NoGo paradigm.

Does dopamine mediate the psychosis-inducing effects of cannabis? A review and integration of findings across disciplines

General population epidemiological studies have consistently found that cannabis use increases the risk of developing psychotic disorders in a dose-dependent manner. While the epidemiological signal between cannabis and psychosis has gained considerable attention, the biological mechanism whereby cannabis increases risk for psychosis remains poorly understood. Animal research suggests that delta-9-tetrahydrocannabinol (THC, the main psychoactive component of cannabis) increases dopamine levels in several regions of the brain, including striatal and prefrontal areas. Since dopamine is hypothesized to represent a crucial common final pathway between brain biology and actual experience of psychosis, a focus on dopamine may initially be productive in the examination of the psychotomimetic effects of cannabis. Therefore, this review examines the evidence concerning the interactions between THC, endocannabinoids and dopamine in the cortical as well as subcortical regions implicated in psychosis, and considers possible mechanisms whereby cannabis-induced dopamine dysregulation may give rise to delusions and hallucinations. It is concluded that further study of the mechanisms underlying the link between cannabis and psychosis may be conducted productively from the perspective of progressive developmental sensitization, resulting from gene-environment interactions.

Adaptive and aberrant reward prediction signals in the human brain

Theories of the positive symptoms of schizophrenia hypothesize a role for aberrant reinforcement signaling driven by dysregulated dopamine transmission. Recently, we provided evidence of aberrant reward learning in symptomatic, but not asymptomatic patients with schizophrenia, using a novel paradigm, the Salience Attribution Test (SAT). The SAT is a probabilistic reward learning game that employs cues that vary across task-relevant and task-irrelevant dimensions; it provides behavioral indices of adaptive and aberrant reward learning. As an initial step prior to future clinical studies, here we used functional magnetic resonance imaging to examine the neural basis of adaptive and aberrant reward learning during the SAT in healthy volunteers. As expected, cues associated with high relative to low reward probabilities elicited robust hemodynamic responses in a network of structures previously implicated in motivational salience; the midbrain, in the vicinity of the ventral tegmental area, and regions targeted by its dopaminergic projections, i.e. medial dorsal thalamus, ventral striatum and prefrontal cortex (PFC). Responses in the medial dorsal thalamus and polar PFC were strongly correlated with the degree of adaptive reward learning across participants. Finally, and most importantly, differential dorsolateral PFC and middle temporal gyrus (MTG) responses to cues with identical reward probabilities were very strongly correlated with the degree of aberrant reward learning. Participants who showed greater aberrant learning exhibited greater dorsolateral PFC responses, and reduced MTG responses, to cues erroneously inferred to be less strongly associated with reward. The results are discussed in terms of their implications for different theories of associative learning.

The relevance of reward pathways for schizophrenia

PURPOSE OF REVIEW

There has been a resurgence of interest in the field of reward processing in schizophrenia in recent years, aided by insights from functional neuroimaging. We examine how disturbances in reward-related processes relate to the pathophysiology and symptomatology of this disorder.

RECENT FINDINGS

Behavioural and functional neuroimaging studies in psychosis demonstrate impairments in the representation of reward value and in reward-related learning and a failure to motivate behaviour for incentives. These impairments are linked to abnormal mesocorticolimbic and mesostriatal function.

SUMMARY

Abnormalities in reward processing offer insights into the symptomatology of schizophrenia and its underlying neurobiology. Further investigation is required into the specificity of these deficits to particular symptom expression and to what extent they are improved by antipsychotic treatment.

The functional neuroanatomy of symptom dimensions in schizophrenia: a qualitative and quantitative review of a persistent question

One of the fundamental goals in understanding schizophrenia is linking the observable symptoms to the underlying unobservable pathophysiology. Given recent advances in medical imaging, researchers are increasingly investigating brain-behavior relationships to better understand the neural substrates of negative, positive, and disorganization symptoms in schizophrenia. This review focused on 25 task-related functional magnetic resonance imaging studies and found meaningful small to moderate associations between specific symptom dimensions and regional brain activity. Negative symptoms were related to the functioning of the ventrolateral prefrontal cortex and ventral striatum. Positive symptoms, particularly persecutory ideation, were related to functioning of the medial prefrontal cortex, amygdala, and hippocampus/parahippocampal region. Disorganization symptoms, although less frequently evaluated, were related to functioning of the dorsolateral prefrontal cortex. Surprisingly, no symptom domain had a consistent relationship with the middle or superior temporal regions. While a number of adaptations in experimental design and reporting standards can facilitate this work, current neuroimaging approaches appear to provide a number of consistent links between the manifest symptoms of schizophrenia and brain dysfunction.

