Sex-specific associations in verbal memory brain circuitry in early psychosis

Correlation between toxoplasmosis and schizophrenia in Egyptian patients and its impact on dopamine serum levels

Toxoplasma gondii, a parasite infecting around one-third of the global population, has been linked to neurological disorders like schizophrenia. Abnormal dopamine levels are linked to the pathophysiology of schizophrenia, but their association remains unclear. This study aimed to investigate the relationship between T. gondii seroprevalence and dopamine serum levels in schizophrenic patients in Egypt. This case-control study included 93 patients diagnosed with schizophrenia and 93 individuals as controls. T. gondii seroprevalence was determined using an enzyme-linked immunosorbent assay (ELISA). Dopamine serum levels were measured using ELISA. Sociodemographic and clinical characteristics were also collected. The study found a higher prevalence of T. gondii IgG antibodies in patients with schizophrenia (68 %) compared to controls (46.2 %). Contact with cats, sausage consumption, and undercooked meat were identified as possible risk factors associated with T. gondii infection. The mean level of serum dopamine was significantly (P < 0.001) higher in patients with schizophrenia (115.3 Pg/ml ±31.8) compared to the control group (75.02 Pg/ml ±26.5). The study found that schizophrenic patients with T. gondii seropositivity had significantly higher dopamine serum levels (mean=145.2 ± 32.1 pg/ml) than those without T. gondii seropositivity (mean=122.5 ± 29.7 pg/ml) (p = 0.001). Logistic regression analysis revealed that T. gondii seropositivity was a significant predictor of increased dopamine serum levels in schizophrenic patients (odds ratio=3.4, 95 % confidence interval=1.8-6.4, p < 0.001). The study suggests that T. gondii seroprevalence may increase dopamine serum levels in Egyptian schizophrenic patients, potentially contributing to dopamine dysregulation in schizophrenia, but further research is needed to confirm these findings and investigate the underlying mechanisms.

A systematic review of structural and functional magnetic resonance imaging studies on the neurobiology of depressive symptoms in schizophrenia spectrum disorders

Depressive symptoms in Schizophrenia Spectrum Disorders (SSDs) negatively impact suicidality, prognosis, and quality of life. Despite this, efficacious treatments are limited, largely because the neural mechanisms underlying depressive symptoms in SSDs remain poorly understood. We conducted a systematic review to provide an overview of studies that investigated the neural correlates of depressive symptoms in SSDs using neuroimaging techniques. We searched MEDLINE, PsycINFO, EMBASE, Web of Science, and Cochrane Library databases from inception through June 19, 2023. Specifically, we focused on structural and functional magnetic resonance imaging (MRI), encompassing: (1) T1-weighted imaging measuring brain morphology; (2) diffusion-weighted imaging assessing white matter integrity; or (3) T2*-weighted imaging measures of brain function. Our search yielded 33 articles; 14 structural MRI studies, 18 functional (f)MRI studies, and 1 multimodal fMRI/MRI study. Reviewed studies indicate potential commonalities in the neurobiology of depressive symptoms between SSDs and major depressive disorders, particularly in subcortical and frontal brain regions, though confidence in this interpretation is limited. The review underscores a notable knowledge gap in our understanding of the neurobiology of depression in SSDs, marked by inconsistent approaches and few studies examining imaging metrics of depressive symptoms. Inconsistencies across studies' findings emphasize the necessity for more direct and comprehensive research focusing on the neurobiology of depression in SSDs. Future studies should go beyond "total score" depression metrics and adopt more nuanced assessment approaches considering distinct subdomains. This could reveal unique neurobiological profiles and inform investigations of targeted treatments for depression in SSDs.

Sex differences in cognition and structural covariance-based morphometric connectivity: evidence from 28,000+ UK Biobank participants

There is robust evidence for sex differences in domain-specific cognition, where females typically show an advantage for verbal memory, whereas males tend to perform better in spatial memory. Sex differences in brain connectivity are well documented and may provide insight into these differences. In this study, we examined sex differences in cognition and structural covariance, as an index of morphometric connectivity, of a large healthy sample (n = 28,821) from the UK Biobank. Using T1-weighted magnetic resonance imaging scans and regional cortical thickness values, we applied jackknife bias estimation and graph theory to obtain subject-specific measures of structural covariance, hypothesizing that sex-related differences in brain network global efficiency, or overall covariance, would underlie cognitive differences. As predicted, females demonstrated better verbal memory and males showed a spatial memory advantage. Females also demonstrated faster processing speed, with no observed sex difference in executive functioning. Males showed higher global efficiency, as well as higher regional covariance (nodal strengths) in both hemispheres relative to females. Furthermore, higher global efficiency in males mediated sex differences in verbal memory and processing speed. Findings contribute to an improved understanding of how biological sex and differences in cognition are related to morphometric connectivity as derived from graph-theoretic methods.