Microstructural organization of cerebellar tracts in schizophrenia

BACKGROUND: Dysconnectivity theories of schizophrenia would suggest that the connectivity of the cerebellum is impaired and that the impairment may be restricted to certain tracts. Attempts to examine the structural connectivity of the cerebellum using diffusion tensor imaging have yielded conflicting results. However, previous studies have employed region-of-interest approaches or have used small or unmatched samples, with a consequent risk of type II error. METHODS: We conducted an appropriately powered case-control study of 33 patients with schizophrenia and 33 matched healthy control subjects. We used tractography to dissect the four white matter tracts of the cerebellum and measured fractional anisotropy (FA) and mean diffusivity (MD) over each tract for each subject. RESULTS: Repeated-measures analysis of variance found that FA was lower in the schizophrenia group compared with the control group, but there were no tract-specific differences between the groups. Mean diffusivity did not differ between the groups. CONCLUSIONS: Though structural connectivity is impaired in the cerebellum, it is not local to any particular tract but appears to have a wider, possibly global, distribution. Reduced fractional anisotropy with normal MD would point to the differences being due to disordered neuronal architecture rather than disordered myelination.