Further evidence for aberrant prefrontal salience coding in schizophrenia

The revised dopamine hypothesis of schizophrenia postulates that dopamine metabolism is impacted differently with increased dopamine in the subcortical mesolimbic system and decreased dopamine in prefrontal cortical regions. Recently, we described findings supporting this hypothesis using a financial reward task in patients with schizophrenia (Walter et al., 2009). In addition to analysing prediction and prediction error coding, we found in this study evidence for aberrant cortical representation of salience in the right ventrolateral prefrontal cortex (VLPFC) in patients. Here, we reanalysed data of four other published reward studies of our group in order to investigate (i) whether we could replicate this finding in an independent cohort of patients with schizophrenia and (ii) how dopaminergic modulation impacts on cortical salience representation. Our main result was that we could replicate the finding of aberrant salience coding in the right VLPFC in patients with schizophrenia. Furthermore, we found evidence that the degree of salience coding in this region was correlated inversely with negative symptoms (anhedonia). Results of dopaminergic modulation showed tentative evidence for an influence of dopaminergic stimulation, but were not conclusive. In summary, we conclude that the right VLPFC might play a crucial role in salience coding and is impaired in schizophrenia.

Functional and dysfunctional synaptic plasticity in prefrontal cortex: roles in psychiatric disorders

Prefrontal cortex (PFC) mediates an assortment of cognitive functions including working memory, behavioral flexibility, attention, and future planning. Unlike the hippocampus, where induction of synaptic plasticity in the network is well-documented in relation to long-term memory, cognitive functions mediated by the PFC have been thought to be independent of long-lasting neuronal adaptation of the network. Nonetheless, accumulating evidence suggests that prefrontal cortical neurons possess the cellular machinery of synaptic plasticity and exhibit lasting changes of neural activity associated with various cognitive processes. Moreover, deficits in the mechanisms of synaptic plasticity induction in the PFC might be involved in the pathophysiology of psychiatric and neurological disorders such as schizophrenia, drug addiction, mood disorders, and Alzheimer's disease.

Basal ganglia pathology in schizophrenia: dopamine connections and anomalies

Schizophrenia is a severe mental illness that affects 1% of the world population. The disease usually manifests itself in early adulthood with hallucinations, delusions, cognitive and emotional disturbances and disorganized thought and behavior. Dopamine was the first neurotransmitter to be implicated in the disease, and though no longer the only suspect in schizophrenia pathophysiology, it obviously plays an important role. The basal ganglia are the site of most of the dopamine neurons in the brain and the target of anti-psychotic drugs. In this review, we will start with an overview of basal ganglia anatomy emphasizing dopamine circuitry. Then, we will review the major deficits in dopamine function in schizophrenia, emphasizing the role of excessive dopamine in the basal ganglia and the link to psychosis.

Assessing the construct validity of aberrant salience

We sought to validate the psychometric properties of a recently developed paradigm that aims to measure salience attribution processes proposed to contribute to positive psychotic symptoms, the Salience Attribution Test (SAT). The “aberrant salience” measure from the SAT showed good face validity in previous results, with elevated scores both in high-schizotypy individuals, and in patients with schizophrenia suffering from delusions. Exploring the construct validity of salience attribution variables derived from the SAT is important, since other factors, including latent inhibition/learned irrelevance (LIrr), attention, probabilistic reward learning, sensitivity to probability, general cognitive ability and working memory could influence these measures. Fifty healthy participants completed schizotypy scales, the SAT, a LIrr task, and a number of other cognitive tasks tapping into potentially confounding processes. Behavioural measures of interest from each task were entered into a principal components analysis, which yielded a five-factor structure accounting for ∼75% of the variance in behaviour. Implicit aberrant salience was found to load onto its own factor, which was associated with elevated “Introvertive Anhedonia” schizotypy, replicating our previous finding. LIrr loaded onto a separate factor, which also included implicit adaptive salience, but was not associated with schizotypy. Explicit adaptive and aberrant salience, along with a measure of probabilistic learning, loaded onto a further factor, though this also did not correlate with schizotypy. These results suggest that the measures of LIrr and implicit adaptive salience might be based on similar underlying processes, which are dissociable both from implicit aberrant salience and explicit measures of salience.

