Current theories describe the creation of cortical areas as occurring through the establishment of a series of genetically controlled anchor points which serve as loci for overlapping gradients of growth factors (Grove & Fukuchi-Shimogori, 2003). Characteristics of specific cortical areas develop over time in response to the local combination of growth factors and activation. It has been argued that primary motor and sensory cortices may serve as core anchor regions whose earliest development is strongly genetically determined (Rosa & Tweedale, 2005). The pattern observed here of genetic effects predominating in these core regions early in childhood may be consistent with their relatively early development, followed by a mature state in which a high degree of plasticity reflects their roles as the direct intermediaries with the external environment.
