The Ontogeny of the Neural Substrate for Language.

It has been known for many years that certain regions of the human cerebral cortex are functionally specialized for language. However, no specific anatomical feature of these cortical areas has yet been shown to account for language. There is considerable variability in the localization of language areas, and they have cytoarchitectonic homologues in non-human primates. In addition, language appears to have emerged relatively rapidly in the history of Homo sapiens, suggesting a non-genetic mechanism of evolution. The existence of a critical period for primary language learning in humans, in conjunction with recent studies in developmental neurobiology, suggest that language may be "wired-into" the brain as a result of the interaction between the developing human and a social-linguistic environment. It is hypothesized that the functional validation of developing synapses serves as the mechanism whereby linguistic function may gain an anatomical foothold in the human brain. The development of the neural substrate for language is made possible partly by the genetically determined complexity and organization of the brain, and partly by the prolonged period of human postnatal maturation.