Phenotypes in hemispheric functional segregation? Perspectives and challenges

Directional hemispheric dominance has been established for numerous cognitive functions in the human brain. Strong population biases with some functions favoring the left and others the right hemisphere generated the popular idea of an advantageous prototypical division of labor between both halves of the brain, molded by evolution and genetically blueprinted. As most empirical studies on functional lateralization focused on a single function at a time, little is known about the relation between different asymmetric functions and the consequences of atypical functional segregation in healthy individuals. Recent investigations suggest the existence of at least three different phenotypes in human functional segregation relevant for future neuroscientific and genetic research. Using atypical language dominance as a starting point, I summarize the existing literature about its behavioral and neural consequences and explore the evidence for intermediate phenotypes in brain functional segregation that could bridge behavioral and genetic data.