A comparison of sex differences revealed by two partitioning schemes of the human corpus callosum

Issue: 
2013
Institution: 
University of California at Los Angeles, Los Angeles, CA

We compared two schemes of partitioning the human corpus callosum, both of which purport to divide
corpus callosum axons into functionally distinct subregions. Witelson’s (1989) scheme was based
largely on data obtained from rhesus macaques. In contrast, Hofer and Frahm’s (2006) scheme was
based on data from humans using Diffusion Tensor Imaging (DTI) and as such should more accurately
partition the human corpus callosum into functional units. Sex differences in the human isthmus have
been reported using the Witelson scheme. Examining Hofer and Frahm’s scheme may reveal sexual
dimorphisms in axon bundles that are allegedly more functionally homogeneous. In this study, we
employed both schemes independently on human corpora callosa and compared results. Analysis of
data from the Witelson’s scheme revealed that the isthmus area was larger in males than in females.
This difference was also observed when corrected for overall brain size. No sex differences were found
in the corpus callosum subregions as defined by the Hofer and Frahm scheme. Witelson’s scheme
designated some axons as part of the isthmus that the Hofer and Frahm scheme designated as part of
splenium. However, an examination of this disputed region revealed no sex difference, so we were
unable to attribute the differential outcomes to this set of axons. We also examined the possibility that
there was proportionately more variance in measurements of the isthmus when using the Hofer and
Frahm scheme relative to the Witelson scheme, but the two schemes generated similar coefficients of
variation. Re-examination of both schemes revealed that neither consistently partitioned the corpus
callosum into functionally homogeneous regions as defined by individual DTI data. Partitioning the
corpus callosum may be best accomplished using an individual’s unique DTI data rather than using any
general scheme for all individuals

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