The positive link between executive function and lifetime cannabis use in schizophrenia is not explained by current levels of superior social cognition

Assessing social cognition in patients with schizophrenia and healthy controls using the reading the mind in the eyes test (RMET): a systematic review and meta-regression

The reading the mind in the eyes test (RMET) - which assesses the theory of mind component of social cognition - is often used to compare social cognition between patients with schizophrenia and healthy controls. There is, however, no systematic review integrating the results of these studies. We identified 198 studies published before July 2020 that administered RMET to patients with schizophrenia or healthy controls from three English-language and two Chinese-language databases. These studies included 41 separate samples of patients with schizophrenia (total n = 1836) and 197 separate samples of healthy controls (total n = 23 675). The pooled RMET score was 19.76 (95% CI 18.91-20.60) in patients and 25.53 (95% CI 25.19-25.87) in controls (z = 12.41, p < 0.001). After excluding small-sample outlier studies, this difference in RMET performance was greater in studies using non-English v. English versions of RMET (Chi [Q] = 8.54, p < 0.001). Meta-regression analyses found a negative association of age with RMET score and a positive association of years of schooling with RMET score in both patients and controls. A secondary meta-analysis using a spline construction of 180 healthy control samples identified a non-monotonic relationship between age and RMET score - RMET scores increased with age before 31 and decreased with age after 31. These results indicate that patients with schizophrenia have substantial deficits in theory of mind compared with healthy controls, supporting the construct validity of RMET as a measure of social cognition. The different results for English versus non-English versions of RMET and the non-monotonic relationship between age and RMET score highlight the importance of the language of administration of RMET and the possibility that the relationship of aging with theory of mind is different from the relationship of aging with other types of cognitive functioning.

Cognitive performance and lifetime cannabis use in patients with first-episode schizophrenia spectrum disorder

INTRODUCTION

Cognitive impairment is among the core features of schizophrenia. In a healthy population, the cognitive deficit is often linked with cannabis abuse, and although the same would be expected in patients with schizophrenia, research has presented contradictory results.

METHODS

Participants were patients with first-episode schizophrenia (FES) spectrum disorder who had been lifetime cannabis users (N = 30), FES non-users (N = 53) as well as healthy controls (HC) also divided into cannabis users (N = 20) and non-users (N = 49). All participants underwent an extensive neurocognitive assessment and filled in a cannabis questionnaire, which allowed for a comparison of the four groups on cognitive functioning.

RESULTS

FES patients using cannabis showed less impaired cognitive functioning with the most prominent difference in visual memory compared to FES non-users. However, they differed neither in the clinical assessment of general psychopathology, positive and negative symptoms, nor in medication from the patient's non-users. A comparison of the HC who used cannabis, and those who did not, revealed no sizeable differences in cognitive performance between the groups.

CONCLUSIONS

The results delivered supporting evidence for the trend of superior neurocognitive performance in FES patients with a lifetime history of cannabis use compared to non-using patients.

Premorbid Adjustment and IQ in Patients With First-Episode Psychosis: A Multisite Case-Control Study of Their Relationship With Cannabis Use

Psychotic patients with a lifetime history of cannabis use generally show better cognitive functioning than other psychotic patients. Some authors suggest that cannabis-using patients may have been less cognitively impaired and less socially withdrawn in their premorbid life. Using a dataset comprising 948 patients with first-episode psychosis (FEP) and 1313 population controls across 6 countries, we examined the extent to which IQ and both early academic (Academic Factor [AF]) and social adjustment (Social Factor [SF]) are related to the lifetime frequency of cannabis use in both patients and controls. We expected a higher IQ and a better premorbid social adjustment in psychotic patients who had ever used cannabis compared to patients without any history of use. We did not expect such differences in controls. In both patients and controls, IQ was 3 points higher among occasional-users than in never-users (mean difference [Mdiff] = 2.9, 95% CI = [1.2, 4.7]). Both cases and control daily-users had lower AF compared to occasional (Mdiff = -0.3, 95% CI = [-0.5; -0.2]) and never-users (Mdiff = -0.4, 95% CI = [-0.6; -0.2]). Finally, patient occasional (Mdiff = 0.3, 95% CI = [0.1; 0.5]) and daily-users (Mdiff = 0.4, 95% CI = [0.2; 0.6]) had better SF than their never-using counterparts. This difference was not present in controls (Fgroup*frequency(2, 2205) = 4.995, P = .007). Our findings suggest that the better premorbid social functioning of FEP with a history of cannabis use may have contributed to their likelihood to begin using cannabis, exposing them to its reported risk-increasing effects for Psychotic Disorders.

