We have reviewed some of our findings on regional fiber composition and of individual variability in callosal structure in the postmortem human and other species, together with anatomical analyses of the human Sylvian fissure, its asymmetry, and its relationship to brain lat-eralization and to callosal connectivity. In our view, these results shed light on two main questions: the original adaptiveness of the corpus callosum in pla-cental mammals, which we propose has to do with the generation of tasks related to midline fusion in the telencephalon, and the relationship between callosal connectivity and hemispheric laterality in the human, in both ontogenetic and phylogenetic terms. An inverse relationship between callosal connectivity and brain lateralization holds in the human, which is apparently the result of early-generated anatomical asymmetry producing a decreased interhemispheric connectivity, especially in males. Eventually, perhaps a reduced interhemispheric communication serves to increase functional laterality. In phylogeny the relationship between callosal connectivity and hemispheric asymmetry is less clear, although comparative studies providing interesting findings are forthcoming.
acknowledgments This work has been supported by FON-DECYT grant 1940450 (Chile) and DTI grant M3604 9633 (Chile).
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