Sexual dimorphism in interhemispheric relations: anatomical-behavioral convergencea

An embryogenetic hypothesis states that hemispheric specialization is inversely related to callosal connectivity (Geschwind and Galaburda, 1985). We tested this hypothesis (i) anatomically by relating postmortem planum temporale asymmetry to regional callosal morphology and (ii) behaviorally by relating the right visual field advantage in a lateralized lexical decision task with associative primes to regional callosal morphometry using magnetic resonance imaging (MRI). The postmortem study showed a significant negative correlation between planum temporale asymmetry and the number of small diameter fibers in the isthmus of the corpus callosum, but only for males. The MRI study showed a significant negative correlation between the right visual hemifield advantage for associated words and the cross section size of the isthmus of the corpus callosum, but again only in males. There was no sex difference in either the anatomical asymmetry, the behavioral asymmetry, or the callosal morphology. These convergent results suggest that there is a sexual dimorphism in interhemispheric relations in humans

The anatomical substrates for language and hemispheric specialization

Three main lines of investigation are discussed in this paper: (1) the comparison between the anatomical arrangement of the language areas and the large-scale neurocognitive cortical networks partly involved in active or working memory; (2) the relations between hemispheric specialization and the development of interhemispheric communication; and (3) the analysis of individual differences in brain organization for language. The hypothesis and evidence presented stem from work being performed in our laboratories