Probabilistic Category Learning and Striatal Functional Activation in Psychosis Risk

BACKGROUND

Psychosis risk is associated with striatal dysfunction, including a previous behavioral study that found that psychosis risk is associated with impaired performance on a probabilistic category learning task (PCLT; ie, the Weather Prediction Task), a task strongly associated with striatal activation. The current study examined whether psychosis risk based on symptom levels was associated with both poor behavioral performance and task-related physiological dysfunction in specific regions of the striatum while performing the PCLT.

METHODS

There were 2 groups of participants: psychosis risk (n = 21) who had both (a) extreme levels of self-reported psychotic-like beliefs and experiences and (b) interview-rated current attenuated psychotic symptoms (APS); and a comparison group (n = 20) who had average levels of self-reported psychotic-like beliefs and experiences. Participants completed the PCLT during fMRI scanning.

RESULTS

The current research replicated previous work finding behavioral PCLT deficits at the end of the task in psychosis risk. Furthermore, as expected, the psychosis risk group exhibited decreased striatal activation on the task, especially in the associative striatum. The psychosis risk group also displayed decreased activation in a range of cortical regions connected to the associative striatum. In contrast, the psychosis risk group exhibited greater activation predominantly in cortical regions not connected to the associative striatum.

CONCLUSIONS

Psychosis risk was associated with both behavioral and striatal dysfunction during performance on the PCLT, suggesting that behavioral and imaging measures using this task could be a marker for psychosis risk.

Altered Expression of a Unique Set of Genes Reveals Complex Etiology of Schizophrenia

Background: The etiology of schizophrenia is extensively debated, and multiple factors have been contended to be involved. A panoramic view of the contributing factors in a genome-wide study can be an effective strategy to provide a comprehensive understanding of its causality. Materials and Methods: GSE53987 dataset downloaded from GEO-database, which comprised mRNA expression data of post-mortem brain tissue across three regions from control (C) and age-matched subjects (T) of schizophrenia (N = Hippocampus [HIP]: C-15, T-18, Prefrontal cortex [PFC]: C-15, T-19, Associative striatum [STR]: C-18, T-18). Bio-conductor-affy-package used to compute mRNA expression, and further t-test applied to investigate differential gene expression. The analysis of the derived genes performed using the PANTHER Classification System and NCBI database. Further, a protein interactome analysis of the derived gene set was performed using STRING v10 database (https://string-db.org/) Results: A set of 40 genes showed significantly altered (p < 0.01) expression across all three brain regions. The analyses unraveled genes implicated in biological processes and events, and molecular pathways relating basic neuronal functions. Conclusions: The aberrant expression of genes maintaining basic cell machinery explains compromised neuronal processing in SCZ.

Associative and sensorimotor cortico-basal ganglia circuit roles in effects of abused drugs

The mammalian forebrain is characterized by the presence of several parallel cortico-basal ganglia circuits that shape the learning and control of actions. Among these are the associative, limbic and sensorimotor circuits. The function of all of these circuits has now been implicated in responses to drugs of abuse, as well as drug seeking and drug taking. While the limbic circuit has been most widely examined, key roles for the other two circuits in control of goal-directed and habitual instrumental actions related to drugs of abuse have been shown. In this review we describe the three circuits and effects of acute and chronic drug exposure on circuit physiology. Our main emphasis is on drug actions in dorsal striatal components of the associative and sensorimotor circuits. We then review key findings that have implicated these circuits in drug seeking and taking behaviors, as well as drug use disorders. Finally, we consider different models describing how the three cortico-basal ganglia circuits become involved in drug-related behaviors. This topic has implications for drug use disorders and addiction, as treatments that target the balance between the different circuits may be useful for reducing excessive substance use.

Stress and neurodevelopmental processes in the emergence of psychosis

The notion that stress plays a role in the etiology of psychotic disorders, especially schizophrenia, is longstanding. However, it is only in recent years that the potential neural mechanisms mediating this effect have come into sharper focus. The introduction of more sophisticated models of the interplay between psychosocial factors and brain function has expanded our opportunities for conceptualizing more detailed psychobiological models of stress in psychosis. Further, scientific advances in our understanding of adolescent brain development have shed light on a pivotal question that has challenged researchers; namely, why the first episode of psychosis typically occurs in late adolescence/young adulthood. In this paper, we begin by reviewing the evidence supporting associations between psychosocial stress and psychosis in diagnosed patients as well as individuals at clinical high risk for psychosis. We then discuss biological stress systems and examine changes that precede and follow psychosis onset. Next, research findings on structural and functional brain characteristics associated with psychosis are presented; these findings suggest that normal adolescent neuromaturational processes may go awry, thereby setting the stage for the emergence of psychotic syndromes. Finally, a model of neural mechanisms underlying the pathogenesis of psychosis is presented and directions for future research strategies are explored.

Divergent activation of ventromedial and ventrolateral dopamine systems in animal models of amphetamine sensitization and schizophrenia

Aberrant dopamine-mediated behaviours are a hallmark of a number of psychiatric disorders, including substance use disorders and schizophrenia. It has been demonstrated recently that rodent models of these diseases display enhanced dopamine neuron activity throughout the ventral tegmental area (VTA). It is known, however, that the VTA is not a homogeneous structure, and that the dopamine neuron population provides discrete, topographical innervation of nucleus accumbens subregions. In addition, these ventromedial and ventrolateral dopamine systems are known to subserve complementary but distinct aspects of goal-directed behaviour. Using in-vivo extracellular recordings of identified dopamine neurons in chloral hydrate-anaesthetized rats, we examined the level of dopamine neuron population activity across the mediolateral extent of the VTA following amphetamine sensitization or gestational methylazoxymethanol acetate (MAM) treatment, a verified rodent model of schizophrenia. Here we demonstrate that both models display an augmented medial VTA-ventromedial striatal dopamine system function that correlates with the augmented locomotor response to amphetamine observed in both models. In contrast, only MAM-treated rats exhibit an increase in VTA-ventrolateral striatal dopamine system function. This latter finding is consistent with human imaging studies in schizophrenia patients. In summary, we demonstrate that, although a number of disorders involving a hyperdopaminergic state demonstrate an increase in dopamine neuron population activity, there is divergence in the exact populations of neurons affected. This distinction probably underlies the observed differences in disease symptomatology.