Syntactic complexity and its brain structural correlates across schizophrenia and depression
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Abstract
In the context of schizophrenia spectrum disorders, a variety of linguistic changes occur, collectively termed "formal thought disorders". These language-related symptoms are not exclusive to schizophrenia spectrum disorders but can also be present in major depressive disorder and healthy individuals. These symptoms include verbosity, production of neologisms, perseverations, and reduced syntactic complexity. While rating scales for formal thought disorders are valuable in clinical settings, they have limitations in capturing the nuanced linguistic abnormalities in schizophrenia spectrum and major depressive disorders. These scales often fail to detect subtle grammatical and phonetic deviations in language production. Moreover, formal thought disorders encompass a broad spectrum of linguistic and cognitive symptoms, resulting in a more generalized symptom assessment. To address these limitations, language analyses have emerged as a promising alternative. These methods offer a more comprehensive approach to examining the intricate linguistic features associated with schizophrenia spectrum and major depressive disorders. Furthermore, language analysis offers practical advantages in clinical settings due to its reproducibility, cost-effectiveness, time efficiency, and non-invasive nature.
Due to further symptomatic, genetic, cognitive, and brain structural commonalities, as well as overlaps in environmental risk factors across schizophrenia spectrum and major depressive disorders, a dimensional approach appears useful. This approach aims to expand on findings from categorical studies to obtain a more holistic picture of syntactic language production in schizophrenia spectrum and major depression disorders.
Thus, many categorical studies have focused on examining syntactic complexity in schizophrenia spectrum disorders in contrast to healthy controls, leading to the question, what does the syntactic performance in major depression disorder look like. Additionally, the relationships between syntax and other language-related neurocognitive functions, as well as psychopathology, are of interest. Finally, brain structural correlates of syntactic complexity and diversity are investigated.
STUDY I showed that less syntactic complexity and diversity were reflected in reduced executive functioning, verbal fluency, and verbal episodic memory as well as in stronger positive and negative formal thought disorders. Thus, a cluster analysis resulted in four clusters across SSD, MDD, and HC with varying degrees of syntactic complexity and diversity, forming networks associated with language-related neuropsychology and psychopathology. Syntactic complexity measures demonstrated a high degree of interconnectedness, in contrast to syntactic diversity emerged as an independent entity. Cross-domain associations were more pronounced in more complex syntactic production.
STUDY II employed general linear models to examine the relationship between syntactic complexity and diversity, and gray matter volume, as well as white matter microstructure (fractional anisotropy, axial, radial, and mean diffusivity), resulting in several cross-diagnostic correlations. Syntactic diversity showed a positive correlation with gray matter volume in the right medial pre- and postcentral gyri, as well as with fractional anisotropy in the temporal part of the left superior longitudinal fasciculus. In contrast, axial diffusivity in the left cingulum bundle and the forceps minor correlated negatively with syntactic diversity. Additionally, axial diffusivity of the right inferior longitudinal fasciculus was positively associated with syntactic complexity. Negative correlations were found between syntactic complexity and fractional anisotropy of the left cingulum bundle, the right superior longitudinal fasciculus, and axial diffusivity of both the forceps minor and the left uncinate fasciculus. Age, sex, total intracranial volume, group, and the interaction between group and syntax were treated as covariates of no interest.
In summary, this dissertation advocates for a stronger inclusion of syntax as a dimensional factor in the analysis of psychiatric disorders. Syntactic complexity and diversity show clear associations with language-related neuropsychology, psychopathology, and brain structural correlates, independent of group membership. These findings support the investigation and a better understanding of psychiatric disorders to formulate increasingly precise statements regarding prognosis and treatment methods.
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Issued: 2026-01-26
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FB20:Medizin
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en
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DoctoralThesis
Keywords
syntactic complexitysyntactic diversitytransdiagnosticschizophreniadepressiongray matter volumewhite matterSyntaxtransdiagnostischGehirnstruktur
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Schneider, Katharina: Syntactic complexity and its brain structural correlates across schizophrenia and depression. : 2026-01-26.
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