Katherine L. Narr, Tonmoy Sharma, A. Edris, Andrew F. Cannestra,
Paul Thompson, Arthur W. Toga
Laboratory of Neuro Imaging, Dept. Neurology, Division of Brain Mapping,
UCLA School of Medicine, Los Angeles CA 90095, USA
Institute of Psychiatry, London.
Background. 2-dimensional analyses from studies examining perisylvian regions in schizophrenia yield mixed results regarding the presence of altered asymmetry in language-gifted cortex.
Methods. A 3-D analysis of Sylvian fissure morphology rendered from MR images investigated the unique patterns of variability and asymmetry present in schizophrenic (SZ) patients (N=17) compared to nonpsychiatric controls (N=18). High-resolution (256x256x124; 1.5 mm slice separation) T1-weighted MR images were first transformed into standardized 3-D space (Talairach coordinate system) to allow for morphometric comparisons across groups. Sylvian fissures were then outlined on a slice by slice basis in each hemisphere according to neuroanatomic landmarks by technicians blind to diagnosis and checked for reliability. 3-D meshes of each internal Sylvian fissure surface were created and averaged by hemisphere in each group. Digital visualization of averaged surface meshes revealed localized patterns of variability, asymmetry and displacement within and across groups. Intra-group variability was higher in SZ and inter-group displacement between meshes larger in the left hemisphere (LH).
Results. Student's t-tests were conducted to examine inter- and intra-group Sylvian fissure parameters. Normal subjects displayed expected left-right asymmetries. Rostral-caudal straight lengths were longer in LH (p<0.001) and sulci reached more superiorly in RH (p<0.001), while differences in curvature between hemispheres approached significance (p<0.06). In SZ, only the rostral-caudal straight lengths were significantly different between hemispheres (p<0.001). Furthermore, significant sex effects were detected in normal controls but not in patients. Between groups analyses revealed significant differences in LH curvature (p<0.02). Finally, subdivisions of the Sylvian fissure determined more precise locations of altered asymmetries within and between groups.
Conclusion. In sum, this 3D study supports the presence of well-localized Sylvian fissure asymmetries in normal controls that are altered in SZ patients. The data also add support to the hypothesis of schizophrenia as a lateralized disease affecting cortical regions important for language processing.
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