Ontogeny of the Neural Language Network
This chapter reviews the neural underpinning of normal language acquisition and asks not only at which age certain milestones in language acquisition are achieved, but moreover to what extent is this achievement dependent on the maturation of particular brain structures. In our recent model, the neural basis of the developing language system is described to reflect two major phases. The available data provide consistent evidence that very early on an infant is able to extract language-relevant information from the acoustic input. This first phase covers the first three years of life when language processing is largely input-driven and supported by the temporal cortex and the ventral part of the network. A second phase extends beyond age 3, when top-down processes come into play, and the left inferior frontal cortex and the dorsal part of the language network are recruited to a larger extent. Development towards full language performance beyond age 3 is dependent on maturational changes in the gray and white matter. An increased language ability is correlated with an increase in structural and functional connectivity between language-related brain regions in the left hemisphere, the inferior frontal gyrus and the posterior superior temporal gyrus/superior temporal sulcus.