• Sylvian fissure
• Psychosis
• Adolecents
• Asymmetry

The normal human brain is characterized by a pattern of gross anatomical asymmetry known as “torque” (a bias in width or volume from right frontal to left occipital). Contributing to the torque the Sylvian (lateral) fissure separates the frontal and parietal from the occipital and temporal lobes, and is reported to have a length bias to the left. The psychoses (schizophrenia and bipolar disorder) are a group of mental disorders characterized by a generally detrimental change in personality and a distorted or diminished sense of objective reality (i.g. they experience delusions and hallucinations). The psychoses occur in all populations with approximately uniform incidence and sex-dependent age of onset. This study aimed to test the hypothesis that individuals who develop psychosis in adolescence have atypical structural asymmetries of the Sylvian fissure.
We examined MRI scans from 32 adolescents (between 13 and 18 years old), divided as 17 controls and 15 patients. Baseline and follow-up magnetic resonance scans were collected through an imaging protocol with diffusion-weighted scanning on a 1.5-T Sonata MR scanner. All the brain scans were analysed through BrainVisa software. That allowed us to measure white matter, grey matter and CSF volumes. We found that grey matter was reduced in both the left (92,9%) and right (92,7%) hemispheres in patients compared to controls. Moreover in white matter (fibre tracts) we observed changes in laterality: controls were symmetrical whereas patients were more lateralised to the left (p = 0,020).
Then focusing on the SF and measuring total lengths, initially we observed no differences between patients and controls. To examine the SF in more detail, we adopted the Witelson and Kigar (1992) classification system that divides the Sylvian fissure into 3 segments: anterior, horizontal and vertical. The data were analysed with respect to a potential diagnosis x side x sex x length x depth interaction. In no analysis was sex found to be a significant variable. With respect to length, the vertical segment was found to be lateralized to the right (p < 0,001) and the posterior (anterior and horizontal together) to the left (p < 0,001). In both segments patients were found to have asymmetries that were reduced relative to controls. Depth asymmetries have so far been relatively neglected in schizophrenia. With BrainVisa we established that there are depth asymmetries of the SF and that these are reduced in individuals with schizophrenia. The core conclusion is that there is a reduction of the anatomical left and right asymmetry in SF in adolescents with schizophrenia (attested by changes in white matter, SF lengths and depths) consistent with the hypothesis that schizophrenia is a disorder of early neurodevelopment associated with anomalous cerebral lateralization. The depth measures will facilitate discovery of the precise anatomical nature of the normal and deviant asymmetries.