Schizotypal Traits are Linked to Dopamine-Induced Striato-Cortical Decoupling: A Randomized Double-Blind Placebo-Controlled Study

Systematic reviews of the acute effects of amphetamine on working memory and other cognitive performances in healthy individuals, with a focus on the potential influence of personality traits

OBJECTIVES

This research aimed to systematically review the acute effects of amphetamine (AMP), a dopamine-releasing agent, on working memory (WM) and other cognitive performances. The investigation also aimed to review the impact of personality traits on the subjective and objective effects of AMP and possible links between personality traits and effects of AMP.

METHODS

Previous double-blind controlled studies assessing the main effects of AMP on WM and other cognitive performances in healthy volunteers were systematically reviewed. An electronic search was performed in the PUBMED and SCOPUS databases. Narrative reviews of the influence of personality traits on the subjective and objective effects of AMP were included.

RESULTS

Nineteen WM studies were included in the current review. Seven studies found effects of AMP on spatial WM, but only one study found the effect of AMP on verbal WM. Thirty-seven independent studies on other aspects of cognitive performance were identified. Twenty-two reported effects of AMP on cognitive functions. Studies also showed that personality traits are associated with the subjective effects of AMP. However, few studies reported the impacts of personality traits on the objective (such as WM) effects of AMP.

CONCLUSION

Overall, findings indicate that AMP has mixed-effects on spatial WM and other cognitive functions, but it lacks effects on verbal WM. Although there are insufficient studies on objective measures, studies also indicated that the subjective effects of AMP administration are linked to between-person variations in personality traits.

Frontotemporal thalamic connectivity in schizophrenia and schizotypal personality disorder

Schizotypal personality disorder (SPD) resembles schizophrenia, but with attenuated brain abnormalities and the absence of psychosis. The thalamus is integral for processing and transmitting information across cortical regions and widely implicated in the neurobiology of schizophrenia. Comparing thalamic connectivity in SPD and schizophrenia could reveal an intermediate schizophrenia-spectrum phenotype to elucidate neurobiological risk and protective factors in psychosis. We used rsfMRI to investigate functional connectivity between the mediodorsal nucleus (MDN) and pulvinar, and their connectivity with frontal and temporal cortical regions, respectively in 43 healthy controls (HCs), and individuals in the schizophrenia-spectrum including 45 psychotropic drug-free individuals with SPD, and 20 individuals with schizophrenia-related disorders [(schizophrenia (n = 10), schizoaffective disorder (n = 8), schizophreniform disorder (n = 1) and psychosis NOS (n = 1)]. Individuals with SPD had greater functional connectivity between the MDN and pulvinar compared to individuals with schizophrenia. Thalamo-frontal (i.e., between the MDN and rostral middle frontal cortex) connectivity was comparable in SPD and HCs; in SPD greater connectivity was associated with less symptom severity. Individuals with schizophrenia had less thalamo-frontal connectivity and thalamo-temporal (i.e., pulvinar to the transverse temporal cortex) connectivity compared with HCs. Thalamo-frontal functional connectivity may be comparable in SPD and HCs, but abnormal in schizophrenia, and that this may be protective against psychosis in SPD.

Polygenic risk for schizophrenia and schizotypal traits in non-clinical subjects

BACKGROUND

Schizotypy is a putative risk phenotype for psychosis liability, but the overlap of its genetic architecture with schizophrenia is poorly understood.

METHODS

We tested the hypothesis that dimensions of schizotypy (assessed with the SPQ-B) are associated with a polygenic risk score (PRS) for schizophrenia in a sample of 623 psychiatrically healthy, non-clinical subjects from the FOR2107 multi-centre study and a second sample of 1133 blood donors.

RESULTS

We did not find correlations of schizophrenia PRS with either overall SPQ or specific dimension scores, nor with adjusted schizotypy scores derived from the SPQ (addressing inter-scale variance). Also, PRS for affective disorders (bipolar disorder and major depression) were not significantly associated with schizotypy.

CONCLUSIONS

This important negative finding demonstrates that despite the hypothesised continuum of schizotypy and schizophrenia, schizotypy might share less genetic risk with schizophrenia than previously assumed (and possibly less compared to psychotic-like experiences).

