Abstracts

Corpus callosum size correlates with a variety of indices of laterality such as handedness and sex. These relationships are said to reflect the role of the callosum in language representation, but few studies to date have examined this proposition directly. Furthermore, studies of the corpus callosum tend to make [italic]a priori[/italic] decisions about its regional topography or make relatively coarse measurements that preclude a refined understanding of the relationship between the structure and any functional correlate. The present research examined the relationship between functional magnetic resonance imaging [ndash] deterimined language representation in patients with focal epilepsy and regional callosal morphology.
Functional magnetic resonance imaging of language was performed using an orthographic lexical retrieval paradigm and a laterality index was derived from the number of significantly activated pixels in the left and right frontal lobes. All subjects underwent high resolution T[sub]1[/sub]-weighted MR images. The images were placed in a standard stereotaxic coordinate space and, using a semi-automated algorithm, the corpus callosum was segmented and callosal thickness was measured at 39 equally spaced nodes along its length. The latter measurement took into account the inherent shape of the callosum.
Correlational analysis of the absolute value of the laterality scores, which reflect the [italic]degree[/italic] of asymmetry rather than its direction, and callosal thickness measurements showed significant positive relationships at nodes 11 to 13 and node 30. The former region corresponds to the anterior midbody, whilst the latter is within the isthmus.
The findings support the notion that interhemispheric fibres that traverse the corpus callosum inhibit homologous cortical regions during well-lateralised tasks. The isthmus of the corpus callosum has previously been implicated in language processing. Our data provide support for this topographic specialisation within the callosum.