Callosal Shapes at the Midsagittal Plane: MRI Differences of Normal Males, Normal Females, and GID.

We investigated differences in corpus callosum shape at the midsagittal plane using MRI for different subjects: normal males, normal females, and subjects with gender identity disorder (GID). We first represented callosal shapes with Fourier descriptors of callosal contours. Using linear support vector machines with soft-margin, we next determined a hyperplane that separates normal males and females most optimally in the vector space spanned by Fourier descriptors. We then proposed a measure that has prominent sex difference: it is defined as the coordinate of a given callosal shape on the subspace orthogonal to the obtained hyperplane. Use of the measure provides discrimination of someone's sex with 74.17% accuracy. We further showed that the value of the measure for GID more strongly reflects their mental sex, i.e. gender, than their physical sex.