A meta-analysis of the associations between theory of mind and neurocognition in schizophrenia

Theory of mind (ToM) refers to the ability to infer the mental states of others. ToM is impaired in schizophrenia and these deficits seem to hinder functional recovery. ToM is thus an important, but complex treatment target, supported by several processes. A large number of studies report significant associations between ToM and neurocognition (e.g. memory, attention), but the neurocognitive domains that are most closely linked to ToM remain to be identified. A meta-analysis was conducted to estimate the magnitude of the associations between ToM and neurocognition in people with schizophrenia. Correlations were extracted from the relevant literature, transformed into effect sizes Zr and pooled as weighted means. Focused-tests were employed to test for differences between neurocognitive domains and for differences linked to the characteristics of ToM tasks. Ninety-one studies (N = 5462) were included. Moderate associations emerged between ToM and each neurocognitive domain (Zrs 0.27-0.43), with no significant difference between domains (χ2(8) = 11.89, p = 0.156). Within the domain of executive functions, abstraction showed a stronger association with ToM (χ2(4) = 18.93, p = 0.001). Several ToM tasks characteristics (e.g. modality of stimuli, type of mental state), were significantly related to the magnitude of the associations between ToM and executive functions, visuospatial/problem solving, attention and episodic memory. These results suggest that ToM is linked to a wide range of neurocognitive abilities in schizophrenia, and that ToM tasks are a significant moderator of these associations. The assessment and treatment of ToM should consider the neurocognitive profile of each patient to understand his difficulties and to tailor interventions.

Schizophrenia, cannabis use and Catechol-O-Methyltransferase (COMT): Modeling the interplay on cognition

Cognitive impairments are considered core features of schizophrenia and are recognized as the most important predictors of functional outcome and quality of life. A better study of the mechanisms underlying the cognition is of extreme relevance. Literature has shown that several genetic and environmental factors affect cognitive performance. In particular, the interaction between Catechol-O-Methyltransferase (COMT) gene and cannabis use has gained increasing attention in the past years. Based on these premises, the present study, aimed to analyze the interplay between cannabis use and COMT polymorphism on cognitive performance in a sample of 135 patients with chronic schizophrenia. Patients were assessed for neurocognitive measures with a broad battery, genotyped for COMT Val158Met polymorphism from peripheral blood sample, and evaluated with a semi-structured interview in order to establish the history of cannabis abuse. Results showed a significant interaction effect between COMT polymorphism and cannabis use on verbal fluency and speed of processing. The analysis revealed significant differences between subjects COMT Val/Val homozygous and Met carriers with history of cannabis use, with a better performance on both tasks among the Met carriers group. These data are in line with literature on healthy subjects that suggests a more detrimental effect of cannabis among subjects with Val/Val genotype. In conclusions, results highlight the need to better disentangle the biological pathways in which cannabis use and COMT are converging, as possible treatment targets, as well as the importance to assess these factors in clinical to optimize individualized interventions.

The neuropsychological profiles of young psychosis patients with and without current cannabis use

INTRODUCTION

Evidence suggests that patients with psychosis who have a history of cannabis use, but currently abstain, demonstrate superior cognitive performance than patients who have never used cannabis. The present study aimed to determine the neurocognitive profiles of patients who are in adolescence or early adulthood, when both illness- and drug-onset typically occur.

METHODS

Subjects were 24 cannabis-using and 79 cannabis-naïve psychosis patients between 16 and 25 years of age. Patients and controls were administered a neurocognitive battery, indexing estimated pre-morbid intelligence, psychomotor speed, mental flexibility, verbal learning and memory, verbal fluency, sustained attention, motor and mental response, and visuospatial learning and memory.

RESULTS

While healthy controls outperformed both patient groups across most cognitive measures, no significant differences between cannabis-using and cannabis-abstinent patients were evident.

CONCLUSION

Evidently although there may be a group of patients who are diagnosed with a non-affective psychosis disorder regardless of external factors (i.e. cannabis use), some may instead have their illness precipitated through cannabis use at a young age, presenting with unique cognitive and symptomatic repercussions later in life. These results demonstrate no cognitive differences between cannabis-using patients and abstinent patients at the time of illness-onset, providing partial support for an alternative pathway to schizophrenia through early cannabis use.

Are cannabis-using and non-using patients different groups? Towards understanding the neurobiology of cannabis use in psychotic disorders

A substantial body of credible evidence has accumulated that suggest that cannabis use is an important potentially preventable risk factor for the development of psychotic illness and its worse prognosis following the onset of psychosis. Here we summarize the relevant evidence to argue that the time has come to investigate the neurobiological effects of cannabis in patients with psychotic disorders. In the first section we summarize evidence from longitudinal studies that controlled for a range of potential confounders of the association of cannabis use with increased risk of developing psychotic disorders, increased risk of hospitalization, frequent and longer hospital stays, and failure of treatment with medications for psychosis in those with established illness. Although some evidence has emerged that cannabis-using and non-using patients with psychotic disorders may have distinct patterns of neurocognitive and neurodevelopmental impairments, the biological underpinnings of the effects of cannabis remain to be fully elucidated. In the second and third sections we undertake a systematic review of 70 studies, including over 3000 patients with psychotic disorders or at increased risk of psychotic disorder, in order to delineate potential neurobiological and neurochemical mechanisms that may underlie the effects of cannabis in psychotic disorders and suggest avenues for future research.