The Prediction Analysis of Autistic and Schizotypal Traits in Attentional Networks

OBJECTIVE

Empirical findings confirmed that autistic and schizotypal traits are associated with attentional function as well as include various dimensions. So far, no study has reported which dimension of these traits relates to attentional networks. This study aimed to find out whether there are associations between attentional networks and autistic traits; and between attentional networks and schizotypal traits.

METHODS

A total of 449 volunteers was included in this study, and autism-spectrum quotient (AQ), schizotypal personality questionnaire (SPQ), and attention network test (ANT) were used to measure autistic traits and schizotypal traits. The three independent attentional networks, including alerting network, orienting network, and executive control network, were also measured.

RESULTS

Autistic traits were associated with the orienting network, whereas schizotypal traits were associated with the orienting network and executive control network. Furthermore, attentional networks could be predicted by specific dimensions of autistic and schizotypal traits. AQ-attention switching [0.104 (-1.175- -0.025), p=0.041] and AQ-attention to detail [-0.097 (-0.798- -0.001), p=0.049] were significant predictors of orienting network and gender were significant predictor of executive network (Beta=0.107; 95% CI=-0.476-10.139; p=0.031). Whereas, schizotypal dimension "interpersonal" was a significant predictor of all three attentional networks [Alerting: 0.147 (-0.010-0.861), p=0.045; Orienting: 0.147 (0.018-0.733), p=0.040; Executive: 0.198 (0.215-1.309), p=0.006].

CONCLUSION

This study demonstrated that autistic and schizotypal traits were associated with attentional networks. The specific dimensions of autistic and schizotypal traits could predict attentional networks. Nevertheless, the attentional networks predicted with these two traits were different.

The Interplay Between Postsynaptic Striatal D2/3 Receptor Availability, Adversity Exposure and Odd Beliefs: A [11C]-Raclopride PET Study

BACKGROUND

Between unaffected mental health and diagnosable psychiatric disorders, there is a vast continuum of functioning. The hypothesized link between striatal dopamine signaling and psychosis has guided a prolific body of research. However, it has been understudied in the context of multiple interacting factors, subclinical phenotypes, and pre-postsynaptic dynamics.

METHOD

This work investigated psychotic-like experiences and D2/3 dopamine postsynaptic receptor availability in the dorsal striatum, quantified by in vivo [11C]-raclopride positron emission tomography, in a sample of 24 healthy male individuals. Additional mediation and moderation effects with childhood trauma and key dopamine-regulating genes were examined.

RESULTS

An inverse relationship between nondisplaceable binding potential and subclinical symptoms was identified. D2/3 receptor availability in the left putamen fully mediated the association between traumatic childhood experiences and odd beliefs, that is, inclinations to see meaning in randomness and unfounded interpretations. Moreover, the effect of early adversity was moderated by a DRD2 functional variant (rs1076560). The results link environmental and neurobiological influences in the striatum to the origination of psychosis spectrum symptomology, consistent with the social defeat and diathesis-stress models.

CONCLUSIONS

Adversity exposure may affect the dopamine system as in association with biases in probabilistic reasoning, attributional style, and salience processing. The inverse relationship between D2/3 availability and symptomology may be explained by endogenous dopamine occupying the receptor, postsynaptic compensatory mechanisms, and/or altered receptor sensitivity. This may also reflect a cognitively stabilizing mechanism in non-help-seeking individuals. Future research should comprehensively characterize molecular parameters of dopamine neurotransmission along the psychosis spectrum and according to subtype profiling.

High schizotypy traits are associated with reduced hippocampal resting state functional connectivity

Altered hippocampal functioning is proposed to play a critical role in the development of schizophrenia-spectrum disorders. Previous resting state functional Magnetic Resonance Imaging (rs-fMRI) studies report disrupted hippocampal connectivity in patients with psychosis and in individuals with clinical high risk, yet hippocampal connectivity has not been investigated in people with high schizotypy traits. Here we used rs-fMRI to examine hippocampal connectivity in healthy people with low (LS, n = 23) and high levels (HS, n = 22) of schizotypal traits assessed using the Schizotypy Personality Questionnaire. Using a bilateral hippocampal seed region, we examined resting state functional connectivity (RSFC) between hippocampus and striatal, thalamic and prefrontal cortex regions of interest. Compared to LS, HS participants showed lower RSFC between hippocampus and striatum and between hippocampus and thalamus. Whilst the group effect of reduced hippocampal RSFC in striatal and thalamic regions was driven by total schizotypy scores, positive schizotypy subfactor scores were significantly positively correlated with hippocampus-caudate/thalamus RSFC. Group differences in RSFC were not observed between hippocampus and prefrontal cortex. These results demonstrate that subclinical schizotypal traits are associated with altered hippocampal connectivity in striatal and thalamic regions and provide further support that hippocampal dysconnectivity confers risk for schizophrenia spectrum disorders.

