Brainless? With a good head on their shoulders! How children without corpus callosum take on developmental challenges

Studies on split-brain cases have helped elucidate a crucial role of the corpus callosum (CC), that is information transfer between the two cerebral hemispheres (Gazzaniga, 2000). Comparative psychology studies suggested that CC plays a role in the acquisition of hemispheric specialisation. The relation between information integration in higher cognitive functions and specialisation development has to be unravelled yet. The contribution of the corpus callosum (CC) to the development of cognitive functions and the concurrent hemispheric specialisation has been relatively neglected until recently. This study examines the developmental trajectories in different domains in callosal agenesis (ACC), a pathology in which the corpus callosum (CC) is absent since birth. When ACC is isolated, children may develop normal intelligence. These extremely rare cases might help understand how the CC contributes to cognitive and linguistic functions epigenesis. Differently from adult split-brains, ACC children can transfer simple tactile and visual information across hemispheres, attesting to neuronal plasticity. Nevertheless, in tasks demanding more of efficient callosal integration (e.g. BFA Banich, 1990), their performance appears quantitatively and qualitatively different from controls. ACC individuals show early motor coordination difficulties, and no patent language impairments in routine clinical tests. At later ages, simple motor coordination problems are overcome, but bimanual coordination difficulties are distinctively reported, alongside with clearer impairments in communication abilities. While in childhood comprehension of language - literal and non-literal - is suboptimal, only in adolescence, metaphors and idioms comprehension, requiring fast inter-hemispheric integration of language skills, reveal frank difficulties. A very similar developmental trajectory emerges from a double single case of complete AgCC, examined experimentally at 8 and 12 years of age. Extent and limits of neuronal plasticity in congenital absence of CC is discussed on the background of the Dennis’ and neuroconstructivist theories. Post Scriptum. As the present work concerns only two participants and other participants are about to be recruited, anybody interested in being updated should contact me at P_de_fabritiis@yahoo.co.uk or pdefabritiis@hotmail.com, Or the Italian Forum about AgCC: agenesiacorpocalloso@hotmail.it