Brain structural networks underlying language.

The unique human ability to process complex language requires the interaction of multiple brain areas located in the inferior frontal and posterior temporal cortex connected by white matter fiber tracts. These fiber tracts underlie the transfer of information between brain regions. In recent years, MRI of white matter brain networks has provided important insights into the plasticity of the structural brain basis underlying language. This structural network is shaped during childhood as a function of language learning by strengthening the connectivity between language-relevant regions mainly in the left hemisphere. In this way, the specific linguistic properties of the native language tongue lead to a modulation of the core language network observable in the adult brain. The brain basis underlying language processing also changes when a second language is learned, as shown by differences in brain connectivity between bilingual and monolingual individuals and by dynamic adaptations during second language learning. Studies of people who use sign language as their native language have shown a domain specificity of the sensory and motor systems rather than the core language network. This separation of the core language system from the sensory-motor system is evolutionarily based. Although the basic auditory-motor interface system is also present in monkeys and apes, the core language system reveals key differences between humans and nonhuman primates. Understanding the function and plasticity of this network is of paramount importance for human cognitive processes, including development and developmental disorders.