Recent structural magnetic resonance imaging (MRI) studies have employed voxel-based morphometry (VBM) to investigate whether there are brain volumetric abnormalities of gray and/or white matter regions in schizophrenia. This VBM study investigated volumetric reductions in corpus callosum (CC) subregions in association with first-episode psychosis (FEP). Also, we investigated whether such changes were related to deficits in interhemispheric transfer of somatosensory information, using the Crossed Finger Localisation Test (CFLT).

122 FEP subjects and 94 controls were examined. MRI processing was performed using Statistical Parametric Mapping. In a subsample of 31 FEP subjects, we investigated correlations between CC volumes and performance on the CFLT. In this task, a fingertip on one hand is touched by the experimenter and the subject's task is to respond by touching with their thumb the corresponding finger on the other hand.

Relative to controls, FEP subjects showed volume reduction in a cluster located in the anterior CC genu (Z=3.77, p<0.001 uncorrected), which retained significance when analyses were restricted to the schizophrenia/schizophreniform subgroup (n=62) compared to controls (Z=3.16, p<0.001 uncorrected). In the subsample of FEP subjects who performed the finger localization task, there were two clusters of significant positive correlation between performance on the CFLT and CC volumes, respectively in the anterior genu (Z=3.77, p<0.001 uncorrected) and the posterior genu (Z=3.30, p<0.001 uncorrected).

These findings indicate the presence of circumscribed foci of reduced CC volumes in association with FEP, and suggest that such abnormalities are related to deficits in interhemispheric transfer of information.