Sex-Related Differences in White Matter Asymmetry and Its Implications for Verbal Working Memory in Psychosis High-Risk State

Abstract

Objective: Sexual dimorphism has been investigated in schizophrenia, although sex-specific differences among individuals who are at clinical high-risk (CHR) for developing psychosis have been inconclusive. This study aims to characterize sexual dimorphism of language areas in the brain by investigating the asymmetry of four white matter tracts relevant to verbal working memory in CHR patients compared to healthy controls (HC). HC typically show a leftward asymmetry of these tracts. Moreover, structural abnormalities in asymmetry and verbal working memory dysfunctions have been associated with neurodevelopmental abnormalities and are considered core features of schizophrenia. Methods: Twenty-nine subjects with CHR (17 female/12 male) for developing psychosis and twenty-one HC (11 female/10 male) matched for age, sex, and education were included in the study. Two-tensor unscented Kalman filter tractography, followed by an automated, atlas-guided fiber clustering approach, were used to identify four fiber tracts related to verbal working memory: the superior longitudinal fasciculi (SLF) I, II and III, and the superior occipitofrontal fasciculus (SOFF). Using fractional anisotropy (FA) of tissue as the primary measure, we calculated the laterality index for each tract. Results: There was a significantly greater right>left asymmetry of the SLF-III in CHR females compared to HC females, but no hemispheric difference between CHR vs. HC males. Moreover, the laterality index of SLF-III for CHR females correlated negatively with Backward Digit Span performance, suggesting a greater rightward asymmetry was associated with poorer working memory functioning. Conclusion: This study suggests increased rightward asymmetry of the SLF-III in CHR females. This finding of sexual dimorphism in white matter asymmetry in a language-related area of the brain in CHR highlights the need for a deeper understanding of the role of sex in the high-risk state. Future work investigating early sex-specific pathophysiological mechanisms, may lead to the development of novel personalized treatment strategies aimed at preventing transition to a more chronic and difficult-to-treat disorder.

Keywords: diffusion-tensor-imaging; high risk of psychosis; sex differences; white matter asymmetry; working memory.

Figure 1

(A) Fiber clustering results of the SLF-I (light blue), SLF-II (green), SLF-III (red), and SOFF (dark blue) of one CHR female, and (B) of the SLF-III of one HC female. Left column, sagittal view; right column, axial view.

Figure 2

Mean laterality indices of the superior occipitofrontal fasciculi (SOFF) and the superior longitudinal fasciculi (SLF) I, II, and III for healthy controls (HC) and individuals at clinical high-risk (CHR). The significant different laterality index of the SLF-III between HC and CHR females is marked with an asterisk. (A) Females and (B) Males. N.S., not significant.

Figure 3

Correlation between FA-based laterality index of the superior longitudinal fasciculus (SLF) III and working memory performance in clinical high-risk females (CHR).