A model of disconnectivity involving abnormalities in the cortex and
connecting white matter pathways may explain the clinical manifestations
of schizophrenia. Recently, diffusion imaging tractography has
made it possible to study white matter pathways in detail and we
present here a study of patients with first-episode psychosis using this
technique. We selected the corpus callosum for this study because there
is evidence that it is abnormal in schizophrenia. In addition, the
topographical organization of its fibers makes it possible to relate focal
abnormalities to specific cortical regions. Eighteen patients with firstepisode
psychosis and 21 healthy subjects took part in the study. A
probabilistic tractography algorithm (PICo) was used to study
fractional anisotropy (FA). Seed regions were placed in the genu and
splenium to track fiber tracts traversing these regions, and a multithreshold
approach 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 with
controls. FA was also lower in the genu in females across both groups,
but there was no gender-by-group interaction. The FA reduction in
patients may be due to aberrant myelination or axonal abnormalities,
but the similar tract volumes in the two groups suggest that severe
axonal loss is unlikely at this stage of the illness.