Dopamine-induced changes in neural network patterns supporting aversive conditioning

The aim of the present paper is to assess the effects of altered dopamine (DA) transmission on the functional connectivity among brain regions mediating aversive conditioning in humans. To this aim, we analyzed a previous published data set from a double-blind design combined with functional magnetic resonance imaging (fMRI) recordings in which healthy volunteers were randomly assigned to one of three drug groups: amphetamine (an indirect DA agonist), haloperidol (DA D2 receptor antagonist), and placebo. Participants were exposed to an aversive classical conditioning paradigm using cutaneous electrical stimulation as the unconditioned stimulus (US), and visual cues as the conditioned stimuli (CS) where one colour (CS+) was followed by the US in 33% of the trials and another colour (CS-) had no consequences. All participants reported awareness of stimulus contingencies. Group analysis of fMRI data revealed that the left ventral striatum (VS) and amygdala activated in response to the CS+ in all the three groups. Because of their activation patterns and documented involvement in aversive conditioning, both regions were used as seeds in the functional connectivity analysis. To constrain the functional networks obtained to relate to the conditioned response, we also correlated seed activity with the Galvanic Skin Response (GSR). In the placebo group, the right ventral tegmental area/substantia nigra (VTA/SN), bilateral caudate, right parahippocampal gyrus, left inferior parietal lobule (IPL), bilateral postcentral gyrus, bilateral middle frontal (BA 46), orbitofrontal, and ventromedial prefrontal cortices (PFC, BA 10/11) correlated with the VS and amygdala seeds in response to the CS+ compared to the CS-. Enhancing dopamine transmission via amphetamine was associated with reduced task differences and significant functional connectivity for both CS+ and CS- conditions between the left VS seed and regions modulated by DA, such as the left VTA/SN, right caudate, left amygdala, left middle frontal gyrus (BA 46), and bilateral ventromedial PFC (BA 10). Blocking dopamine transmission via haloperidol was associated with significant functional connectivity across an alternate network of regions including the left amygdala seed and the right insula, the left ACC (BA 24/32), bilateral IPL (BA 40), precuneus (BA 7), post-central gyrus, middle frontal gyrus (BA 46), and supplementary motor area (SMA, BA 6) to the CS+ versus the CS-. These data provide insight into the distinct effects of DA agents on the functional connectivity between striatal, limbic, and prefrontal areas.

Illusions and delusions: relating experimentally-induced false memories to anomalous experiences and ideas

The salience hypothesis of psychosis rests on a simple but profound observation that subtle alterations in the way that we perceive and experience stimuli have important consequences for how important these stimuli become for us, how much they draw our attention, how they embed themselves in our memory and, ultimately, how they shape our beliefs. We put forward the idea that a classical memory illusion – the Deese–Roediger–McDermott (DRM) effect – offers a useful way of exploring processes related to such aberrant belief formation. The illusion occurs when, as a consequence of its relationship to previous stimuli, a stimulus that has not previously been presented is falsely remembered. Such illusory familiarity is thought to be generated by the surprising fluency with which the stimulus is processed. In this respect, the illusion relates directly to the salience hypothesis and may share common cognitive underpinnings with aberrations of perception and attribution that are found in psychosis. In this paper, we explore the theoretical importance of this experimentally-induced illusion in relation to the salience model of psychosis. We present data showing that, in healthy volunteers, the illusion relates directly to self reported anomalies of experience and magical thinking. We discuss this finding in terms of the salience hypothesis and of a broader Bayesian framework of perception and cognition which emphasizes the salience both of predictable and unpredictable experiences.

'Salience syndrome' replaces 'schizophrenia' in DSM-V and ICD-11: psychiatry's evidence-based entry into the 21st century?

OBJECTIVE

Japan was the first country to abandon the 19th century term of 'mind-splitting disease' (schizophrenia). Revisions of DSM and ICD are forthcoming. Should the rest of the world follow Japan's example?

METHOD

A comprehensive literature search was carried out in order to review the scientific evidence for the validity, usefulness and acceptability of current concepts of psychotic disorder.

RESULTS

The discussion about re-classifying and renaming schizophrenia and other psychotic disorders is clouded by conceptual confusion. First, it is often misunderstood as a misguided attempt to change societal stigma instead of an attempt to change iatrogenic stigma occasioned by the use of misleading and mystifying terminology. Second, the debate is misunderstood as purely semantic, whereas in actual fact it is about the core concepts underlying psychiatric nosology. Third, it has been suggested that the debate is political. However, solid scientific evidence pointing to the absence of nosological validity of diagnostic categories lies at the heart of the argument. Fourth, there is confusion about what constitutes a syndrome (a group of symptom dimensions that cluster in different combinations in different people and for which one or more underlying diseases may or may not be found) and a disease (a nosologically valid entity with specific causes, symptoms, treatment and course).

CONCLUSION

Scientific evidence favours a syndromal system of classification combining categorical and dimensional representations of psychosis. The concept of 'salience' has the potential to make the public recognize psychosis as relating to an aspect of human mentation and experience that is universal. It is proposed to introduce, analogous to the functional-descriptive term 'Metabolic syndrome', the diagnosis of 'Salience syndrome' to replace all current diagnostic categories of psychotic disorders. Within Salience syndrome, three subcategories may be identified, based on scientific evidence of relatively valid and specific contrasts, named Salience syndrome with affective expression, Salience syndrome with developmental expression and Salience syndrome not otherwise specified.

