Chapter Summary from Current Diagnosis & Treatment
For a clinical review of the topic in Current Diagnosis & Treatment, 3e please go to Chapter 5: Aphasia, Apraxia, & Agnosia.
LANGUAGE IS UNIQUELY HUMAN and arguably our greatest skill and our highest achievement. Despite its complexity, all typically developing children master it by the age of 3. What causes this universal developmental phenomenon, and why are children so much better at acquiring a new language than adults? What brain systems are involved in mature language processing, and are these systems present at birth? How does brain damage produce the various disorders of language known as the aphasias?
For centuries, these questions about language and the brain have prompted vigorous debate among theorists. In the last decade, however, an explosion of information regarding language has taken us beyond the nature–nurture debates and beyond the standard view that a few specialized brain areas are responsible for language. Two factors have brought about this change.
First, functional brain imaging techniques such as positron emission tomography (PET), functional magnetic resonance imaging (fMRI), electroencephalography (EEG), and magnetoencephalography (MEG) have allowed us to examine activation patterns in the brain while a person carries out language tasks—naming objects or actions, listening to sounds or words, and detecting grammatical anomalies. The results of these studies reveal a far more complex picture than the one first proposed by Carl Wernicke in 1874. Moreover, structural brain imaging techniques, such as diffusion tensor imaging (DTI), tractography, and quantitative magnetic resonance imaging (qMRI), have revealed a network of connections that link specialized language areas in the brain. These discoveries are taking us beyond previous, simpler views of the neural underpinnings of language processing and production that assumed involvement of only a few specific brain areas and connections.
Second, behavioral and brain studies of language acquisition show that infants begin to learn language earlier than previously thought, and in ways that had not been previously envisioned. Well before children produce their first words, they learn the sound patterns underlying the phonetic units, words, and phrase structure of the language they hear. Listening to language alters the infant brain early in development, and early language learning affects the brain for life.
Taken together, these advances are shaping a new view of the functional anatomy of language in the brain as a complex and dynamic network in the adult brain, one in which multiple, spatially distributed brain systems cooperate functionally via long-distance neural fascicles (axon fiber bundles). This mature network arises from the considerable brain structure and function in place at birth and develops in conjunction with powerful innate learning mechanisms responsive to linguistic experience. This new view of language encompasses not only its development and mature state, but also its dissolution when brain damage leads to aphasia.