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Abnormal brain connectivity in first-episode psychosis: A diffusionMRI tractography study of the corpus callosum
Price G, Cercignani M, Parker GJM, Altman D, Barnes T, Barker G, Joyce E, Ron M
Neuroimage. 2007;35:458-466.
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Abstract
A model of disconnectivity involving abnormalities in the cortex andconnecting white matter pathways may explain the clinical manifestationsof schizophrenia. Recently, diffusion imaging tractography hasmade it possible to study white matter pathways in detail and wepresent here a study of patients with first-episode psychosis using thistechnique.We selected the corpus callosum for this study because thereis evidence that it is abnormal in schizophrenia. In addition, thetopographical organization of its fibers makes it possible to relate focalabnormalities to specific cortical regions. Eighteen patients with firstepisodepsychosis and 21 healthy subjects took part in the study. Aprobabilistic tractography algorithm (PICo) was used to studyfractional anisotropy (FA). Seed regions were placed in the genu andsplenium to track fiber tracts traversing these regions, and a multithresholdapproach to study the probability of connection was used.Multiple linear regressions were used to explore group differences. FA,a measure of tract coherence, was reduced in tracts crossing the genu,and to a lesser degree the splenium, in patients compared withcontrols. FA was also lower in the genu in females across both groups,but there was no gender-by-group interaction. The FA reduction inpatients may be due to aberrant myelination or axonal abnormalities,but the similar tract volumes in the two groups suggest that severeaxonal loss is unlikely at this stage of the illness.