Abstract
Evidence shows that there are reductions in gray matter volume (GMV) and changes in long association white matter fibres within the left insula-temporoparietal junction (TPJ) during the early stages of psychotic disorders but less is known about short association fibres (sAFs). In this study we sought to characterise the changes in sAFs and associated volumetric changes of the left insula-TPJ during the early stages of psychosis. Magnetic resonance imaging was obtained from a sample of young people with psychosis (n = 42) and healthy controls (n = 45), and cortical parcellations of the left insula-TPJ were used as seeding masks to reconstruct 13 sAFs. Compared to healthy counterparts, the psychosis group showed significant reductions in fractional anisotropy (FA) in the sAFs connecting the superior (STG) and middle temporal gyri (MTG) and as well as reduced GMV within the inferior temporal gyrus and increased white matter volume (WMV) within Heschl's gyrus (HG). Furthermore, adolescent-onset psychosis subjects (onset 18 year or earlier) showed FA reductions in the STG-HG sAF when compared to adult-onset subjects, but this was not associated with changes in GMV nor WMV of the STG or HG. These findings suggest that during the early stages of psychosis, changes in sAFs and associated cortical GMV and WMV appear to occur independently, however age of onset of a psychotic syndrome/disorder influences the pattern of neuroanatomical abnormalities.
Highlights
Short association fibres comprise either local association fibres (U-fibres of Mynert) [1] that arch through the cortical sulci to connect adjacent gyri or neighbouring association fibres that connect nearby cortical gyri [2], as opposed to long association fibres that connect distant cortical regions [3]
We have reported that young people at the early stages of psychiatric disorders have reduced left anterior insula gray matter volume (GMV) that was correlated with worse attention-set shifting [6]
Contrasting by onset (Table 3), the adult-onset psychosis group had larger Heschl’s gyrus (HG) white matter volume (WMV) compared to controls and the adolescent-onset psychosis group showed significantly reduced middle temporal gyri (MTG) WMV compared with the adult-onset psychosis group. This present study shows that of the 13 short association fibres (sAFs) that connect regions of the left insula-temporo-parietal junction (TPJ), people in the early stages of psychosis have significant fractional anisotropy (FA) reductions within the sAFs connecting the superior temporal gyrus (STG) and MTG relative to controls
Summary
Short association fibres (sAFs) comprise either local association fibres (U-fibres of Mynert) [1] that arch through the cortical sulci to connect adjacent gyri or neighbouring association fibres that connect nearby cortical gyri [2], as opposed to long association fibres that connect distant cortical regions [3]. We have reported that young people at the early stages of psychiatric disorders (psychosis, bipolar, depression and anxiety disorders) have reduced left anterior insula gray matter volume (GMV) that was correlated with worse attention-set shifting [6]. This evidence suggest that in the early stages of psychosis, deficits in attention and verbal fluency are underpinned by left anterior insula GMV reductions and reduced cortical thickness of the left TPJ without involvement of the left uncinate that connects the two regions. To further understand the relationship between neurostructural abnormalities in the left hemisphere that underpin cognitive deficits in young people at the early stages of psychosis, we sought to characterise the sAFs that connects the left insula-TPJ
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