Schizotypy in Parkinson's disease predicts dopamine-associated psychosis

Psychosis is the most common neuropsychiatric side-effect of dopaminergic therapy in Parkinson’s disease (PD). It is still unknown which factors determine individual proneness to psychotic symptoms. Schizotypy is a multifaceted personality trait related to psychosis-proneness and dopaminergic neurotransmission in healthy subjects. We investigated whether (1) PD patients exhibit lower schizotypy than controls and (2) dopamine-related neuropsychiatric side-effects can be predicted by higher schizotypy. In this cross-sectional study, we used the Oxford-Liverpool Inventory of Feelings and Experiences in 56 PD patients (12 women, mean ± sd age: 61 ± 11 years) receiving their usual dopaminergic medication and 32 age-matched healthy controls (n = 32; 18 women, mean ± sd age: 57 ± 6 years). We further compared schizotypy scores of patients with (n = 18, 32.1%) and without previously experienced psychosis. We found that patients exhibited lower schizotypy than controls. Further, patients with a history of psychosis exhibited higher schizotypy than patients without these symptoms. Using an information theoretic measure and a machine learning approach, we show that schizotypy yields the greatest predictive value for dopamine-associated hallucinations compared to other patient characteristics and disease related factors. Our results indicate an overlap between neural networks associated with schizotypy and the pathophysiology of PD and a relationship between schizotypy and psychotic side-effects of dopaminergic medication.

The association of striatal volume and positive schizotypy in healthy subjects: intelligence as a moderating factor

BACKGROUND

Schizotypy, a putative schizophrenia endophenotype, has been associated with brain-structural variations partly overlapping with those in psychotic disorders. Variations in precuneus structure have been repeatedly reported, whereas the involvement of fronto-striatal networks - as in schizophrenia - is less clear. While shared genetic architecture is thought to increase vulnerability to environmental insults, beneficial factors like general intelligence might buffer their effect.

METHODS

To further investigate the role of fronto-striatal networks in schizotypy, we examined the relationship of voxel- and surface-based brain morphometry and a measure of schizotypal traits (Schizotypal Personality Questionnaire, with subscores Cognitive-Perceptual, Interpersonal, Disorganised) in 115 healthy participants [54 female, mean age (s.d.) = 27.57(8.02)]. We tested intelligence (MWT-B) as a potential moderator.

RESULTS

We found a positive association of SPQ Cognitive-Perceptual with putamen volume (p = 0.040, FWE peak level-corrected), moderated by intelligence: with increasing IQ, the correlation of SPQ Cognitive-Perceptual and striatal volume decreased (p = 0.022). SPQ Disorganised was positively correlated with precentral volume (p = 0.013, FWE peak level-corrected). In an exploratory analysis (p < 0.001, uncorrected), SPQ total score was positively associated with gyrification in the precuneus and postcentral gyrus, and SPQ Disorganised was negatively associated with gyrification in the inferior frontal gyrus.

CONCLUSIONS

Our findings support the role of fronto-striatal networks for schizotypal features in healthy individuals, and suggest that these are influenced by buffering factors like intelligence. We conclude that protective factors, like general cognitive capacity, might attenuate the psychosis risk associated with schizotypy. These results endorse the idea of a continuous nature of schizotypy, mirroring similar findings in schizophrenia.

