[Interhemispheric transfer and agenesis of the corpus callosum. Capacities and limitations of the anterior commissure].

In case of agenesis of the corpus callosum, four hypotheses may be proposed to explain how compensation of the interhemispheric transfer might take place. These hypotheses include the use of cross-cueing behavioral strategies, the bilateral representation of speech-functions, the increased use of ipsilateral sensory-motor pathways, and the use of noncallosal commissures. Among all these compensatory mechanisms, the last one, namely the increased use of the anterior commissure, is the most significant. It can easily explain that acallosal patients with an anterior commissure (which can be increased in size), have better results in interhemispheric transfer tests, and in neuropsychologic tests, than patients having no anterior commissure. However, the anterior commissure alone, even increased in size, cannot normalize all the interhemispheric transfer tests, because of the big difference between the field of origin of the callosal fibers, and the field of origin of the anterior commissure fibers.