Functional hemispheric lateralization for language in patients with schizophrenia

Abstract

Background: It is widely reported that patients with schizophrenia exhibit decreased hemispheric lateralization. However, no study has evaluated relationships between the hemispheric anatomical and functional asymmetry in language areas. The present study aimed to determine whether decreased leftward hemispheric lateralization could be related to asymmetry of the grey matter volume in patients with schizophrenia. This investigation was the first to use a functional index of laterality to analyze the global functional network specifically involved in the language task.

Methods: Twenty-seven right-handed patients with schizophrenia and 54 right-handed control subjects underwent a session of a functional magnetic resonance imaging (fMRI) with a speech listening paradigm. Functional laterality indices (FLI) were calculated (Wilke, M. and Lidzba, K., 2007. LI-tool: a new toolbox to assess lateralization in functional MR-data. J Neurosci Methods. 163, 128-136). The indices of asymmetry in the volume of grey matter (GVAIs) were computed from the functional language network.

Results: Patients with schizophrenia exhibited significantly decreased leftward hemispheric lateralization. There was a positive correlation between GVAIs and FLIs in healthy subjects, while no such correlation was seen in patients with schizophrenia.

Discussion: This study reports for the first time a significant relationship between the anatomical and functional asymmetry in healthy subjects, but not in patients with schizophrenia. While decreased leftward functional lateralization for language was observed in patients with schizophrenia compared to the control group, this functional abnormality was not related to asymmetry in the volume of grey matter.

Keywords: AHRS; Auditory Hallucinations Rating Scale; BOLD; CS; CSi; DSM IV; EPI; ET; FA; FLI; FOV; FWE; FWHM; Functional hemispheric lateralization; Functional magnetic resonance imaging; GM; GVAI; Grey matter volume asymmetry; HRF; IT; LH; Language; MINI; MNI; Mini International Neuropsychiatric Interview; Montreal Neurological Institute; PANSS; Positive And Negative Syndrome Scale; RH; ROI; RT; SD; SPM5; Schizophrenia; blood oxygen level dependent; comprehension score; degree of freedom; diagnostic and statistical manual of mental disorders 4th edition; dof; echo planar imaging; echo time; fMRI; family wise error; field of view; flip angle; full width at half maximum; functional laterality index; functional magnetic resonance imaging; grey matter; grey matter volume asymmetry index; hemodynamic response function; individual comprehension score; inversion time; left hemisphere; n; n-CS; normalized comprehension scores; number; regions of interest; repetition time; right hemisphere; standard deviation; statistical parametric mapping 5.