Abstract
Background
Psychotic disorders are characterized by neurobiological deviations, including in the macro and microstructure of white matter. White matter alterations are also seen in psychosis-proneness and in individuals who have a high risk of psychosis. For example, studies have indicated decreases in white matter integrity in the genu/forceps minor of corpus callosum (CC) in the latter populations. Anterior corona radiata (ACR) is one crucial white-matter tract connecting the anterior cingulate cortex to the striatum. Indeed, reductions in the white matter structure of anterior genu of CC significantly predict the transition from ultra-high risk to psychosis. However, there is a gap in the literature related to observing the psychosis-proneness by applying both micro and macrostructural brain analyses, and most of the microstructural white matter studies in psychosis focus on fractional anisotropy (FA) and not include mean diffusivity (MD). Thus, the current study aims to assess whether white matter deviations in CG, ACR, and CC, are associated with psychosis proneness by combining both tract-based spatial statistics (TBSS) and voxel-based morphometry (VBM) analyses in a sample of participants with psychosis proneness (PP) and without psychosis proneness (NPP).
Methods
The study included 53 participants (29 PP vs. 24 NPP) whose ages were between 17 and 24 years. Participants were split into two groups based on their scores on Structured Interview for Schizotypy assessment, a well-validated instrument of psychosis proneness. White matter integrity was analyzed via diffusion tensor imaging (DTI) and white matter volume (WMV) via VBM. Two sample t-test was used in GLM for both DTI and VBM analyses. FA, MD, and VMV were compared between two groups to observe micro and macro white matter structure alterations in the region of interest.
Results
DTI analysis revealed decreased FA values in the right ACR and right genu of the CC in the psychosis-proneness group (F(1,52)= 7.37, p= 0.009). Moreover, VBM showed a significant WMV decreases in the right CG, Brodmann areas 8, 9, and 32 in the PP group (F(1,52)= 50.85, uncorrected p<0.01). However, MD did not differ between the two groups (F(1,51)= 3.65, p=0.06)
Discussion
These findings suggest that PP associated with decreased white matter integrity in ACR, genu of CC, and also reduced white matter volumes in the right CG, Brodmann areas 8, 9, and 32. Significant FA decreases might result from alterations in radial or axial diffusivity since we did not observe significant MD differences between two groups. The current findings suggested that participants with PP had both macro and micro white matter structure disruptions, mostly in frontal parts of the right cerebrum, compared to no PP group.
Longitudinal study examining abnormal white matter integrity using a tract-specific analysis in individuals with a high risk for psychosis
