Uniquely human developmental timing may drive cerebral lateralization and interhemispheric collaboration

Cerebral lateralization is intertwined with virtually every cognitive function that we think makes us human. Yet a clear dichotomy has never been explained: lateralized processing suggests independent, local development of neural circuits, but the complementary nature of lateralized functions and extremely strong functional coupling between homologous areas suggest robust interhemispheric interactions. Here, we review literature and present modeling evidence that this dichotomy can be explained by the uniquely steep trajectory of human post-natal brain growth. This drastic volumetric change cause most long distance, interhemispheric connections to be more unreliable than shorter, intrahemispheric connections, leading to lateralization. Strong interhemispheric collaboration is enabled by the later maturation and myelination of long-distance callosal connections. We also review and reanalyze a well-cited modeling paper (Ringo, Doty, Demeter, and Simard (1994)) thought to show a relationship between the degree of hemispheric coordination and length of conduction delays, showing that previous claims have a clear alternative explanation.