Dopamine-Induced Dysconnectivity Between Salience Network and Auditory Cortex in Subjects With Psychotic-like Experiences: A Randomized Double-Blind Placebo-Controlled Study

Dopamine is involved in the pathophysiology of schizophrenia. Disrupted salience processing by the salience network (SN) may be a central link between dysregulated dopamine function and psychotic symptoms. However, dopaminergic influence on the SN and its presumed influence on psychotic and subpsychotic symptoms or psychotic-like experiences in healthy individuals remain unclear. Therefore, we investigated dopamine-induced changes in functional connectivity of the right anterior insula (rAI), a central SN hub, and their association with psychotic-like experiences. We enrolled 54 healthy, right-handed male subjects in a randomized, double-blind, cross-sectional placebo-controlled experiment. Psychotic-like experiences were assessed using the revised Exceptional Experiences Questionnaire (PAGE-R). They then received either placebo (n = 32) or 200 mg L-DOPA (n = 33), a dopamine precursor, orally and underwent resting-state functional magnetic resonance imaging. In a seed-to-voxel approach, we analyzed dopamine-induced changes in functional connectivity of the rAI and assessed the relationship between functional connectivity changes and PAGE-R score. L-DOPA reduced functional connectivity between the rAI and the left auditory cortex planum polare. In the placebo group, we found a strong negative correlation between PAGE-R score and rAI to planum polare functional connectivity; in the L-DOPA group, there was a strong positive correlation between PAGE-R score and functional connectivity between rAI and planum polare. The PAGE-R score explained about 30% of the functional connectivity variation between rAI and planum polare in the two groups. Our findings suggest that psychotic-like experiences are associated with dopamine-induced disruption of auditory input to the SN, which may lead to aberrant attribution of salience.

Stress and cognitive biases in schizotypy: A two-site study of bias against disconfirmatory evidence and jumping to conclusions

The dysfunctional cognitive and reasoning biases which underpin psychotic symptoms are likely to present prior to the onset of a diagnosable disorder and should therefore be detectable along the psychosis continuum in individuals with schizotypal traits. Two reasoning biases, Bias Against Disconfirmatory Evidence (BADE) and Jumping to Conclusions (JTC), describe how information is selected and weighed under conditions of uncertainty during decision making. It is likely that states such as elevated stress exacerbates JTC and BADE in individuals with high schizotypal traits vulnerable to displaying these information gathering styles. Therefore, we evaluated whether stress and schizotypy interacted to predict these reasoning biases using separate samples from the US (JTC) and England (BADE). Generally speaking, schizotypal traits and stress were not independently associated with dysfunctional reasoning biases. However, across both studies, the interaction between schizotypy traits and stress significantly predicted reasoning biases such that increased stress was associated with increased reasoning biases, but only for individuals low in schizotypal traits. These patterns were observed for positive schizotypal traits (in both samples), for negative traits (in the England sample only), but not for disorganization traits. For both samples, our findings suggest that the presence of states such as stress is associated with, though not necessarily dysfunctional, reasoning biases in individuals with low schizotypy. These reasoning biases seemed, in some ways, relatively immutable to stress in individuals endorsing high levels of positive schizotypal traits.

Aberrant Salience Across Levels of Processing in Positive and Negative Schizotypy

Schizotypy is a multidimensional construct conceptualized as the expression of the underlying vulnerability for schizophrenia. Certain traits of positive schizotypy, such as odd beliefs, unusual perceptual experiences, suspiciousness, and referential thinking show associations with aberrant salience. Positive schizotypy may involve hyper-attribution of salience toward insignificant events, whereas negative schizotypy may involve hypo-attribution of salience, even toward important events. Attribution of salience is thought to involve dopamine-mediated processes, a mechanism that is disrupted in schizotypy; however, little is known about the cognitive processes potentially underlying salience attribution. The present study assessed the relationship between aberrant salience and latent inhibition (LI), as well as their associations with positive and negative schizotypy. Salience was measured at various stages of processing, including visual salience, attributions of salience to contingency illusions, and self-reported experience of salience. Schizotypy traits were differentially associated with self-reported aberrant salience experiences: positive schizotypy showed positive associations (β = 0.67, f2 = 0.82, large effect) and negative schizotypy showed inverse associations (β = -0.20, f2 = 0.07, small effect). However, neither schizotypy dimension was associated with visual salience, contingency illusions, or LI. Salience processing across perceptual, cognitive, and experiential levels likely involves different mechanisms, some of which may not show major disruption in subclinical manifestations of schizotypy.