Altered reward functions in patients on atypical antipsychotic medication in line with the revised dopamine hypothesis of schizophrenia

OBJECTIVE

To study the mesolimbic dopamine system during expectation and receipt or omission of rewards in partially remitted patients with schizophrenia treated with the atypical antipsychotic olanzapine.

METHODS

We studied 16 patients with a current episode of schizophrenia, all treated with the atypical drug olanzapine, and 16 healthy subjects using functional magnetic resonance imaging. Subjects performed a delayed incentive paradigm with monetary rewards.

RESULTS

During reward expectation, both, patients with schizophrenia and healthy control subjects, showed activation of the ventral striatum and midbrain in the vicinity of the ventral tegmental area. Significant categorical group differences emerged in the anterior cingulate cortex with only healthy controls showing increasing activation with increasing reward. In the patients, activation of this region was inversely correlated with positive symptoms. During outcome, both, patients with schizophrenia and healthy controls, showed activation of the ventral striatum and the mesial prefrontal cortex. Significant categorical group differences emerged in the right ventrolateral prefrontal cortex for the salience contrast with healthy controls showing a U-shaped activation curve, i.e., higher activation for either omission or receipt of reward compared to no reward.

CONCLUSIONS

Our findings partially support the current concept of dopaminergic dysfunction in schizophrenia, suggesting a rather hyperactive mesolimbic dopamine system and reduced prefrontal activation, at least in partially remitted patients treated with atypical antipsychotics.

Schizophrenia

Schizophrenia is still one of the most mysterious and costliest mental disorders in terms of human suffering and societal expenditure. Here, we focus on the key developments in biology, epidemiology, and pharmacology of schizophrenia and provide a syndromal framework in which these aspects can be understood together. Symptoms typically emerge in adolescence and early adulthood. The incidence of the disorder varies greatly across places and migrant groups, as do symptoms, course, and treatment response across individuals. Genetic vulnerability is shared in part with bipolar disorder and recent molecular genetic findings also indicate an overlap with developmental disorders such as autism. The diagnosis of schizophrenia is associated with demonstrable alterations in brain structure and changes in dopamine neurotransmission, the latter being directly related to hallucinations and delusions. Pharmacological treatments, which block the dopamine system, are effective for delusions and hallucinations but less so for disabling cognitive and motivational impairments. Specific vocational and psychological interventions, in combination with antipsychotic medication in a context of community-case management, can improve functional outcome but are not widely available. 100 years after being so named, research is beginning to understand the biological mechanisms underlying the symptoms of schizophrenia and the psychosocial factors that moderate their expression. Although current treatments provide control rather than cure, long-term hospitalisation is not required and prognosis is better than traditionally assumed.

Diverse and often opposite behavioural effects of NMDA receptor antagonists in rats: implications for "NMDA antagonist modelling" of schizophrenia

RATIONALE

Little attention has been paid to the relative equivalence of behavioural effects of NMDA receptor antagonists in rodents, with different compounds often used interchangeably to "model" aspects of schizophrenia in preclinical studies.

OBJECTIVES

To further resolve such conjecture, the present study systematically compared eight different NMDA receptor antagonists: MK-801, PCP, ketamine, memantine, SDZ 220,581, Ro 25-6981, CP 101-606 and NVP-AAM077, in a series of variable interval (VI) schedules of reinforcement. Aspects of motivation as indexed in these tasks may well be impaired in schizophrenia and undoubtedly impact on the capacity to perform more complex, explicit tasks of cognition.

METHODS AND RESULTS

An initial locomotor activity assessment demonstrated that all antagonists tested, except the NR2A-subunit preferring antagonist NVP-AAM077, induced hyperactivity, albeit of greatly differing magnitudes, qualities and temporal profiles. Three distinct patterns of antagonist effect were evident from the VI assays used: a uniform decrease in responding produced by (S)-(+)-ketamine, memantine and NVP-AAM077, a uniform increase in responding caused by the NR2B-subunit preferring antagonists Ro 25-6981 and CP 101-606, and variable bidirectional effects of PCP, SDZ 220,581 and MK-801.

CONCLUSION

Despite nominally common mechanisms of action and often presumed biological equivalence, the NMDA antagonists tested produced very diverse effects on the expression of instrumental action. Other aspects of responding were left intact, including switching and matching behaviours, and the ability to respond to conditional stimuli. The implications of such findings with regard to animal modelling of schizophrenic psychotic symptoms are manifold.